ROUTE 642-902 Category

Policy Based Routing Sim

February 8th, 2019 digitaltut 257 comments

Question

Company TUT has two links to the Internet. The company policy requires that web traffic must be forwarded only to Frame Relay link if available and other traffic can go through any links. No static or default routing is allowed.

BGP_Policy_Based_Routing_Sim.jpg

 

Answer and Explanation:

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EIGRP OSPF Redistribution Sim

January 8th, 2019 digitaltut 286 comments

Question

OSPF_EIGRP_Redistribution.jpg

Answer and Explanation:

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OSPF Sim

January 8th, 2019 digitaltut 219 comments

Question

OSPF is configured on routers Amani and Lynaic. Amani’s S0/0 interface and Lynaic’s S0/1 interface are in Area 0. Lynaic’s Loopback0 interface is in Area 2.

OSPFSim

Your task is to configure the following:

Portland’s S0/0 interface in Area 1
Amani’s S0/1 interface in Area 1
Use the appropriate mask such that ONLY Portland’s S0/0 and Amnani’s S0/1 could be in Area 1.
Area 1 should not receive any external or inter-area routes (except the default route).

Answer and Explanation:

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IPv6 OSPF Virtual Link Sim

May 8th, 2018 digitaltut 152 comments

Question

TUT is a small company that has an existing enterprise network that is running IPv6 OSPFv3. However, R4’s loopback address (FEC0:4:4) cannot be seen in R1. Identify and fix this fault, do not change the current area assignments. Your task is complete when R4’s loopback address (FEC0:4:4) can be seen in the routing table of R1.

OSPFv3_IPv6_VirtualLink

Special Note: To gain the maximum number of points you must remove all incorrect or unneeded configuration statements related to this issue.

Answer and Explanation:

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EIGRP Stub Sim

May 8th, 2018 digitaltut 147 comments

Question

TUT Corporation has just extended their business. R3 is the new router from which they can reach all Corporate subnets. In order to raise network stableness and lower the memory usage and broadband utilization to R3, TUT Corporation makes use of route summarization together with the EIGRP Stub Routing feature. Another network engineer is responsible for this solution. However, in the process of configuring EIGRP stub routing connectivity with the remote network devices off of R3 has been missing.

EIGRPStubSim

Presently TUT has configured EIGRP on all routers in the network R2, R3, and R4. Your duty is to find and solve the connectivity failure problem with the remote office router R3. You should then configure route summarization only to the distant office router R3 to complete the task after the problem has been solved.

The success of pings from R4 to the R3 LAN interface proves that the fault has been corrected and the R3 IP routing table only contains two 10.0.0.0 subnets.

Answer and Explanation:

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Practice Real ROUTE Labs with GNS3

May 8th, 2017 digitaltut 280 comments

Well, the title said it all. Here are some screenshots of the labs in GNS3:

+ OSPF Sim:

OSPF_Sim.jpg

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Drag and Drop Questions

May 8th, 2014 digitaltut 103 comments

Here you will find answers to Drag and Drop questions

Question 1

Drag each item to its proper location

Place the BGP attributes in the correct order used for determining a route.

BGPAttributes1

 

Answer:

BGPAttributes1_Answer

Question 2

Place the BGP commands to the proper locations

BGP_commands.jpg

Answer:

+ show ip bgp: path selection values
+ show ip bgp summary: Memory usage
+ show ip route bgp: AD of BGP
+ show ip bgp neighbor: Notification, update…

Question 3

Place the EIGRP commands to the proper locations

EIGRP_commands.jpg

 

Answer:

Sources of routes information: show ip eigrp neighbor

What being learned: show ip eigrp topology

What actually being used: show ip route eigrp

Verify eigrp information for each network: show ip interface eigrp

Question 4

Place the EIGRP terms to the proper locations

EIGRP_terms.jpg

 

Answer:

lists adjacent routers: Neighbor table

route entries for all destinations: Topology table

primary route to destination: Successor

best routers to destinations: Routing table

backup route to destination: Feasible successor

Question 5

Place the EIGRP packets to the proper locations

EIGRP_packets_function.jpg

 

Answer:

Neighbor discovery/recovery mechanism: Hello

Indicate receipt of any EIGRP packet: Acknowledgement

Convey reachability of destinations: Update

Provides specific and reliable information of neighbors: Query

Instruct the originator not to recompute the route because feasible successors exist: Reply

 

Drag and Drop 2

May 8th, 2014 digitaltut No comments

Here you will find answers to Drag and Drop Questions – Part 2

Question 1

Header_fields.jpg

 

Answer:

Identifies the source of the packet: Router ID

Identifies the area to which the packet belongs: Area ID

Contains the authentication type. All OSPF protocol exchanges are authenticated: Authentication Type

Checks contents of the entire packet for any damage suffered during transmission: Checksum

Contains authentication information: Authentication

Contains encapsulated upper-layer information: Data

Question 2

LSA_Names.jpg

 

Answer:

Maintains the list of routers connected to the network: Network-LSA

Describes the collected states of the routers interfaces to an area: Router-LSA

Describes a route to a destination in another autonomous system: AS-external-LSA

Describes a route to a destination outside the area: Summary-LSA

Question 3

A virtual private network (VPN) is a computer network that is layered on the top of an underlying computer network. VPNs are of different technologies, such as Trusted VPNs, Secure VPNs, and Hybrid VPNs, each having distinct requirements. Drag the various VPN names to their appropriate places.

VPN_names.jpg

 

Answer:

All traffic on the VPN must be encrypted and authenticated: Secure VPN

The routing and addressing used must be established before the VPN is created: Trusted VPN

The address boundaries must be extremely clear: Hybrid VPN

Question 4

IPv6 to IPv4 transition methods

IPv4_to_IPv6_transition_methods.jpg

 

Answer:

NAT-PT

6 to 4 tunnels

GRE tunnels

ISATAP tunnels

Question 5

IP tunneling is a method to encapsulate IP datagram within IP datagrams, which allows datagrams intended for one IP address to be wrapped and redirected to another IP address. IPv6 packets are encapsulated directly behind the IPv4 header. Drag the header fields to the appropriate places:

Tunneling_Header_Fiels.jpg

 

Answer:

The correct order is:

IPv4 Header | IPv6 Header | Extension Headers | Upper Layer PDU

Explanation

The structure of a normal IPv6 packet is:

IPv6 Header | Extension Headers | Upper Layer PDU

The IPv6 header is always present and is a fixed size of 40 bytes. Zero or more extension headers can be present and are of varying lengths. The upper layer protocol data unit (PDU) usually consists of an upper layer protocol header and its payload (for example, an ICMPv6 message, a UDP message, or a TCP segment).

Because “IPv6 packets are encapsulated directly behind the IPv4 header” so we can deduce an IPv4 Header must be placed before an IPv6 header.

Question 6

Drag each OSPF states into correct definition.

OSPF_states.jpg

 

Answer and Explanation

The OSPF states below are described in the correct order when OSPF adjacency is formed:

Down: No information has been received, but Hello packets can still be sent to the neighbor
Init: A Hello packet is received, but the ID of the receiving router was not included in the Hello packet.
2-way: Each router see its own Router ID in the neighbor field of the Hello packet; there is a DR/BDR election.
Exstart: The routers and their DR and BDR establish a master-slave relationship.
Exchange: Routers exchange DBD packets that describe the contents of the entire link-state database.
Loading: Based on the information provided by the DBDs, routers send link-state request packets
Full: All the router and network LSAs are exchanged and the router databases are synchronized

A detailed explanation of OSPF states can be found here: http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13685-13.html.

Drag and Drop 3

May 8th, 2014 digitaltut No comments

Here you will find answers to Drag and Drop Questions – Part 3

Question 1

Drag the “show” commands on the left to their proper locations on the right.

EIGRP_show_commands.jpg

 

Answer:

+ show ip route eigrp: show EIGRP routing tables in routing table / confirm what is actually being used / does routing

+ show ip eigrp interface: show information about interface configured for EIGRP / Verify the routing of specific interface /
show what being used

+ show ip eigrp traffic: show the number of EIGRP packets sent and received

+ show ip eigrp neighbors: Displays the neighbor discovered by EIGRP. Show what is learned

+ show ip eigrp topology: shows the routes known to a router’s EIGRP routing process. Confirm what EIGRP Learning show what does it learned

Question 2

LSA corresponding area type.

OSPF_LSA_types.jpg

 

Answer:

+ stub: LSA 1,2,3
+ NSSA: LSA 1,2,3,7
+ Backbone or transit: LSA 1,2,3,4,5
+ Totally NSSA: LSA 1,2,7
+ Totally stubby: LSA 1,2

Question 3

Place the BGP attributes in the correct order used for determining a route.

BGP_attributes_MED_weight_local_preference.jpg

 

Answer:

+ MED: Propagated between AS
+ weight: Propagated within local preference / used with multiple exit points out of an AS
+ Local Preference: Propagated within AS

Question 4

WAN_technologies.jpg

 

Answer:

+ Bandwidth Management: low-speed WAN links
+ Authentication: WAN link to an external supplier
+ Redistribution: integrating two merging companies
+ Stubs: 256 kb/s CIR FR hub and spokes

Question 5

Click the resources on the left that you need to create an implementation plan for an OSPF project and drag them to the target zone on the right.

OSPF_implementation_plan.jpg

 

Answer:

+ Summarization boundaries
+ OSPF process ID that will be used
+ Authentication type that will be used
+ OSPF area and associated prefix

Question 6

BGP_attributes_effects.jpg

 

Answer:

+ Which is used by router if route has more than one exit: weight
+ Which is not propagated in updates: weight
+ Which is spread through in the AS: local preference
+ Which goes to other AS: MED

Question 7

Click and drag the BGP attribute characterization on the left to the correct BGP attribute on the right.

BGP_attribute_characteristics.jpg

 

Answer:

MED Attribute is propagated between autonomous systems
Local Preference Attribute is propagated throughout the local autonomous system
Weight Attribute + is not advertised to neighboring routers
+ used for one router with multiple exit points out of the autonomous system

DHCP Questions

May 8th, 2014 digitaltut 2 comments

Here you will find answers to DHCP Questions

Question 1

Refer to the exhibit. The DHCP configuration that is shown is configured on a Cisco router. Which statement is true?

ip_dhcp_pool.jpg

A. The router will distribute IP addresses from pool 1 until its addresses are exhausted. Then the router will begin distributing addresses from pool 2.
B. The router will choose which pool to use based upon the interface the DHCP request was received on.
C. The configuration is invalid because the DHCP options are global configuration commands.
D. The configuration is incomplete until the DHCP pools are bound to the appropriate interface or interfaces.

 

Answer: B

Explanation

Notice that these commands are not configured under interface mode, the router notices the incoming interface of the DHCP Request and compares the connected subnets to the pools and picks a pool that matches the address range. For example, in this question when this router receives a DHCP Request from 172.16.1.1/24 it will use pool 1.

OSPF Hotspot

May 7th, 2014 digitaltut 1 comment

Here you will find answers to OSPF Hotspot Questions

Question

The company and the company network have both been growing rapidly. Multiple adds, moves and changes have been applied to the network. Your boss has asked you to troubleshoot a recent OSPF synchronization problem that has arisen. There have been synchronization problems at separate locations in the OSPF area 0. There have been reported link failures during the rapid growth of the company network. You are required to resolve the OSPF problem. OSPF must be able to converge when the network changes.

 

OSPF_Hotspot.jpg

Refer to the information above to answer the following 4 questions:

Question 1
Examine the following excerpt from the “show ip ospf” command on D1:

Area BACKBONE (0)
Number of interfaces in the this area is 1
Area has no authentication
SPF algorithm last executed 00:00:31.280 ago
SPF algorithm executed 5 times
Area ranges are
Number of LSA 13. Checksum Sum 0x16F0FD
Number of opaque link LSA 0. Checksum Sum 0x000000
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Area 16
Number of interfaces in this area is 2
Area has message digest authentication
SPF algorithm last executed 00:00:34.928 ago
SPF algorithm executed 7 times
Area ranges are
Number of LSA 5. Checksum Sum 0x02FCD3
Number of opaque link LSA 0. Checksum Sum 0x000000
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0

Based on the information shown above, what is most likely causing the different missing routes throughout the network?

A. Area 16 is configured with authentication.
B. Area 16 has been configured to use the same interfaces as Area 0.
C. Area 0 and Area 32 have been configured with mismatched LSA numbers.
D. Area 16 has been configured as a total stub network
E. Area 16 has been configured as a stub network
F. Area 0 is discontiguous.
G. None of the above

 

Answer: F

Explanation

From the topology, we see D1 has 2 interfaces belong to Area 0, that are interfaces Fa0/1 & Fa0/2 but the output says there is only one interface in Area 0 (Number of interfaces in the this area is 1). Therefore we can deduce that a link in area 0 was down and area 0 is discontiguous.

Question 2

Which configuration command on D1 (with a similar command on D2) will provide an immediate solution to the missing route problem?

A. no area 16 stub
B. no area 16 authentication message-digest
C. area 16 virtual-link 8.187.175.82
D. area 16 virtual-link 172.16.4.2
E. no area 16 stub no-summary
F. network 172.16.0.0.0.0.255.255 area 16
G. None of the above

 

Answer: C

Explanation

To fix this problem immediately without changing the topology we need to create virtual link between D1 & D2. If you are still confused how to use the virtual link, check out the IPv6 OSPF Virtual Link Sim article.

Question 3

The log of d1 reports the following:

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to down
%LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to down
%OSPF-5-ADJCHG: Process 1, Nbr 8.187.175.82/32 on FasstEthernet0/1 from FULL to DOWN,
Neighbor Down: Interface down or detached

This event was anticipated due to maintenance; however, it resulted in excessive lost routes. Which route should be the only one removed from the routing tables of the routers?

A. 8.187.175.82/32
B. 10.138.43.0/30
C. 10.206.180.0/30
D. 4.249.113.59/32
E. 10.201.0.0/30
F. None of the above

 

Answer: E

Explanation

From the log we learn that the link of Interface Fa0/1 has been down. This link belongs to network 10.201.0.0/30 so we just need to remove this route from the routing table.

Question 4

The R2 router has lost connectivity to R1. The following is R1’s current route table:

172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks
O IA 172.16.230.0/24 [110/21] via 10.138.43.1, 00:00:03, FastEthernet0/0
O IA 172.16.209.0/24 [110/22] via 10.138.43.1, 00:00:03, FastEthernet0/0
O IA 172.16.1.0/30 [110/21] via 10.138.43.1, 00:00:03, FastEthernet0/0
10.0.0.0/30 is subnetted, 1 subnets
C 10.138.43.0 is directly connected, FastEthernet0/0

Which expected route is missing from R1’s route table based on the topology during the maintenance period?’

A. o 172.16.0.0 [110/2] via 10.138.43.1, 00:00:09, FastEthernet0/0
B. o IA 9.152.105.122 [110/3] via 10.138.43.1, 00:00:09, FastEthernet0/0
C. o IA 10.138.0.0 [110/3] via 10.138.43.1, 00:00:09, FastEthernet0/0
D. o IA 10.249.0.0 [110/2] via 10.138.43.1, 00:00:09, FastEthernet0/0
E. o IA 4.249.113.59 [110/2] via 10.138.43.1, 00:00:09, FastEthernet0/0
F. o 8.187.175.82 [110/3] via 10.138.43.1, 00:00:09, FastEthernet0/0
G. O 10.206.180.0/30 [110/3] via 10.138.43.1, 00:00:09, FastEthernet0/0
H. O IA 10.206.180.0/30 [110/3] via 10.138.43.1, 00:00:09, FastEthernet0/0

 

Answer: G

Explanation

In the past, I used to choose answer F as the correct answer but the explanation from DOX3003 (commented on November 19th, 2010) seems to be correct:

“Which expected route is missing from R1′s route table based on the topology during the maintenance period?
X…….
X. O 10.206.180.0/30 [110/3] via 10.138.43.1, 00:00:09, FastEthernet0/0
X. O IA 10.206.180.0/30 [110/3] via 10.138.43.1, 00:00:09, FastEthernet0/0
X…….

You can see there are 2 options for the network between D2 and R2. One with “IA” and one without. O – OSPF, IA – OSPF inter area.
Before link failures between D1 and D2 the network 10.206.180.0/30 has been appearing as “intra area” network in R1′s routing table.
Because they were in the same Area 0.
So the correct answer should be
X. O 10.206.180.0/30 [110/3] via 10.138.43.1, 00:00:09, FastEthernet0/0″”

OSPF Questions

May 6th, 2014 digitaltut 2 comments

Here we will find answers to OSPF questions

Question 1

An administrator Pipes in the command router ospf 1 and receives the error message: “OSPF process 1 cannot start.” (Output is omitted.) What should be done to correctly set up OSPF?

A – Ensure that an interface has been configured with an IP address
B – Ensure that an interface has been configured with an IP address and is up
C – Ensure that IP classless is enabled
D – Ensure that the interfaces can ping their directly connected neighbors

 

Answer: B

Question 2

During a recent OSPF election among three routers. RTA was elected the DR and RTB was elected the BDR, as seen in the graphic. Assume that RTA fails, and that RTB takes the place of the DR while RTC becomes the new BDR. What will happen when RTA comes back online?

OSPF_DR_DBR

A – RTA will take the place of DR immediately upon establishing its adjacencie
B – RTA will take the place of DR only if RTB fails
C – RTA will take the place of DR only if both RTB and RTC fail
D – A new election will take place establishing an all new DR and BDR based on configured priority levels and MAC addresses

 

Answer: C

Question 3

Refer to the exhibit. During the process of configuring a virtual link to connect area 2 with the backbone area, the network administrator received this console message on R3:
*Mar 1 00:25:01.084: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual link but not found from 20.20.20.1, Serial 0

How should the virtual link be configured on the OSPF routers to establish full connectivity between the areas?

OSPF_virtual_link

A – R1(config-router)# area 1 virtual-link 30.30.30.3
R3(config-router)# area 1 virtual-link 20.20.20.1
B – R1(config-router)# area 1 virtual-link 20.20.20.2
R3(config-router)# area 1 virtual-link 30.30.30.2
C – R1(config-router)# area 0 virtual-link 1.1.1.1
R3(config-router)# area 2 virtual-link 3.3.3.3
D – R1(config-router)# area 1 virtual-link 3.3.3.3
R3(config-router)# area 1 virtual-link 1.1.1.1
E – R1(config-router)# area 1 virtual-link 2.2.2.2
R3(config-router)# area 1 virtual-link 2.2.2.2

Answer: D

Explanation

When designing a multi-area OSPF network, all areas should be connected to the backbone area. However, there may be instances when an area will need to cross another area to reach the backbone area like area 2 in this case. A virtual link has the following two requirements:

+ It must be established between two routers that share a common area and are both ABRs.
+ One of these two routers must be connected to the backbone.

In this case, two routers that satisfy the above requirements are R1 and R3. The syntax for creating a virtual link across an area is:

area area-id virtual-link neighbor-router-id

The area-id is the number of the transit area, in this example Area 1 and neighbor-router-id is the IP address of the highest loopback interface configured or can be manually set on the neighboring router.

Question 4

As shown in the exhibit ,OSPF is configured over a Frame Relay network. All PVCs are active. However, P4S1 and P4S3 fail to see all OSPF routes in their routing tables. The show ip ospf neighbor command executed on P4S2 displays the state of the neighbors. In order to fix the problem , what should be done?

OSPF_NBMA_Frame_Relay

A – The neighbor command should be configured under the OSPF routing process on all routers
B – The ip ospf network broadcast command should be configured on each Frame Relay interface
C – The ip ospf network non-broadcast command should be configured on each Frame Relay interface
D – The ip ospf priority value on the spoke routers should be set to 0

 

Answer: D

Explanation

In an NBMA network topology, neighbors are not discovered automatically. OSPF tries to elect a DR and a BDR due to the multi-access nature of the network, but the election fails since neighbors are not discovered because NBMA environment doesn’t forward broadcast and multicast packets. Neighbors must be configured manually to overcome these problems.

Also, additional configuration is necessary in a hub and spoke topology to make sure that the hub routers, which have connectivity with every other spoke router, are elected as the DR and BDR. You must set the spoke interfaces to an OSPF priority of zero, this ensures that the spokes will not become the DR or BDR.

Question 5

The following exhibit shows ipv6 route output. What would the metric be for a summary route that summarizes all three OSPFv3 routes displayed?

cost_of_summary_route

A – 160
B – 140
C – 120
D – 100

 

Answer: D

Explanation

The cost of the summarized routes is the highest cost of the routes being summarized. In fact, in the old RFC 1583 standard, the cost of the summary route was the cost of the lowest metric. But when OSPF was updated in RFC 2178 and RFC 2328, the summary route should have the same cost as the highest-cost summarized route. In this case, the highest-cost is 100 according to the second entry.

Question 6

Study the exhibit below carefully. In order to summarize all routes from area 0 to area 1, what must be configured on the router?

area_range_summary_OSPF

A – area 0 range 172.16.96.0 255.255.224.0
B – area 1 range 172.16.96.0 255.255.224.0
C – area 1 range 172.16.96.0 255.255.0.0
D – area 0 range 172.16.96.0 255.255.255.0

 

Answer: A

OSPF Questions 2

May 6th, 2014 digitaltut 2 comments

Here you will find answers to OSPF Questions – Part 2

Question 1

Into which two types of areas would an area border router (ABR) inject a default route? (Choose two)

A. the autonomous system of a different interior gateway protocol (IGP)
B. area 0
C. totally stubby
D. NSSA
E. stub
F. the autonomous system of an exterior gateway protocol (EGP)

 

Answer: C E

Explanation

Both stub area & totally stubby area allow an ABR to inject a default route. The main difference between these 2 types of areas is:

+ Stub area replaces LSA Type 5 (External LSA – created by an ASBR to advertise network from another autonomous system) with a default route
+ Totally stubby area replaces both LSA Type 5 and LSA Type 3 (Summary LSA – created by an ABR to advertise network from other areas, but still within the AS, sometimes called interarea routes) with a default route.

Below summarizes the LSA Types allowed and not allowed in area types:

Area Type Type 1 & 2 (within area) Type 3 (from other areas) Type 4 Type 5 Type 7
Standard & backbone Yes Yes Yes Yes No
Stub Yes Yes No No No
Totally stubby Yes No No No No
NSSA Yes Yes No No Yes
Totally stubby NSSA Yes No No No Yes

Question 2

Which three restrictions apply to OSPF stub areas? (Choose three)

A. No virtual links are allowed.
B. The area cannot be a backbone area.
C. Redistribution is not allowed unless the packet is changed to a type 7 packet.
D. The area has no more than 10 routers.
E. No autonomous system border routers are allowed.
F. Interarea routes are suppressed.

 

Answer: A B E

Question 3

Refer to the partial configurations in the exhibit. What address is utilized for DR and BDR identification on Router1?

Router1#show run

**** output omitted ******

interface serial1/1
ipv6 address 2001:410:FFFE:1::64/64
ipv6 ospf 100 area 0
!
interface serial2/0
ipv6 address 3FFF:B00:FFFF:1::2/64
ipv6 ospf 100 area 0
!
ipv6 router ospf
router-id 10.1.1.3

A. the serial 1/1 address
B. the serial 2/0 address
C. a randomly generated internal address
D. the configured router-id address

 

Answer: D

Explanation

In OSPFv3 and OSPF version 2, the router uses the 32-bit IPv4 address to select the router ID for an OSPF process. The router ID selection process for OSPFv3 is described below (same as OSPF version 2):

1. The router ID is used if explicitly configured with the router-id command.
2. Otherwise, the highest IPv4 loopback address is used.
3. Otherwise, the highest active IPv4 address.
4. Otherwise, the router ID must be explicitly configured.

In this case the router ID 10.1.1.3 is explicitly configured -> D is correct.

Question 4

By default, which statement is correct regarding the redistribution of routes from other routing protocols into OSPF?

A. They will appear in the OSPF routing table as type E1 routes.
B. They will appear in the OSPF routing table as type E2 routes.
C. Summarized routes are not accepted.
D. All imported routes will be automatically summarized when possible.
E. Only routes with lower administrative distances will be imported.

 

Answer: B

Explanation

Type E1 external routes calculate the cost by adding the external cost to the internal cost of each link that the packet crosses while the external cost of E2 packet routes is always the external cost only. E2 is useful if you do not want internal routing to determine the path. E1 is useful when internal routing should be included in path selection. E2 is the default external metric when redistributing routes from other routing protocols into OSPF -> B is correct.

Question 5

Which statement is true about OSPF Network LSAs?

A. They are originated by every router in the OSPF network. They include all routers on the link, interfaces, the cost of the link, and any known neighbor on the link.
B. They are originated by the DR on every multi-access network. They include all attached routers including the DR itself.
C. They are originated by Area Border Routers and are sent into a single area to advertise destinations outside that area.
D. They are originated by Area Border Router and are sent into a single area to advertise an Autonomous System Border Router.

 

Answer: B

Explanation

Popular LSA Types are listed below:

LSA Type Description Details
1 Router LSA Generated by all routers in an area to describe their directly attached links
2 Network LSA Advertised by the DR of the broadcast network (does not cross ABR)
3 Summary LSA Advertised by the ABR of originating area
4 Summary LSA Generated by the ABR of the originating area to advertise an ASBR to all other areas in the autonomous system
5 AS external LSA Used by the ASBR to advertise networks from other autonomous systems
7 Defined for NSSAs Generated by an ASBR inside a Not-so-stubby area (NSSA) to describe routes redistributed into the NSSA

Question 6

Refer to the exhibit. OSPF is configured on all routers in the network. On the basis of the show ip ospf neighbor output, what prevents R1 from establishing a full adjacency with R2?

show_ip_ospf_neighbor.jpg

A. Router R1 will only establish full adjacency with the DR and BDR on broadcast multiaccess networks.
B. Router R2 has been elected as a DR for the broadcast multiaccess network in OSPF area
C. Routers R1 and R2 are configured as stub routers for OSPF area 1 and OSPF area 2.
D. Router R1 and R2 are configured for a virtual link between OSPF area 1 and OSPF area 2.
E. The Hello parameters on routers R1 and R2 do not match.

 

Answer: A

Explanation

From the output, we learn that R4 is the DR and R3 is the BDR so other routers will only establish full adjacency with these routers. All other routers have the two-way adjacency established -> A is correct.

Question 7

Refer to the exhibit. On the basis of the configuration provided, how are the Hello packets sent by R2 handled by R5 in OSPF area 5?

OSPF_Hello_packets.jpg

A. The Hello packets will be exchanged and adjacency will be established between routers R2 and R5.
B. The Hello packets will be exchanged but the routers R2 and R5 will become neighbors only.
C. The Hello packets will be dropped and no adjacency will be established between routers R2 and R5.
D. The Hello packets will be dropped but the routers R2 and R5 will become neighbors.

 

Answer: C

Explanation

Recall that in OSPF, two routers will become neighbors when they agree on the following: Area-id, Authentication, Hello and Dead Intervals, Stub area flag.

We must specify Area 5 as a stub area on the ABR (R2) and all the routers in that area (R5 in this case). But from the output, we learn that only R2 has been configured as a stub for Area 5. This will drop down the neighbor relationship between R2 and R5 because the stub flag is not matched in the Hello packets of these routers.

Question 8

When an OSPF design is planned, which implementation can help a router not have memory resource issues?

A. Have a backbone area (area 0) with 40 routers and use default routes to reach external destinations.
B. Have a backbone area (area 0) with 4 routers and 30,000 external routes injected into OSPF.
C. Have less OSPF areas to reduce the need for interarea route summarizations.
D. Have multiple OSPF processes on each OSPF router. Example, router ospf 1, router ospf 2

 

Answer: A

Question 9

When verifying the OSPF link state database, which type of LSAs should you expect to see within the different OSPF area types? (Choose three)

A. All OSPF routers in stubby areas can have type 3 LSAs in their database.
B. All OSPF routers in stubby areas can have type 7 LSAs in their database.
C. All OSPF routers in totally stubby areas can have type 3 LSAs in their database.
D. All OSPF routers in totally stubby areas can have type 7 LSAs in their database.
E. All OSPF routers in NSSA areas can have type 3 LSAs in their database.
F. All OSPF routers in NSSA areas can have type 7 LSAs in their database.

 

Answer: A E F

Explanation

Below summarizes the LSA Types allowed and not allowed in area types:

Area Type Type 1 & 2 (within area) Type 3 (from other areas) Type 4 Type 5 Type 7
Standard & backbone Yes Yes Yes Yes No
Stub Yes Yes No No No
Totally stubby Yes No No No No
NSSA Yes Yes No No Yes
Totally stubby NSSA Yes No No No Yes

Popular LSA Types are listed below:

LSA Type Description Details
1 Router LSA Generated by all routers in an area to describe their directly attached links
2 Network LSA Advertised by the DR of the broadcast network (does not cross ABR)
3 Summary LSA Advertised by the ABR of originating area
4 Summary LSA Generated by the ABR of the originating area to advertise an ASBR to all other areas in the autonomous system
5 AS external LSA Used by the ASBR to advertise networks from other autonomous systems
7 Defined for NSSAs Generated by an ASBR inside a Not-so-stubby area (NSSA) to describe routes redistributed into the NSSA

Question 10

You are troubleshooting an OSPF problem where external routes are not showing up in the OSPF database. Which two options are valid checks that should be performed first to verify proper OSPF operation? (Choose two)

A. Are the ASBRs trying to redistribute the external routes into a totally stubby area?
B. Are the ABRs configured with stubby areas?
C. Is the subnets keyword being used with the redistribution command?
D. Is backbone area (area 0) contiguous?
E. Is the CPU utilization of the routers high?

 

Answer: A C

Explanation

A totally stubby stubby area cannot have an ASBR so it will discard this type of LSA (LSA Type 5) -> A is a valid check.

Each stubby area needs an ABR to communicate with other areas so it is normal -> B is not a valid check.

When pulling routes into OSPF, we need to use the keyword “subnets” so that subnets will be redistributed too. For example, if we redistribute these EIGRP routes into OSPF:

+ 10.0.0.0/8
+ 10.10.0.0/16
+ 10.10.1.0/24

without the keyword “subnets”

router ospf 1
redistribute eigrp 1

Then only 10.0.0.0/8 network will be redistributed because other routes are not classful routes, they are subnets. To redistribute subnets we must use the keyword “subnets”

router ospf 1
redistribute eigrp 1 subnets

-> C is a valid check.

We don’t need to care if area 0 is contiguous or not -> D is not a valid check.

CPU utilization cannot be the cause for this problem -> E is not a valid check.

For this question, please read our tutorial about OSPF LSA Types for more detail.

OSPF Questions 3

May 6th, 2014 digitaltut 1 comment

Here you will find answers to OSPF Questions – Part 3

Question 1

Refer to the exhibit. You are the network administrator responsible for the NProuter, the 10.1.1.1 router, and the 10.1.1.2 router. What can you determine about the OSPF operations from the debug output?

NProuter#debug ip ospf events

OSPF events debugging is on

NProuter#
00:02:03: OSPF: Rev hello from 172.16.1.1 area 0 from Serial0/0 10.1.1.1
00:02:03: OSPF: Mismatched hello parameter from 10.1.1.1
00:02:03: OSPF: Dead R 120 C 10, Hello R 30 C 30
00:02:26: OSPF’ Rcv hello from 192.168.1.2 area 0 from Serial0/0 10.1.1.2
00:02:26: OSPF: Mismatched hello parameters from 10.1.1.2
00:02:26: OSPF: Dead R 120 C 10, Hello R 30 C 30

A. The NProuter has two OSPF neighbors in the “Full” adjacency state.
B. The NProuter serial0/0 interface has the OSPF dead timer set to 10 seconds.
C. The NProuter serial0/0 interface has been configured with an OSPF network type of “point-to-point”.
D. The 10.1.1.1 and 10.1.1.2 routers are not using the default OSPF dead and hello timers setting.
E. The “Mismatched” error is caused by the expiration of the OSPF timers.

 

Answer: B

Explanation

First we should understand clearly about the line

Dead R 120 C 10, Hello R 30 C 30

The “R” here means “Received” and “C” means “Configured”. In other words, “Dead R” is the Dead Timer Received from the neighbor and the “Dead C” is the Dead Timer of the local router.

Therefore in this case “Dead R 120 C 10” means the Death Timer of the neighbor is 120 seconds while the local Dead Timer is 10 seconds, which causes a mismatch. Also we can learn that the local OSPF dead timer is set to 10 seconds -> B is correct.

For your information, by default, OSPF uses a 10-second hello timer and 40-second hold timer on broadcast and point-to-point links, and a 30-second hello timer and 120-second hold timer for all other network types. So we can’t confirm answer D is correct or not.

Question 2

You have just completed an OSPF implementation. While executing your verification plan, you determine that R1 is not able to establish full OSPF adjacency with R2. The show ip ospf neighbor command output on R1 shows that R2 is stuck in the INIT state.

What could be the cause of this problem?

A. DR and BDR election errors between R1 and R2.
B. The R2 router has not received the OSPF hello packets from the R1 router.
C. Mismatched interface maximum transmission unit (MTU) configuration between the R1 and R2.
D. Mismatched OSPF hello interval configuration between the R1 and R2.
E. Corrupted LSAs exchanges between the R1 and R2.

 

Answer: B

Explanation

When a router receives an OSPF Hello from a neighbor, it sends the Hello packet by including that neighbor’s router ID in the Hello packet. If the neighbor does not receive this packet (means that it doesn’t see itself in this packet), it will be stuck in INIT state. INIT state can be understood as a one-way Hello. An example of a router stuck in INIT state is shown below:

show_ip_ospf_neighbor_INIT_state.jpg

Question 3

Refer to the exhibit. You have completed an OSPF implementation, and you are verifying OSPF operation. You notice that router A and router B are stuck in the two-way state. From the show ip ospf interface command output, what is the cause of this issue?

OSPF_show_ip_ospf_interface.jpg

A. All OSPF implementations must have at least one interface in area 0.
B. You are attempting to run in the broadcast mode over an NBMA interface.
C. Both routers are configured to function as a BDR; therefore, there is no DR router.
D. Someone has changed the OSPF router ID; therefore you must clear the OSPF process.
E. The OSPF priority is set to 0 on both routers; therefore neither can become the DR.

 

Answer: E

Explanation

When OSPF adjacency is formed, a router goes through several state changes before it becomes fully adjacent with its neighbor. The states are Down, Attempt, Init, 2-Way, Exstart, Exchange, Loading, and Full.

An OSPF neighbor reaches the 2-way state when bidirectional communication is established (each router has seen the other’s hello packet). This is the beginning of an OSPF adjacency. On broadcast media and non-broadcast multiaccess networks, the DR and BDR are elected in this state. But the priority on both routers are 0 so no DR and BDR are elected -> These routers stay in the 2-way state.

(Reference and a good resource of OSPF Neighbor states: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0e.shtml)

Question 4

You have completed an OSPF implementation, and you are verifying OSPF operation. During this verification, you notice that the OSPF route of 172.16.10.0 is repeatedly appearing and disappearing from the routing table. Further investigation finds that the OSPF CPU utilization is very high and the routers are constantly performing SPF calculations. You determine that 172.16.20.2 is the source of the 172.16.10.0 route. Using the show ip ospf database router 172.16.20.1 command, you notice that when this show command is performed repeatedly, the contents of the LSA change every few seconds.

What could be the cause of this problem?

A. OSPF authentication errors between some of the routers.
B. Two routers have the same OSPF router ID.
C. Issues with mistuned OSPF timers.
D. OSPF LSA pacing issues between some of the routers.
E. OSPF neighbor adjacency problems between some of the routers.

 

Answer: B

Question 5

The maximum number of routers per OSPF area typically depends on which three factors? (Choose three)

A. the kind of OSPF areas being implemented
B. the number of external LSAs in the network
C. the number of DRs and BDRs in the areas
D. the number of virtual links in the areas
E. how well the areas can be summarized
F. the use of LSA filters

 

Answer: A B E

Explanation

The maximum number of routers per area depends on several factors, including the following:
+ What kind of area do you have?
+ What kind of CPU power do you have in that area?
+ What kind of media?
+ Will you be running OSPF in NBMA mode?
+ Is your NBMA network meshed?
+ Do you have a lot of external LSAs in the network?
+ Are other areas well summarized?

For this reason, it’s difficult to specify a maximum number of routers per area. Consult your local sales or system engineer for specific network design help.

(Reference: http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml#t40)

Question 6

When verifying OSPF virtual link problems, which is an important item to check on the two transit OSPF routers?

A. OSPF process ID
B. OSPF router ID
C. OSPF network type
D. OSPF memory usage
E. OSPF CPU utilization
F. OSPF stub area configurations

 

Answer: B

Explanation

The OSPF router IDs of the two transit OSPF routers are used to form the virtual link (with the area area-id virtual-link neighbor-router-id command) so it is an important item to check -> B is correct.

Question 7

The administrator wants to verify the current state of the OSPF database loading process.
Which show command should the administrator use?

A. show ip ospf [process-id] interface
B. show ip ospf neighbor
C. show ip ospf [process-id]
D. show ip ospf [process-id area-id] database

 

Answer: B

Explanation

The “show ip ospf neighbor” command can be used to view the current state of the OSPF database loading process. In the output below we can see router 2.2.2.2 is in 2way state, router 3.3.3.3 is elected as the BDR & router 4.4.4.4 is the BR.

show_ip_ospf_neighbor_OSPF_database_loading.jpg

Question 8

Which two statements about route redistribution when implementing OSPF are true? (Choose two)

A. Routes learned using any IP routing protocol can only be redistributed into non IP routing protocols.
B. OSPF can import routes learned using EIGRP, RIP, and IS-IS.
C. OSPF routes cannot be exported into EIGRP, RIP, and IS-IS.
D. At the interdomain level, OSPF cannot import routes learned using BGP.
E. OSPF routes can be exported into BGP.

 

Answer: B E

Question 9

An administrator types in the command router ospf 1 and receives the error message: “OSPF process 1 cannot start.” (Output is omitted.)
What should be done to correctly set up OSPF?

A. Ensure that an interface has been configured with an IP address.
B. Ensure that an interface has been configured with an IP address and is up.
C. Ensure that IP classless is enabled.
D. Ensure that the interfaces can ping their directly connected neighbors.

 

Answer: B

Explanation

OSPF can be only started when there is at least one interface up and configured with an IP address on the router.

Question 10

Which three are advantages to creating multiple areas in OSPF? (Choose three)

A. less frequent SPF calculations
B. fewer hello packets
C. smaller routing tables
D. reduced LSU overhead
E. fewer adjacencies needed

 

Answer: A C D

Explanation

OSPF routers within an area only need to know about other routers within their own area, not outside their area, and all OSPF routers within a given area share the same link state database. This keeps the routing tables small enough to prevent processing bottlenecks from occurring -> C is correct.

Also SPF only needs to calculate paths to routers within that area -> A is correct.

If a router receives an LSA with old information then it will send a LSU to the sender to update the sender with the newer information. The Link State Update (LSU) holds the LSAs. Instead of sending multiple LSUs the ABR / ASBR summarizes a route and sends only one LSU-> D is correct.

Note: The LSA has a 30 minute timer that causes the router to send an LSU to everyone on the network once it ages out.

Question 11

OSPF Questions 4

May 6th, 2014 digitaltut No comments

Here you will find answers to OSPF Questions – Part 4

Question 1

Refer to the exhibit. Two routers are connected by Frame Relay and are running OSPF between them. Each router has been configured with the appropriate network statements under router ospf 1, but the routers are not forming an adjacency. Which of the following three commands could be configured on each router to correct this problem? (Choose three)

OSPF_Frame_Relay.jpg

 

A.
RouterC(config-if )#ip ospf network broadcast
RouterD(config-if )#ip ospf network broadcast

B.
RouterC(config-if)#ip ospf network point-to-point
RouterD(config-if)#ip ospf network point-to-point

C.
RouterC(config-router)#neighbor 10.100.100.4
RouterD(config-router)#neighbor 10.100.100.3

D.
RouterC(config-router)#neighbor 10.255.255.254
RouterD(config-router)#neighbor 10.255.255.253

 

Answer: A B D

Explanation

By default, Frame Relay is classified as a non-broadcast network, meaning it doesn’t send any broadcasts/multicasts like RIP, OSPF or EIGRP updates across the network (hello packets of OSPF are multicast to 224.0.0.5). Hence, in NBMA network, the neighbors are not discovered automatically; they must be configured manually. There are two ways to simulate a broadcast model on an NBMA network:

+ Define the network type as broadcast with the “ip ospf network broadcast” interface sub-command
+ Configure the neighbor statements under router ospf mode (though configuring the neighbor statement on one end is sufficient to form adjacency, it is a good practice to have it configured on both the ends)

Besides these two ways, another way for making OSPF work with Frame Relay is configuring the network as a Point-to-Point network (or Point-to-Multipoint, notice that OSPF treats Point-to-Multipoint network as a collective of point-to-point links).

Some information about Point-to-Multipoint (or Point-to-Point) network:

Note: Point-to-Multipoint networks do not maintain a DR/BDR relationship.

Question 2

Refer to the exhibit. What is the effect of the OSPF configuration on router B?

OSPF_ABR.jpg

A. All interfaces will be in area 0.
B. The router will be an ABR with s1/0 in area 0 and 0/0 and 0/1 in area 1.
C. The router will be an ABR with s1/0 in area 0 and 0/0 and 0/1 in area 2.
D. The router will be an ABR with s1/0 in area 0, f0/0 in area 1, and f0/1 in area 2.

 

Answer: D

Question 3

OSPF is enabled on router A. You execute the following command on router A and receive the accompanying output:

RouterA#ping 224.0.0.5 repeat 1
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 224.0.0.5, timeout is 2 seconds:
Reply to request 0 from 10.100.100.1, 4 ms

10.100.100.1 is the IP address of a loopback interface on router A. What can you conclude about router A?

A. Only the router A loopback interface is participating in the OSPF routing process.
B. None of the router A interfaces are participating in the OSPF routing process.
C. Router A is using the loopback interface IP address as its OSPF router ID.
D. Router A does not have any reachable OSPF neighbors.

 

Answer: D

Explanation

The 224.0.0.5 address is the multicast for OSPF routers. Therefore when you ping to this address all the interfaces running OSPF will reply but from the output we learn that only the local router responded -> Router A does not have any reachable OSPF neighbors -> D is correct.

Question 4

Your network has a mixture of Fast Ethernet and Gigabit Ethernet links. What needs to be done to ensure optimal data routing when using OSPF?

A. Nothing. OSPF will determine the most optimal path for routing data by default.
B. Adjust the hello and dead timers for more rapid detection of link failures.
C. Increase the reference-bandwidth used to calculate the interface default metrics, on all routers in your network.
D. Set the priority values on every broadcast interface to ensure that the designated and backup designated routers are the routers with the most processor and memory resources.

 

Answer: C

Explanation

The default formula to calculate the cost for the OSPF metric is (108/BW). Therefore when using default reference bandwidth (100M) to calculate ospf, Gi and Fa interfaces could have the same cost (1). This problem can be fixed by configuring reference bandwidth to 1000M.

Default Bandwidth (100M) Configured Bandwidth (1000M)
Fa = 100M / 100M = 1
Gi = 100M / 1000M = 0.1 -> round up to 1
Fa = 1000M / 100M = 10
Gi = 1000M / 1000M = 1

This is how to configure reference bandwidth to 1000Mbps:

Router(config)#router ospf 1
Router(config-router)#auto-cost reference-bandwidth 1000

Question 5

OSPF_events.jpg

RouterA#debug ip ospf events
OSPF events debugging is on
RouterA#
04:43:16: OSPF: Rev pkt from 10.3.0.2, Ethernet0/1, area 0.0.0.1 mismatch area 0.0.0.2 in the header
04:43:19: OSPF: Rev hello from 10.100.100.3 area 0 from Ethernet0/0 10.1.0.1
04:43:19: OSPF: End of hello processing

Refer to the exhibits. What can be done to fix the problem?

A. Change router B E0/1 interface to area 0.
B. Change router A interface E0/1 to area 0.0.0.2.
C. Configure the E0/1 interfaces of router A and router B to be in area 0.
D. Shut down the E0/1 interfaces in router A and router B as OSPF does not allow “back doors” between areas.
E. Remove the E0/1 interfaces in router A and router B from the OSPF process. Use static routes to route data directly from router A to router B to avoid passing data through router C in area 0.

 

Answer: C

Question 6

Which two statements are true of the OSPF link-state routing protocol? (Choose two)

A. Using the Bellman-Ford algorithm, each OSPF router independently calculates its best paths to all destinations in the network.
B. Using the DUAL algorithm, each OSPF router independently calculates its best paths to all destinations in the network.
C. OSPF sends summaries of individual link-state entries every 30 minutes to ensure LSDB synchronization.
D. OSPF sends triggered updates when a network change occurs.
E. OSPF sends updates every 10 seconds.
F. When a link changes state, the router that detected the change creates a link-state advertisement (LSA) and propagates it to all OSPF devices using the 224.0.0.6 multicast address.

 

Answer: C D

Question 7

Given the following partial configuration for Router A:

interface serial 0
ip address 10.1.1.1 255.255.255.0
encapsulation frame-relay
ip ospf network point-to-multipoint

router ospf 7
network 10.1.1.0 0.0.0.255 area 0

Which two statements are correct? (Choose two)

A. DR/BDR elections do not take place.
B. The router is restricted to a hub and spoke topology.
C. The area 0 NBMA cloud is configured as more than one subnet.
D. OSPF neighbor statements are not necessary.

 

Answer: A D

Explanation

The command “ip ospf network point-to-multipoint” configures this interface as point-to-multipoint for broadcast media. In broadcast networks, there is no need to specify neighbors. No DR or BDR is elected in this network type.

Note: If we configure this interface as a point-to-point non-broadcast (with the “ip ospf network point-to-multipoint non-broadcast” command) then we need to manually declare the OSPF neighbors.

Question 8

What are two Cisco IOS commands that can be used to view neighbor adjacencies? (Choose two)

A. show ip ospf database
B. show ip ospf neighbors
C. show ip ospf protocols
D. show ip ospf interfaces

 

Answer: B D

Explanation

The output of these commands are shown below:

show_ip_ospf_neighbor_INIT_state.jpg

show_ip_ospf_interface.jpg

Notice that for the “show ip ospf interface” command, the “Neighbor Count” is the number of OSPF neighbors discovered on this interface while the “Adjacent neighbor count” is the number of routers running OSPF that are fully adjacent with this router. Adjacent means that their databases are fully synchronized. In this example, this router has one neighbor on its Ethernet0 interface.

Question 9

Refer to the exhibit. What additional commands should be used to configure OSPF area 5 as a Totally Stubby area?

OSPF_Totally_Stubby_Area.jpg

A. area 0 stub on routers R4 and R5
B. area 5 stub on routers R4 and R5
C. area 5 stub no-summary on routers R4 and R5
D. area 0 stub no-summary on router R4 and area 5 stub no-summary on router R5
E. area 5 stub no-summary on router R4 and area 5 stub on router R5

 

Answer: E

Explanation

To define a totally stub area, use the area area-id stub no-summary command on the ABR (in OSPF router configuration) and the area area-id stub on the totally stub router. The ABR will inject a default route into the area so routers in this type of area only see routing information local to their area, plus a default route pointing to the ABR, from which they can reach all other areas and all other networks

 

Question 10

According to RFC 2328, what is the stateful order in which an OSPF router transitions to a full adjacency with a neighbor router?

A. Down, Init, 2-Way, Exstart, Exchange, Loading, and Full
B. Down, Init, 2-Way, Exchange, Exstart, Loading, and Full
C. Down, 2-Way, Init; Loading, Exstart, Exchange, and Full
D. Down, 2-Way, Init, Exchange, Exstart, Loading, and Full
E. Down, Init, 2-Way, Loading, Exstart, Exchange, and Full
F. Down, 2-Way, Init, Exstart, Exchange, Loading, and Full

 

Answer: A

Explanation

When OSPF adjacency is formed, a router goes through several state changes before it becomes fully adjacent with its neighbor. The states are Down -> Attempt (optional) -> Init -> 2-Way -> Exstart -> Exchange -> Loading -> Full. Short descriptions about these states are listed below:

Down: no information (hellos) has been received from this neighbor.

Attempt: only valid for manually configured neighbors in an NBMA environment. In Attempt state, the router sends unicast hello packets every poll interval to the neighbor, from which hellos have not been received within the dead interval.

Init: specifies that the router has received a hello packet from its neighbor, but the receiving router’s ID was not included in the hello packet
2-Way: indicates bi-directional communication has been established between two routers.

Exstart: Once the DR and BDR are elected, the actual process of exchanging link state information can start between the routers and their DR and BDR.

Exchange: OSPF routers exchange database descriptor (DBD) packets

Loading: In this state, the actual exchange of link state information occurs

Full: routers are fully adjacent with each other

(Reference: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0e.shtml)

OSPF Questions 5

May 6th, 2014 digitaltut 4 comments

Here you will find answers to OSPF Questions – Part 5

Question 1

A network administrator has enabled OSPF across an NBMA network and has issued the command ip ospf network nonbroadcast. Given those facts, which two statements are true? (Choose two)

A. DR and BDR elections will occur.
B. DR and BDR elections will not occur.
C. All routers must be configured in a fully meshed topology with all other routers.
D. The neighbor command is required to build adjacencies.
E. Interfaces will automatically detect and build adjacencies with neighbor routers.

 

Answer: A D

Explanation

When using the command “ip ospf network nonbroadcast”, we turn the network into a nonbroadcast network so routers can not send broadcast or multicast. But OSPF uses multicast address 224.0.0.5 to send Hello packet periodically. Therefore we have to manually define the neighbor (via the neighbor command) to make OSPF send Hello packets to its adjacent routers -> D is correct.

For Multi-access network (for example Ethernet or Frame Relay), a designated router (DR) and a backup designated router (BDR) are elected ->A is correct.

Note: By default, Frame Relay environment is nonbroadcast so it is actually not necessary to use the command “ip ospf network nonbroadcast” on Frame Relay network.

Question 2

RouterA#
~~~~~
!
router ospf 1
log-adjacency-changes
network 10.0.0.0 0.255.255.255 area 1
network 172.16.1.0 0.0.0.255 area 1
!
~~~~~

RouterB#
~~~~~
router ospf 1
log-adjacency-changes
network 10.0.0.0 0.255.255.255 area 2
network 172.16.2.0 0.0.0.255 area 2
!
~~~~~

RouterC#
~~~~~
!
router ospf 1
log-adjacency-changes
network 10.0.0.0 0.255.255.255 area 0
!
~~~~~

Refer to the exhibits. You are verifying your OSPF implementation, and it does not seem to be functioning properly. What can you conclude from the exhibit and the show running-configuration command output?

OSPF_configuration.jpg

What can you conclude from the exhibit and the show running-configuration command output?

A. The OSPF areas are not configured correctly.
B. The wildcard masks for the 10.x.x.x networks are incorrect.
C. The 172.16.x.x networks need to be connected to area 0 using virtual links.
D. The 172.16.x.x networks are discontiguous. OSPF is automatically summarizing them to 172.16.0.0/16 and data is being “black holed”.
E. There is not enough information to make a determination.

 

Answer: A

Explanation

The E0/0 & E0/1 interfaces of router C belong to area 0 while E0/0 of router A belongs to area 1; E0/0 of router B belongs to area 2 -> it is not correct. Both E0/0 interfaces of router A & B should be in area 0 -> A is correct.

Question 3

Which two routing interface parameters are supported in OSPF implementations? (Choose two)

A. retransmit-interval
B. dead-interval
C. stub area
D. virtual link
E. NSSA area

 

Answer: A B

Explanation

When OSPF sends an advertisement to an adjacent router, it expects to receive an acknowledgment from that neighbor. If no acknowledgment is received, the router will retransmit the advertisement to its neighbor. The retransmit-interval timer controls the number of seconds between retransmissions. To edit the retransmit-interval, use the “ip ospf retransmit-interval seconds” in interface configuration mode -> A is correct.

Dead-interval is the number of seconds without hello packets before an adjacency is declared down. To edit the dead-interval, use the “ip ospf dead-interval seconds” in interface configuration mode -> B is correct.

Other answers are not correct because they are not interface parameters.

Question 4

One of the most important characteristics of OSPF is Multiple areas. Which statement best describes why this feature is such an important enhancement to earlier routing protocols?

A. The network domain, when divided into areas, allows for the use of both IANA classful addressing and private addressing.
B. The use of multiple areas allows for the use of prioritization.
C. All computation is kept within the area, with minimum communication between the areas, allowing the network to scale to larger sizes.
D. It is easier to implement security.

 

Answer: C

Question 5

When other routing protocol routes are being redistributed into OSPF, what is one of the most common problems?

A. missing the tag option in the redistribute command.
B. missing the subnet option in the redistribute command.
C. missing the metric option in the redistribute command.
D. misconfiguring the metric-type option in the redistribute command to type-1.
E. misconfiguring the metric-type option in the redistribute command to type-2.

 

Answer: B

Explanation

When pulling routes into OSPF, we need to use the keyword “subnets” so that subnets will be redistributed too. For example, if we redistribute these EIGRP routes into OSPF:

+ 10.0.0.0/8
+ 10.10.0.0/16
+ 10.10.1.0/24

without the keyword “subnets”

router ospf 1
redistribute eigrp 1

Then only 10.0.0.0/8 network will be redistributed because other routes are not classful routes, they are subnets. To redistribute subnets we must use the keyword “subnets”

router ospf 1
redistribute eigrp 1 subnets

-> B is correct.

Question 6

Refer to the exhibit. Which statement is true about the configuration?

OSPF_adjacency.jpg

A. RTA will not establish an OSPF adjacency with RTB.
B. RTA will not accept OSPF hello packets from RTB.
C. RTA will send OSPF hello packets, but will not send OSPF updates.
D. RTA will send OSPF updates, but will not establish an adjacency with RTB.

 

Answer: A

Explanation

Passive-interface command is used to disable sending updates out from a specific interface. For OSPF it prevents Hello packets from being sent out or received through the interface. This will not allow to create a neighbor adjacency and prevent a router from learning prefixes from those neighbors.

For RIP, configuring an interface as passive will still allow the interface to listen to incoming routing updates for other RIP neighbors, but the interface will no longer send them.

Note: The passive-interface command is used in router configuration mode, not interface mode.

Question 7

Refer to the exhibit. Which statement is true?

OSPF_show_ip_ospf_neighbor.jpg

A. Router RTA is directly connected to interface 192.168.45.1.
B. Neighbor 192.168.45.1 has changed its OSPF priority number.
C. Router RTA and neighbor 192.168.45.2 are exchanging OSPF LSAs.
D. Router RTA is the BDR.

 

Answer: None (but we recommend the best choice is D)

Explanation

There are only 3 routers in this segment. From the output we learn that RTB (10.0.0.2) is the DR and RTC (10.0.0.1) is not the DR or BDR so we can deduce RTA is the BDR.

But there is a problem with the output on RTA. If RTA is the BDR, the connecting state to RTC should be FULL/DROTHER, not 2-WAY/DROTHER. So we suppose the exhibit in this question is not correct.

A is not correct because 192.168.45.1 may not be an interface. It can be a router-id which can be set by the “router-id …” command.
B is not correct because as we can see in the output above, the OSPF priority number of RTB is 1 and it is the default value.
If the output above is correct then RTA and RTC are not DR or BDR -> they don’t exchange OSPF LSAs -> C is not correct.

(Good link for reference: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094059.shtml)

So what will happen if we set the OSPF priority number of RTA to 0? Well, you will get the same output as above but the problem here is none of the above answers is correct.

In conclusion, answer D is only correct when the connecting state from RTA to RTC is FULL/DROTHER.

Question 8

Refer to the exhibit. All routers have simultaneously been reloaded, and the DR election has concluded as expected. Which state is RTC in?

OSPF_DR_election.jpg

A. 2WAY/DROTHER
B. 2WAY/BDR
C. 2WAY/DR
D. FULL/DROTHER
E. FULL/BDR
F. FULL/DR

 

Answer: E

Explanation

All the routers are allowed to take part in the DR/BDR election because all the “Pri”s (Priority) are 1 and they are equal so with default parameters, the router with highest IP address will become DR (RTD in this case) and the router with second highest IP address (RTC) will become BDR.

Question 9

The Dev-1 and Dev-3 routers are OSPF neighbors over the Ethernet 0/0 connection. Based on the show ip ospf neighbor output from the Dev-1 and Dev-3 routers, which statement is true?

OSPF_show_ip_ospf_neighbor-2.jpg

A. Dev-1 is the DR because it has a higher OSPF router priority.
B. Dev-1 is the DR because it has a lower OSPF router ID.
C. Dev-3 is the DR because it has a higher OSPF router priority.
D. Dev-3 is the DR because it has a lower OSPF router ID.
E. Both Dev-1 and Dev-3 are using the default OSPF router priority.

 

Answer: A

Explanation

The priority helps determine the DR and BDR on the network to which this interface is connected. Priority is an 8-bit field based on which DRs and BDRs are elected. The router with the highest priority becomes the DR. If the priorities are the same, the router with the highest router ID becomes the DR. By default, priorities are set to 1.

Notice that the Priorities shown in the output above are the priorities of the neighbors so the priority of router Dev-1 is 2 while the priority of Dev-3 is 1 -> the priority of Dev-1 is higher than that of Dev-3 -> Dev-1 is the DR.

Question 10

Which three statements about OSPF areas are true? (Choose three)

A. Areas introduce a boundary on the link-state updates.
B. Areas are logical definitions specific to any given router.
C. All routers within an area have the exact link-state database.
D. The calculation of the Dijkstra algorithm on a router is limited to changes within an area.
E. The area designated router will always have a priority of 0.

 

Answer: A C D

OSPF Questions 6

May 6th, 2014 digitaltut No comments

Here you will find answers to OSPF Questions – Part 6

Question 1

You are developing a verification plan for an upcoming OSPF implementation. Part of this plan is to verify the status of type 3 LSAs within the network. Which routers should you verify first to ensure that the configurations are correct for generating type 3 LSAs?

A. Internal routers within the backbone area (area 0)
B. Internal routers within the NSSAs
C. Internal routers within the stubby areas
D. ASBRs
E. ABRs
F. DRs and BDRs

 

Answer: E

Explanation

Type 3 LSA (Summary LSA) is advertised by the ABR of originating area to advertise network from other areas so we should check the ABRs first.

Question 2

To make OSPF area 4 totally stubby, the following command was issued on the ABR in router configuration mode:
area 4 stub
Which two things need to be done to finish making area 4 a totally stubby area? (Choose two)

A. Apply the area 4 stub command to all routers in the area.
B. On the ABR, use the area 4 stub command with the no-summary keyword.
C. On the ABR, specify a default cost for the area with the area default-cost command.
D. On the ABR, use the default-information originate command to inject a default route into area 4.
E. Use the auto-cost command on each router in the area to automatically determine the cost to other OSPF areas.

 

Answer: A B

Explanation

To make an area “totally stubby” we must apply the “area area-id stub no-summary” command on the ABR and area area-id stub” commands to all other routers in that area.

Note: The ABR in a totally stubby area does not create Type 3 summary LSA. It only creates a default route to outside destinations.

Question 3

Refer to the exhibit. Router C was configured so that it could form an adjacency with three OSPF neighbors, one connected to each of its three physical interfaces. Which statement is correct about router C?

show_ip_interface_brief_show_ip_ospf.jpg

A. It is configured and functioning correctly as an OSPF internal router.
B. It is configured and functioning correctly as an ABR attached to stub area 4.
C. It is configured and functioning correctly as an ASBR attached to external area 4.
D. It is configured and functioning correctly as an ABR attached to totally stubby area 4.
E. It is not configured correctly to function as specified.

 

Answer: D

Explanation

From the output of the “show ip ospf” command we notice 2 lines:

+ It is an area border router
+ It is a stub area, no summary LSA in this area (in Area 4)

Therefore we can conclude RouterC is an ABR and it is attached to a totally stubby area (with no summary LSA advertised) -> D is correct.

Question 4

Refer to the diagram. Which OSPF configuration command is required to configure Area 3 as a totally stubby area?

OSPF_totally_stub_area.jpg

A. On the ABR
router ospf 10
area 3 nssa
B. On the ABR
router ospf 10
area 3 stub
C. On all Area 3 routers
router ospf 10
area 3 stub no-summary
D. On all Area 3 routers
router ospf 10
area 3 stub
E. On the ABR
router ospf 10
area 3 stub no-summary

 

Answer: E

Explanation

To make an area “totally stubby” we must apply the “area area-id stub no-summary” command on the ABR (the middle router in this case) and area area-id stub” commands to all other routers in that area.

Question 5

Which show command will display only the Type 5 LSAs in the OSPF topology database?

A. show ip route
B. show ip route ospf
C. show ip ospf database summary
D. show ip ospf database nssa-external
E. show ip ospf database external

 

Answer: E

Explanation

The “show ip ospf database external” command displays information only about external LSAs (Type 5 LSAs) -> E is correct.

Below is an example of the “show ip ospf database external” command

OSPF_show_ip_ospf_database_external.jpg

Notice the line “LS Type: AS External Link”, which means LSA Type 5. For your information, the “Link State ID: 143.105.0.0” indicates the network being advertised; the “Advertising Router: 10.187.70.6” indicates the router that originated this LSA.

Note:

+ The “show ip ospf database summary” command displays information only about the summary LSAs.
+ The “show ip ospf database nssa-external” command displays information only about the not so stubby area (NSSA) external LSAs.

Question 6

When learning a new route, if a LSA received is not found in the topological database, what will an internal OSPF router do?

A. The sequence numbers are checked, and if the LSA is valid it is entered into the topology database.
B. The LSA is placed in the topological database and an acknowledgement is sent to the transmitting router.
C. The LSA is dropped and a message is sent to the transmitting router.
D. The LSA is flooded immediately out of all the OSPF interfaces, except the interface from which the LSA was received.

 

Answer: D

Question 7

Refer to the exhibit. What two statements are true? (Choose two)

show_interfaces.jpg

A. Interface FastEthernet 0/0 was configured with the ipv6 ospf 1 area 1 command.
B. OSPF version 2 has been enabled to support IPv6.
C. The IP address of the backup designated router (BDR) is FE80::205:5FFF:FED3:5808.
D. The output was generated by the show ip interface command.
E. The router was configured with the commands:
router ospf 1
network 172.16.6.0 0.0.0.255 area 1
F. This is the designated router (DR) on the FastEthernet 0/0 link.

 

Answer: A C

Question 8

Refer to the exhibit. OSPF has been configured on all routers in the network. However, router R1 does not receive a default route to router R2 as intended. Which configuration change would ensure that R1 would receive a default route from R2?

OSPF_default-information_originate.jpg

A. Add the area 1 stub command on routers R1.
B. Add the always keyword to the default-information originate configuration command on router R2.
C. Remove the default information originate configuration command from router R2 and place it on router R1.
D. Add the ip route 5.0.0.0 255.255.255.0 0.0.0.0 command to router R2.

 

Answer: B

Explanation

The default-information originate command advertises a default route into a normal area, provided the advertising router already has a default route. If we want the router to advertise the default route even if it does not have a default route then we can append the keyword always after the above command.

In this question, notice that R2 does not have a default route (something like this: ip route 0.0.0.0 0.0.0.0 6.0.0.2) so the “default-information originate” will not advertise this default route to R1 -> We need to add the keyword “always” or declare a default route -> B is correct.

Question 9

Refer to the exhibit. OSPF is configured on all routers in the network. Area 5 is configured as an NSSA area. The RIPv2 routes are redistributed into the OSPF domain on router R5. What two types of LSAs will be originated by router R5? (Choose two)

Redistribute_RIPv2_OSPF.jpg

A. type 1 Router LSA
B. type 2 Network LSA
C. type 3 Network Summary LSA
D. type 4 ASBR Summary LSA
E. type 5 AS External LSA
F. type 7 NSSA External LSA

 

Answer: A F

Explanation

Each router creates Type 1 LSA to describe itself, its interfaces, and neighbors -> A is correct.

Notice that LSA Type 7 is generated by an ASBR inside a Not-so-stubby area (NSSA) to describe routes redistributed into the NSSA -> F is correct.

For your information, the main difference between LSA Type 7 and Type 5 is Type 7 is generated inside a NSSA while Type 5 is generated inside a standard area.

Question 10

Refer to the exhibit. Based on this command output, what can we conclude about R3?

OSPF_show_ip_ospf_database.jpg

A. R3 is an ABR.
B. R3 is not connected to the backbone.
C. R3 has four neighbors.
D. R3 is the DR for area 2.

 

Answer: A

Explanation

From the output we learned that this router is getting Type 3 LSAs (Summary Net Link States) for both Area 0 and Area 3 -> It is an ABR between Area 0 & Area 3 -> A is correct; B is not correct.

From the LSA Type 1 we learn that R3 only has 1 neighbor, which is 192.168.0.4 -> C is not correct.

To find the DR for an area, we need to look at the LSA Type 2 of that area. In this case we find out 116.16.35.5 is the DR for area 2, not R3 -> D is not correct.

To help you understand more clearly about the “show ip ospf database” command, we want to explain more about the fields in the output:

OSPF_show_ip_ospf_database_Explained.jpg

+ Link ID is the OSPF Router-ID of a router in the area for LSA Type 1 & 2 but it is can be the Router-ID or the network address for LSA Type 3, 5 & 7.
+ The ADV Router is the ID of the router that sent the LSA (Advertising Router) into the area
+ Age: The max age of the link state
+ Seq# and Checksum: these fields are used to verify link-state integrity.

For example, from the Router Link States (Area 0.0.0.0):

OSPF_show_ip_ospf_database_Router_LSA.jpg

The first “Link ID” 172.16.1.1 is the Router-ID of the local router R3 (because it is the same as “OSPF Router with ID”). This “Link ID” is, of course, advertised by itself so the ADV Router has the same value.

The second “Link ID” is the Router-ID of 192.168.0.4, which is advertised by 192.168.0.4 so it is directly connected to R3.

Notice that these 2 routers belong to Area 0.

From the Net Link States:

OSPF_show_ip_ospf_database_Net_Link.jpg

We learn that the “Link ID” 116.16.34.4 is advertised from the neighbor 192.168.0.4, which is directly connected to R3. This router (116.16.34.4) also belongs to Area 0 and it is the DR of that segment.

The Summary Net Link States gives us information about LSA Type 3 (advertised by the ABR of area 0. Recall that ABRs generate a Type 3 LSA for each subnet in one area, and advertises each Type 3 LSA into the other areas)

OSPF_show_ip_ospf_database_Summary_Net_Link_State.jpg

From the output we learn that the subnet 116.16.35.0 is advertised via 172.16.1.1 and four routers (in fact, interfaces) are advertised by 192.168.0.4. Notice that these routers (interfaces) can belong to other areas.

OSPF Questions 7

May 6th, 2014 digitaltut 3 comments

Here you will find answers to OSPF Questions – Part 7

Question 1

Refer to the exhibit. ROUTE.com is planning to implement a new secure OSPF network to support traffic between clients on the 172.16.10.0/24 network and the file server on the 172.16.20.0/24 network. You have been asked to review the implementation plan for the OSPF project.
Which statement about the plan is true?

OSPF_Implementation_Plan.jpg

A. It is complete as written.
B. It should include a task that shuts down all unused interfaces.
C. It should include tasks that enable and verify OSPF authentication.
D. It should include a task that establishes a file transfer baseline before and after the configuration is changed.

 

Answer: C

Explanation

The complete implementation plan should be

1. Enable OSPF process 1 on all routers
2. Enable area 0 on R2, R3 and R4
3. Enable area 10 on R1, R2 and R3
4. Enable area 20 on R4 and R5
5. Enable and verify OSPF authentication
6. Verify that all routers contain a complete routing table
7. Verify that the clients can successfully access the server
8. Document configuration changes

Question 2

Refer to the exhibit. ROUTE.com is planning to implement a secure OSPF network to support traffic between clients on the 172.16.10.0/24 network and the file server on the 172.16.20.0/24 network. You have been asked to review the implementation and verification plans.
Which statement about the plan is true?

OSPF_Verification_Plan.jpg

A. It is complete as written.
B. It should include a task that verifies that the interarea routes are using the proper MED.
C. The plan should include a task that verifies that load sharing is active on the appropriate links.
D. The plan should include a task that verifies end-to-end connectivity between the clients and the file server.

 

Answer: D

Question 3

Refer to the exhibit. ROUTE.com is planning to implement a secure OSPF network to support traffic between clients on the 172.16.10.0/24 network and the file server on the 172.16.20.0/24 network. You have been asked to review the implementation and verification plans for this OSPF project.
Which statement about the plan is true?

OSPF_Verification_Plan-2.jpg

A. It is complete as written.
B. It should include a task that verifies that the interarea routes are using the proper MED.
C. it should include a task that verifies that load sharing is active on R1 and R4.
D. It should include a task that verifies that all redundant links will become active when the primary links are shut down.

 

Answer: D

Question 4

Refer to the exhibit. Which two Cisco IOS commands on R2 would verify its OSPF neighbor relationships? (Choose two)

OSPF_neighbor_relationship.jpg

A. show ip ospf
B. show ip ospf interface
C. show ip ospf neighbor
D. show ip ospf database
E. show ip ospf statistics
F. show running-config | begin router ospf

 

Answer: B C

Explanation

The show ip ospf interface command shows us information about the neighbor count and adjacent neighbor count:

show_ip_ospf_interface-2.jpg

The show ip ospf neighbor command shows us the role of each neighbor (DR, BDR, DROTHER).

OSPF_show_ip_ospf_neighbor-2.jpg

Question 5

Which command displays the number of times that the OSPF Shortest Path First (SPF) algorithm has been executed?

A. show ip protocol
B. show ip ospf interface
C. show ip ospf
D. show ip ospf database

 

Answer: C

Explanation

Below is the output of this command:

show_ip_ospf.jpg

Question 6

Refer to the exhibit. Will redistributed RIP routes from OSPF Area 2 be allowed in Area 1?

OSPF_Redistribute_RIP_OSPF.jpg

A. Because Area 1 is an NSSA, redistributed RIP routes will not be allowed.
B. Redistributed RIP routes will be allowed in Area 1 because they will be changed into type 5 LSAs in Area 0 and passed on into Area 1.
C. Because NSSA will discard type 7 LSAs, redistributed RIP routes will not be allowed in Area 1.
D. Redistributed RIP routes will be allowed in Area 1 because they will be changed into type 7 LSAs in Area 0 and passed on into Area 1.
E. RIP routes will be allowed in Area 1 only if they are first redistributed into EIGRP.

 

Answer: A

Explanation

Area 1 is a NSSA so we can inject EIGRP routes into this area with Type 7 LSAs. Notice that Type 7 LSAs can only be existed in a NSSA. The NSSA ABR of area 1 must converted it into LSA Type 5 before flooding to the whole OSPF domain.

When redistribute RIP into area 2, LSA Type 5 will be created an sent through area 0. But a NSSA is an extension of a stub area. The stub area characteristics still exist, which includes no type 5 LSAs allowed.

Note: A stub area only allows LSA Type 1, 2 and 3.

(Reference & good resource: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a88.shtml)

Question 7

Refer to the exhibit. OSPF has been configured on all routers in the network and Area 1 has been configured as a NSSA. Which statement is true about the NSSA Area 1?

OSPF_Redistribute_IGRP_OSPF.jpg

A. Redistributed RIP and IGRP routes will appear in Area 1. They will be advertised via type 5 LSAs.
B. Only redistributed RIP routes will appear in Area 1. They will be advertised via type 7 LSAs.
C. Only redistributed IGRP routes will appear in Area 1. They will be advertised via type 7 LSAs.
D. No redistributed routes can appear in Area 1, only summary routes.

 

Answer: C

Explanation

Same explanation of Question 6. Please notice that the IGRP routes are redistributed to NSSA area 1 via LSA Type 7. The NSSA ABR of area 1 will convert it into a LSA Type 5 before flooding to area 0 & area 2.

Question 8

Refer to the exhibit. Based on the command output, what is one reason why no routes from the OSPF neighbor 192.168.0.5 are installed in the IP routing table?

show_ip_ospf_neighbor_show_ip_route_ospf.jpg

A. R3 will only install routes from the neighbor with the lowest priority (Pri). If routes have the same priority, routes from the neighbor with the lowest IP address are used.
B. R3 did not receive any LSAs from 192.168.0.5.
C. Routes from backup designated routers are never installed in the IP routing table.
D. 192.168.0.5 is a redundant link to 192.168.0.4, and load balancing is not enabled.

 

Answer: B

Explanation

R3 may not receive any LSAs from neighbor 192.168.0.5 because a distribute-list blocks it. But notice that the LSAs are not filtered out in the LSDB since all routers in an OSPF area must be the same (synchronized).

Question 9

Refer to the exhibit. OSPF is running throughout the network. You want to minimize the propagation of LSAs into and out of Area 1.
Which OSPF feature would best achieve this goal?

OSPF_minimize_LSA.jpg

A. stub
B. totally stubby
C. NSSA
D. totally NSSA

 

Answer: D

Explanation

We need to redistribute RIP from R1 to Area 1 so Area 1 cannot be a stub or totally stubby area. To minimize the propagation of LSAs into and out of Area 1 we should configure it as a totally NSSA. Notice that a NSSA allows LSA Type 3 & 7 while a Totally NSSA only allows LSA Type 7.

Note:
Both Totally Stubby Area & Totally Stubby NSSA do not accept external AS routes or inter-area routes (LSA Types 3, 4 and 5). They recognize only intra-area routes and the default route 0.0.0.0. The main difference between them is Totally Stubby NSSA accepts routes from other AS while Totally Stubby Area does not.

Below summarizes the LSA Types allowed and not allowed in area types:

Area Type Type 1 & 2 (within area) Type 3 (from other areas) Type 4 Type 5 Type 7
Standard & backbone Yes Yes Yes Yes No
Stub Yes Yes No No No
Totally stubby Yes No No No No
NSSA Yes Yes No No Yes
Totally (stubby) NSSA Yes No No No Yes

Question 10

Refer to the exhibit. A company would prefer all Internet-bound OSPF routed traffic to use ISP ABC with ISP DEF as a backup. As the network consultant, what three configuration changes might you make? (Choose three)

OSPF_Troubleshooting.jpg

A. The default-information originate command should be configured on router B1 and B4.
B. The default-information originate command should be configured on router B2 and B3.
C. If the metric value for ISP ABC is set at the default, the ISP DEF metric value should be set to 1.
D. If the metric value for ISP ABC is set at the default, the ISP DEF metric value should be set to 25.
E. The metric type value should be set to type 1.
F. The metric type value should be set to type 2.

 

Answer: B D F

Explanation

Routers B2 & B3 need to advertise a default route to the Internet for “inside” OSPF routers so we should use the “default-information originate” command with a default route (something like “ip route 0.0.0.0 0.0.0.0”) pointing to the ISP router -> B is correct.

If no metric is specified, OSPF puts a default value of 20 when redistributing routes from all protocols except BGP routes (BGP routes get a metric of 1). We use ISP DEF as a backup so its metric value should be set to a higher value than 20 -> D is correct.

There are two types of external routes: external type 1 and external type 2. The difference between the two is in the way the cost (metric) of the route is being calculated:
+ The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.
+ Type 1 cost is the addition of the external cost and the internal cost used to reach that route.

-> We should configure the type 2 external route to make sure the ISP ABC is always referred over ISP DEF because internal routing does not determine the path.

Note: E2 is the default external metric, but E1 is preferred over E2 if two equal-cost paths exist.

Question 11

Refer to the exhibit. A network administrator wants to reduce the number of OSPF routes advertised from Area 1 into Area 2. As the router configuration specialist, what two things would you do to accomplish this goal? (Choose two)

OSPF_Reduce_Advertise_routes.jpg

A. Enter the configuration on router B1.
B. Enter the configuration on router B4.
C. On the same router, enter the Summary-address 10.10.1.0 255.255.255.128 subcommand.
D. On the same router, enter the Area 1 range 10.10.1.0 255.255.255.128 subcommand.
E. On the same router, enter the Area 2 range 10.10.1.0 255.255.255.128 subcommand.

 

Answer: A D

OSPF Questions 8

May 6th, 2014 digitaltut No comments

Here you will find answers to OSPF Questions – Part 8

Question 1

Refer to the exhibit. On the basis of the information presented, which statement is true?

RTA#show ip route ospf

O IA 6.0.0.0/8 [110/65] via 5.0.0.2, 00:00:18, Serial2/1/0
O*N2 0.0.0.0/0 [110/1] via 5.0.0.2, 00:00:18, Serial2/1/0

A. A default route is configured on the local router.
B. Network 6.0.0.0/8 was learned from an OSPF neighbor within the area.
C. OSPF router 5.0.0.2 is an ABR.
D. The default route is learned from an OSPF neighbor.

 

Answer: C

Explanation

The “O IA” here means”OSPF Inter-Area”. This means that RTA learned the route 6.0.0.0/8 from another OSPF neighbor outside its area. Moreover the “O*N2” is the LSA Type 7 which only appears on the ABR. You can read a lab about OSPF LSA Types here: http://www.digitaltut.com/ospf-lsa-types-lab.

Question 2

Refer to the exhibit. Given the exhibited router output, which command sequence can be added to R1 to generate a default route into the OSPF domain?

OSPF_default-information_originate_always_default_route.jpg

A. default-router
B. ip default-network
C. default-information originate always
D. ip default-gateway

 

Answer: C

Explanation

The default-information originate command advertises a default route to other routers, telling something like “please send me your unknown traffic”. With the always parameter, the default route is advertised even if there is no default route in the router’s routing table. In this case we don’t see any default route in the configuration of R1 (like ip route 0.0.0.0 0.0.0.0 ….) so it must include the keyword “always” so that the default route is advertised.

Question 3

What are three kinds of OSPF areas? (Choose three)

A. stub
B. active
C. remote
D. backbone
E. ordinary or standard

 

Answer: A D E

Explanation

There are 4 kinds of OSPF areas:

+ Standard (Ordinary) Areas
+ Stub Areas
+ Totally Stubby Areas
+ Not-so-stubby Areas

Note: The backbone area (area 0) is also listed as a standard area.

Question 4

When implementing OSPFv3, which statement describes the configuration of OSPF areas?

A. In interface configuration mode, the OSPFv3 area ID combination assigns interfaces to OSPFv3 areas.
B. In router configuration mode, the network wildcard area ID combination assigns networks to OSPFv3 areas.
C. In interface configuration mode, the IPv6 OSPF process area ID combination assigns interfaces to OSPFv3 areas.
D. In router configuration mode, the IPv6 OSPF interface area ID combination assigns interfaces to OSPFv3 areas.

 

Answer: C

Explanation

An example of configuring IPv6 OSPF process area combined with OSPFv3 areas is shown below:

interface s1/0
ipv6 address 3FFE:B00:FFFF:1::2/64
ipv6 ospf 100 area 1

Note: OSPFv3 requires areas & OSPF process to be configured under interface, not in router mode.

Question 5

Refer to the exhibit. Why is the 140.140.0.0 network not used as the gateway of last resort even though it is configured first?

R3#show run | include default-
ip default-network 140.140.0.0
ip default-network 130.130.0.0

R3#show ip route | begin Gateway
Gateway of last resort is 0.0.0.0 to network 130.130.0.0
116.0.0.0/8 is variably subnetted, 5 subnets, 3 masks
C 116.16.37.0/30 is directly connected, Serial1/0.2
C 116.16.32.0/30 is directly connected, Serial2/0.2
C 116.16.34.0/28 is directly connected, Serial1/0.1
C 116.16.35.0/28 is directly connected, Serial2/0.1
S 116.0.0.0/8 [1/0] via 116.16.34.0
* 140.140.0.0/32 is subnetted, 3 subnets
O 140.140.1.1 [110/65J via 116.16.34.4, 00:14:54, Serial1/0.1
O 140.140.3.1 [110/65] via 116.16.34.4, 00:14:54, Serial1/0.1
O 140.140.2.1 [110/65] via 116.16.34.4, 00:14:54, Serial1/0.1
* 130.130.0.0/16 is variably subnetted, 4 subnets, 2 masks
D* 130.130.0.0/16 is a summary, 00:30:04, Null0
C 130.130.1.0/24 is directly connected, Ethernet0/0
C 130.130.2.0/24 is directly connected, Ethernet0/1
C 130.130.3.0/24 is directly connected, Ethernet1/0
D 150.150.0.0/16 [90/679936] via 116.16.35.5, 00:02:58, Serial2/0.1

A. The last default-network statement will always be preferred.
B. A route to the 140.140.0.0 network does not exist in the routing table.
C. Default-network selection will always prefer the statement with the lowest IP address.
D. A router will load balance across multiple default-networks; repeatedly issuing the show ip route command would show the gateway of last resort changing between the two networks.

 

Answer: B

Explanation

In the routing table of R3, we can only see the route 130.130.0.0/16 is learned via EIGRP (marked with D) and is being chosen as the “Gateway of last resort”. The route to 140.140.0.0 is not present in the routing table so the command “ip default-network 140.140.0.0” has no effect. Remember that a route must appear in the routing table (via static route or learned via a routing protocol before it can be set as “Gateway of last resort” by the “ip default-network” command.

Question 6

Refer to the exhibit. A network administrator wants to reduce the number of OSPF routes advertised from Area 1 into Area 2. As the router configuration specialist, what two things would you do to accomplish this goal? (Choose two)

OSPF_Reduce_Advertise_routes.jpg

A. Enter the configuration on router B1.
B. Enter the configuration on router B4.
C. On the same router, enter the Summary-address 10.10.1.0 255.255.255.128 subcommand.
D. On the same router, enter the Area 1 range 10.10.1.0 255.255.255.128 subcommand.
E. On the same router, enter the Area 2 range 10.10.1.0 255.255.255.128 subcommand.

 

Answer: A D

Explanation

This is how to configure manual summarization on B1:

router ospf 1
area 1 range 10.10.1.0 255.255.255.128

 

Question 7

Which command displays the number of times that the OSPF Shortest Path First (SPF) algorithm has been executed?

A. show ip protocol
B. show ip ospf interface
C. show ip ospf
D. show ip ospf database

 

Answer: C

Explanation

The output of the “show ip ospf” command is shown below:

OSPF_show_ip_ospf.jpg

Question 8

For IPv6, what term or phrase best describes a type 9 LSA in OSPF?

A. router LSA
B. interarea prefix LSA
C. link LSA
D. interarea prefix LSA for ABRs

 

Answer: B

Question 9

Given the above OSPF network, which command will RTB use to summarize routes for the 192.168.16.0/22 supernet before injecting them into Area 0?

OSPF_area_range.jpg

A. area 10 range 192.168.16.0 255.255.252.0
B. summary-address 192.168.16.0 255.255.252.0
C. ip summary-address ospf 101 192.168.16.0 255.255.252.0
D. area 0 range 192.168.16.0 255.255.252.0
E. ip summary-address area 0 192.168.16.0 255.255.252.0

 

Answer: A

Question 10

Which command would display OSPF parameters such as filters, default metric, maximum paths, and number of areas configured on a router?

A. show ip protocol
B. show ip route
C. show ip ospf interface
D. show ip ospf

 

Answer: A

Explanation

The output of the show ip protocol is shown below:

OSPF_show_ip_protocols.jpg

This command is used to display the parameters and current state of the active routing protocol process. This command displays all the filters (outgoing/incoming update filter list for all interfaces…), distance (default is 110 in this case for OSPF), metric (can be calculate by the formula 108 / Bandwidth), maximum paths (4, in this case), number of areas (3).

Below is the output of the same command but EIGRP is running, just for your reference:

show_ip_protocols_for_EIGRP.jpg

OSPF Questions 9

May 6th, 2014 digitaltut 1 comment

Here you will find answers to OSPF Questions – Part 9

Question 1

In IPv6, the interfaces running OSPF can be configured with multiple address prefixes. Which statement is true about the IPv6 addresses that can be included into the OSPF process?

A. Specific addresses cannot be selected for importation into the OSPF process.
B. Specific addresses can be selected using an ACL.
C. Specific addresses can be selected using a route map.
D. Specific addresses can be selected using a prefix list.

 

Answer: A

Explanation

When importing (redistributed) a set of addresses specified on an interface on which OSPFv3 is running into OSPFv3, you cannot select specific addresses to be imported. Either all addresses are imported, or no addresses are imported.

Question 2

Which statement is true about the command ipv6 ospf 1 area 0?

A. It must be issued in router global configuration mode to enable the OSPF process for IPv6.
B. It must be issued in interface configuration mode to enable the OSPF process for IPv6.
C. It must be issued before the network command to enable the OSPF process for IPv6.
D. It must be issued after the network command to enable the OSPF process for IPv6.

 

Answer: B

Question 3

Refer to the exhibit. Based on the output from the show command on RT1 which statement is true?

show_ipv6_ospf_interface_link_local.jpg

A. OSPFv3 uses global IPv6 addresses to establish neighbor adjacencies.
B. RT1 has a subnet mask of 64 bits.
C. RT1 has FastEthernet0/0 set as a DR for network type broadcast.
D. OSPFv3 uses Link-local addresses to establish neighbor adjacencies.
E. RT1 does not have a global IPv6 address set on FastEthernet0/0.
F. OSPFv3 uses IPv4 addresses to establish neighbor adjacencies.

 

Answer: D

Explanation

Link local address is a special type of address intended for communications within the local network segment or a point-to-point connection. Routers do not forward packets with link local address. The link local address gets a FE80::/10 prefix.

The OSPFv3 uses Link-local address to form neighbor adjacency by sending and receiving the hello packet to the neighbor router.

Question 4

What command should be used for a totally stubby area on the router connected to area 0 backbone?

A. totally stubby on the ABR
B. stub no-summary on the ABR
C. totally stubby on all routers in the area
D. stub no-summary on the ASBR
E. stub no-summary on all routers in the area
F. totally stubby on the ASBR

 

Answer: B

Question 5

Refer to the output. What IOS command produces this output?

show_ipv6_ospf_output.jpg

A. show ip ospf
B. show ip ospf interface
C. show ipv6 ospf interface
D. show ipv6 ospf

 

Answer: D

Explanation

The command “show ipv6 ospf” is used to display general information about OSPF routing processes.

Question 6

Which three statements are true when configuring redistribution for OSPF? (Choose three)

A. The default metric is 10.
B. The default metric is 20.
C. The default metric type is 2.
D. The default metric type is 1.
E. Subnets do not redistribute by default.
F. Subnets redistribute by default.

 

Answer: B C E

Question 7

To create an NSSA totally stubby area in Area 1, what commands should be configured on the NSSA ABR?

A. router ospf 1
area 1 nssa

B. router ospf 1
area 1 nssa no-summary

C. router ospf 1
area 1 nssa no-redistribution

D. router ospf 1
area 1 nssa default-information originate

E. router ospf 1
area 1 nssa default-information originate metric-type 2

 

Answer: B

Question 8

How is the configuration of a totally stubby area different from that of a stub area?

A. The totally stubby area requires the no-summary command on the ABR.
B. The totally stubby area requires the totally stubby command on the ABR.
C. The no-summary command should be included on all routers within the totally stubby area.
D. The totally stubby command should be included on all routers within the totally stubby area.
E. The totally stubby area requires the no-summary command on the ASBR.

 

Answer: A

Question 9

Which three statements about configuring OSPF in a IPv6 network are true? (Choose three)

A. OSPF version 2 will support IPv6.
B. OSPF version 3 will support IPv6.
C. Multiple instances of OSPF for IPv6 can be run on a link.
D. Networks must be explicitly configured using the network command in router OSPF configuration mode.
E. IPv4 addresses cannot be used as the router ID in OSPF for IPv6.
F. The interface command ipv6 ospf area is all that is required to enable OSPF for IPv6 on an interface.

 

Answer: B C F

Question 10

In which state do DR and BDR establish adjacency with each OSPF router in the network?

A. Init State
B. Exstart State
C. Exchange State
D. Loading State

 

Answer: A

Explanation

When OSPF adjacency is formed, a router goes through several state changes before it becomes fully adjacent with its neighbor. The states are: Down, Attempt, Init, 2-Way, Exstart, Exchange, Loading, and Full.

Suppose two routers are just turned on and want to establish DR\BDR adjacency. Both are in DOWN state, each router sends a multicast Hello and moves to INIT state. After a router has both received a Hello and verified that all the required parameters agree, the router lists the other router’s RID in the Hello message as being seen. When a router receives a Hello that lists its own RID as having been seen by the other router, the router can transition to 2-Way state.

(Reference: CCNP ROUTE 642-902 Official Certification Guide)

OSPF Questions 10

May 6th, 2014 digitaltut No comments

Here you will find answers to OSPF Questions – Part 10

Question 1

Refer to the exhibit. Which statement is true?

Redistribute_RIP_OSPF_LSA_type_7.jpg

A. RTA will redistribute the RIP routers into the NSSA as type 7 LSAs. RTB will translate the type 7 LSAs into type 5 LSAs and flood them throughout the OSPF backbone.
B. RTA will redistribute the RIP routers into the NSSA as type 7 LSAs. RTB will flood the type 7 LSAs throughout the backbone.
C. RTA will redistribute the RIP routers into the NSSA as type 5 LSAs. RTB will flood the type 5 LSAs throughout the backbone.
D. RTA will redistribute the RIP routers into the NSSA as type 5 LSAs. RTB will translate the type of 5 LSAs into type 7 LSAs and flood them throughout the OSPF backbone.
E. RTA will not redistribute the RIP routers into the NSSA.

 

Answer: A

Question 2

What is the sequence, from first to last, that OSPF will follow when choosing a router ID?

A. 1. the highest IP address on any active loopback interface;
2. The router-id command results;
3. The highest IP address of any active physical interface.

B. 1. the highest IP address on any active loopback interface;
2. The highest IP address of any active Physical interface;
3. The router-id command result.

C. 1. The highest IP address of any active Physical interface;
2. the highest IP address on any active loopback interface;
3. The router-id command results.

D. 1. The highest IP address of any active Physical interface;
2. The router-id command result;
3. The highest IP address of any active physical interface.

E. 1. The router-id command results;
2. The highest IP address of any active Physical interface;
3. The highest IP address of any active physical interface.

F. 1. the router-id command result;
2. the highest IP address on any active loopback interface;
3. the highest IP address of any active physical interface

 

Answer: F

Question 3

Refer to the network topology diagram shown in the exhibit. The routing table of R3 contains all the proper OSPF routes except the 10.4.4.0/24 OSPF route. Which show command on R3 will be the most useful to determine the cause of this problem and why?

OSPF_virtual-link_troubleshooting.jpg

A. Perform show ip ospf virtual-link to examine if the virtual link between R3 and R4 is configured and in the up state.
B. Perform show run to examine if area 3 is configured as a stubby area.
C. Perform show run to examine if area 3 is configured as a nssa area.
D. Perform show ip ospf neighbor to examine which router is elected as the DR on the e2 interface.
E. Perform show ip ospf database to examine the OSPF database entries.

 

Answer: A

Question 4

A network administrator recently redistributed RIP routes into an OSPF domain. However, the administrator wants to configure the network so that instead of 32 external type-5 LSAs flooding into the OSPF network, there is only one. What must the administrator do to accomplish this?

summary_address_RIP_OSPF.jpg

A. Configure summarization on R1 with area 1 range 172.16.32.0 255.255.224.0
B. Configure summarization on R1 with summary-address 172.16.32.0 255.255.224.0
C. Configure area 1 as a stub area with area 1 stub
D. Configure area 1 as a NSSA area with area 1 stub nssa

 

Answer: B

Question 5

Refer to the exhibit. Routers R2, R3, R4, and R5 have OSPF enabled. What should be configured on the routers in area 1 to ensure that all default summary routes and redistributed EIGRP routes will be forwarded from R6 to area 1, and only a default route for all other OSPF routes will be forwarded from R5 to area 1.

OSPF_nssa_no_summary.jpg

A. R5(config-router)# area 1 stub
R6(config-router)# area 1 stub

B. R5(config-router)# area 1 stub no-summary
R6(config-router)# area 1 stub

C. R5(config-router)# area 1 nssa
R6(config-router)# area 1 nssa

D. R5(config-router)# area 1 nssa no-summary
R6(config-router)# area 1 nssa

 

Answer: D

EIGRP Questions

May 5th, 2014 digitaltut 3 comments

Here you will find answers to EIGRP questions

Question 1

Which three statements about the EIGRP routing protocol are true? (Choose three)

A – EIGRP sends periodic hello packets to the multicast IP address 224.0.0.9
B – EIGRP sends periodic hello packets to the multicast IP address 224.0.0.10
C – EIGRP supports five generic packet types. including hello, update, query, reply, and ACK packets
D – EIGRP supports five generic packet types, including hello, database description (DBD), link-state request (LSR), link-state update (LSU), and LSAck
E – E. EIGRP will form a neighbor relationship with another peer even when their K values are mismatched
F – A. EIGRP will not form a neighbor relationship with another peer when their K values are mismatched

 

Answer: B, C, F

Question 2

After DUAL calculations, a router has identified a successor route, but no routes have qualified as a feasible successor. In the event that the current successor goes down, what process will EIGRP use in the selection of a new successor?

A – EIGRP will find the interface with the lowest MAC address
B – The route will transition to the active state
C – The route will transition to the passive state
D – EIGRP will automatically use the route with the lowest feasible distance (FD)
E – EIGRP will automatically use the route with the lowest advertised distance (AD)

 

Answer: B

Explanation

When a route (current successor) goes down, the router first checks its topology table for a feasible successor but it can’t find one. So it goes active on the that route to find a new successor by sending queries out to its neighbors requesting a path to the lost route.

Question 3

Refer to the exhibit. Routers R1 and R2 have established a neighbor relationship and are exchanging routing information. The network design requires that R1 receive routing updates from R2, but not advertise any routes to R2. Which configuration command sequence will successfully accomplish this task?

neighbor_relationship_distribute_list

A – R1(config)# router eigrp 1
R1(config-router)# passive-interface serial 0

B – R2(config)# router eigrp 1
R2(config-router)# passive-interface serial 0

C – R1(config)# access-list 20 deny any
R1(config)# router eigrp 1
R1(config-router)# distribute-list 20 out serial 0

D – R2(config)# access-list 20 deny any
R2(config)# router eigrp 1
R2(config-router)# distribute-list 20 out serial 0

E – R1(config)# access-list 20 permit any
R1(config)# router eigrp 1
R1(config-router)# distribute-list 20 in serial 0

F – R2(config)# access-list 20 permit any
R2(config)# router eigrp 1
R2(config-router)# distribute-list 20 in serial 0

 

Answer: C

Explanation

We can not use passive-interface to accomplish this task because the “passive-interface…” command (in EIGRP or OSPF) will shut down the neighbor relationship of these two routers (no hello packets are exchanged). And to filter routing updates we should configure a distribute list on R1 with an access list that deny all and apply it to the outbound direction so that R1 can receive but can not send routing updates.

Question 4

EIGRP has been configured to operate over Frame Relay multipoint connections. What should the bandwidth command be set to?

A – the CIR rate of the lowest speed connection multiplied by the number of circuits
B – the CIR rate of the lowest speed connection
C – the CIR rate of the highest speed connection
D – the sum of all the CIRs divided by the number of connections

 

Answer: A

Explanation

If the multipoint network has different speeds allocated to the VCs, take the lowest CIR and simply multiply it by the number of circuits. This is because in Frame-relay all neighbors share the bandwidth equally, regardless of the actual CIR of each individual PVC, so we have to get the lowest speed CIR rate and multiply it by the number of circuits. This result will be applied on the main interface (or multipoint connection interface).

Question 5

EIGRP_Active_state

Refer to the exhibit. EIGRP is configured on all routers in the network. On a basis of the show ip eigrp topology output provided, what conclusion can be derived?

A – Router R1 can send traffic destined for network 10.6.1.0/24 out of interface FastEthernet0/0
B – Router R1 is waiting for a reply from the neighbor 10.1.2.1 to the hello message sent out before it declares the neighbor unreachable
C – Router R1 is waiting for a reply from the neighbor 10.1.2.1 to the hello message sent out inquiring for a second successor to network 10.6.1.0/24
D – Router R1 is waiting for a reply from the neighbor 10.1.2.1 in response to the query sent out about network 10.6.1.0/24

 

Answer: D

Explanation

From the output, we notice that there is an active route (A) and the reply status flag (r) was set. An active EIGRP route is the state when a network change occurs and a feasible successor is not found by a EIGRP router for a given route (10.6.1.0/24); and the reply status flag (r) means that R1’s queries were sent out to the neighbors asking for routing information to the 10.6.1.0/24 network but hasn’t received a reply yet. Therefore the answer A – router R1 can send traffic destined for network 10.6.1.0/24 is not correct because router R1 can’t find a path to that network. Answers B and C are not correct because R1 doesn’t send a hello message but a query asking for routing information to the desired network.

 

EIGRP Questions 2

May 5th, 2014 digitaltut No comments

Here you will find answer to EIGRP Questions – Part 2

Question 1

Refer to the exhibit. EIGRP has been configured on all routers in the network. What additional configuration statement should be included on router R4 to advertise a default route to its neighbors?

EIGRP_Default-route.jpg

A. R4(config)#ip default-network 10.0.0.0
B. R4(config)#ip route 0.0.0.0 0.0.0.0 10.1.1.1
C. R4(config)#ip route 10.0.0.0 255.0.0.0 10.1.1.1
D. R4(config-router)# default-information originate

 

Answer: A

Explanation

The “ip default-network ” command will direct other routers to send its unknown traffic to this network. Other router (R1,R2,R3) will indicate this network as the “Gateway of last resort”.

There is another way to route unknown traffic to 10.1.1.0/24 network: create a static route using “ip route 0.0.0.0 0.0.0.0 10.1.1.2” command then inject this route using the “network 0.0.0.0” command, or using “redistribute static” command.

Note: In EIGRP, default routes cannot be directly injected (as they can in OSPF with the default-information originate command. Also, EIGRP does not have the “default-information originate” command).

Question 2

Refer to the exhibit. Router RTA is the hub router for routers RTB and RTC. The Frame Relay network is configured with EIGRP, and the entire network is in autonomous system 1. However, router RTB and RTC are not receiving each other’s routes. What is the solution?

EIGRP_Frame_Relay.jpg

A. Configure the auto summary command under router eigrp 1 on router RTA.
B. Issue the no ip split horizon command on router RTA.
C. Configure subinterfaces on the spoke routers and assign different IP address subnets for each subinterface.
D. Check and change the access lists on router RTA.
E. Issue the no ip split horizon eigrp 1 command on router RTA.

 

Answer: E

Explanation

RTB and RTC cannot see each other because of the split horizon rule: “A router never sends information about a route back in same direction which is original information came”. To overcome this problem we can configure subinterfaces or disable split horizon with the command “no ip split horizon eigrp 1” on RTA.

Question 3

When troubleshooting an EIGRP connectivity problem, you notice that two connected EIGRP routers are not becoming EIGRP neighbors. A ping between the two routers was successful. What is the next thing that should be checked?

A. Verify that the EIGRP hello and hold timers match exactly.
B. Verify that EIGRP broadcast packets are not being dropped between the two routers with the show ip EIGRP peer command.
C. Verify that EIGRP broadcast packets are not being dropped between the two routers with the show ip EIGRP traffic command.
D. Verify that EIGRP is enabled for the appropriate networks on the local and neighboring router.

 

Answer: D

Question 4

Refer to the exhibit. You are the network administrator of the Route.com company. You have been tasked to implement a hub and spoke EIGRP topology over Frame Relay to provide connectivity between the networks at headquarters and all 300 spokes.

Before you begin the actual implementation, which three pieces of information are more important to know than the others? (Choose three)

EIGRP_flap_stub.jpg

A. the Committed Information Rate of all the Frame Relay PVCs
B. the Cisco IOS version running on all the routers
C. the router model number of all the spoke routers
D. the number of HQ networks connected behind the headquarter routers
E. the routing policy, such as whether or not the spokes can be used as backup transient point between the two headquarter routers

 

Answer: A B E

Question 5

Refer to the exhibit. The Route.com company is running EIGRP between all the routers. Currently, if one of the LAN links (LAN1 or LAN2) at the headquarters flaps (goes up and down), the HQ-RTR1 and HQ-RTR2 routers will experience high CPU usage and have a long EIGRP convergence time. As the new network administrator, you are asked to investigate this situation and determine if there is a quick way to resolve this issue.

Which is the most important thing that you can quickly verify first to resolve this issue?

EIGRP_flap_stub.jpg

A. Verify that the bandwidth setting on all WAN links is correct.
B. Verify that the HQ-RTR1 and HQ-RTR2 routers are configured to send only a default route to all the spoke routers.
C. Verify that the HQ-RTR1 and HQ-RTR2 routers are configured for EIGRP Nonstop Forwarding.
D. Verify that all the spoke routers are configured for autosummarization.
E. Verify that all the spoke routers are configured as EIGRP stub.

 

Answer: E

Question 6

Refer to the exhibit. When you examine the routing table of R1 and R4, you are not able to see the R1 Ethernet subnet on the R4 routing table. You are also not able to see the R4 Ethernet subnet on the R1 routing table.

Which configuration change should be made to resolve this issue? Select the routers where the configuration change will be required, and select the required EIGRP configuration command(s). (Choose two)

EIGRP_summary.jpg

A. R1 and R4
B. R2 and R3
C. ip summary-address eigrp 1 10.1.1.0 255.255.255.0 and ip summary-address eigrp 1
D. variance 2
E. eigrp stub connected
F. no auto-summary

 

Answer: B F

Question 7

Refer to the exhibit. The actual speed of the serial links between R2 and R3 are 256 kb/s and 512 kb/s respectively. When configuring EIGRP on routers R2 and R3, the network administrator configured the bandwidth of both serial interfaces to 512 kb/s. What will be the effect?

EIGRP_summary.jpg

A. EIGRP will overutilize the 512 kb/s link.
B. The interface “delay” value used in the EIGRP metric calculation will be inaccurate on the 256 kb/s serial interface.
C. The amount of bandwidth used for EIGRP routing protocol traffic on the 256 kb/s link can become excessive.
D. EIGRP can load balance between the two serial links only if the variance is set to 2 or higher.
E. Unequal cost load balancing will be disabled.

 

Answer: C

EIGRP Questions 3

May 5th, 2014 digitaltut 2 comments

Here you will find answers to EIGRP Questions – Part 3

Note: If you are not sure about EIGRP, please read my EIGRP tutorial.

Question 1

Refer to the exhibit. ROUTE.com has just implemented this EIGRP network. A network administrator came to you for advice while trying to implement load balancing across part of their EIGRP network.
If the variance value is configured as 2 on all routers and all other metric and K values are configured to their default values, traffic from the Internet to the data center will be load balanced across how many paths?

EIGRP_load_balancing.jpg

A. 1
B. 2
C. 3
D. 4

 

Answer: C

Explanation

First we should list all the paths from the Internet to the data center:

+ A-B-C-H with a metric of 70 (40 + 15 + 15)
+ A-B-E-H with a metric of 60 (40+10+10)
+ A-D-E-H with a metric of 30 (10+10+10)
+ A-D-E-B-C-H with a metric of 60 (10+10+10+15+15)
+ A-D-E-F-G-H with a metric of 70 (10+10+10+20+20)
+ A-F-G-H with a metric of 60 (20+20+20)
+ A-F-E-H with a metric of 40 (20+10+10)

So the path A-D-E-H will be chosen because it has the best metric. But EIGRP can support unequal cost path load balancing. By configuring the variance value of 2, the minimum metric is increased to 60 (30 * 2) and all the routes that have a metric of less than or equal to 60 and satisfy the feasibility condition will be used to send traffic.

Besides the main path A-D-E-H we have 4 more paths that have the metric of less than or equal to 60 (we also include the Advertised Distances of these routes for later comparison):

+ A-B-E-H with an AD of 20
+ A-D-E-B-C-H with an AD of 50
+ A-F-G-H with an AD of 40
+ A-F-E-H with an AD of 20

Now the last thing we need to consider is the feasible condition. The feasible condition states:

“To qualify as a feasible successor, a router must have an AD less than the FD of the current successor route”

The FD of the current successor route here is 30 (notice that the variance number is not calculated here). Therefore there are only 2 paths that can satisfy this conditions: the path A-B-E-H & A-F-E-H.

In conclusion, traffic from the Internet to the data center will be load balanced across 3 paths, including the main path (successor path) -> C is correct.

Question 2

Which condition must be satisfied before an EIGRP neighbor can be considered a feasible successor?

A. The neighbor’s advertised distance must be less than or equal to the feasible distance of the current successor.
B. The neighbor’s advertised distance must be less than the feasible distance of the current successor.
C. The neighbor’s advertised distance must be greater than the feasible distance of the current successor.
D. The neighbor’s advertised distance must be equal to the feasible distance of the current successor.
E. The neighbor’s advertised distance must be greater than or equal to the feasible distance of the current successor.

 

Answer: B

Explanation

As explained in question 1, this is called the feasible condition.

Question 3

Which statement about a non-zero value for the load metric (k2) for EIGRP is true?

A. A change in the load on an interface will cause EIGRP to recalculate the routing metrics and send a corresponding update out to each of its neighbors.
B. EIGRP calculates interface load as a 5-minute exponentially weighted average that is updated every 5 minutes.
C. EIGRP considers the load of an interface only when sending an update for some other reason.
D. A change in the load on an interface will cause EIGRP to recalculate and update the administrative distance for all routes learned on that interface.

 

Answer: C

Explanation

The load metric (k2) represents the worst load on a link between source and destination.

EIGRP routing updates are triggered only by a change in network topology (like links, interfaces go up/down, router added/removed), and not by change in interface load or reliability -> A & D are not correct.

The load is a five minute exponentially weighted average that is updated every five seconds (not five minutes) -> B is not correct.

EIGRP considers the load of an interface only when sending an update for some other reason (like a link failure, topology change). Updates are not sent out each time the load changes -> C is correct.

Note: To learn how to calculate EIGRP metric, please read my EIGRP tutorial – Part 3.

Question 4

Your network consists of a large hub-and-spoke Frame Relay network with a CIR of 56 kb/s for each spoke.
Which statement about the selection of a dynamic protocol is true?

A. EIGRP would be appropriate if LMI type ANSI is NOT used.
B. EIGRP would be appropriate, because the Frame Relay spokes could be segmented into their own areas.
C. EIGRP would be appropriate, because by default, queries are not propagated across the slow speed Frame Relay links.
D. EIGRP would be appropriate, because you can manage how much bandwidth is consumed over the Frame Relay interface.

 

Answer: D

Explanation

By default, EIGRP will limit itself to using no more than 50% of the interface bandwidth. The primary benefit of controlling EIGRP’s bandwidth usage is to avoid losing EIGRP packets, which could occur when EIGRP generates data faster than the interface line can absorb it. This is of particular benefit on Frame Relay networks, where the access interface bandwidth and the PVC capacity may be very different.

For example, in our Frame Relay topology a Hub is connected with 4 Spoke routers. The main Frame Relay interface on Hub router is 512Kpbs which is not enough to use for 6 links of 128 Kbps ( = 768 Kbps).

EIGRP_Frame_Relay_CIR.jpg

The solution here is we can use 512 / 6 = 85 Kbps on each subinterface of Hub by using “bandwidth 85” command. For example:

Hub(config)#interface Serial0/0.1 point-to-point
Hub(config-subif)#bandwidth 85

Also on Spoke routers we need to set this value. For example on Spoke1:

Spoke1(config)#interface Serial0/1.0 point-to-point
Spoke1(config-subif)#bandwidth 85

Notice that by default, EIGRP limits itself to use no more than 50% of the configured interface bandwidth. In this case EIGRP will not use more than 42.5 Kbps (50% of 85 Kbps).

(For more information about implementing EIGRP over Frame Relay, please read http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094063.shtml)

Question 5

When an EIGRP topology change is detected, what is the correct order of events when there is a FS?

A.
The neighbor adjacency is deleted.
The feasible route is used.
DUAL is notified.
Remove all topology entries learned from that neighbor.

B.
DUAL is notified.
Remove all topology entries learned from that neighbor.
The neighbor adjacency is deleted.
Routes enter the Active state and the feasible route is used.

C.
The neighbor adjacency is deleted.
Routes enter the Active state and the feasible route is used.
DUAL is notified.
Remove all topology entries learned from that neighbor.

D.
DUAL is notified.
The neighbor adjacency is deleted.
Remove all topology entries learned from that neighbor.
The feasible route is used.

 

Answer: D

Question 6

Refer to the exhibit. You want to use all the routes in the EIGRP topology for IP load balancing.

EIGRP_show_ip_eigrp_topology.jpg

Which two EIGRP subcommands would you use to accomplish this goal? (Choose two)

A. traffic-share balanced
B. distance
C. maximum-paths
D. default-network
E. variance

 

Answer: C E

Explanation

Notice that the “maximum-paths” command is used to share traffic to equal cost path while the “variance” command can share traffic to unequal cost path.

In the output above we learn that EIGRP is using 2 successors to send traffic. By using the “variance 2” command we can share traffic to other feasible successor routes. But by default, EIGRP only shares traffic to 4 paths. So we need to use the “maximum-paths 6” to make sure all of these routes are used.

Question 7

Refer to the exhibit. R1 accesses the Internet using E0/0. You have been asked to configure R1 so that a default route is generated to its downstream devices (191.0.0.1 and 192.0.0.1). Which commands would create this configuration?

EIGRP_default_route.jpg

A.
router eigrp 190
redistribute static
!
ip route 0.0.0.0 0.0.0.0 Null0

B. ip default-network 20.0.0.0

C.
router eigrp 190
redistribute static
!
ip route 0.0.0.0 255.255.255.255 Null0

D. ip default-network 20.20.20.0

 

Answer: A

Question 8

Which command will display EIGRP packets sent and received, as well as statistics on hello packets, updates, queries, replies, and acknowledgments?

A. debug eigrp packets
B. show ip eigrp traffic
C. debug ip eigrp
D. show ip eigrp interfaces

 

Answer: B

Explanation

Below is the output of the “show ip eigrp traffic” command:

EIGRP_show_ip_eigrp_traffic.jpg

Question 9

Which three statements are true about EIGRP operation? (Choose three)

A. When summarization is configured, the router will also create a route to null 0.
B. The summary route remains in the route table, even if there are no more specific routes to the network.
C. Summarization is configured on a per-interface level.
D. The maximum metric for the specific routes is used as the metric for the summary route.
E. Automatic summarization across major network boundaries is enabled by default.

 

Answer: A C E

Question 10

Which two statements about the EIGRP DUAL process are correct? (Choose two)

A. An EIGRP route will go active if there are no successors or feasible successors in the EIGRP topology table.
B. An EIGRP route will go passive if there are no successors in the EIGRP topology table.
C. DUAL will trigger an EIGRP query process while placing the flapping routes in the holddown state.
D. A feasible successor in the EIGRP topology table can become the successor only after all the query requests have been replied to.
E. The stuck in active state is caused when the wait for the query replies have timed out.
F. EIGRP queries are sent during the loading state in the EIGRP neighbor establishment process.

 

Answer: A E

Question 11

What are three key concepts that apply when configuring the EIGRP stub routing feature in a hub and spoke network? (Choose three)

A. A hub router prevents routes from being advertised to the remote router.
B. Only remote routers are configured as stubs.
C. Stub routers are not queried for routes.
D. Spoke routers connected to hub routers answer the route queries for the stub router.
E. A stub router should have only EIGRP hub routers as neighbors.
F. EIGRP stub routing should be used on hub routers only.

 

Answer: B C E

EIGRP Questions 4

May 5th, 2014 digitaltut 6 comments

Here you will find answers to EIGRP – Part 4

Question 1

Which three statements are true about EIGRP route summarization? (Choose three)

A. Manual route summarization is configured in router configuration mode when the router is configured for EIGRP routing.
B. Manual route summarization is configured on the interface.
C. When manual summarization is configured, the summary route will use the metric of the largest specific metric of the summary routes.
D. The ip summary-address eigrp command generates a default route with an administrative distance of 90.
E. The ip summary-address eigrp command generates a default route with an administrative distance of 5.
F. When manual summarization is configured, the router immediately creates a route that points to null0 interface

 

Answer: B E F

Explanation

The ip summary-address eigrp {AS number} {address mask} command is used to configure a summary aggregate address for a specified interface. For example with the topology below:

EIGRP_ip_summary-address_eigrp.jpg

R2 has 5 loopback interfaces but instead of advertising all these interfaces we can only advertise its summarized subnet. In this case the best summarized subnet should be 1.1.1.0/29 which includes all these 5 loopback interfaces.

R2(config)#interface fa0/0
R2(config-if)#ip summary-address eigrp 1 1.1.1.0 255.255.255.248

This configuration causes EIGRP to summarize network 1.1.1.0 and sends out Fa0/0 interface

After configuring manual EIGRP summary, the routing table of the local router will have a route to Null0:

EIGRP_ip_summary-address_eigrp_R2.jpg

So why is this route inserted in the routing table when doing summarization? Well, you may notice that although our summarized subnet is 1.1.1.0/29 but we don’t have all IP addresses in this subnet. Assignable IP addresses of subnet 1.1.1.0/29 are from 1.1.1.1 to 1.1.1.6. Imagine what happens if R1 sends a packet to 1.1.1.6. Because R1 do believe R2 is connected with this IP so it will send this packet to R2. But R2 does not have this IP so if R2 has a default-route to R1 (for example R1 is connected to the Internet and R2 routes all unknown destination IP packets to R1) then a loop will occur.

To solve this problem, some routing protocols automatically add a route to Null0. A packet is sent to “Null0” means that packet is dropped. Suppose that R1 sends a packet to 1.1.1.6 through R2, even R2 does not have a specific route for that IP, it does have a general route pointing to Null0 which the packet sent to 1.1.1.6 can be matched -> That packet is dropped at R2 without causing a routing loop!

By default, EIGRP summary routes are given an administrative distance value of 5. Notice that this value is only shown on the local router doing the summarization. On other routers we can still see an administrative distance of 90 in their routing table.

EIGRP_ip_summary-address_eigrp_R1.jpg

Question 2

After implementing EIGRP on your network, you issue the show ip eigrp traffic command on router C. The following output is shown:

RouterC#show ip eigrp traffic
IF-EIGRP Traffic Statistics for process 1
Hellos sent/received: 481/444
Updates sent/received: 41/32
Queries sent/received: 5/1
Replies sent/received: 1/4
Acks sent/received: 21/25
Input queue high water mark 2, 0 drops
SIA-Queries sent/received: 0/0
SIA-Replies sent/received: 0/0

Approximately 25 minutes later, you issue the same command again. The following output is shown:

RouterC#show ip eigrp traffic
IP-EIGRP Traffic Statistics for process 1
Hellos sent/received: 1057/1020
Updates sent/received: 41/32
Queries sent/received: 5/1
Replies sent/received: 1/4
Acks sent/received: 21/25
Input queue high water mark 2, 0 drops
SIA-Queries sent/received: 0/0
SIA-Replies sent/received: 0/0

Approximately 25 minutes later, you issue the same command a third time. The following output is shown:

RouterC#show ip eigrp traffic
IP-EIGRP Traffic Statistics for process 1
Hellos sent/received: 1754/1717
Updates sent/received: 41/32
Queries sent/received: 5/1
Replies sent/received: 1/4
Acks sent/received: 21/25
Input queue high water mark 2, 0 drops
SIA-Queries sent/received: 0/0
SIA-Replies sent/received: 0/0

What can you conclude about this network?

A. The network has been stable for at least the last 45 minutes.
B. There is a flapping link or interface, and router C knows an alternate path to the network.
C. There is a flapping link or interface, and router A does not know an alternate path to the network.
D. EIGRP is not working correctly on router C.
E. There is not enough information to make a determination.

 

Answer: A

Explanation

In three times using the command, the “Queries sent/received” & “Replies sent/received” are still the same -> the network is stable.

Question 3

After implementing EIGRP on your network, you issue the show ip eigrp traffic command on router C. The following output is shown:

RouterC#show ip eigrp traffic
IP-EIGRP Traffic Statistics for process 1
Hellos sent/received: 2112/2076
Updates sent/received: 47/38
Queries sent/received: 5/3
Replies sent/received: 3/4
Acks sent/received: 29/33
Input queue high water mark 2, 0 drops
SIA-Queries sent/received: 0/0
SIA-Replies sent/received: 0/0

Moments later, you issue the same command a second time and the following output is shown:

RouterC#show ip eigrp traffic
IP-EIGRP Traffic Statistics for process 1
Hellos sent/received: 2139/2104
Updates sent/received: 50/39
Queries sent/received: 5/4
Replies sent/received: 4/4
Acks sent/received: 31/37
Input queue high water mark 2, 0 drops
SIA-Queries sent/received: 0/0
SIA-Replies sent/received: 0/0

Moments later, you issue the same command a third time and the following output is shown:

RouterC#show ip eigrp traffic
IP-EIGRP Traffic Statistics for process 1
Hellos sent/received: 2162/2126
Updates sent/received: 53/42
Queries sent/received: 5/5
Replies sent/received: 5/4
Acks sent/received: 35/41
Input queue high water mark 2, 0 drops
SIA-Queries sent/received: 0/0
SIA-Replies sent/received: 0/0

What information can you determine about this network?

A. The network is stable.
B. There is a flapping link or interface, and router C knows an alternate path to the network.
C. There is a flapping link or interface, and router C does not know an alternate path to the network.
D. EIGRP is not working correctly on router C.
E. There is not enough information to make a determination.

 

Answer: B

Explanation

We notice that the “Queries received” number is increased so router C has been asked for a route. The “Replies sent” number is also increased -> router C knows an alternate path to the network.

Question 4

R1 and R2 are connected and are running EIGRP on all their interfaces, R1 has four interfaces, with IP address 172.16.1.1/24, 172.16.2.3/24,172.16.5.1/24, and 10.1.1.1/24. R2 has two interfaces, with IP address 172.16.1.2/24 and 192.168.1.1/24. There are other routers in the network that are connected on each of the interfaces of these two routers that are also running EIGRP. Which summary routes does R1 generate automatically (assuming auto-summarization is enable)? (choose two)

A. 192.168.1.0/24
B. 10.0.0.0/8
C. 172.16.1.0/22
D. 172.16.0.0/16
E. 10.1.1.0/24

 

Answer: B D

Question 5

EIGRP_variance.jpg

There was an exhibit, 172.16.1.0/24 to 172.16.2.0/24 with the 4 paths with mentions of eigrp metric and asked if the variance is put to 2 in exhibit then what 2 paths are not used by eigrp routing table? (Choose two)

A. R1—R2—R6
B. R1—R3—R6
C. R1—R4—R6
D. R1—R5—R6

 

Answer: C D

Question 6

What does the default value of the EIGRP variance command of 1 mean?

A. Load balancing is disabled on this router.
B. The router performs equal-cost load balancing.
C. Only the path that is the feasible successor should be used.
D. The router only performs equal-cost load balancing on all paths that have a metric greater than 1.

 

Answer: B

Question 7

Refer to the exhibit. EIGRP has been configured on all routers in the network. The command metric weights 0 0 1 0 0 has been added to the EIGRP process so that only the delay metric is used in the path calculations. Which router will R1 select as the successor and feasible successor for Network A?

EIGRP_delay_metric.jpg

A. R4 becomes the successor for Network A and will be placed in the routing table. R2 becomes the feasible successor for Network A.
B. R4 becomes the successor for Network A and will be included in the routing table. No feasible successor will be selected as the advertised distance from R2 is higher than the feasible distance.
C. R2 becomes the successor and will be placed in the routing table. R4 becomes the feasible successor for Network A.
D. R2 becomes the successor and will be placed in the routing table. No feasible successor will be selected as the reported distance from R4 is lower than the feasible distance.

 

Answer: B

Question 8

Based on the exhibited output, which three statements are true? (Choose three)

EIGRP_show_ip_eigrp_topology_Passive.jpg

A. R1 is in AS 200.
B. R1 will load balance between three paths to reach the 192.168.1.48/28 prefix because all three paths have the same advertised distance (AD) of 40512000.
C. The best path for R1 to reach the 192.168.1.48/28 prefix is via 192.168.1.66.
D. 40512000 is the advertised distance (AD) via 192.168.1.66 to reach the 192.168.1.48/28 prefix.
E. All the routes are in the passive mode because these routes are in the hold-down state.
F. All the routes are in the passive mode because R1 is in the query process for those routes.

 

Answer: A C D

Explanation

In the statement “IP-EIGRP Topology Table for process 200”, process 200 here means AS 200 -> A is correct.

There are 3 paths to reach network 192.168.1.48/28 but there is only 1 path in the routing table (because there is only 1 successor) so the path with least FD will be chosen -> path via 192.168.1.66 with a FD of 40537600 will be chosen -> C is correct.

The other parameter, 40512000, is the AD of that route -> D is correct.

Question 9

Characteristics of the routing protocol EIGRP? (choose two)

A. Updates are sent as broadcast.
B. Updates are sent as multicast.
C. LSAs are sent to adjacent neighbors.
D. Metric values are represented in a 32-bit format for granularity.

 

Answer: B D

Explanation

EIGRP updates are sent as multicast to address 224.0.0.10 -> B is correct.

EIGRP metric values, for example an entry in the “show ip route” command:

D 10.1.21.128/27 [90/156160] via 10.1.4.5, 00:00:21, FastEthernet1/0/1

EIGRP metric here is 156160 and it is a 32-bit value. For more information please read here:

http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/enhanced-interior-gateway-routing-protocol-eigrp/whitepaper_C11-720525.html

Question 10

Which EIGRP packet statement is true?

A. On high-speed links, hello packets are broadcast every 5 seconds for neighbor discovery.
B. On low-speed links, hello packets are broadcast every 15 seconds for neighbor discovery.
C. Reply packets are multicast to IP address 224.0.0.10 using RTP.
D. Update packets route reliable change information only to the affected routers.
E. Reply packets are used to send routing updates.

 

Answer: D

EIGRP Questions 5

May 5th, 2014 digitaltut 3 comments

Here you will find answers to EIGRP Questions – Part 5

Question 1

Which three descriptions are correct based on the exhibited output? (Choose three)

EIGRP_show_ip_route.jpg

A. R1 is configured with the variance command.
B. The route to 10.2.0.0/16 was redistributed into EIGRP.
C. A default route has been redistributed into the EIGRP autonomous system.
D. R1 is configured with the ip summary-address command.

 

Answer: A C D

Explanation

From the routing table above, we see that network 172.16.1. can be reached via 2 unequal paths (with FD of 23072000 & 20640000) so surely R1 has been configured with the “variance” command -> A is correct.

By configuring a default route and redistribute it into EIGRP you will get the line “D *EX 0.0.0.0/0 …” line in the routing table of that router -> C is correct.

From the line “10.2.0.0/16 is a summary, 00:16:18, Null0” we know that this network has been summarized with the “ip summaray-address” command (notice that 10.2.0.0 is not the major network of net-> D is correct.

Question 2

Refer to the exhibit. Which two statements are true? (Choose two)

EIGRP_stub.jpg

A. The eigrp stub command prevents queries from being sent from R2 to R1.
B. The eigrp stub command will automatically enable summarization of routes on R2.
C. The eigrp stub command prevents all routes except a default route from being advertised to R1.
D. Router R1 will advertise connected and summary routes only.
E. Router R1 will advertise connected and static routes. The sending of summary routes will not be permitted.
F. Router R1 is configured as a receive-only neighbor and will not send any connected, static or summary routes.

 

Answer: A D

Explanation

The command “eigrp stub” turns R1 into a stub router so R2 will never send any query to R1 because R2 knows that a stub router will only route packets for networks it has explicitly advertised -> A is correct.

The command “eigrp stub” is same as “eigrp stub connected summary” command because connected and summarized routes are advertised by default -> D is correct.

Note: Because the network 192.168.50.0 is not advertised by “network” statement, it is necessary to redistribute connected route with the “redistribute connected” command.

Question 3

Refer to the exhibits. Router B should advertise the network connected to the E0/0/0 interface to router A and block all other network advertisements. The IP routing table on router A indicates that it is not receiving this prefix from router B.
What is the probable cause of the problem?

EIGRP_receive_prefix.jpg

EIGRP_debug_ip_eigrp.jpg

A. An access list on router B is causing the 192.168.3.16/28 network to be denied.
B. An access list on router B is causing the 192.168.3.32/28 network to be denied.
C. The distribute list on router B is referencing a numbered access list that does not exist on router B.
D. The distribute list on router B is referencing the wrong interface.

 

Answer: A

Explanation

This is an unclear question. The question says “Router B should advertise the network connected to the E0/0/0 interface to router A and block all other network advertisements. The IP routing table on router A indicates that it is not receiving this prefix from router B.” That means the network 192.168.3.16/28 (including the IP 192.168.3.21/28) is not received on router A -> A is the most suitable answer.

Note: Distribute list are used to filter routing updates and they are based on access lists.

Question 4

Study the exhibit carefully. What must be done on router A in order to make EIGRP work effectively in a Frame Relay multipoint environment?

EIGRP_Frame_Relay_point_to_multipoint.jpg

A. Issue the command bandwidth 56 on the physical interface.
B. Issue the command bandwidth 56 on each subinterface.
C. Issue the command bandwidth 224 on each subinterface.
D. Issue the command bandwidth 224 on the physical interface.

 

Answer: D

Explanation

In Frame Relay, all neighbors share the same bandwidth, regardless of the actual CIR of each individual PVC. In this case the CIR of each PVC is the same so we can find the bandwidth of the main interface (multipoint connection interface) by 56 x 4 = 224.

Notice that if the bandwidth on each PVC is not equal then we get the lowest bandwidth to multiply.

Question 5

Refer to the exhibit. ROUTE Enterprises has many stub networks in their enterprise network, such as router B and its associated network. EIGRP is to be implemented on router A so that neither the prefix for the S/0/0/0 interface nor the prefixes from router B appear in the routing tables for the router in the enterprise network.
Which action will accomplish this goal?

EIGRP_exclude_prefix.jpg

A. Declare router B a stub router using the eigrp stub command.
B. Use the passive-interface command for interface Serial0/0/0.
C. Use a mask with the network command to exclude interface Serial0/0/0.
D. Implement a distribute list to exclude the link prefix from the routing updates.

 

Answer: C

Explanation

If we declare router B a stub router then the routers in Enterprise Network still learn about the network for S0/0/0 interface and the network behind router B -> A is not correct.

If we use the passive-interface command on s0/0/0 interface then router A & B can not become neighbor because they don’t exchange hello messages -> A can not send traffic to the network behind B -> B is not correct.

Theoretically, we can use a distribute list to exclude both the link prefix and the prefix from router B but it is not efficient because:

+ We have many stub networks so we will need a “long” distribute list.
+ We declare networks in stub routers (like router B) while filter them out at router A -> it is a waste.

I am not totally sure about answer C because if we “use a mask with the network command to exclude interface Serial0/0/0” then router A and B can not become neighbors and the situation is same as answer B. But from many discussions about this question, maybe C is the best answer.

Question 6

Refer to the exhibit. EIGRP is configured with the default configuration on all routers. Autosummarization is enabled on routers R2 and R3, but it is disabled on router R1. Which two EIGRP routes will be seen in the routing table of router R3? (Choose two)

EIGRP_auto_summary.jpg

A. 10.0.0.0/8
B. 10.10.0.0/16
C. 10.10.10.0/24
D. 172.16.0.0/16
E. 172.16.0.0/24
F. 172.16.10.0/24

 

Answer: C D

Explanation

EIGRP performs an auto-summarization each time it crosses a border between two different major networks. In this case all different networks are in different major networks so EIGRP will perform auto-summarization when it exits an interface. But R1 has been configured with “no auto-summary” command so EIGRP will not summarize on S0 interface of R1. So the routing table of R2 will have the network 10.10.10.0/24 (not be summarized).

When exiting S1 interface of R2, EIGRP summarizes network 172.16.10.0/24 into the major 172.16.0.0/16 network but it does not summarize network 10.10.10.0/24 because it is not directly connected with this network. Therefore in the routing table of R3 there will have:

+ Network 10.10.10.0/24 ( not summarized)
+ Network 172.16.0.0/16 (summarized)

-> C and D are correct.

Note: I simulated this question on GNS3, you can see the final outputs of the “show ip route” commands on these routers (I connected these routers via FastEthernet, not Serial interfaces so the outputs are slightly different but the main points are not changed).

EIGRP_show_ip_route_no_auto-summary_R1.jpg

EIGRP_show_ip_route_no_auto-summary_R2.jpg

EIGRP_show_ip_route_no_auto-summary_R3.jpg

Question 7

Refer to the exhibit. In a redundant hub-and-spoke deployment using EIGRP, what feature can be used to ensure that routers C through F are not used as transit routers for data traveling from router B to network 10.1.1.0?

EIGRP_hub_spoke.jpg

A. Use address summarization at routers C, D. E, and F.
B. Use the EIGRP Stub feature on routers C, D, E, and F.
C. Use passive-interface on the spoke links in routers A and B.
D. Change the administrative distance in routers A and B for routes learned from routers Cr D. E, and F.

 

Answer: B

Explanation

By configuring “stub” feature on routers C D E and F, routers A and B will not try to transit traffic through these routers. For example, if the network connecting from routers A and B is down, router B will not send to network 10.1.1.0/24 from router B -> routerC/D/E/F -> router A -> network 10.1.1.0/24.

Question 8

Refer to the exhibit. How would you confirm on R1 that load balancing is actually occurring on the default-network (0.0.0.0)?

show_ip_route.jpg

A. Use ping and the show ip route command to confirm the timers for each default network resets to 0.
B. Load balancing does not occur over default networks; the second route will only be used for failover.
C. Use an extended ping along with repeated show ip route commands to confirm the gateway of last resort address toggles back and forth.
D. Use the traceroute command to an address that is not explicitly in the routing table.

 

Answer: D

Explanation

The most simple method to test load balancing is to use the “traceroute” command. If load balancing is working correctly, we will see different paths to reach the destination each time we use that command.

Unknown address will be routed via the default-network 0.0.0.0 so we must use an address that is not explicitly in the routing table.

Question 9

Refer to the exhibit. ROUTE.com is planning to implement load balancing for traffic between host on the 172.16.10.0/24 and 172.16.20./24 networks. You have been asked to review the implementation plan for this project. Which statement about the plan is true?

EIGRP_load_balance.jpg

A. It is complete as written.
B. It should include a task to configure EIGRP multipath equal to 2 on R1 and R4.
C. It should include a task to implement OSPF because it handles unequal cost load balancing most efficiently using variance.
D. It should include a task that establishes a baseline before and after the configuration has been changed.

 

Answer: D

Explanation

A complete implementation plan should be:

1. Configure variance on R1 and R4
2. Use traceroute to validate load balancing has been activated
3. Document configuration changes
4. Establish a new traffic throughput baseline
5. Compare the new and old baselines and verify that load balancing is implemented as desired.

Question 10

Refer to the exhibit. ROUTE.com is planning to implement load balancing for traffic between host on the 172.16.10.0/24 and 172.16.20./24 networks. You have been asked to review the implementation plan for this project. Which statement about the plan is true?

EIGRP_load_balance-2.jpg

A. It is complete as written.
B. It should include a task to configure multipath to equal a value of 2 on R1 and R4.
C. It should use a ping instead of a traceroute to validate that load balancing has been activated.
D. It should contain a task that documents the changes made to the configurations.

 

Answer: D

Explanation

Same as questions 9

Question 11

Refer to the exhibit. EIGRP had converged in AS 1 when the link between router R1 and R2 went down. The console on router R2 generated the following messages:

*Mar 20 12:12:06: %DUAL-5-NBRCHANGE: IP-EIGRP 1: Neighbor 10.1.4.3 (Serial0) is down: stuck in active
*Mar 20 12:15:23: %DUAL-3-SIA: Route 10.1.1.0/24 stuck-in-active state in IP-EIGRP 1.
Cleaning up

The network administrator issued the show ip eigrp topology active command on R2 to check the status of the EIGRP network. Which statement best describes the reason for the error messages?

 

EIGRP_stuck_in_active.jpg

A. Incorrect bandwidth configuration on router R3 prevents R2 from establishing neighbor adjacency.
B. Incorrect bandwidth configuration on router R5 prevents R2 from establishing neighbor adjacency.
C. Router R3 did not reply to the query about network 10.1.1.0/24 sent by router R2.
D. Router R5 did not reply to the query about network 10.1.1.0/24 sent by router R2.

 

Answer: C

Explanation

When the link between R1 and R2 is down, R2 loses its successor for the network 10.1.1.0/24. R2 checks its topology table for a feasible successor but it can’t find one. So R2 goes active on the that route to find a new successor by sending queries out to its neighbors (R3 and R5) requesting a path to the lost route. Both R3 and R5 also go “active” for the that route. But R5 doesn’t have any neighbor to ask besides R2 so it will send an “unreachable message” to indicate it has no alternative path for that route and has no other neighbor to query. R3 also checks its EIRGP topology table for a feasible successor but it has none, too. Unlike R5, R3 has a neighbor (R4) so it continues to query this router.

Now suppose there is a problem on the link between R3 and R4 so R4 never receives the query from R3 and of course, R3 also never receives a reply back from R4. Therefore, R3 can’t reply back to R2. After about 3 minutes, the “Stuck in active” (SIA) timer on R2 expires and R2 marks the route 10.1.1.0/24 as “stuck in active” route.

The output line “via 10.1.3.3 (Infinity/Infinity), r, Seiral0, serno 1232” indicates R2 has sent a query to 10.1.3.3 and is waiting for a reply (the lowercase r) -> C is correct.

(Reference: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008010f016.shtml)

Question 12

Refer to the exhibit. EIGRP has been configured on routers R1 and R2. However, R1 does not show R2 as a neighbor and does not accept routing updates from R2. What could be the cause of the problem?

EIGRP_routing_update.jpg

A. The no auto-summary command has not been issued under the EIGRP process on both routers.
B. Interface E0 on router R1 has not been configured with a secondary IP address of 10.1.2.1/24.
C. EIGRP cannot exchange routing updates with a neighbor’s router interface that is configured with two IP addresses.
D. EIGRP cannot form neighbor relationship and exchange routing updates with a secondary address.

 

Answer: D

Explanation

EIGRP updates always use the primary IP address of the outgoing interface as the source address. In this case R2 will use the 10.1.2.2/24 address, which is not in the same subnet of R1, to send EIGRP update to R1. Therefore R1 does not accept this update and generates the “not on common subnet” error message.

Answer D is a bit unclear. It should state that “EIGRP cannot form neighbor relationship and exchange routing updates if the two primary addresses on two routers are not in the same subnet”.

Notice that although R1 does not accept R2 as its EIGRP neighbors but R2 accepts R1 as its EIGRP neighbor accepts R1 hello packets..

For more information about this problem, please read http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a0080093f09.shtml.

Question 13

Refer to the exhibit. A Boston company bought the assets of a New York company and is trying to route traffic between the two data networks using EIGRP over EoMPLS. As a network consultant, you were asked to verify the interoperability of the two networks.

From the show ip route command output, what can you tell the customer about the traffic flow between the subnet in New York (172.16.8.0/24) and the subnets in Boston (172.16.16.0/24 and 10.10.16.0/24)?

EIGRP_traffic_flow.jpg

A. Traffic is flowing between the 172.16.8.0 subnet and subnets 172.16.16.0 and 10.10.16.0 and no configuration changes are needed.
B. Auto-summary must be disabled on N1 and B1 before traffic can flow between the 172.16.8.0 subnet and subnets 172.16.16.0 and 10.10.16.0.
C. Traffic will flow between the 172.16.8.0 subnet and 172.16.16.0 without any further configuration changes. However, auto-summary must be disabled on N1 and B1 before traffic can flow between the 172.16.8.0 subnet and the 10.10.16.0 subnet.
D. Auto-summary must be disabled on N1 and B1 before traffic can flow between the 172.16.8.0 subnet and the 172.16.16.0 subnet. However, traffic will flow between the 172.16.8.0 subnet and 10.10.16.0 without any further configuration changes.

 

Answer: B

Question 14

Refer to the exhibit. A Boston company bought the assets of a New York company and is trying to route traffic between the two data networks using EIGRP. The show command output shows that traffic will not flow between the networks. As a network consultant, you were asked to modify the configuration and certify the interoperability of the two networks. For traffic to flow from subnet 172.16.8.0/24 to the 172.16.16.0/24 subnet, which configuration change do you recommend?

EIGRP_auto_summary_Boston_NewYork.jpg

A. Turn off autosummarization on routers N1 and B1.
B. Add IP summary addresses to the Internet-pointing interfaces of routers N1 and B1.
C. Turn off autosummarization on routers N2 and B2.
D. Add wildcard masks to the network commands on routers N2 and B2.

 

Answer: A

EIGRP Questions 6

May 5th, 2014 digitaltut 1 comment

Here you will find answers to EIGRP questions – Part 6

Question 1

Which two statements are true about EIGRP manual summarization? (Choose two)

A. Manual summarization is configured on a per interface basis.
B. Manual summaries can be configured with the classful mask only.
C. When manual summarization is configured, autosummarization is automatically disabled by default.
D. The summary address is assigned an administrative distance of 10 by default.
E. The summary address is entered into the routing table and is shown to be sourced from the Null0 interface.

 

Answer: A E

Explanation

EIGRP allows you to summarize internal and external routes on virtually any bit boundary using manual summarization. And the manual summarization is configured under interface mode.

An example of manual summarization is shown below:

interface Serial0
ip address 10.1.50.1 255.255.255.0
ip summary-address eigrp 2000 192.1.0.0 255.255.252.0

(Reference: http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml#manualsummarization)

Question 2

Which is the correct command format to configure EIGRP summary route?

A. ip auto-summary as-number address mask
B. ip summary-address as-number address mask
C. ip auto-summary eigrp as-number address mask
D. ip summary-route eigrp as-number address mask
E. ip summary-address eigrp as-number address mask

 

Answer: E

Explanation

Same as above question.

Question 3

Which is the most effective technique to contain EIGRP queries?

A. route summarization
B. configuring route filters
C. using a hierarchical addressing scheme
D. establishing separate autonomous systems

 

Answer: A

Question 4

Identify three characteristics of EIGRP feasible successors? (Choose three)

A. A feasible successor is selected by comparing the advertised distance of a non-successor route to the feasible distance of the best route.
B. If the advertised distance of the non-successor route is less than the feasible distance of best route, then that route is identified as a feasible successor.
C. If the successor becomes unavailable, then the feasible successor can be used immediately without recalculating for a lost route.
D. The feasible successor can be found in the routing table.
E. Traffic will be load balanced between feasible successors with the same advertised distance.

 

Answer: A B C

Question 5

Which two routing protocols require a metric to be configured when redistributing routes from other protocols? (Choose two)

A. RIP
B. OSPF
C. EIGRP
D. IS-IS
E. BGP

 

Answer: A C

Explanation

(RIP) metric is based on hop count, but Interior Gateway Routing Protocol (IGRP) and Enhanced Interior Gateway Routing Protocol (EIGRP) use a composite metric based on bandwidth, delay, reliability, load, and maximum transmission unit (MTU), where bandwidth and delay are the only parameters used by default. When we redistribute other routing protocols into RIP or IGRP/EIGRP, we must specify the seed metric for that route.

Note: When redistributing into OSPF, all routes are assigned a default metric of 20.

Question 6

Based on the need to limit processing and bandwidth utilization due to dynamic routing protocol operation, the following routing requirements have been specified for your network.

– partial and incremental routing updates
– only the devices affected by a topology change perform route recomputation
– route recomputation only occurs for routes that were affected

Which dynamic routing protocol should be deployed in your network to best meet these requirements?

A. BGP
B. OSPF
C. IS-IS
D. EIGRP
E. RIPv2

 

Answer: D

Explanation

For link-state protocols (like OSPF) when a change in topology is detected, a link-state advertisement (LSA) is sent to all routers in that OSPF area to inform the change. This causes all routers within that OSPF area to recalculate all of their routes using Dijkstra algorithm. For large networks, this is a CPU intensive task and could cause a CPU overload.

Also incremental routing update is also a unique feature of EIGRP.

Question 7

ACME Rocket Sleds is growing, and so is their network. They have determined that they can no longer continue using static routes and must implement a dynamic routing protocol. They want to have data use multiple paths to the destinations, even if the paths are not equal cost. Which routing protocol has the ability to do this?

A. EIGRP
B. OSPF
C. RIPv1
D. RIPv2
E. BGP
F. IS-IS

 

Answer: A

Explanation

An advantage of EIGRP is the use of unequal cost path to load balance traffic. This cannot be done in OSPF or RIP. BGP should only be used between ISPs. But notice that EIGRP is a Cisco proprietary protocol so it is not as popular as OSPF.

Question 8

Which command displays statistics on EIGRP hello, updates, queries, replies, and acknowledgments?

A. debug eigrp packets
B. show ip eigrp traffic
C. show ip eigrp topology
D. show ip eigrp neighbors

 

Answer: B

Explanation

The “show ip eigrp traffic” command displays the number of Enhanced Interior Gateway Routing Protocol (EIGRP) packets sent and received:

EIGRP_show_ip_eigrp_traffic.JPG

Question 9

Refer to the exhibit. EIGRP is enabled on all routers on the network. What additional configuration is required for the routers connected over the Frame Relay multipoint interfaces to compensate for a low-speed NBMA connection?

Frame_Relay_multipoint_interfaces_bandwidth.jpg

A. Configure the EIGRP hello interval on all Frame Relay interfaces to 5 seconds.
B. Configure the EIGRP hello interval on all Frame Relay interfaces to 60 seconds.
C. Configure the EIGRP hold time on all Frame Relay interfaces to 16 seconds.
D. Configure the EIGRP hold time on all Frame Relay interfaces to 180 seconds.
E. Configure the bandwidth on all EIGRP Frame Relay interfaces to the committed information rate (CIR).
F. Configure the bandwidth on all EIGRP Frame Relay interfaces to the lowest CIR multiplied by the number of PVCs for the multipoint connection.

 

Answer: F

Explanation

If the multipoint network has different speeds allocated to the VCs, take the lowest CIR and simply multiply it by the number of circuits. This is because in Frame-relay all neighbors share the bandwidth equally, regardless of the actual CIR of each individual PVC, so we have to get the lowest speed CIR rate and multiply it by the number of circuits. This result will be applied on the main interface (or multipoint connection interface).

Question 10

Refer to the exhibit. If the configuration shown below is added to RTA, which three route entries will EIGRP advertise to neighboring routers?(Choose three.)

router eigrp 10
network 10.0.0.0
eigrp stub

show_ip_route_advertised_three_routes.jpg

A. 10.1.3.0/24
B. 10.1.2.0/24
C. 10.0.0.0/8
D. 10.1.1.0/24
E. 192.168.20.0/24

 

Answer: A C D

Explanation

The “eigrp stub” command is equivalent to the “eigrp stub connected summary” command which only advertises directly connected and summarized routes to other routers.

EIGRP Questions 7

May 5th, 2014 digitaltut 2 comments

Here you will find answers to EIGRP questions – Part 7

Question 1

What action does an EIGRP router take when it cannot find a feasible successor for a network?

A. It examines the routing and neighbor tables for the next best path.
B. It transitions from passive to active state for that network and queries its neighbors.
C. It examines the topology table for a next best path.
D. It transitions from active to passive state for that network and queries its neighbors.

 

Answer: B

Question 2

Based on the exhibited command output, which two statements are true? (Choose two)

show_ip_eigrp_topology_recomputation_query.jpg

A. The EIGRP network is stable.
B. The router at 10.1.1.3 has not replied to the R1 query packet.
C. The route to 172.19.0.0/16 is undergoing recomputation.
D. The route to 172.19.0.0/16 is stuck-in-active.
E. R1 has sent a query packet to 10.1.1.2.

 

Answer: C E

Explanation

The route to 172.19.0.0/16 is in Active state (letter “A”). The route is in Active state when a router is undergoing a route recomputation -> C is correct.

Also, the lower letter “r” in “via 10.1.12, r, Serial0/0” indicates R1 has sent a query to 10.1.1.2 and is waiting for a reply -> E is correct.

Question 3

A network administrator would like to configure an EIGRP router as a stub router that advertises directly connected and summary routes only. What command must the administrator issue to accomplish this?

A. eigrp stub
B. eigrp stub connected
C. eigrp stub summary
D. eigrp stub connected static
E. eigrp stub receive-only

 

Answer: A

Explanation

The command “eigrp stub” is equivalent to the command “eigrp stub connected summary” because the connected and summary options are enabled by default.

Question 4

Which two among the following are used to indicate external type of route in routing table? (Choose two)

A. D EX
B. IA
C. E2
D. R E2
E. i L2

 

Answer: A C

Question 5

Which show command will display the two values used in the calculation of the EIGRP metric?

A. show protocol
B. show ip eigrp interface
C. show interface
D. show ip eigrp neighbor

 

Answer: C

Explanation

First, recall the formula of calculating EIGRP metric:

metric = [K1 * bandwidth + (K2 * bandwidth)/(256 – load) + K3 * delay] * [K5/(reliability + K4)]

The four outputs of the above commands are shown below:

+ show protocols: this command does not show any information about 4 values of EIGRP metric.

EIGRP_show_protocols.jpg

+ show interfaces: this command has all 4 values of metric. This is the most suitable answer.

EIGRP_show_interfaces.jpg

+ show ip eigrp interfaces: no information about values of metric.

show_ip_eigrp_interfaces_metric.jpg

+ show ip eigrp neighbor: this command does not have any values of metric.

EIGRP_show_ip_eigrp_neighbors.jpg

Note: As you remember, we have to specify 5 values when redistributing into EIGRP. But notice that these are not the five “K” values.

Question 6

A network administrator is troubleshooting an EIGRP configuration across a discontiguous network. What must the administrator do to ensure the routers have the correct routing information?

A. Nothing, EIGRP supports discontiguous networks by default.
B. The administrator must disable automatic summarization with the command no auto-summary.
C. The administrator must enable manual summarization with the command ip summary-address.
D. The administrator must enable classless routing with the command ip classless.
E. The administrator must specify a default network with the command ip default-network.

 

Answer: B

Question 7

What is the purpose of the eigrp stub configuration command?

A. to increase scalability by limiting the EIGRP query range
B. to reduce the size of the routing table by blocking the D EX (External EIGRP) routes into the EIGRP stub router
C. to reduce the convergence time by enabling the EIGRP stub router to propagate the EIGRP queries from the EIGRP hub router
D. to reduce the convergence time by enabling the EIGRP stub router to also perform query requests to the EIGRP hub router

 

Answer: A

Explanation

Stub router provides network architects with greater flexibility for designing EIGRP networks by enabling improved control over traffic flows and limitations of query flooding.

Question 8

Which EIGRP packet statement is true?

A. On high-speed links, hello packets are broadcast every 5 seconds for neighbor discovery.
B. On low-speed links, hello packets are broadcast every 15 seconds for neighbor discovery.
C. Reply packets are multicast to IP address 224.0.0.10 using RTP.
D. Update packets route reliable change information only to the affected routers.
E. Reply packets are used to send routing updates.

 

Answer: D

Explanation

The default hello timer for a high-speed broadcast network link is 5 seconds and the hold-down timer is 15 seconds whereas the default timers for slow-speed NBMA link are 60 seconds hello and 180 seconds dead. A slow-speed NBMA link is classified as any NBMA link with speeds equal to or less than 1544Kbps (A single T1) -> A and B are not correct.

EIGRP sends update packets using multicast address 224.0.0.10 but it acknowledges updates using unicast hello packets with no data (also uses RTP) -> C is not correct.

Unlike OSPF which requires calculation of all routes when the topology changes, EIGRP only sends routing updates to affected routers -> D is correct.

Reply packets (for hello packets) are just used to acknowledge the hello packets with no data -> E is not correct.

Question 9

Refer to the exhibit. What happens when the router stops receiving advertisements for the 10.1.2.0/24 network?

Router# show ip route
C 10.1.3.0/24 is directly connected, Serial2
D 10.1.2.0/24 [90/10537472] via 10.1.1.2, 00:23:24, Serial1
D 10.0.0.0/8 is a summary, 00:23:20, Null0
C 10.1.1.0/24 is directly connected, Serial1
S 192.168.20.0/24 is directly connected, Ethernet0

A. The summary route will be removed from the table.
B. The summary route will remain in the table.
C. The more specific routes will be advertised from the table.
D. 10.1.2.0/24 will still be advertised but packets destined for it will be dropped when they reach this router.

 

Answer: B

Explanation

There are two cases for the line “D 10.0.0.0/8 is a summary, 00:23:20, Null0” to appear in the routing table:

+ By the “auto-summary” command under EIGRP mode.
+ By the “ip summary-address eigrp AS-number 10.0.0.0 255.0.0.0″ under interface mode.

When we create a summary route, one summary route will be created automatically pointing towards Null0 interface. This is a loop prevention mechanism.

Even when the router stops receiving advertisements for the 10.1.2.0/24 network, other networks that belong to 10.0.0.0/8 still exist so the summary route will still remain in the routing table. The summary route only disappears only when all of its related networks are turned off.

For more information about summarization & Null0 interface, please read my Auto and Manual Summary Routes to Null0 with EIGRP tutorial.

Question 10

Refer to the exhibit. EIGRP is configured on all routers in the network. On the basis of the output provided, which statement is true?

EIGRP_authentication_key.jpg

A. Because the key chain names do not match, router R1 will not be able to ping routers R2 and R3.
B. Because the key strings do not match, router R1 will not be able to ping routers R2 and R3.
C. Because authentication is misconfigured on interfaces Gi0/0 and Gi0/1 on router R2, router R1 will not be able to ping routers R2 and R3.
D. Because autosummarization needs to be turned on for EIGRP on all routers, router R1 will not be able to ping routers R2 and R3.
E. Router R1 will be able to ping routers R2 and R3.

 

Answer: E

EIGRP Questions 8

May 5th, 2014 digitaltut No comments

Here you will find answers to EIGRP questions – Part 8

Question 1

Which of the below mentioned conditions form a neighbor relation in EIGRP?(Choose three)

A. Hello or ACK received
B. AS number match
C. Hello timer match
D. Identical metric (k values)
E. Dead Timer Match
F. Network Time Match

 

Answer: A B D

Explanation

To become a neighbor, the following conditions must be met:
+ The router must hear a Hello packet from a neighbor.
+ The EIGRP autonomous system (AS) must be the same.
+ K-values must be the same.

Question 2

Which command should you issue first to configure EIGRP for IP?

A. ip eigrp routing
B. router eigrp process-id
C. ip eigrp autonomous-system-number
D. router eigrp autonomous-system-number

 

Answer: D

Question 3

Based on the topology shown in the network diagram, what optional EIGRP configurations will be required in order to achieve full connectivity within AS 100?

EIGRP_full_connectivity_no_auto_summary.jpg

A. Use the EIGRP no auto-summary command on R1 and R2.
B. Use the EIGRP no auto-summary command on R3 and R4.
C. Use the passive interface on the R1 and R2 interface that connects to the 10.1.1.0/24 and 10.1.2.0/24 subnet respectively.
D. Use the passive interface command between the R3 and R1 connection and between the R3 and R2 connection.
E. Use the variance command on R3.

 

Answer: A

Explanation

When routing updates are sent to another major network (in this case 192.168.1.0/24 & 192.168.2.0/24), EIGRP will summarize the advertised networks automatically by default -> we have to use the EIGRP no auto-summary command on R1 and R2.

Question 4

A network administrator is managing a hub-and-spoke network with EIGRP routing that has been enabled. The hub router is trying to query a remote router. However, delays are occurring that are caused by certain paths being stuck in active (SIA). How should the administrator configure EIGRP in order to limit the scope of the query range and prevent SIA from occurring?

A. Configure the hub router with a scope limit of 1.
B. Configure the remote router with a scope limit of 1.
C. Configure the hub to indicate that the remote router is a stub router,
D. Configure the hub and remote router as stub routers.
E. Configure the remote router as a stub router.
F. Disable the SIA feature of EIGRP on the remote router.

 

Answer: E

Question 5

What are two possible causes for EIGRP Stuck-ln-Active routers? (Choose two)

A. Some query or reply packets are lost between the routers.
B. The neighboring router starts receiving route updates from this router.
C. A failure causes traffic on a link between two neighboring routers to flow in only one direction (unidirectional link).
D. The neighboring router stops receiving ACK packets from this router.

 

Answer: A C

Question 6

When configuring EIGRP to run across a 56 Kbps serial PPP link, what command do you need to put under the serial interface ensure proper convergence of EIGRP routes?

A. bandwidth 56
B. bandwidth 56000
C. ip bandwidth-percent eigrp 1 56
D. ip bandwidth-percent eigrp 1 56000

 

Answer: A

Question 7

The following command was issued on RouterA. Given the above output, which statement is true?

RouterA# show ip route

C 10.1.1.0 is directly connected, FastEthernet0/0
D 172.16.0.0/16 [90/156160] via 10.1.1.1, 00:07:46, FastEthernet0/0
D EX 192.168.1.10/24 [170/1308160] via 10.1.1.1, 00:00:11, FastEthernet0/0

A. 192.168.1.0 is a static route.
B. 192.168.1.0 is a summarized route.
C. 192.168.1.0 is a redistributed route into EIGRP.
D. 192.168.1.0 is equal path load balancing with 172.16.1.0.

 

Answer: C

Question 8

If the primary path goes down, what will EIGRP use to reach a destination?

A. administrative distance
B. advertised successor
C. successor
D. feasible successor

 

Answer: D

Question 9

A stub area is typically created using what kind of topology?

A. Broadcast
B. Point-to-point
C. Hub and spoke
D. Full Mesh

 

Answer: C

Question 10

In EIGRP, when the IP default-network command is configured on a router, what is generated in the router’s configuration?

A. A static route
B. A directly connected route
C. An EIGRP route
D. A default route

 

Answer: D

EIGRP Questions 9

May 5th, 2014 digitaltut No comments

Here you will find answers to EIGRP questions – Part 9

Question 1

Which of the following are methods EIGRP uses to initially populate (seed) its EIGRP topology table, before learning topology data from neighbors? (Choose two)

A. By adding all subnets listed by the show ip route connected command
B. By adding the subnets of working interfaces over which static neighbors have been defined
C. By adding subnets redistributed on the local router from another routing source
D. By adding all subnets listed by the show ip route static command

 

Answer: B C

Question 2

Which three statements are true regarding EIGRP? (Choose three)
A. By default, EIGRP performs auto-summarization across classful network boundaries.
B. EIGRP uses an area hierarchy to increase network scalability.
C. To speed convergence, EIGRP attempts to maintain a successor and feasible successor path for each destination.
D. EIGRP uses hellos to establish neighbor relationships.
E. By default, EIGRP uses the Dijkstra algorithm to determine the best path to a destination network based on bandwidth and delay.

 

Answer: A C D

Question 3

Which of the following settings could prevent two potential EIGRP neighbors from becoming neighbors? (Choose two)

A. The interface used by one router to connect to the other router is passive in the EIGRP process
B. Duplicate EIGRP router IDs
C. Mismatched Hold Timers
D. IP addresses of 10.1.1.1/24 and 10.2.2.2/24, respectively

 

Answer: A D

Question 4

Refer to the following.

Router# sh ip route eigrp
13.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 13.0.0.0/8 is a summary, 00:00:32, Null0

What happens to packets that are forwarded from the 13.0.0.0/8 network to the Null0 interface?

A. Flagged
B. Accepted
C. Summarized
D. Dropped

 

Answer: D

Question 5

An engineer has added the following configuration snippet to an implementation planning document. The configuration will be added to Router R1, whose Fa0/0 interface connects to a LAN to which Routers R2 and R3 also connect. R2 and R3 are already EIGRP neighbors with each other. Assuming the snippet shows all commands on R1 related to EIGRP authentication, which answer lists an appropriate comment to be made during the implementation plan peer review?

key chain fred
key 3
key-string whehew
interface fa0/0
ip authentication key-chain eigrp 9 fred

A. The configuration is missing one authentication-related configuration command.
B. The configuration is missing two authentication-related configuration commands.
C. Authentication type 9 is not supported; type 5 should be used instead.
D. The key numbers must begin with key 1, so change the key 3 command to key 1.

 

Answer: A

Question 6

Which two types of routes will be advertised with the EIGRP configuration as shown? (Choose two)

router eigrp 100
network 10.0.0.0
eigrp stub

A. static
B. receive-only
C. summary
D. stub
E. connected
F. dynamic

 

Answer: C E

Question 7

What administrative distance is given to EIGRP summary routes?

A. 0
B. 1
C. 5
D. 90
E. 95
F. 170

 

Answer: C

Question 8

Which configuration command is used to enable EIGRP unequal-cost path load balancing?

A. maximum-paths
B. distance
C. metric
D. variance
E. default-metric

 

Answer: D

Question 9

Which two statements are EIGRP characteristics? (Choose two)

A. Updates are sent as multicast.
B. Updates are sent as broadcast.
C. Metric values are represented in a 32-bit format for granularity.
D. LSAs are sent to adjacent neighbors.

 

Answer: A C

Question 10

Which three features are related to EIGRP? (Choose three)

A. Fast Convergence
B. External Administrative distance is 100
C. Partial routing updates.
D. used by other vendors than Cisco.
E. Link-state protocol.
F. Support VLSM and discontiguous subnets

 

Answer: A C F

EIGRP Questions 10

May 5th, 2014 digitaltut 1 comment

Here you will find answers to EIGRP questions – Part 10

Question 1

Refer to the exhibit. Network administrators have set up a hub and spoke topology with redundant connections using EIGRP. However, they are concerned that a network outage between Router R1 and Router R2 will cause traffic from the 10.1.1.x network to the 10.1.2.x network to traverse the remote office links and overwhelm them. What command should be used to configure the spoke routers as EIGRP stub routers that will not advertise connected networks, static routes, or summary addresses?

EIGRP_hub_spoke_topology_stub_receive_only.jpg

A. eigrp stub
B. eigrp stub receive-only
C. eigrp stub connected static
D. no eigrp stub connected static
E. No additional command is needed beyond a default EIGRP configuration.

 

Answer: B

Question 2

A network administrator is troubleshooting an EIGRP connection between RouterA, IP address 10.1.2.1, and RouterB, IP address 10.1.2.2. Given the debug output on RouterA, which two statements are true?

RouterA#debug eigrp packets

01:39:13: EIGRP: Received HELLO on Serial0/0 nbr 10.1.2.2
01:39:13: AS 100, Flags 0x0, Seq idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
01:39:13: K-value mismatch

A. RouterA received a hello packet with mismatched autonomous system numbers.
B. RouterA received a hello packet with mismatched hello timers.
C. RouterA received a hello packet with mismatched authentication parameters.
D. RouterA received a hello packet with mismatched metric-calculation mechanisms.
E. RouterA will form an adjacency with RouterB.
F. RouterA will not form an adjacency with RouterB.

 

Answer: D F

Question 3

Observe the exhibit. If the command variance 3 were added to RTE, which path or paths would be chosen to route traffic to network X?

EIGRP_variance_3.jpg

A. E-B-A
B. E-B-A and E-C-A
C. E-C-A and E-D-A
D. E-B-A, E-C-A and E-D-A

 

Answer: B

Explanation

Please notice that routes must first satisfy the feasible condition to be considered for “variance” command:

The feasible condition states:
“To qualify as a feasible successor, a router must have an AD less than the FD of the current successor route”.

In this case, the current successor route is E -> C -> A and the FD of this successor route is 20. But the AD of route E-D-A is 25 which is bigger than the FD of the successor route -> It will not be put into the routing table even if the “variance 3” command is used.

Question 4

Router E is configured with the EIGRP variance 2 command. What path will Router E take to reach Router A?

EIGRP_variance_3.jpg

A. only E-D-A
B. only E-B-A
C. only E-C-A
D. both E-B-A and E-C-A
E. both E-B-A and E-D-A
F. all available paths.

 

Answer: D

Question 5

Refer to the exhibit. Which router configuration command can be given that will restrict router RTB from sharing its routing information with router RTA?

EIGRP_eigrp_stub_receive-only.jpg

A. The eigrp stub command on router RTA.
B. The eigrp stub command on router RTB.
C. The eigrp stub connected command on router RTA
D. The eigrp stub connected command on router RTB
E. The eigrp stub receive-only command on router RTA
F. The eigrp stub receive-only command on router RTB

 

Answer: F

Explanation

The receive-only keyword will restrict the router from sharing any of its routes with any other router in that EIGRP autonomous system, and the receive-only keyword will not permit any other option to be specified because it prevents any type of route from being sent. The three other optional keywords (connected, static, and summary) can be used in any combination but cannot be used with the receive-only keyword.

(Reference: http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/eigrpstb.html)

Question 6

Refer to the exhibit. On all routers in the network, EIGRP has been configured for load balancing across the three links. However, traffic destined for Network B from R1 is only load balanced over paths R1-R2-R5 and R1-R3-R5. What is the cause of the problem?

EIGRP_load_balancing_variance_3.jpg

A. EIGRP will not select more than two links for unequal cost path load balancing.
B. Because the path has a different link type, EIGRP will not select path R1-R4-R5 for load balancing.
C. Because Router R4 is not a feasible successor, EIGRP will not select path R1-R4-R5 for load balancing.
D. EIGRP will not select path R1-R4-R5 for load balancing unless the value of the variance parameter is increased.

 

Answer: C

Explanation

The feasible condition states:
“To qualify as a feasible successor, a route must have an AD less than the FD of the current successor route”. In this case the AD of R4 is 25 (to network B, which is larger than the FD of the current successor R2 (its FD is 10 + 10 = 20) -> R4 is not a feasible successor.

Question 7

Refer to the exhibit. Which statement about dynamic routing protocols for this network is true?

EIGRP_Summarization_point.jpg

A. No dynamic interior routing protocol can summarize as shown.
B. Unless configured otherwise, EIGRP would automatically summarize the prefixes as shown in the exhibit.
C. With this IP addressing scheme, EIGRP can be manually configured to summarize prefixes at the specified summarization points.
D. The IP address design lends itself to OSPF. Each summarizing router would be an ABR, summarizing to the next area in the address hierarchy.

 

Answer: C

Question 8

Refer to the topology diagram R2 is redistributing the EIGRP routers into OSPF. What will the EIGRP routes appear in the routing table of R1?

Redistribute_EIGRP_OSPF_O_E2.jpg

A. O
B. O IA
C. O E2
D. D
E. D EX

 

Answer: C

Explanation

By default, routes redistributed into OSPF will be considered External route – Type 2 (E2) with the default metric of 20. For E2 route, the cost is only from the ASBR to the final destination.

Question 9

Refer to the Exhibit. Routers in the Diagram are configured with EIGRP. If RB and RC fail, which action will RA take with respect to the HQ network?

EIGRP_active_state.jpg

A. RA will automatically route packets via RD to the HQ network.
B. RA will place the route via RD into the hold down state.
C. RA will go into the active state for all routes.
D. RA will go into the active state for the route to HQ network.

 

Answer: D

Explanation

The cost advertised from RD is too big (100) so it cannot be a feasible successor -> RA will go to the active state if both RB and RC fail.

BGP Questions

May 4th, 2014 digitaltut 2 comments

Here you will find answers to BGP questions

Question 1

Refer to the exhibit. Router RIP is attempting to establish BGP neighbor relationships with routers RT1 and RT3. On the basis of the information that is presented in the exhibit, which two statements are true? (Choose two)

BGP_MD5Digest1

BGP_MD5Digest2

A – RTR has a BGP password set but neighbor 10.0.0.1 does not
B – RTR has a BGP password set but neighbor 10.0.0.5 does not
C – RTR has a BGP password set but neighbor 10.0.0.1 has an incorrect password set
D – RTR has a BGP password set but neighbor 10.0.0.5 has an incorrect password set
E – Neighbor 10.0.0.1 has a BGP password set but RTR does not
F – Neighbor 10.0.0.5 has a BGP password set but RTR does not

 

Answer: A D

Explanation:

You can configure MD5 authentication between two BGP peers, MD5 authentication must be configured with the same password on both BGP peers; otherwise, the connection between them will not be made. If a router has a password configured for a peer, but the other peer does not, a message “No MD5 digest from…” will appear on the console while the routers attempt to establish a Multicast Source Discovery Protocol (MSDP) session between them. Therefore A is correct because RT1 (with an ip address of 10.0.0.1) is not configured with a password.

Similarly, if the two routers have different passwords configured, a message “Invalid MD5 digest from…” will appear on the screen.

Question 2

Refer to the exhibit diagram and configuration. RTB is summarizing its networks from AS 64100 with the aggregate-address command. However, the show ip route command on RTA reveals the RTB individual networks as well as its summary route. Which option would ensure that only the summary route would appear in the routing table of RTA?

BGP_summary

A – Delete the four network statements and leave only the aggregate-address statement in the BGP configuration
B – Add the keyword summary-only to the aggregate-address command
C – Add a static route with a prefix of 192.168.24.0 255.255.252.0 pointing to the null interface
D – Create a route map permitting only the summary address

 

Answer: B

Explanation

When the aggregate-address command is used within BGP routing, the aggregated address is advertised, along with the more specific routes. The exception to this rule is through the use of the summary-only command. The “summary-only” keyword suppresses the more specific routes and announces only the summarized route.

Question 3

Refer to the exhibit The neighbor 10.1.1.1 weight 200 BGP configuration command has been configured on router A. What will be the result of this configuration?

BGP_weight

A – Router A will prefer the path through router B for network 172.20.0.0
B – Router A will prefer the path through router C for network 172.20.0.0
C – Packets from router D will prefer the path through router B for networks advertised by router A
D – Packets from router D will prefer the path through router C for networks advertised by router A

 

Answer: A

Explanation

The weight attribute is a special Cisco attribute that is used in the path selection process when there is more than one route to the same destination. The higher the weight value, the better the path. The default weight is 0. Therefore, by configuring weight 200 to the neighbor 10.1.1.1, router A will prefer the path through router B for network 172.20.0.0 then the path through router C.

The weight attribute is local to the router and not propagated to other routers. In this case the weight is local to router A so it has no effect on the decision of transferring packets from router D.

Question 4

Based on the show ip bgp summary output. which two statements are true? (Choose two)

BGP_States

A – The BGP session to the 10.1.1.1 neighbor is established
B – The BGP session to the 10.2.2.2 neighbor is established
C – The BGP session to the 10.3.3.3 neighbor is established
D – The router is attempting to establish a BGP peering session with the 10.1.1.1 neighbor
E – The BGP session to the 10.3.3.3 neighbor is established, but the router has not received any BGP routing updates from the 10.3.3.3 neighbor
F – The router is attempting to establish a BGP peering session with the 10.2.2.2 neighbor

 

Answer: A F

Explanation

The main point of this question is the “State/PfxRcd” column, which shows the BGP states. Below is the list of BGP states in order, from startup to peering:

1 – Idle: the initial state of a BGP connection. In this state, the BGP speaker is waiting for a BGP start event, generally either the establishment of a TCP connection or the re-establishment of a previous connection. Once the connection is established, BGP moves to the next state.

2 – Connect: In this state, BGP is waiting for the TCP connection to be formed. If the TCP connection completes, BGP will move to the OpenSent stage; if the connection cannot complete, BGP goes to Active

3 – Active: In the Active state, the BGP speaker is attempting to initiate a TCP session with the BGP speaker it wants to peer with. If this can be done, the BGP state goes to OpenSent state.

4 – OpenSent: the BGP speaker is waiting to receive an OPEN message from the remote BGP speaker

5 – OpenConfirm: Once the BGP speaker receives the OPEN message and no error is detected, the BGP speaker sends a KEEPALIVE message to the remote BGP speaker

6 – Established: All of the neighbor negotiations are complete. You will see a number (2 in this case), which tells us the number of prefixes the router has received from a neighbor or peer group.

Question 5

Which command displays the IBGP and EBGP neighbors that are configured?

A – show ip bgp
B – show ip bgp paths
C – show ip bgp peers
D – show ip bgp summary

 

Answer: D

Explanation

The picture below shows the output of the show ip bgp summary

BGP_show_ip_bgp_summary

Notice that the “show ip bgp” command to display BGP topology database. Below is the output of the “show ip bgp” command:

BGP_show_ip_bgp

Question 6

BGP contains two paths to a destination. Assuming both routes were originated locally and have an equal weight. what will be the next determining factor in choosing the best path?

A – lowest MED
B – highest local preference
C – lowest neighbor IP address
D – lowest origin code
E – shortest AS-path

 

Answer: B

Explanation

Memorizing the BGP decision process steps is very useful and you should remember them. The table below lists the complete path selection process:

1. Weight (Bigger is better)
2. Local preference
(Bigger is better)
3. Self originated (Locally injected is better than iBGP/eBGP learned)
4. AS-Path (Smaller is better)
5. Origin
(Prefer ORIGIN code I over E, and E over ?)
6. MED (Smaller is better)
7. External (Prefer eBGP over iBGP)
8. IGP cost (Smaller is better)
9. EBGP Peering (Older is better)
10. RID (Lower is better)

Question 7

Which BGP path attribute is Cisco proprietary?

A. weight
B. MED
C. local preference
D. origin
E. next-hop
F. AS-path

 

Answer: A

Explanation

The weight attribute is a Cisco proprietary technology. This attribute is local to a router and is not advertised to neighboring routers. If the router learns about more than one route to the same destination, the route with the highest weight will be preferred and will be installed in the routing table. By default, the value of weight is 0 and the range is from 0 to 65535.

The route with the highest weight will be installed in the IP routing table.

Question 8

Which attribute must exist in the BGP update packet?

A. LOCAL_PREF
B. AGGREGATOR
C. AS_Path
D. Weight

 

Answer: C

Explanation

Origin, AS_Path, Next_Hop are well-known mandatory BGP attributes that all BGP Updates must include.

Note:

There are 4 BGP attribute types:

+ Well-known Mandatory: recognized by all implementations of BGP and must appear in a BGP update message. If missing, a notification error will be generated.
+ Well-Known Discretionary: recognized by all implementations of BGP but may not be sent in the BGP update message (include LOCAL_PREF, ATOMIC_AGGREGATOR).
+ Optional Transitive: may or may not be recognized by all BGP implementations. Because the attribute is transitive, BGP accepts and advertises the attribute even if it is not recognized (include Community attribte).
+ Optional Nontransitive: may or may not be recognized by all BGP implementations. Whether or not the receiving BGP router recognizes the attribute, it is nontransitive and is not passed along to other BGP peers (include MED).

Question 9

When the BGP path selection process is being performed on a Cisco router, which BGP attribute is used first when determining the best path?

A. local preference
B. MED
C. weight
D. origin
E. next-hop
F. AS-path

 

Answer: C

Explanation

Weight is the first attribute BGP uses in the route selection process. Route with a higher weight is preferred when multiple routes exist to the same destination.

Question 10

Which BGP attribute will not be advertised in routing updates to its neighboring routers?

A. weight
B. local preference
C. origin
D. AS_path
E. next hop

 

Answer: A

Explanation

Same as Question 7.

BGP Questions 2

May 4th, 2014 digitaltut No comments

Here you will find answers to BGP Questions – Part 2

Question 1

Study the configuration presented in the exhibit carefully. What is the objective of the route map named test?

router bgp 50001
network 10.0.0.0
network 172.16.0.0
neighbor 10.1.1.1 remote-as 5003
neighbor 10.1.1.1 route-map test out
!
access-list 1 permit 10.0.0.0
access-list 2 permit any
!
route-map test permit 10
match ip address 1
set metric 200
!
route-map test permit 20 match ip address 2

A. marks all prefixes received from the 10.1.1.1 neighbor with a MED of 200
B. marks the 10.0.0.0/8 prefix received from the 10.1.1.1 neighbor with a MED of 200
C. marks the 10.0.0.0/8 prefix advertised to the 10.1.1.1 neighbor with a MED of 200
D. marks all prefixes advertised to the 10.1.1.1 neighbor with a MED of 200

 

Answer: C

Explanation

From the command “neighbor 10.1.1.1 route-map test out” we learn the “test” route map is applied on the outbound direction to the neighbor 10.1.1.1. In the “test” route map, we see 3 statements:

“route-map test permit 10
match ip address 1
set metric 200″

They mean “if the access list 1 is matched, set the Multi Exit Discriminator (MED) of that route to 200”.

Question 2

What technique should be used on BGP edge routers to prevent a multi-homed autonomous system from becoming a transit system?

A. Advertise with a high MED value all networks that are discovered via external BGP.
B. Remove the AS-Path information on all routes in the BGP table prior to advertising externally.
C. Only advertise networks externally if they have been discovered via internal BGP.
D. Use an outgoing distribution list to filter all networks not originating from inside the autonomous system.
E. Set the no-export community attribute on all networks that are advertised externally.
F. Set the origin code to incomplete for all networks that are discovered via external BGP.

 

Answer: D

Explanation

A transit AS is an AS that routes traffic from one external AS to another external AS. Let’s see an example below:

BGP_transit_AS.jpg

Suppose your company has 2 internet links to 2 different ISPs. If one connection to the ISP goes down, your traffic can be sent through the other ISP. It is a good way to make sure your company can access the internet any time. But if your routers are not configured carefully, your company AS may become a transit AS. For example, AS 65002 learned the route 10.10.10.0/24 from ISP1. If R2 advertises that route to ISP2 then ISP2 may use it to send traffic to that network -> your company becomes a transit AS.

There are two popular ways to prevent a multi-homed autonomous system from becoming a transit system:

+ Use a distribute-list or filter-list to filter all networks not originating from inside the autonomous system.
+ Use the no-export community attribute on all networks not originating from inside the autonomous system.

Answer E seems to be correct but in fact it is not because “all networks that are advertised externally” include networks originating from inside and outside our AS. We should only filter networks originating from outside our AS. In some cases, the routers in our company may advertise some internal networks (for remote access, for example).

We create 2 GNS3 labs to explain them in more detail. You can read them here:

+ Use Distribute-list to filter Routing Updates in BGP
+ BGP next-hop-self, community no-export & send-community – GNS3 Lab

Question 3

Refer to the exhibit. By default, when RTB passes BGP advertisements from RTA about network 192.168.2.0 to RTC, what address will be listed as the next-hop address?

BGP_next_hop.jpg

A. 10.1.1.1
B. 10.1.1.2
C. 192.168.1.49
D. 192.168.1.50

 

Answer: D

Explanation

This is a rule for BGP advertisement:

“For EBGP, the next hop is always the IP address of the neighbor specified in the neighbor command. For IBGP, the protocol states that the next hop advertised by EBGP should be carried into IBGP“.

In this case, when RTA (in AS 65000, which is an EBGP for RTB) advertises a route to RTB, it specifies its interface (192.168.1.50) as the next-hop. But when RTB passes this advertisement to RTC, it specifies RTA interface (also 192.168.1.50) as the next-hop (IBGP). This can cause some routing failures because if RTC does not know a way to reach RTA interface via IGP (OSPF, EIGRP…), it will drop that packet. To fix this problem, add the “neighbor 10.1.1.2 next-hop-self” command under BGP mode in RTB. You can find out more about this problem in our BGP next-hop-self, community no-export & send-community – GNS3 Lab.

Question 4

What are the two reasons for the appearance of 0.0.0.0 as the next hop for a network in the show ip bgp command output? (Choose two)

A. The network was originated via redistribution of an interior gateway protocol into BGP.
B. The network was defined by a static route.
C. The network was originated via a network or aggregate command.
D. The network was learned via EBGP.
E. The network was learned via IBGP.

 

Answer: A C

Explanation

You can read my BGP Summary Route to see “the network was originated via a network or aggregate command” has the next hop of 0.0.0.0. In short, the router on which you use the “network” or “aggregate” command will set the next hop of 0.0.0.0 for that route.

About redistribution please refer to the Understanding Redistribution of OSPF Routes into BGP: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800943c5.shtml you will see after the network 2.0.0.0 has been redistributed in BGP it has the next hop of 0.0.0.0.

Question 5

Which BGP attribute is used by BGP to prevent routing loops?

A. AS-path
B. next-hop
C. MED
D. weight
E. local preference
F. origin

 

Answer: A

Explanation

The AS-PATH attribute is used to prevent BGP routing loops. When receiving an BGP advertisement, the router checks the AS-PATH attribute, if it see it’s own AS number in the AS-Path then it is a routing loop so the router will not install this route in its BGP table.

Question 6

Refer to the exhibit. It is desired to set up a BGP neighbor relationship between routers R1 and R4. BGP packets between them could travel through R2 or R3. What is the simplest configuration that will allow for failover?

BGP_loopback_update_source.jpg

A. Configure BGP neighbor relationships between all interfaces on R1 and R4.
B. Install a direct connection between R1 and R4.
C. Configure loopback interfaces on R1 and R4 to provide the update source address for BGP packets.
D. Configure only one neighbor relationship between R1’s 192.168.1.2 interface and R4’s 172.16.10.2 interface.

 

Answer: C

Explanation

Assume R4 only uses this configuration:

R4(config)#router bgp 65000
R4(config-router)#neighbor 192.168.1.2 remote-as 65000

Then if R1 sends BGP packets to R4 via R3, the source IP address of the packets is 192.168.2.2. But R4 does not recognize this IP address because 192.168.2.2 is not configured in the “neighbor” command of R4. Therefore the IBGP session between R1 & R4 is not established -> these packets will be dropped.

The simplest configuration to allow R1 and R4 communicate via both R2 & R3 is to use a loopback interface address rather than a physical interface address as the source IP address for all BGP packets. To do this, use the command:

R4(config-router)#neighbor 1.1.1.1 update-source loopback0

(In which 1.1.1.1 is the loopback interface of R1). In practical, we should establish neighborship with the loopback interface rather than the physical interface because if the physical interface goes down, the neighborship would be lost while a loopback interface never goes down.

Also, when configuring “1.1.1.1” as the neighbor, you must configure on R1 the “neighbor 4.4.4.4 update-source loopback0” command so that the source IP address of packets sent from R1 (loopback0 – 1.1.1.1) will be matched with the neighbor command configured on R4.

Question 7

Refer to the exhibit. Network 10.0.0.0/8 is being advertised to autonomous system 65550 via both external links. Which statement about the preferred path to the 10.0.0.0/8 network is true?

bgp_higher_local_preference.jpg

A. Router R1 will be preferred because its neighbor has the higher autonomous system number.
B. Router R1 will be preferred because it has the lower neighbor IP address.
C. Router R1 will be preferred because it has a lower local preference.
D. Router R2 will be preferred because its neighbor has a lower autonomous system number.
E. Router R2 will be preferred because it has the higher neighbor IP address.
F. Router R2 will be preferred because it has a higher local preference.

 

Answer: F

Explanation

Local preference is an indication to the AS about which path has preference to exit the AS in order to reach a certain network. A path with a higher local preference is preferred more. The default value for local preference is 100.

Unlike the weight attribute, which is only relevant to the local router, local preference is an attribute that routers exchange in the same AS. The local preference is set with the “bgp default local-preference value” command.

In this case, both R1 & R2 learn about the network 10.0.0.0/8 but R2 has higher local-preference so R2 will be chosen as the preferred exit point from AS 65550.

(Reference: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml#localpref)

Question 8

During BGP configuration on a router that has peered with other BGP speakers, the BGP command aggregate-address 172.32.0.0 255.255.252.0 is issued. However, the peers do not receive this aggregate network in BGP advertisements. Also, the router does not have this aggregate network in its BGP table. Which option indicates a possible reason this command did not cause the router to advertise the aggregate network to its peers?

A. Interface NULL 0 is likely shutdown.
B. The BGP command no synchronization is missing.
C. The BGP command no auto-summary is missing.
D. Subnets of 172.32.0.0/22 do not exist in the BGP table.
E. The IGP running on this router does not have network 172.32.0.0/22 installed.
F. The next hop IP address must be a loopback address.

 

Answer: D

Explanation

A rule of aggregation is “Aggregation applies only to routes that exist in the BGP routing table. An aggregated route is forwarded if at least one more specific route of the aggregation exists in the BGP routing table.

Question 9

Which two methods advertise internal networks to external ISPs via BGP? (Choose two)

A. using aggregate routes
B. disabling synchronization
C. forcing the next-hop address
D. defining routes via the network statement

 

Answer: A D

Question 10

Which BGP command provides the router ID, local preference, next hop, and BGP path in its output?

A. show ip route bgp
B. show ip bgp
C. show ip bgp neighbors
D. show ip bgp summary

 

Answer: B

Explanation

The “show ip bgp” command is used to display entries in the BGP routing table. An example of the “show ip bgp” output is shown below:

show_ip_bgp.jpg

In the output you can see the router ID, local preference, next hop, and BGP path.

BGP Questions 3

May 4th, 2014 digitaltut No comments

Here you will find answers to BGP Questions – Part 3

Question 1

Which option is true regarding the synchronization rule?

A. Do not use or internally advertise a route until the route is learned from a source other than BGP.
B. Do not use or advertise a route until the route is learned from a BGP peer.
C. Do not use or advertise routes marked PARTIAL.
D. Wait until a CONFIRM message is received before using routes from BGP neighbors.

 

Answer: A

Explanation

The complete synchronization rule is “A BGP router should not use, or advertise to an external neighbor, a route learned by IBGP, unless that route is local or is learned from the IGP.”

With the default of synchronization disabled, BGP can use and advertise to external BGP neighbors routes learned from an IBGP neighbor that are not present in the local routing table

The “synchronization” here means “synchronization between iBGP with its IGP (such as OSPF, EIGRP…)

You can disable synchronization if one of the following conditions is true:
Your AS does not pass traffic from one AS to another AS.
All the transit routers in your AS run BGP.

 

Note: BGP synchronization is disabled by default in Cisco IOS Software Release 12.2(8)T and later.

For more information about BGP Synchronization please read the explanation of Question 5 in this page. Also another good resource is : http://docwiki.cisco.com/wiki/Internetworking_Case_Studies_–_Using_the_Border_Gateway_Protocol_for_Interdomain_Routing#Synchronization

Question 2

Refer to the exhibit. Router RT-1 and router RT-2 both advertise network 131.25.0.0/16 to router RT-3 via internal BGP. What is the reason that router RT-3 chose router RT-1 as its best path to network 131.25.0.0/16.

BGP_router_ID.jpg

A. It advertises the best AS-path.
B. It advertises the best origin code.
C. It advertises the best MED.
D. It advertises the best local preference.
E. It has a better router ID.
F. It advertises a lower autonomous system.

 

Answer: E

Explanation

Recall the route selection decision process in BGP:

Consider only (synchronized) routes with no AS loops and a valid next hop, and then:

Route selection decision process (from top to bottom) In this question…
Prefer highest weight (local to router) RT-3 is not an exit point
Prefer highest local preference (global within AS) same local preference of 100
Prefer route originated by the local router (next hop = 0.0.0.0) both routes are from IBGP
Prefer shortest AS path same
Prefer lowest origin code (IGP < EGP ) both are incomplete (EGP > IGP > Incomplete)
Prefer lowest MED (exchanged between autonomous systems) both MEDs are 0
Prefer EBGP path over IBGP path both are IBGP
Prefer the path through the closest IGP neighbor (IGP cost) not used because IBGPs are used
Prefer oldest route for EBGP paths. not used
Prefer the path with the lowest neighbor BGP router ID. the router-id 162.105.11.1 is lower than 165.105.3.2
Prefer the path with the lowest neighbor IP address.  

Question 3

Refer to the exhibit. Router RT-1 chooses one path to network 198.133.219.0/24. Indicate the reason Router RT-1 chooses this “best” path.

BGP_Origin_Compare.jpg

A. In making its decision about the best path, RT-1 gives precedence to the origin code.
B. In making its decision about the best path, RT-1 gives precedence to the BGP MED values.
C. IP address 128.107.2.2 is lower than 128.107.255.2.
D. In making its decision about the best path, RT-1 prefers the IGP metrics.
E. RT-1 prefers internal BGP routes.
F. IP address 128.107.254.2 is lower than 128.107.255.2.

 

Answer: A

Explanation

As explained in question 3, the IGP is preferred over incomplete.

Question 4

The Border Gateway Protocol (BGP) is the core routing protocol of the Internet. Refer to the exhibit. Routers A and B are running BGP but the session is active. What command needs to be added to establish the BGP session?

BGP_establish_session.jpg

hostname A
!
interface loopback 0
ip address 10.10.10.2 255.255.255.255
!
interface serial 0/0
ip address 172.16.10.2 255.255.255.252
!
interface serial 0/1
ip address 172.16.10.5 255.255.255.252
!
router bgp 65444
neighbor 10.10.10.1 remote-as 65111
neighbor 10.10.10.1 update-source loopback 0
neighbor 10.10.10.1 ebgp-multihop

A. ip route 10.10.10.1 255.255.255.255 s0/0
ip route 10.10.10.1 255.255.255.255 s0/ 1
B. no synchronization
C. network 10.10.10.0
D. neighbor 10.10.10.1 next-hop-self

 

Answer: A

Explanation

In this case we want to achieve load balancing so the loopback interface must be used to establish neighborship.

If we check the routing table of router A, we will see that there is no entry for the remote network 1.1.1.1/32 -> router A does not know how to reach the loopback interface on router B -> a TCP session can’t be established to router B. Therefore we need to tell router A a way to reach router B.

(Reference and a good resource: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml)

Question 5

Refer to the exhibit. Autonomous systems 200 and 300 have EBGP sessions established with their directly connected routers in autonomous system 100. IGP has been configured on all routers in autonomous system 100 and they successfully exchange routing updates. Traffic originated in autonomous system 200 cannot reach the destination autonomous system 300. What configuration should be done on the routers in autonomous system 100 in order for the traffic coming from autonomous system 200 to be forwarded to autonomous system 300?

BGP_IBGP_synchronization.jpg

A. IBGP session must be established between routers R1 and R3, and the synchronization must be turned on.
B. IBGP session must be established between routers R1 and R3, and the synchronization must be turned off.
C. IBGP session must be established between routers R1 R2 and R2 R3. and the synchronization must be turned on.
D. IBGP session must be established between routers R1 R2 and R2 R3, and the synchronization must be turned off.
E. IBGP speakers within autonomous 100 must be fully meshed, and the synchronization must be turned on.
F. IBGP speakers within autonomous 100 must be fully meshed, and the synchronization must be turned off.

 

Answer: F

Explanation

The synchronization rule states that if an AS provides transit service to another AS, BGP should not advertise a route until all of the routers within the AS have learned about the route via an IGP. To understand why this rule exists, let’s take an example if this rule is not there.

BGP_IBGP_synchronization_Example.jpg

Suppose Rt-A wants RT-B to access its local LAN 1.1.1.0, so it advertises this network through R1. R1 and R3 are running IBGP so R1 sends this update to R3 through R2 (using the next-hop-self to use its own interface’s IP address). In turn, R3 announces to RT-B that it can reach 1.1.1.0 via R3.

Now Rt-B really wants to send traffic to 1.1.1.0 so it will send to R3. R3 does a look up and sees that the network can be reachable via R1. It then does a lookup for R1’s IP address and sees that it is reachable via R2 -> so it forwards packets to R2. But R2, running IGP (like OSPF), does not find an entry for 1.1.1.0 so R2 drops all the packets for that network – a black-hole is created!

That is why the BGP synchronization rule is born. With this rule, when R3 receives an advertisement for 1.1.1.0 from R1, it adds that route to its BGP table and before sending advertisement to RT-B, it first checks its IGP routing table to see whether an entry exists for that route. In this example, R3’s IGP routing table does not know how to reach 1.1.1.0 so R3 will not advertise this network to RT-B. This route is only advertised to RT-B when IGP makes an entry in the routing table for 1.1.1.0.

Well, now you understand the importance of BGP Synchronization rule but now I wish to explain why this rule causes trouble in fully-meshed IBGP!

BGP_IBGP_synchronization_fully-messed.jpg

Synchronization prevents fully-meshed IBGP from working properly. Because no IGP is running so R3 cannot advertise any route to RT-B even if no black-hole exists in this topology.

Note: A “fully-meshed” can be a physical fully-meshed topology or a topology where all routers in the same AS established IBGP connections with each other (although they do not need to be directly connected). So in the topology above, the connection between R1 & R3 is represented by a dashed line, which means it can be physically connected or not (but an IBGP connection must be established on both routers).

Therefore if all routers in AS 100 is fully-meshed, the synchronization rule must be turned off -> F is correct.

Question 6

Which one of the following statements about BGP is FALSE?

A. BGP uses TCP port 179.
B. BGP ensures reliability of updates by using the reliable transport services of TCP.
C. The network command with the mask option never installs a prefix into the BGP table unless there is a matching prefix exists in the IP route table.
D. A TCP connection is required before exchanging updates.
E. BGP uses notification and the update messages to establish and maintain the BGP neighbor relationship.

 

Answer: E

Explanation

An underlying connection between two BGP speakers is established before any routing information is exchanged. This connection takes place on TCP port 179.

Unlike other routing protocols, the router must be manually configured with the neighbor information on both sides of the connection -> E is correct (which is FALSE in this question)

Question 7

Which BGP option is required when load sharing over multiple equal-bandwidth parallel links from a single CE router to a single ISP router over eBGP?

A. eBGP Multipath
B. eBGP Multihop
C. BGP Synchronization
D. Public AS numbers

 

Answer: B

Explanation

The eBGP multihop allows a neighbor connection between two external peers that do not have direct connection. The multihop is only for eBGP and not for iBGP. For example, in the topology below router A wants to establish neighbor relationship with the loopback0 of router B (to allow load balancing), which does not have direct connection so it must use “ebgp-multihop”

BGP_ebgp-multihop.jpg

For your reference, the full configurations of both router A & B are shown below:

A# int loopback 0
ip address 10.10.10.2 255.255.255.255
router bgp 1
neighbor 10.10.10.1 remote-as 2
neighbor 10.10.10.1 ebgp-multihop
neighbor 10.10.10.1 update-source loopback 0
network 10.10.10.2 mask 255.255.255.255
ip route 10.10.10.1 255.255.255.255 172.16.10.1
ip route 10.10.10.1 255.255.255.255 172.16.10.6
B# int loopback 0
ip address 10.10.10.1 255.255.255.255
router bgp 2
neighbor 10.10.10.2 remote-as 1
neighbor 10.10.10.2 ebgp-multihop
neighbor 10.10.10.2 update-source loopback 0
network 10.10.10.1 mask 255.255.255.255
ip route 10.10.10.2 255.255.255.255 172.16.10.2
ip route 10.10.10.2 255.255.255.255 172.16.10.5

Note: If router B wants to establish neighbor relationship with the directly connected interface of router A, it only needs these commands:

B#
router bgp 2
neighbor 172.16.10.2 remote-as 1

But notice the traffic from router B would be sent to 172.16.10.2 interface only and load balancing would not take place.

(Reference: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml)

Question 8

Which statement is true about IBGP routers?

A. They must be fully meshed.
B. They can be in a different AS.
C. They must be directly connected,
D. They do not need to be directly connected.

 

Answer: D

Question 9

Refer to the exhibit. On the basis of the configuration that is provided, how would the BGP updates that come from router R1 be replicated inside autonomous system 65200?

BGP_no_synchronization.jpg

A. All BGP updates that are received on router R2 will be sent to routers R3 and R4. Routers R3 and R4 will then forward those BGP updates to router R5.
B. All BGP updates that are received on router R2 will not be sent to routers R3 and R4.
C. All BGP updates that are received on router R2 will be sent directly to router R5.
D. None of the BGP updates that are received on router R2 will ever be received by router R5.

 

Answer: D

Explanation

All BGP updates that are received on router R2 will be sent to routers R3 and R4 but R3 & R4 will not forward those BGP updates to R5. This is called the BGP split-horizon rule (which states that a route learned from one IBGP neighbor will not be advertised to another IBGP neighbor) -> A is not correct.

The BGP updates received on router R2 will be sent to R3 and R4 without violating the BGP split-horizon rule because R2 receives updates from an EBGP (R1), not IBGP -> B is not correct.

From the configuration of R2, we learn that R2 did not establish neighbor relationship with R5 so they are not neighbors -> no BGP updates will be sent from R2 to R5 -> C is not correct.

The BGP split-horizon rule prevents updates received on R2 from being sent to R5 -> D is correct.

Question 10

The 192.168.0.0 network is not being propagated throughout the network. Observe the BGP configuration commands from the advertising router. What is the reason the 192.168.0.0 route is not being advertised?

router bgp 65111
neighbor 172.16.1.1 remote-as 65111
neighbor 172.16.2.1 remote-as 65112
network 192.168.0.0
network 10.0.0.0
!
ip route 192.168.0.0 255.255.0.0 null0

A. The network 192.168.0.0 statement is missing mask 255.255.0.0
B. The network 192.168.0.0 statement is missing mask 0.0.255.255.
C. The network 10.0.0.0 statement is missing mask 255.0.0.0.
D. The network 10.0.0.0 statement is missing mask 0.255.255.255.
E. The auto-summary configuration is missing.

 

Answer: A

Explanation

The “network” statement in other routing protocols (EIGRP, OSPF, RIP…) is used to enable routing protocol on the interfaces within that “network” statement. But in BGP, the function of a network statement is to tell the router to search the IP routing table for a particular network, and if that network is found, originate it into the BGP database. But notice that you must have an exact match in the IP routing table to appear the network in the BGP routing table (in this case we don’t see the auto-summary command so we suppose it is disabled in this case). For example:
+ network 10.10.10.0/8 will appear in BGP if network 10.10.10.0/8 appears in the IP routing table.
+ network 10.10.10.0/24 will appear in BGP if network 10.10.10.0/24 appears in the IP routing table.

Therefore, in this question the static route “ip route 192.168.0.0 255.255.0.0 null0” was used to put a route to 192.168.0.0/16 into the routing table (although it points to Null0 but this command really makes that route appears in the routing table). But the “network 192.168.0.0” statement tells the router to lookup network 192.168.0.0/24 (if the network statement under BGP-mode does not specify a subnet mask, the default subnet mask of that class will be used). The router only finds network 192.168.0.0/16 -> The network 192.168.0.0 is not being propagated throughout the network because of the mismatch of the subnet mask -> A is correct.

Just for your information, in fact we have to suppose there is no entry of the network 192.168.0.0/24 exist in the routing table except the static route “ip route 192.168.0.0 255.255.0.0 null0”. If such an entry exists (for example, a directly connected entry like “C 192.168.0.0/24 is directly connected”) then the router still advertises it with the “network 192.168.0.0” (without mask 255.255.0.0) command.

BGP Questions 4

May 4th, 2014 digitaltut 2 comments

Here you will find answers to BGP Questions – Part 4

Question 1

Which two conditions can cause BGP neighbor establishment to fail? (Choose two)

A. There is an access list blocking all TCP traffic between the two BGP neighbors.
B. The IBGP neighbor is not directly connected.
C. BGP synchronization is enabled in a transit autonomous system with fully-meshed IBGP neighbors.
D. The BGP update interval is different between the two BGP neighbors.
E. The BGP neighbor is referencing an incorrect autonomous system number in its neighbor statement.

 

Answer: A E

Explanation

An underlying connection between two BGP speakers must be established before any routing information is exchanged. This connection takes place on TCP port 179 so if an access list blocks all TCP traffic between the two BGP neighbors, BGP neighbor relationship can not be established -> A is correct.

The IBGP neighbors don’t need to be directly connected -> B is not correct.

BGP synchronization only prevents routes sent to other EBGP neighbors before that route exists in the routing table. It doesn’t prevent BGP neighbor relationship -> C is not correct.

After the first initial exchange (which exchanges routes and synchronize their tables), a BGP speaker will only send further updates upon a change in the network topology -> BGP does not have a fixed update interval -> D is not correct.

BGP neighbor relationship is established when both ends (routers) are manually configured with the “neighborneighbor-IP remote-as neighbor-AS” command on both sides of the connection. If the neighbor-AS is wrong, the neighbor relationship can not be established -> E is correct.

Question 2

Which statement is true about EBGP?

A. An internal routing protocol can be used to reach an EBGP neighbor.
B. The next hop does not change when BGP updates are exchanged between EBGP neighbors.
C. A static route can be used to form an adjacency between neighbors.
D. EBGP requires a full mesh.

 

Answer: C

Explanation

When two EBGP neighbors want to establish neighbor relationship without using the directly connected interfaces (for example, use loopback interface), they must tell each other how to reach their interfaces. A static route is the most simple way to do this, especially when they are in different ASs.

Question 3

Why should iBGP sessions be fully meshed within a Transit AS?

A. BGP requires redundant TCP sessions between iBGP peers.
B. A full mesh allows for optimal routing within the Transit AS.
C. Routes learned via iBGP are never propagated to other eBGP peers.
D. Routes learned via iBGP are never propagated to other iBGP peers.
E. Routes learned via eBGP are never propagated to other iBGP peers.

 

Answer: D

Explanation

BGP split-horizon rule states that a route learned from one IBGP neighbor will not be advertised to another IBGP neighbor so IBGP sessions should be fully meshed. For example in the topology below, routes learned from R1 about AS 200 will be advertised to R2. For R2, the route learned from R1 is a route learned from one IBGP neighbor so R2 will not advertise this route to R3 and AS 100 can never be a transit AS -> IBGP sessions should be fully meshed within a transit AS -> D is correct.

BGP_IBGP_synchronization.jpg

Question 4

Which BGP feature should be used to avoid high memory utilization on a router?

A. soft-reconfiguration
B. route refresh
C. BGP communities
D. full-mesh BGP peering

 

Answer: B

Explanation

BGP routers have enormous routing tables so it uses much memory to proceed these routes. When a BGP policy is changed, the BGP session needs to be reset for the policy to take effect. But the resetting results in route churn and route flapping. There are two ways to clear a BGP session without resetting the TCP session between them (this is often called “soft reset”):

Soft-reconfiguration: stores all received (inbound) routing policy updates without modification in a table so that when a new filter is applied, the router will use this table to calculate the changes without resetting the TCP session between the two BGP peers . This is a memory-intensive (high memory utilization) method and is not recommended.

Route-refresh: allows a BGP router to request a remote peer resend its BGP Adj-RIB-Out. This allows the BGP router to reapply the inbound policy. The route-refresh capability requires no extra memory on the local router

Question 5

For the accompanying router output, which of the following statements describes the state that neighbor 172.16.254.3 is in?

show_ip_bgp_neighbors.jpg

A. The router will not accept connections from the peer.
B. The router has sent out an active TCP connection request to the peer.
C. The router is listening on its server port for connection requests from the peer.
D. BGP can exchange routing information in this state.

 

Answer: C

Explanation

The BGP state in the output is “Active”, which means BGP speaker is attempting to initiate a TCP session with the BGP speaker it wants to peer with. If this can be done, the BGP state goes to OpenSent state.

Question 6

A router has two paths to reach another network in a different autonomous system. Neither route was generated by the local router and both routes have the same default weight and local preference values. Which statement is true about how BGP would select the best path?

A. If the command bgp always-compare-med has been given, then the router will prefer the route with the highest MED.
B. The router will prefer the route with the lower MED.
C. The router will prefer the shortest autonomous system path.
D. To influence one route to be preferred, its default local preference value will be changed via the use of the command bgp default local-preference 50.

 

Answer: C

Explanation

In the Route selection decision process, if the weight, local preference & route originated are the same then the shortest AS path will be chosen.

The full Route selection decision process is listed below:

1. Prefer highest weight (local to router)
2. Prefer highest local preference (global within AS)
3. Prefer route originated by the local router (next hop = 0.0.0.0)
4. Prefer shortest AS path
5. Prefer lowest origin code (IGP < EGP )
6. Prefer lowest MED (exchanged between autonomous systems)
7. Prefer EBGP path over IBGP path
8. Prefer the path through the closest IGP neighbor (IGP cost)
9. Prefer oldest route for EBGP paths
10. Prefer the path with the lowest neighbor BGP router ID
11. Prefer the path with the lowest neighbor IP address

Question 7

Refer to the exhibit. Which two statements are correct? (Choose two)

BGP_show_ip_bgp_route.jpg

A. All six routes will be installed in the routing table.
B. Two routes will be installed in the routing table.
C. Four routes will be installed in the routing table.
D. All the routes were redistributed into BGP from an IGP.
E. All the routes were originated by BGP with the network command.

 

Answer: C D

Explanation

Only the valid & best routes (represented by *>) will be installed into the routing table -> C is correct.

The “?” under the “Path” column means that origin of the path is not clear. Usually, this is a router that is redistributed into BGP from an IGP. -> D is correct. (Reference: http://www.cisco.com/c/en/us/td/docs/ios/iproute_bgp/command/reference/irg_book/irg_bgp5.html)

 

Question 8

Which two statements are true about IBGP neighbor relationships? (Choose two)

A. An EGP or static routing is required between IBGP neighbors.
B. A full-mesh IBGP requires that neighbor relationships be established between all BGP enabled routers in the autonomous system.
C. IBGP neighbors must be in different autonomous systems.
D. The BGP split-horizon rule specifies that routes learned via EBGP are never propagated to other IBGP peers.
E. The BGP split horizon rule specifies that routes learned via IBGP are never propagated to other IBGP peers.

 

Answer: B E

Question 9

Refer to the exhibit. Which two statements are true about the partial configuration that is provided. (Choose two)

router bgp 100
neighbor internal peer-group
neighbor internal remote-as 100
neighbor internal update-source loopback 0
neighbor internal route-map set-med out
neighbor internal filter-list 1 out
neighbor internal filter-list 2 in
neighbor 171.69.232.53 peer-group internal
neighbor 171.69.232.54 peer-group internal
neighbor 171.69.232.55 peer-group internal
neighbor 171.69.232.55 filter-list 3 in

A. All the configured neighbors are in autonomous system 100.
B. The peer group shortens the IBGP configuration.
C. The peer group shortens the EBGP configuration.
D. Only the outgoing filters are applied to BGP updates.
E. Three AS-path filters are applied to each BGP neighbor.

 

Answer: A B

Explanation

This is an IBGP peer group because the AS numbers in “router bgp {AS number}” and “neighbor internal remote-as {AS number} are the same -> A is correct.

A BGP peer group reduces the load on system resources by allowing the routing table to be checked only once, and updates to be replicated to all peer group members instead of being done individually for each peer in the peer group. In addition, a BGP peer group also simplifies the BGP configuration -> B is correct.

This is the process of creating a peer-group (used the output above):

neighbor internal peer-group Create a peer-group (named internal)
neighbor internal remote-as 100
neighbor internal update-source loopback 0
neighbor internal route-map set-med out
neighbor internal filter-list 1 out
neighbor internal filter-list 2 in
Configure needed commands for the peer-group
neighbor 171.69.232.53 peer-group internal
neighbor 171.69.232.54 peer-group internal
neighbor 171.69.232.55 peer-group internal
Assign BGP neighbor into a peer group

Just one thing to notice is the last command “neighbor 171.69.232.55 filter-list 3 in” indicates the filter-list 3 will be applied for neighbor 171.69.232.55 while other neighbors will be applied filter-list 2 as the inbound filter-list (all neighbors use outbound filter-list 1).

Question 10

Observe the diagram. RTC is the hub router and RTA and RTB are the spokes. There are no virtual circuits between the spoke locations. What is needed to successfully route traffic to the 11.11.11.0/24 network from RTA?

BGP_IBGP_Hub_Spoke.jpg

A. The neighbor 10.10.10.1 next-hop-self command on RTA.
B. The neighbor 10.10.10.1 next-hop-self command on RTB.
C. The neighbor 10.10.10.1 next-hop-self command on RTC.
D. Nothing is required. This is the default behavior on this topology.

 

Answer: C

Explanation

The next-hop-self command must be used on RTC to specify RTC’s IP address as the source address in the packets sent to RTB (and RTB knows how to reach RTC but it does not know how to reach RTA).

Question 11

A router is running BGP and receives more than one route for a particular prefix. Assume all the routes for this prefix have the same attributes. Which three path features would be reasons be for the router to ignore some of the routes and not consider them as candidates for the best path? (Choose three)

A. paths that are marked as synchronized in the show ip bgp output
B. paths that are marked as not synchronized in the show ip bgp output
C. paths for which the NEXT_HOP is accessible
D. paths for which the NEXT_HOP is inaccessible
E. paths from an external BGP (eBGP) neighbor if the local autonomous system (AS) appears in the AS_PATH
F. paths from an internal BGP (iBGP) neighbor if the local autonomous system (AS) appears in the AS_PATH

 

Answer: B D E

Explanation

Only synchronized routes (answer B) with no AS loops (answer E) and a valid next hop (answer D) will be considered as candidates for the best path route selection decision process.

BGP Questions 5

May 4th, 2014 digitaltut 13 comments

Here you will find answers to BGP Questions – Part 5

Question 1

Above is the output from show ip bgp neighbors command. What is line 21 stating about the BGP connection?

BGP neighbor is 172.16.254.3, remote AS 150, internal link
1. BGP version 4, remote router ID 172.16.254.3
2. BGP state = Established, up for 19:24:07
3. Last read 00:00:06, hold time is 180, keepalive interval is 60 seconds
4. Neighbor capabilities:
5. Route refresh:advertised and received(new)
6. Address family IPv4 Unicast:advertised and received
7. Graceful Restart Capability:advertised and received
8. Remote Restart timer is 120 seconds
9. Address families preserved by peer
10. IPv4 Unicast
11. Received 4231 messages, 0 notifications, 0 in queue
12. Sent 4167 messages, 0 notifications, 0 in queue
13. Default minimum time between advertisement runs is 5 seconds
14. For address family:IPv4 Unicast
15. BGP table version 159559, neighbor version 159559
16. Index 90, Offset 11, Mask 0x4
17. Route refresh request:received 0, sent 0
18. 10031 accepted prefixes consume 441364 bytes
19. Prefix advertised 29403, suppressed 0, withdrawn 9801
20. Number of NLRIs in the update sent:max 242, min 0
21. Connections established 2; dropped 1
22. Last reset 19:26:54, due to NSF peer closed the session
23. Connection state is ESTAB, I/O status:1, unread inout bytes:0
24. Local host:150.254.254.2, Local port:11005
25. Foreign host:172.16.254.3, Foreign port:179

A. the number of consecutive TCP connections to the specified remote neighbor
B. the number of times the router has established a TCP connection
C. the number of total TCP connections that the router has
D. the number of neighbors that the router has

 

Answer: B

According to http://www.cisco.com/en/US/docs/ios/12_3/iproute/command/reference/ip2_s2g.html#wp1040913, “Connections established” is the number of times a TCP and BGP connection have been successfully established while “dropped” is the number of times that a valid session has failed or been taken down.

Question 2

Refer to the exhibit. Routing updates for the 192.168.1.0 network are being received from all three neighbors. Which statement is correct regarding the result of the configuration shown?

BGP_route-map.jpg

A. The router will prefer the next hop of 172.16.1.1 for packets destined for the 192.168.1.0 network.
B. The router will prefer the next hop of 172.26.1.1 for packets destined for the 192.168.1.0 network.
C. The router will advertise the 192.168.1.0 network only to 172.30.1.1.
D. The router will advertise the 192.168.1.0 network only to 172.26.1.1.
E. The router will prefer the next hop of 172.26.1.1 for packets except those destined for the

 

Answer: B

Explanation

The local-preference of the next hop 172.26.1.1 is set to 200, which is higher than the default value (100) so this path is preferred for packets destined to the 192.168.1.0 network.

Question 3

Refer to the exhibit. Which statement is true about the 6.6.6.0/24 prefix?

BGP_show_ip_bgp_community.jpg

A. If another path advertises the 6.6.6.0/24 path and has the default local preference, that path is more preferred.
B. The command neighbor send-community is configured on BGP neighbor 10.10.23.3.
C. The route 10.10.23.3 is not being advertised to other BGP neighbors.
D. Route 6.6.6.0/24 is learned by an IBGP peer.

 

Answer: B

Explanation

By default, the community attributes are not advertised to BGP neighbors. But in the output we see the “Community: 100:250” which means the command “neighbor … send-community” was used to send community attributes of the local router to the neighbor. For more information about this command please read my BGP next-hop-self, community no-export & send-community – GNS3 Lab.

Question 4

Refer to the exhibit. Currently the two eBGP links between AS100 and AS200 have an average inbound load of 65% and 20% respectively. After further investigation, traffic to 10.10.1.16/28 accounts for 45%, and traffic to 10.10.1.32/28 and to 10.10.1.48/28 each account for 20% of the inbound load. The BGP attributes are currently set at their default values in both autonomous systems.
If you want to influence how AS200 sends traffic to AS100, which eBGP configurations would you configure in AS100 to influence AS200 to use the eBGP links more evenly? (Choose two.)

BGP_load_sharing_percent.jpg

A. neighbor 192.168.30.2 route-map as_50 out
B. neighbor 192.168.20.2 route-map as_50 out

C. route-map as_50 permit 10
match ip address 50
set metric 150
access-list 50 permit 10.10.1.16 0.0.0.240

D. route-map as_50 permit 10
match ip address 50
set metric 150
access-list 50 permit 10.10.1.32 0.0.0.240

 

Answer: B D

Explanation

Note: The wildcard masks in the access-list are not correct, they should be 0.0.0.15 instead of 0.0.0.240.

First let’s recall about MED. If you want to influence external neighbors about the path it sends traffic then MED, also called the metric, should be used. A lower MED value is preferred over a higher value. The default MED value is 0.

Also, an important point I wish to notice in this question is: for Policy-based routing, if no match is made, the packets are forwarded normally via the routing table.

In answer C & B (combined), the MED for prefix 10.10.1.16/28 through router A is set to 150. This would make traffic for this route (45%) go through router B (because the MED default value is 0, which is lower than 150). Since the access-list will also NOT match prefixes: 10.10.1.32/28 & 10.10.1.48/28 – traffic for these two prefixes will be forwarded just normally (via the routing table) ->
Traffic for prefix: 10.10.1.32/28 will continue to go via the upper E-A link (now just 20% total load), while traffic for prefixes 10.10.1.16/28 and 10.10.1.48/28 will be going through the lower F-B link (now 65% total load) -> Original unbalanced (65/20) load is maintained, although it has been reversed between the upper (A-E) and lower (B-F) link -> C is not correct.

For more information about Policy-based routing matches you can read this article: http://www.ciscopress.com/articles/article.asp?p=426637&seqNum=2

If answer D is applied for router A, the MED for 10.10.1.32 set to 150 would make traffic for this route go through router B (because the MED default value is 0, which is lower than 150). So router A will be responsible for 45% traffic and router B will receive 40% traffic -> D is correct.

(For detailed information about how to use route map with MED, please read my BGP Route map and MED – GNS3 Lab)

(Also thanks to Buddy who contributed nice explanation for this question)

Question 5

Refer to the exhibit. A client has asked you to consult on an eBGP loading question. Currently the AS 100 eBGP links have an average outbound load of 65% and 20% respectively. On further investigation, traffic from 10.10.24.0 accounts for 45%, and 10.10.25.0 and 10.10.32.0 accounts for 20% each of the outbound load. The customer wants to spread the load between the two eBGP links more evenly. The BGP attributes are currently set at their default values.
If you are located at AS 100 and want to influence how AS 100 sends traffic to AS 200, what BGP attribute could you configure to cause AS 100 outbound traffic to load the eBGP links more evenly?

BGP_load_sharing_evenly.jpg

A. On router A, set the default local-preference to 50.
B. On router B, set the default metric to 150.
C. On router B, configure a route map for 10.10.25.0/24 with a local preference of 150 linked to neighbor 192.168.30.2.
D. On router B, set the default local-preference to 150.

 

Answer: C

Explanation

To make the eBGP links more evenly we should use the link B-F for network 10.10.25.0/24 so that the total traffic going through B-F link is about 40%. In this case we should apply a route map on B to set the local preference of 10.10.25.0/24 to a higher value than 100. But notice that we must use a second clause to permit other traffic if not they will be filtered out.

Note: The default value for local preference is 100. A path with higher local preference is preferred.

Question 6

Refer to the exhibit. AS 65500 is not advertising the prefix 192.168.12.0/22 to its provider. AS 65500 is running OSPF as its IGP.
Which of the following additions to the configuration is most likely to solve the problem?

BGP_neighbor_advertise.jpg

A. RouterA(config)#ip cef
B. RouterA(config)#ip route 192.168.12.0 255.255.252.0 null 0
C. RouterA(config-router)#ebgp multihop 1
D. RouterA(config-router)#redistribute ospf 1
E. RouterA(config-router)#neighbor 192.168.14.253 next-hop-self
F. RouterA(config-router)#neighbor 192.168.14.253 local-as 65500

 

Answer: B

Explanation

The synchronization rule states “A BGP router should not use, or advertise to an external neighbor, a route learned by IBGP, unless that route is local or is learned from the IGP”. Notice that IGP here can be a static route.

In this case, unless there is an entry about network 192.168.12.0 in the routing table of RouterA, RouterA will not advertise this network to its EBGP -> B is correct (even if this static route points to Null0).

Note: Although this question states that OSPF is being used as IGP but for some reasons, network 192.168.12.0/22 is not advertised to RouterA -> RouterA does not have this route in its routing table.

Question 7

A company has a BGP network and a BGP route of 196.27.125.0/24 that should be propagated to all of the devices. The route is not now in any of the routing tables. The administrator determines that an access list is the cause of the problem. The administrator changes the access list to allow this route, but the route still does not appear in any of the routing tables. What should be done to propagate this route?

A. Clear the BGP session.
B. Use the release BGP routing command.
C. Use the service-policy command to adjust the QoS policy to allow the route to propagate.
D. Change both the inbound and outbound policy related to this route.

 

Answer: A

Explanation

BGP routing protocol is slow convergence due to its distance-vector nature, slow propagation of routing updates and enormous amounts of time it usually takes to detect a BGP neighbor loss so we should clear the BGP session. It is a method for soft reset the exchange of route refresh requests and routing information between BGP routers.

Note: The most popular command to clear the BGP session is clear ip bgp * command.

Question 8

Refer to the exhibit. What will RTB do with a packet sourced from within AS 64200 with a destination address of 192.168.25.1?

BGP_static_route_forward.jpg

A. It will be dropped because network 192.168.25.0 is not in the RTA routing table.
B. It will be dropped because network 192.168.25.0 is not in the RTB routing table.
C. It will be forwarded to the null 0 interface of RTB and dropped.
D. It will be forwarded to the RTB 192.168.25.0 network.

 

Answer: D

Explanation

First I want to make it clear that the above configuration belongs to RTB (with AS 64100).

The “network” statement in other routing protocols (EIGRP, OSPF, RIP…) is used to enable routing protocol on the interfaces within that “network” statement. But in BGP, the function of a network statement is to tell the router to search the IP routing table for a particular network, and if that network is found, originate it into the BGP database. But notice that you must have an exact match in the IP routing table to appear the network in the BGP routing table (in this case we don’t see the auto-summary command so we suppose it is disabled in this case). For example:
+ network 10.10.10.0/8 will appear in BGP if network 10.10.10/8 appears in the IP routing table.
+ network 10.10.10.0/24 will appear in BGP if network 10.10.10.0/24 appears in the IP routing table.

Therefore, in this question the static route “ip route 192.168.24.0 255.255.252.0 null0″ was used to put a route to 192.168.24.0/22 into the routing table (although it points to Null0 but this command really makes that route appears in the routing table). Notice this network 192.168.24.0/22 also coverts network 192.168.25.0 -> RTB will forward that packet to 192.168.25.0 network.

Question 9

Which two statements are true about external BGP neighbor relationships? (Choose two)

A. Static routes or an interior gateway protocol is required between EBGP neighbors.
B. EBGP neighbors must be in different autonomous systems.
C. EBGP neighbors use TCP port 179 to exchange BGP routing tables.
D. Loopback addresses should be used between EBGP neighbors.
E. The BGP split-horizon rule specifies that routes learned via IBGP are never propagated to other EBGP peers.
F. When an EBGP neighbor receives an update from another EBGP neighbor, it should not forward the update to other EBGP neighbors.

 

Answer: B C

Explanation

An External BGP (EBGP) is a neighbor in another AS -> B is correct.

An underlying connection between two BGP speakers is established before any routing information is exchanged. This connection takes place on TCP port 179. Port 179 is also used to send routing updates (via TCP) -> C is correct.

Question 10

The command bgp always-compare-med is added to a router configuration. What will this command accomplish?

A. forces the router to compare metrics of routes from different autonomous systems
B. forces the router to compare the local preference of routes from different autonomous systems
C. forces the router to compare the weight of routes from different autonomous systems
D. forces the router to compare the communities of routes from different autonomous systems

 

Answer: A

BGP Questions 6

May 4th, 2014 digitaltut 1 comment

Here you will find answers to BGP questions – Part 6

Question 1

Which attribute must exist in the BGP update packet?

A. LOCAL, PREF
B. AGGREGATOR
C. AS_Path
D. Weight

 

Answer: C

Explanation

Origin, AS_Path, Next_Hop are well-known mandatory BGP attributes that all BGP Updates must include.

Note:
There are 4 BGP attribute types:
+ Well-known Mandatory: recognized by all implementations of BGP and must appear in a BGP update message. If missing, a notification error will be generated.
+ Well-Known Discretionary: recognized by all implementations of BGP but may not be sent in the BGP update message (include LOCAL_PREF, ATOMIC_AGGREGATOR).
+ Optional Transitive: may or may not be recognized by all BGP implementations. Because the attribute is transitive, BGP accepts and advertises the attribute even if it is not recognized (include Community attribte).
+ Optional Nontransitive: may or may not be recognized by all BGP implementations. Whether or not the receiving BGP router recognizes the attribute, it is nontransitive and is not passed along to other BGP peers (include MED).

Question 2

To enable BGP tunneling over an IPv4 backbone, the IPv4 address 192.168.30.1 is converted into a valid IPv6 address. Which three IPv6 addresses are acceptable formats for the IPv4 address? (Choose three)

A. 192.168.30.1:0:0:0:0:0:0
B. 0:0:0:0:0:0:192.168.30.1
C. ::192.168.30.1
D. C0A8:1E01::
E. 192.168.30.1::
F. ::C0A8:1E01

 

Answer: B C F

Question 3

A problem was reported that the 10.10.10.0/24 prefix was not injected into the local BGP table on RouterA. The following information is available from RouterA. Why is this prefix not in the local BGP table?

configuration:
router bgp 65001
network 10.0.0.0
neighbor 172.16.1.1 remote-as 65002
no auto-summary
routing table information
show ip route | include 10
O 10.10.10.0/24 [110/11] via 192.168.1.1, 2d00h, Ethernet0/0

A. This route is not a BGP learned route.
B. The network command is wrong.
C. The 172.16.1.1 neighbor is down.
D. The prefix 10.10.10.0/24 is not ‘connected’ route.

 

Answer: B

Explanation

The correct network statement should be “network 10.0.0.0 255.255.255.0”. BGP will not advertise a prefix unless the prefix is also already installed in the routing table. Here the prefix installed in the routing table is “O 10.10.10.0/24”, but network command is 10.0.0.0 without a subnet mask. Therefore, the BGP process will use the default classful subnet mask of /8 and will not advertise it because it cannot find an exact prefix match in the routing table also. (Thanks dj for your explanation)

Question 4

Refer to the exhibit. All routers are configured for BGP. EBGP routes received on router R2 show up in the BGP table on routers R1 and R3 but not in their IP routing table. What would cause this? (Choose two)

EBGP_IGP_routing_table.jpg

A. Synchronization in autonomous system 100 is turned is on.
B. Synchronization in autonomous system 100 is turned is off.
C. EBGP multihop is not configured on routers R1 and R3.
D. Routers R1 and R3 do not receive the same routes via an IGP.
E. The BGP routers in autonomous system 100 are not logically fully-meshed.

 

Answer: A D

Explanation

The synchronization rule states BGP should not advertise a route until all of the routers within the AS have learned about the route via an IGP so in this case if R1 and R3 have not learned that route via IGP, they cannot appear in their routing tables.

Question 5

Based on the R3 show ip bgp output, which statement is true?

show_ip_bgp_best_path.jpg

A. The best path to reach the 192.168.11.0 prefix is via 10.200.200.11.
B. The best path to reach the 192.168.11.0 prefix is via 10.200.200.12.
C. The best path to reach the 192.168.11.0 prefix is via both 10.200.200.11 and 10.200.200.12; BGP will automatically load balance between the two.
D. The 192.168.11.0 and 192.168.12.0 prefixes were learned via EBGP from the 10.200.200.11 and 10.200.200.12 EBGP neighbors.

 

Answer: B

Redistribute Questions

May 3rd, 2014 digitaltut 1 comment

Here you will find answers to Redistribute Questions

Question 1

Refer to the exhibit. Which statement is true?

hostname RAR1
!

!
router bgp 100
neighbor 172.16.1.2 remote-as 200
neighbor 172.16.1.2 distribute-list 101 in
!
access-list 101 permit ip 10.10.0.0 0.0.31.255 0.0.0.0 0.0.0.0

A. Router RAR1 will accept only route 10.10.0.0/19 from its BGP neighbor.
B. Router RAR1 will send only route 10.10.0.0/19 to its BGP neighbor.
C. Only traffic with a destination from 10.10.0.0/19 will be permitted.
D. Only traffic going to 10.10.0.0/19 will be permitted.

 

Answer: A

Question 2

Refer to the exhibit. Which three statements accurately describe the result of applying the exhibited route map? (Choose three)

router eigrp 1
redistribute ospf 1 route-map ospf-to-eigrp
default-metric 20000 2000 255 1 1500
!
!
route-map ospf-to-eigrp deny 10
match tag 6
match route-type external type-2
!
route-map ospf-to-eigrp permit 20
match ip address prefix-list pfx
set metric 40000 1000 255 1 1500
!
route-map ospf-to-eigrp permit 30
set tag 8

A. The map prohibits the redistribution of all type 2 external OSPF routes with tag 6 set.
B. The map prohibits the redistribution of all type 2 external OSPF routes.
C. The map redistributes into EIGRP all routes that match the pfx prefix list and the five metric values 40000, 1000, 255, 1, and 1500.
D. The map prohibits the redistribution of all external OSPF routes with tag 6 set.
E. All routes that do no match clauses 10 and 20 of the route map are redistributed with their tags set to 8.
F. The map permits the redistribution of all type 1 external OSPF routes.

 

Answer: A E F

Explanation

In the route-map:

route-map ospf-to-eigrp deny 10
match tag 6
match route-type external type-2

The deny clause rejects route matches from redistribution. If several match commands are present in a clause, all must succeed for a given route in order for that route to match the clause (in other words, the logical AND algorithm is applied for multiple match commands). In this question, both the “match tag 6” and “match route-type external type-2” must be matched for this route to be denied -> A is correct.

If a match command is not present, all routes match the clause. In this question, all routes that reach clause 30 match and their tags are set to 8 -> E is correct.

If a route is not matched with clause 10 or 20 then it will be matched with clause 30 for sure -> F is correct.

Note: Route-maps that are applied to redistribution behave the same way as ACLs: if the route does not match any clause in a route-map then the route redistribution is denied, as if the route-map contained deny statement at the end.

(Reference: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008047915d.shtml)

Question 3

Refer to the exhibit. On the basis of the information in the exhibit, which two statements are true? (Choose two)

Redistribute_BGP.jpg

A. The output was generated by entering the show ip bgp command on the ISP router.
B. The output was generated by entering the show ip bgp command on the SanJose1 router.
C. The serial0/0/1 interface on the ISP router has been configured with the set metric 50 command.
D. The serial 0/0/1 Interface on the ISP router has been configured with the set metric 75 command.
E. When traffic is sent from the ISP to autonomous system 64512, the traffic will be forwarded to SanJose1 because of the lower MED value of SanJose1.
F. When traffic is sent from the ISP to autonomous system 64512, the traffic will be forwarded to SanJose2 because of the higher MED value of SanJose2.

 

Answer: A E

Explanation

From the output, we notice that the “local router ID” is 192.168.100.1 which is an interface on ISP router -> A is correct.

The show ip bgp command is used to display entries in the Border Gateway Protocol (BGP) routing table

Multi-Exit Discriminator (MED) is used when we have multiple entry points (connections) to another AS. A lower MED value is preferred over a higher value. Notice that the comparison between the MED only occurs if the first AS is the same in two (or more) paths. In this question, the first AS is 64512 which is the same -> the comparison can occur.

From the output, we learn that ISP router is receiving the 172.16.0.0 network from SanJose1 (192.168.1.6) with a metric of 50 and from SanJose2 (192.168.1.2) with a metric of 75. Also note that BGP has chosen the best path 192.168.1.6 to the 172.16.0.0 network (the “>” indicates it is the best path). The Weight, Local Preference (LocPrf) and AS-Path values between two next hops (192.168.1.2 & 192.168.1.6) are the same so we can deduce the traffic from ISP is sent from the ISP to SanJose1 because of the lower MED value.

Note: An entry of 0.0.0.0 in the “Next Hop” indicates that the router has some non-BGP routes to this network.

Question 4

Refer to the exhibit. Routers R1 and R2 have been configured to operate with OSPF. Routers R1 and R3 have been configured to operate with RIP. After configuring the redistribution between OSPF and RIP on R1, no OSPF routes are distributed into RIP. What should be done to correct this problem?

Redistribute_RIP_OSPF.jpg

A. The redistribution command should be reentered with the match route-type parameter included.
B. The redistribution command should be reentered with the route-map map-tag parameter included.
C. The redistribution command should be reentered with the metric metric-value parameter included.
D. Routes will first need to be distributed into another protocol, and then into RIP.

 

Answer: C

Explanation

Notice that RIP metric is based on hop count only, and the maximum valid metric is 15. Anything above 15 is considered infinite. By default, when no metric is assigned when redistributing from EIGRP, OSPF, IS-IS, BGP into RIP, the default metric will be infinite. Therefore we must define a metric that is understandable to the receiving protocol. Usually, we should use a small value (like 1, 2, 3) so that after redistributing, that route can be advertised through many routers (because the limit is 15).

Question 5

router eigrp 123
redistribute ospf 123
network 116.16.35.0 0.0.0.255
network 130.130.0.0
auto-summary
!
router ospf 123
log-adjacency-changes
network 116.16.34.0 0.0.0.255 area 0
neighbor 116.16.34.4

Refer to the exhibit. Why are the EIGRP neighbors for this router not learning the routes redistributed from OSPF?

A. Redistribution must be enabled mutually (in both directions) to work correctly.
B. Auto-summary causes the OSPF routes redistributed into EIGRP to be summarized; thus the OSPF network 116.16.34 is summarized to 116.34.0.0, which is already covered by the EIGRP protocol.
C. Default metrics are not configured under EIGRP.
D. Both routing protocols must have unique autonomous system numbers for redistribution to function correctly.

 

Answer: C

Explanation

Same as RIP, when redistribute into EIGRP from OSPF, the default metric is infinite -> We must set a seed metric when redistributing into EIGRP. Below lists the default seed metrics when redistributing from a routing protocol into another:

Redistributed Protocol Default Seed Metric
RIP Infinity
IGRP/EIGRP Infinity
OSPF 20 for all (except for BGP, which is 1)
BGP is set to IGP metric value

Question 6

If a metric is not specified for routes that are redistributed into OSPF, the default metric that is assigned to the routes is 20, except for redistributed BGP routes. What is the metric that is assigned to redistributed BGP routes?

A. 0
B. 1
C. 10
D. 200

 

Answer: B

Explanation

Same explanation of Question 5

Question 7

During a redistribution of routes from OSPF into EIGRP, an administrator notices that none of the OSPF routes are showing in EIGRP. What are two possible causes? (Choose two)

A. incorrect distribute lists have been configured
B. missing ip classless command
C. CEF not enabled
D. no default metric configured for EIGRP

 

Answer: A D

Explanation

An incorrect distribute list can filter out updates therefore none of the OSPF routes are showing in EIGRP -> A is correct.

The default metric when redistributing into EIGRP is infinite so we must specify a seed metric for EIGRP to work with -> D is correct.

Question 8

During the redistribution process configured on RTA, some of the EIGRP routes, such as 10.1.1.0/24 and 10.2.2.0/24, are not being redistributed into the OSPF routing domain. Which two items could be a solution to this problem? (Choose two)

Redistribute_EIGRP_to_OSPF.jpg

A. Change the metric-type to 2 in the redistribute command.
B. Configure the redistribute command under router eigrp 1 instead.
C. Change the EIGRP AS number from 100 to 1 in the redistribute command.
D. Add the subnets option to the redistribute command.
E. Change the metric to ah EIGRP compatible metric value (bandwidth, delay, reliability, load, MTUs) in the redistribute command.

 

Answer: C D

Explanation

The AS of EIGRP in the output above is not correct and we need to fix it into “eigrp 1”. Also, some of EIGRP routes, such as 10.1.1.0/24 and 10.2.2.0/24 are subnets so we must use the keyword “subnets” so that OSPF can see these routes. The full commands should be:

router ospf 1
redistribute eigrp 1 metric 20 metric-type 1 subnets

Question 9

You want the redistributed EIGRP AS 10 routes to have an administrative distance of 121 when they appear as RIP routes in the routing table of A1. Which command should you use on a router to accomplish this goal?

Redistribute_RIP_EIGRP_distance.jpg

A. redistribute eigrp 10 metric 121
B. redistribute rip metric 121
C. default-metric 121
D. distance 121 10.1.1.6 0.0.0.0

 

Answer: D

Question 10

Refer to the exhibit. Which three commands should be used on router B1 to redistribute the EIGRP AS 10 routes into RIP? (Choose three)

Redistribute_RIP_EIGRP_distance.jpg

A. router rip
B. router eigrp 10
C. redistribute eigrp 10
D. redistribute rip
E. default-metric 10000 100 255 1 1500
F. default-metric 5

 

Answer: A C F

Redistribute Questions 2

May 3rd, 2014 digitaltut 4 comments

Here you will find answers to Redistribute Questions – Part 2

Question 1

Refer to the exhibit and the partial configuration on router R2. On router R4 all RIP routes are redistributed into the OSPF domain. A second redistribution is configured on router R2 using a route map. Based on the configuration on router R2, which EIGRP external routes will be present in the routing table of R1?

Redistribute_EIGRP_external_route.jpg

A. the routes originating from the RIP routing domain
B. the routes originating from the OSPF stub area
C. all OSPF inter and intra-area routes
D. all routes originating from RIP and OSPF routing domains

 

Answer: A

Explanation

R2 sees the routes from RIP domain as external routes while it sees the routes from OSPF Stub Area as internal routers. From the output we learn that the “route-type external” is redistributed from OSPF to EIGRP (via route-map ABC) so we will see the routes from the RIP domain (external) in the routing table of R1 -> A is correct.

In the case we want to redistribute routes from OSPF Stub Area (Area 1) to EIGRP we need to use the “match route-type internal” command instead.

Question 2

Refer to the exhibit. Router B is performing bidirectional redistribution between EIGRP and OSPF. The network 10.100.1.0/24 should not be reachable from the 10.100.9.0/24 network. However, it needs to be reachable from any network within the EIGRP domain. All other networks should be seen in both domains.
Which change to router B would accomplish these goals?

Redistribute_OSPF_EIGRP_bidirection.jpg

A. Under the EIGRP process, insert the distribute-list block_net_1 out ospf 1 command.
B. Under the OSPF process, insert the distribute-list block_net_1 in serial1/0 command.
C. Under the EIGRP process, insert the distribute-list block_net_1 in serial1/0 command.
D. Under the OSPF process, insert the distribute-list block_net_1 out eigrp 1 command.

 

Answer: D

Explanation

The network 10.100.1.0/24 should not be reachable from network 10.100.9.0/24 -> we need to filter updates from EIGRP to OSPF so that the routing table of router C doesn’t have network 10.100.1.0/24 -> we need to filter it under OSPF process and the direction should be out of router B -> D is correct.

Question 3

Which three route filtering statements are true? (Choose three)

A. After the router rip and passive-interface s0/0 commands have been issued, the s0/0 interface will not send any RIP updates, but will receive routing updates on that interface.
B. After the router eigrp 10 and passive-interface s0/0 commands have been issued, the s0/D interface will not send any EIGRP updates, but will receive routing updates on that interface
C. After the router ospf 10 and passive-interface s0/0 commands have been issued , the s0/0 interface will not send any OSPF updates, but will receive routing updates on that interface
D. When you use the passive-interface command with RIPv2, multicasts are sent out the specified interface
E. When you use the passive-interface command with EIGRP, hello messages are not sent out the specified interface
F. When you use the passive-interface command with OSPF, hello messages are not sent out the specified interface

 

Answer: A E F

Explanation

The “passive-interface …” command in EIGRP or OSPF will shut down the neighbor relationship of these two routers (no hello packets are exchanged) -> E, F are correct.

In RIP, this command will not allow sending multicast updates via a specific interface but will allow listening to incoming updates from other RIP speaking neighbors. This means that the router will still be able to receive updates o­n that passive interface and use them in its routing table -> A is correct.

Question 4

Refer to the exhibit. The routing protocols EIGRP and OSPF have been configured as indicated in the exhibit. Given the partial configuration of router R2, which network will be present in the routing table of R4?

Redistribute_OSPF_EIGRP_default-metric.jpg

A. Network A
B. Network B
C. Network A and Network B
D. neither Network A nor Network B

 

Answer: B

Explanation

From the show running-config output, we learn that only OSPF is redistributed into EIGRP AS 100 so only network B will be present in the routing table of R4. Notice that we must specify the metric when redistributing into EIGRP so that it can work well.

Question 5

Refer to the exhibit. Which three statements are true? (Choose three)

Redistribute_RIP_OSPF_EIGRP.jpg

A. On the routing table of R4, the 10.1.1.0/24 route appears as an O E2 route.
B. On R4, the 172.16.1.0/24 route has a metric of 20.
C. The R3 S0/0 interface should not need the no ip split-horizon eigrp 1 configuration command for the 172.16.1.0/24 route to appear in the routing table of R2 as an D EX route.
D. The administrative distance of the 172.16.1.0/24 route in the routing table of R3 is 170.
E. On R5, the 4.0.0.0/8 route will have an administrative distance of 120 and a hop count of 6.

 

Answer: A B D

Explanation

When redistributing into OSPF, the default route type is E2 -> A is correct. Notice that the cost of E2 type is always the cost of external route only.

Also, the default seed metric when redistributing into OSPF is always 20 (except for BGP, which is 1) -> B is correct.

When redistributing into EIGRP, the external EIGRP routes have an administrative distance of 170 by default -> D is correct.

Question 6

Refer to the exhibit. Looking at the topology diagram and the partial router configurations shown, which statement is true?

Redistribute_RIP_OSPF_EIGRP.jpg

A. A routing loop will occur due to mutual route redistribution occurring on R1 and R2.
B. Suboptimal routing will occur due to mutual route redistribution occurring on R1 and R2.
C. Additional route filtering configurations using route maps and ACLs are required on the R1 and R2 routers to prevent routing loops.
D. R2 will not be able to redistribute the EIGRP subnets into OSPF, because R2 is missing the default seed metric for OSPF.
E. The 10.1.1.0/24 subnet will appear as 10.0.0.0/8 in the R5 routing table.

 

Answer: E

Explanation

RIPv1 is a classful routing protocol so the subnet 10.1.1.0/24 will be summarized to 10.0.0.0/8 in the R5 routing table. If we use RIPv2 on R1, R5 and use the “no auto-summary” command on R1 then the 10.1.1.0 subnet will appear in the routing table of R5. Notice that even if the “auto-summary” command is configured under “router eigrp 1” of R1 but when redistributing into another routing protocol EIGRP still advertises the detailed network.

Question 7

Refer to the exhibit. R1 and R2 have been configured to share routing information via EIGRP. What will be the result of the configuration section shown for R2?

EIGRP_distriute_list.jpg

A. Any routes learned by R2 from the interface tied to the 172.16.0.0 network will not be advertised to neighbors on the 192.168.2.0 network.
B. Only routes learned by R2 from the interface tied to the 172.16.0.0 network will be advertised to neighbors on the 192.168.2.0 network.
C. Only the 172.16.0.0 network will be advertised to neighbors on the 192.168.2.0 network.
D. All networks, except the 172.16.0.0 network will be advertised to neighbors on the 192.168.2.0 network.

 

Answer: C

Question 8

Refer to the exhibit. EIGRP has been configured on router D. Router C is performing mutual redistribution between EIGRP and OSPF. While verifying that the redistribution is functioning properly, you discover that while router C has all of the EIGRP routes in its routing table, router A does not have any routes from the EIGRP domain. What on router C may be the cause of the problem?

EIGRP_OSPF_mutual_redistribute.jpg

A. The no auto-summary command needs to be added under router eigrp 1.
B. The subnets keyword was not included in the redistribute command under router ospf 1.
C. The metric specified for the redistributed EIGRP routes is too large; making the EIGRP routes unreachable by router A.
D. The defauft-information originate command needs to be added under router ospf 1.
E. The administrative distance of either OSPF or EIGRP must be changed so that EIGRP has a higher administrative distance than OSPF.

 

Answer: B

Explanation

If we don’t use the “subnets” keyword when redistributing routes learned from another routing process into OSPF, only classful routes will be redistributed. This is an important thing to remember when redistributing into OSPF -> B is correct.

Question 9

You have implemented mutual route redistribution between OSPF and EIGRP on a border router. When checking the routing table on one of the EIGRP routers within the EIGRP routing domain, you are seeing some, but not all of the expected routes. What should you verify to troubleshoot this problem?

A. The border router is using a proper seed metric for OSPF.
B. The border router is using a proper seed metric for EIGRP.
C. The administrative distance is set for OSPF and EIGRP.
D. The missing OSPF routes are present in the routing table of the border router.
E. The subnet keyword on the border router in the redistribute OSPF command.

 

Answer: D

Explanation

We are checking the routing table on EIGRP routers not OSPF so we don’t need to check the seed metric for OSPF. Besides OSPF doesn’t need to specify seed metric as all external routes get a default metric of 20 (except for BGP, which is 1) -> A is not correct.

We must specify seed metrics when redistributing into EIGRP (and RIP). If not all the redistributed routes will not be seen but the question says only some routes are missing -> B is not correct.

The default administrative distance for external routes redistributed into EIGRP is 170 so we don’t need to set it -> C is not correct.

The sunbet keyword is only used when redistributing into OSPF, not to other routing protocols -> E is not correct.

We should check the routing table of the border router to see the missing OSPF routes are there or not. An incorrect distribute-list can block some routes and we can’t see it in other EIGRP routers -> D is correct.

Question 10

Refer to the exhibit. Which two statements are correct regarding the routes to be redistributed into OSPF? (Choose two)

Redistribute_RIP_OSPF_route_map.jpg

A. The network 192.168.1.0 will be allowed and assigned a metric of 100.
B. The network 192.168.1.0 will be allowed and assigned a metric of 200.
C. All networks except 10.0.0.0/8 will be allowed and assigned a metric of 200.
D. The network 172.16.0.0/16 will be allowed and assigned a metric of 200.
E. The network 10.0.10.0/24 will be allowed and assigned a metric of 200.

 

Answer: A D

Explanation

These rules apply when using route-map with an access-list:
* If you use an ACL in a route-map permit clause, routes that are permitted by the ACL are redistributed.
* If you use an ACL in a route-map deny clause, routes that are permitted by the ACL are not redistributed.
* If you use an ACL in a route-map permit or deny clause, and the ACL denies a route, then the route-map clause match is not found and the next route-map clause is evaluated.

And in each route-map:
* Multiple match criteria in the same line use a logical OR
* Each vertical match uses a logical AND

Therefore in this question, the networks in the access lists 10 and 20 (10.0.10.0/24 & 192.168.1.0/24) will be permitted while the network in access list 30 (10.0.0.0/8) will be denied.

Notice that there is no “match” line in the clause 30 so all networks that are not matched with clause 10 & 20 will be matched in the clause 30 and will be set a metric of 200, type 2 -> answer D is correct.

In this question please don’t be confused between the route-map clause number (sequence number) and the access-list number. The “match ip address” specifies which access lists are matched. The route-map clause number only uses to specify the order in which the clauses are executed.

Redistribute Questions 3

May 3rd, 2014 digitaltut 4 comments

Here you will find answers to Redistribute Questions – Part 3

Question 1

Given the accompanying output, which additional command is needed to redistribute IGRP into EIGRP?

Router eigrp 123
Network 10.10.10.0
No auto-summary
!
Router igrp 123
Network 172.16.0.0
Network 172.17.0.0

A. Under the router igrp mode add redistribute eigrp 123
B. Under the router eigrp mode add redistribute igrp 123
C. Under the router eigrp mode add redistribute igrp 123 subnets
D. None, EIGRP and IGRP are automatically redistributed in this instance.

 

Answer: D

Explanation

If IGRP and EIGRP use the same Autonomous System (AS) then redistribution occurs automatically. In this case both IGRP & EIGRP use the same AS 123 so they are automatically redistributed.

If IGRP and EIGRP use different AS numbers then redistribution must be done manually.

Question 2

Study the exhibit carefully. Router R1 is connected to networks 172.16.1.0/26 and 172.16.1.64/27. Based on the partial output in the exhibit, which description is correct?

prefix-list.jpg

A. Router R1 should be reconfigured with an ACL instead of an ip prefix-list command.
B. Router R1 will advertise both routes.
C. Router R1 will deny the 172.16.1.0/27 route while permitting the 172.16.1.0/26 route to be advertised.
D. Router R1 will deny the 172.16.1.0/26 route while permitting the 172.16.1.64/27 route to be advertised.

 

Answer: C

Explanation

Prefix lists are configured with permit or deny keywords to either permit or deny the prefix based on the matching condition. A prefix list consists of an IP address and a bit mask. The IP address can be a classful network, a subnet, or a single host route. The bit mask is entered as a number from 1 to 32.

Prefix lists are configured to match an exact prefix length or a prefix range. The ge and le keywords are used to specify a range of the prefix lengths to match, providing more flexible configuration than can be configured with just the network/length argument. The prefix list is processed using an exact match when neither ge nor le keyword is entered.

Therefore in this case the exact 172.16.1.0/26 network is permitted while other networks are denied.

(Reference: http://www.cisco.com/en/US/docs/ios/12_3t/ip_route/command/reference/ip2_i2gt.html)

Question 3

Refer to the exhibit. The partial configuration for an OSPF ASBR and an Area 0 ABR is shown. Assume the OSPF configurations throughout the network are operable. Which statement about these configurations is true?

Redistribute_OSPF_ASBR_ABR.jpg

A. The ASBR route-maps are basically useless, because there are no deny prefix-lists.
B. LSA Type 5s will not be received by the ABR from the ASBR.
C. The OSPF backbone will not learn any RFC 1918 addresses.
D. The matched prefix-list addresses will be given a metric of 255, which is essentially unreachable.

 

Answer: C

Explanation

The ASBR accepts RFC 1918 addresses and set these networks to “tag 255” but when advertising into Area 0, the ABR Area 0 filters out these networks because they match “tag 255” so the OSPF backbone will not learn any RFC 1918 addresses.

Note that if you use an ACL in a route-map deny clause, routes that are permitted by the ACL are not redistributed.

All the networks with “tag 255” are blocked by the clause 10 while all other networks are permitted by the clause 20 of the route-map (if a match command is not present, all routes match the clause).

Note:

RFC 1918 addresses include:

+ Class A: 10.0.0.0 – 10.255.255.255 (10/8 prefix)
+ Class B: 172.16.0.0 – 172.31.255.255 (172.16/12 prefix)
+ Class C: 192.168.0.0 – 192.168.255.255 (192.168/16 prefix)

Question 4

A network administrator is troubleshooting a redistribution of RIP routes into OSPF. Given the exhibited configuration commands, which statement is true?

rooter rip
network 10.0.0.0
!
router ospf 5
network 172.10.0.0 0.0.255.255 area 0
redistribute rip

A. Redistributed routes will be tagged as external type 1 (E1) with a metric of 30.
B. Redistributed routes will be tagged as external type 2 (E2) with a metric of 20.
C. Redistributed routes will maintain their original RIP routing metric.
D. Redistributed routes will have a default metric of 0 and will be treated as unreachable and not advertised.
E. Redistributed routes will have a default metric of 0 but will not be treated as reachable and will be advertised.

 

Answer: B

Explanation

By default, all routes redistributed into OSPF will be tagged as external type 2 (E2) with a metric of 20, except for BGP routes (with a metric of 1).

Note: The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route. A type 1 cost is the addition of the external cost and the internal cost used to reach that route.

Question 5

Refer to the exhibit. On the basis of the partial configuration, which two statements are correct? (Choose two)


!
router rip
distribute-list 2 out ethernet 0
distribute-list 1 out
!
access-list 1 permit 10.0.0.0 0.255.255.255
access-list 2 permit 10.0.1.0 0.0.0.255
!

A. Only routes matching 10.0.1.0/24 will be advertised out Ethernet 0.
B. Only routes 10.0.1.0/24 will be sent out all interfaces.
C. Only routes 10.0.1.0/24 will be allowed in the routing table.
D. Only routes matching 10.0.0.0/8 will be advertised out Ethernet 0.
E. Only routes matching 10.0.0.0/8 will be advertised out interfaces other than Ethernet 0.
F. All routes will be advertised out interfaces other than Ethernet 0.

 

Answer: A E

Explanation

In this case, the following algorithm is used when multiple distribute-lists are used:

1. First check which interface is being sent out. If it is Ethernet 0, distribute-list 2 is applied first. If the network is denied then no further checking is done for this network. But if distribute-list 2 permits that network then distribute-list 1 is also checked. If both distribute-lists allow that network then it will be sent out.

2. If the interface is not Ethernet 0 then only distribute-list 1 is applied.

Now let’s take some examples.
+ If the advertised network is 10.0.1.0/24, it will be sent out all interfaces, including Ethernet 0.
+ If the advertised network is 10.0.2.0/24, it will be sent out all interfaces, excepting Ethernet 0.
+ If the advertised network is 11.0.0.0/8, it will be dropped.

Note: It is possible to define one interface-specific distribute-list per interface and one protocol-specific distribute-list for each process/autonomous-system.

(For more information, please read: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080208748.shtml)

Question 6

Refer to the exhibit. Examine the partial configuration and the routing table excerpt. Which routes would be redistributed into OSPF area 1?

redistribute_ospf_subnets.jpg

A. 10.10.10.16/28 only
B. 10.10.10.16/28 and 10.10.10.64/26
C. 10.10.10.16/28, 10.10.10.64/26, and 172.16.10.0/24
D. 10.10.10.64/26 only

 

Answer: B (but in the exam you should choose D)

Explanation

The network 172.16.10.0/24 belongs to OSPF (we know from the “network 172.16.0.0 0.0.255.255 area 1” command) so it will not be redistributed.

When using the “subnets” keyword, all the connected networks will be redistributed so 10.10.10.16/28 & 10.10.10.64/26 will be redistributed, too. You can read my GNS3 lab about this topic here: http://www.digitaltut.com/redistribute-eigrp-and-ospf-gns3-lab.

Therefore the correct answer should be B but in the exam you should choose D. Maybe it is a mistake of Cisco.

Question 7

Refer to the exhibit. A partial routing configuration is shown. Complete the configuration so that only the default-network is redistributed from EIGRP 190 into EIGRP 212. Which ACL statement completes the configuration correctly?

router eigrp 190
redistribute eigrp 212
network 192.0.0.0 0.0.0.3
!
router eigrp 212
redistribute eigrp 190 route-map default_route
network 212.50.185.96 0.0.0.31
!
route-map defau1t_route permit 10
match ip address 100

A. access-list 100 permit ip 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0
B. access-list 100 permit ip host 0.0.0.0 any
C. access-list 100 permit ip any host 0.0.0.0
D. A default-network cannot be redistributed between routing processes.

 

Answer: C

Explanation

The command “access-list 100 permit ip any host 0.0.0.0” means permit any source address with the destination of 0.0.0.0/0, which is the default route

Note:

any equals 0.0.0.0 255.255.255.255

host 0.0.0.0 equals 0.0.0.0 0.0.0.0

Question 8

Refer to the exhibit. Router B and router C are performing mutual redistribution between OSPF and EIGRP, and their default metrics are configured the same. Router D has equal cost paths to networks where both paths are not really equal cost. For example, network 172.16.54.0 shows equal cost through both router B and router C, though in reality the cost is greater using router C. Other routers, though not shown, are connected to the 172.16.54.0 and 172.16.55.0 networks, and the same issues exist to those routers and the networks connected to them.
What can be done so that data will be routed along the most optimal path in the network?

mutual_redistribute_EIGRP_OSPF.jpg

A. Redistribute connected interfaces on router B and router C.
B. Set the maximum number of equal cost paths to 1 in all routers.
C. When redistributing EIGRP into OSPF, set the external metric type to type E1.
D. Adjust the default metrics in router B and router C so that the values are different in each router.
E. None of these solutions will fix the problem. Migrate to a single dynamic routing protocol.

 

Answer: E

Explanation

Let’s discuss about answers C & D first.

From the output, we learn that all the External OSPF routes have metrics of 100 (the second parameters in [110/100]). This is not the default metric of OSPF Type 2 External route (the default value is 20) so the metrics of redistributed routes have been modified. Maybe when redistributing into OSPF, the “metric” in the “redistribute” command or the “default-metric” command was used on router B & C to assign the metric of these routes. Something like this:

router ospf 1
redistribute eigrp 1 metric 100 subnets

or

router ospf 1
…..
default-metric 100

Therefore even if we use the metric type E1 the problem still exists because the link B-D & C-D seems to have the same metric -> the total metrics remains the same -> C is not correct.

We can use route-map and set different metrics for each networks but some unshown networks will have the same issues -> D is not a good choice

So the best answer should be E.

Question 9

Refer to the exhibit. A new TAC engineer comes to you for advice. The engineer wants to configure RIPv2-OSPF two-way redistribution while avoiding routing loops. Which two additions to the router B1 configuration should the engineer make? (Choose two)

RIPv2_OSPF_Redistribute.jpg

A. access-list 40 deny 172.16.1.0 0.0.0.255
access-list 40 permit any
router rip
redistribute ospf 100 metric 5
distribute-list 40 out ospf 100

B. ip prefix-list rip_routes permit 172.16.1.16/25 ge 26 le 28
route-map redis-ospf deny 10
match ip address prefix-list rip_routes
router rip
redistribute ospf 10 route-map redis-ospf subnets

C. ip prefix-list rip-to-ospf permit 10.1.1.8/25 ge 26 le 28
route-map redis-rip deny 20
match ip address prefix-list rip-to-ospf
router ospf 100
redistribute rip route-map redis-rip subnets

D. access-list 15 deny 10.1.1.0 0.0.0.63
access-list 15 permit any
route-map redis-rip deny 10
match ip address 15
route-map redis-rip permit 20
router ospf 100
redistribute rip route-map redis-rip subnets

 

Answer: A D

Explanation

B1 is not the only router that redistributes between RIP & OSPF. The “small” router below B1 can be configured for this task too so B1 can try to redistribute networks advertised by that “small” router again. Therefore it is necessary to filter out networks that have been advertised by the “small” router. For example, we need to prevent network 172.16.1.0/24 from advertised back into RIPv2 or network 10.1.1.0/26 from advertised back into OSPF. Notice that all networks in OSPF domain (including 10.1.1.8/30, 10.1.1.12/30, 10.1.1.48/28, 10.1.1.32/28) can be summarized as 10.1.1.0/26 and all networks in RIP domain (including 172.16.1.24/30, 172.16.1.20/30, 172.16.1.32/28, 172.16.1.48/28) can be summarized as 172.16.1.0/24 -> answers A & D are correct.

In answer B, the command “ip prefix-list rip_routes permit 172.16.1.16/25 ge 26 le 28” means:

+ First check the first 25 bits of the address -> this will allow addresses from 172.16.1.0 to 172.16.1.127

ip_prefix_list.jpg

+ If those match then check the subnet mask, which in this case can be GREATER THAN or EQUAL to 26 bits & LESS THAN or EQUAL to 28 bits -> meaning that /26, /27, /28 subnet masks would match.

For example, networks 172.16.1.0/26; 172.16.1.16/28 would match (but notice networks 172.16.1.0/25; 172.16.1.128/26 wouldn’t).

In the “ip prefix-list rip_routes permit 172.16.1.16/25 ge 26 le 28”, the prefix-list “rip_routes” only covers networks 172.16.1.32/28 & 172.16.1.48/28 but can’t cover networks 172.16.1.24/30 & 172.16.1.20/30. Also, the OSPF process in the “redistribute” command should be 100, not 10 -> B is not correct.

Same problem as answer B, the prefix-list in answer C can’t cover networks 10.1.1.8/30 & 10.1.1.12/30 -> C is not correct.

Question 10

Refer to the exhibit. The network administrator is trying to configure mutual redistribution between EIGRP and OSPF. Autosummarization in EIGRP 100 AS is disabled. After adding OSPF configuration to router E31, the network administrator checked the routing table of router B2, but none of the EIGRP routes appeared there.
To redistribute the EIGRP AS 100 routes into OSPF, which command should be added, or edited, on router B1 under router ospf 10?

Redistribute_OSPF_EIGRP_subnets.jpg

A. redistribute eigrp 100 metric-type 1
B. redistribute eigrp 100 subnets
C. no auto-summary 10.0.0.0 255.0.0.0
D. area 0 range 10.10.0.0 255.255.0.0

 

Answer: B

Explanation

When redistributing into OSPF without keyword “subnets”, only classful networks will be redistributed. Classful networks here mean networks with the default major subnet masks (for example 10.0.0.0/8; 180.1.0.0/16; 200.200.200.0/24…).

In fact, the routing table on the exhibit above is not totally correct. The network 192.168.110.0/24 will be redistributed and shown in the routing table of B2 even if the keyword “subnets” is not used because it belongs to class C with the default subnet mask of class C.

To make all the networks, including subnets appear in the routing table of B2 we must use keyword “subnets” when redistributing into OSPF. This is also an important thing to remember when redistributing into OSPF.

Please read my Redistribute EIGRP and OSPF – GNS3 Lab if you are still not sure about this.

Question 11

Refer to the exhibit. Routers R1 and R2 are running EIGRP and have converged. On the basis of the information that is presented, which statement is true?

Redistribute_distribute-list-passive-interface.jpg

A. All outgoing routing updates from router R1 to router R2 will be suppressed, but the inbound updates will continue to be received.
B. All incoming routing updates from R2 will be suppressed, but the outgoing updates will continue to be sent.
C. Both outgoing and incoming routing updates on R1 will be stopped because of the passive-interface Serial0/0 configuration statement.
D. Both outgoing and incoming routing updates on R1 will be permitted because the distribute-list 20 out Serial0/0 command cannot be used with association with the outgoing interface.

 

Answer: C

Explanation

In EIGRP (and OSPF) the passive-interface command stops sending outgoing hello packets, hence the router can not form any neighbor relationship via the passive interface. This behavior stops both outgoing and incoming routing updates -> the distribute-list has no use here.

Redistribute Questions 4

May 3rd, 2014 digitaltut No comments

Here you will find answers to Redistribute Questions – Part 4

Question 1

You have implemented mutual route redistribution between OSPF and EIGRP on a border router. When checking the routing table on one of the OSPF routers within the OSPF routing domain, you are seeing some, but not all of the expected routes.

Which two things should you verify to troubleshoot this problem? (Choose two)

A. The border router is using a proper seed metric for OSPF.
B. The border router is using a proper seed metric for EIGRP.
C. The administrative distance is set for OSPF and EIGRP.
D. The missing EIGRP routes are present in the routing table of the border router.
E. The subnet keyword on the border router in the redistribute EIGRP command.

 

Answer: D E

Explanation

Answer D is obvious that we should check all the routes we want to redistribute are present in the routing table of the border router. Let’s discuss about answer E.

A rule of thumb when redistributing into OSPF is we should always include the “subnets” keyword after the redistributed route. For example:

router ospf 1
redistribute eigrp 100 subnets

This keyword makes sure all of the routes, including subnets are redistributed correctly into OSPF. For example these routes are learned via EIGRP:

+ 192.168.1.0/24
+ 192.168.2.0/25
+ 192.168.3.0/26

Then without the keyword “subnets”, only 192.168.1.0/24 network is redistributed into OSPF.

For more information about “subnets” keyword, please read my Redistribute EIGRP and OSPF in GNS3 guide.

Question 2

Which three steps are most helpful in verifying proper route redistribution? (Choose three)

A. On the routers not performing the route redistribution, use the show ip route command to see if the redistributed routes show up.
B. On the ASBR router performing the route redistribution, use the show ip protocol command to verify the redistribution configurations.
C. On the ASBR router performing the route redistribution, use the show ip route command to verify that the proper routes from each routing protocol are there.
D. On the routers not performing the route redistribution, use the show ip protocols command to verify the routing information sources.
E. On the routers not performing the route redistribution, use the debug ip routing command to verify the routing updates from the ASBR.

 

Answer: A B C

Question 3

A router is configured for redistribution to advertise EIGRP routes into OSPF on a boundary router. Given the configuration:

router ospf 1
redistribute eigrp 1 metric 25 subnets

What is the function of the 25 parameter in the redistribute command?

A. It specifies the seed cost to be applied to the redistributed routes.
B. it specifies the administrative distance on the redistributed routes.
C. It specifies the metric limit of 25 subnets in each OSPF route advertisement.
D. It specifies a new process-id to inject the EIGRP routes into OSPF.

 

Answer: A

Question 4

Which command should be added to RTB under router bgp 100 to allow only the external OSPF routes to be redistributed to RTC?

Redistribute_OSPF_BGP_external.jpg

A. redistribute ospf 1
B. redistribute ospf 1 match external 1
C. redistribute ospf 1 match external 2
D. redistribute ospf 1 match external 1 external 2

 

Answer: D

Question 5

Refer to the exhibit. Will redistributed RIP routes from OSPF Area 2 be allowed in Area 1?

Redistributed_RIP_OSPF

A – Because Area 1 is an NSSA, redistributed RIP routes will not be allowed.
B – Redistributed RIP routes will be allowed in Area 1 because they will be changed into type 5 LSAs in Area 0 and passed on into Area 1
C – Because NSSA will discard type 7 LSAs, redistributed RIP routes will not be allowed in Area 1
D – Redistributed RIP routes will be allowed in Area 1 because they will be changed into type 7 LSAs in Area 0 and passed on into Area 1

 

Answer: A

Explanation

Because Area 1 is a Not-so-stubby-area (NSSA), we can inject EIGRP routes into the OSPF NSSA domain with the creation of type 7 LSAs. Redistributed RIP routes are not allowed in Area 1 because NSSA is an extension to the stub area (recall that a stub area does not accept external route unless it is connected through a ASBR, doing that will make it become a NSSA). The type 7 LSAs are converted to Type 5 LSAs when flooded into Area 0 by the ABR router.

Question 6

Look at the following exhibit. Which of the following correctly states the routes to be redistributed into OSPF? (Choose two)

route_map_redistribute

A – The network 10.0.10.0/24 will be allowed and assigned a metric of 200
B – All networks except 10.0.0.0/8 will be allowed and assigned a metric of 200
C – The network 172.16.0.0/16 will be allowed and assigned a metric of 200
D – The network 192.168.1.0 will be allowed and assigned a metric of 100

 

Answer: C D

Explanation

Let’s analyze each route-map clause. The first one is:

route-map rip-in permit 10
match ip address 10 20
set metric 100
set metric-type type-1

If a match command refers to several objects in one command, either of them should match (the logical OR algorithm is applied). For example, in the match ip address 10 20 command, a route is permitted if it is permitted by access list 10 or access list 20 -> The networks 10.0.10.0/24 and 192.168.1.0/24 will be matched and be set metric of 100 and metric-type of Type-1. -> D is correct.

If the traffic is not matched by the first clause, the second clause is used to check:

route-map rip-in deny 20
match ip address 30

In this clause, the keyword “deny” will cause the network matched by access-list 30 to be dropped -> Network 10.0.0.0/8 will be dropped.

The last clause is:

route-map rip-in permit 30
set metric 200
set metric-type type-2

In this clause no match statement is found so all remaining routes (networks) are matched here. They will be set a metric of 200 and metric-type of Type-2. -> “network 172.16.0.0/16 will be allowed and assigned a metric of 200” -> C is correct.

(Good resource about route-map: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/49111-route-map-bestp.html)

Policy Based Routing Questions

May 2nd, 2014 digitaltut 1 comment

Here you will find answers to Policy Based Routing Questions

Question 1

Refer to the exhibit. Based upon the configuration, you need to understand why the policy routing match counts are not increasing. Which would be the first logical step to take?

show_route-map_divert.jpg

A. Confirm if there are other problematic route-map statements that precede divert.
B. Check the access list for log hits.
C. Check the routing table for 212.50.185.126.
D. Remove any two of the set clauses. (Multiple set clause entries will cause PBR to use the routing table.)

 

Answer: B

Explanation

First we should check the access-list log, if the hit count does not increase then no packets are matched the access-list -> the policy based routing match counts will not increase.

Question 2

When policy-based routing (PBR) is being configured, which three criteria can the set command specify? (Choose three)

A. all interfaces through which the packets can be routed
B. all interfaces in the path toward the destination
C. adjacent next hop router in the path toward the destination
D. all routers in the path toward the destination
E. all networks in the path toward the destination
F. type of service and precedence in the IP packets

 

Answer: A C F

Explanation

The set command specifies the action(s) to take on the packets that match the criteria. You can specify any or all of the following:

* precedence: Sets precedence value in the IP header. You can specify either the precedence number or name.
* df: Sets the “Don’t Fragment” (DF) bit in the ip header.
* vrf: Sets the VPN Routing and Forwarding (VRF) instance.
* next-hop: Sets next hop to which to route the packet.
* next-hop recursive: Sets next hop to which to route the packet if the hop is to a router which is not adjacent.
* interface: Sets output interface for the packet.
* default next-hop: Sets next hop to which to route the packet if there is no explicit route for this destination.
* default interface: Sets output interface for the packet if there is no explicit route for this destination.

route_map_set_command1.jpg

route_map_set_command.jpg

(Reference: http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcfpbr_ps1835_TSD_Products_Configuration_Guide_Chapter.html)

Question 3

Refer to the exhibit. Which command would verify if PBR reacts to packets sourced from 172.16.0.0/16?

Policy_Based_Routing_route-map.jpg

A. show ip route
B. show policy-map
C. show access-lists
D. show route-map

 

Answer: D

Explanation

The “show route-map “route-map name” displays the policy routing match counts so we can learn if PBR reacts to packets sourced from 172.16.0.0/16 or not.

show_route-map_divert.jpg

Question 4

A policy needs to be implemented on Router B so that any traffic sourced from 172.16.11.0/24 will be forwarded to Router C. Which configuration on Router B will achieve the desired effect?

Policy_Based_Routing_set_ip_next-hop.jpg

A. access-list 1 permit 172.16.11.0 0.0.0.255
!
interface s0
ip policy route-map policy
!
route-map policy permit 10
match ip address 1
set ip next-hop 172.16.12.3

B. access-list 1 permit 172.16.11.0 0.0.0.255
!
interface e0
ip policy route-map policy
!
route-map policy permit 10
match ip address 1
set ip next-hop 172.16.12.2

C. access-list 1 permit 172.16.11.0 0.0.0.255
!
interface e0
ip policy route-map policy
!
route-map policy permit 10
match ip address 1
set ip next-hop 172.16.14.4

D. access-list 1 deny 172.16.11.0 0.0.0.255
!
interface s0
ip policy route-map policy
!
route-map policy permit 10
match ip address 1
set ip next-hop 172.16.12.2

 

Answer: A

Explanation

The “next-hop” IP address should be the E1 interface of router C (172.16.12.3) -> A is correct.

IPv6 Questions

May 1st, 2014 digitaltut No comments

Here you will find answers to IPv6 questions

If you are not sure about IPv6, please read my IPv6 tutorial

Question 1

Which two reductions are the correct reductions of the IPv6 address 2001:0d02:0000:0000:0014:0000:0000:0095? (Choose two)

A – 2001:0d02:::0014:::0095
B – 2001:d02::14::95
C – 2001:d02:0:0:14::95
D – 2001:d02::14:0:0:95

 

Answer: C D

Explanation

A is not correct because we can’t use triple colons (:::) in IPv6 presentation. B is not correct because we can’t use double colons (::) twice. You can use it only once in any address because if two double colons are
placed in the same address, there will be no way to identify the size of each block of 0s. Remember the following techniques to shorten an IPv6 address:

– Omit leading 0s in the address field, so :0000 can be compressed to just :0 and :0d02 can be com-
pressed to :d02 (but :1d00 can not be compressed to :1d)

– Use double colons (::), but just once, to represent a contiguous block of 0s, so 2001:0d02:0000:0000:0014:0000:0000:0095 can be compressed to 2001:0d02::14:0:0:95 or 2001:0d02:0:0:14::95

Question 2

What is the IPv6 address FF02::2 used for?

A – all hosts in a local segment
B – all routers in a local segment
C – all hosts in a particular rnulticast group
D – all routers in an autonomous system

 

Answer: B

Explanation

Below lists some reserved and well-known IPv6 multicast address in the reserved multicast address range (FF00:: to FF0F::)

Multicast Address Multicast Group
FF01::1 All IPv6 nodes within the node-local scope
FF01::2 All IPv6 routers within the node-local scope
FF02::1 All IPv6 nodes within the link-local scope
FF02::2 All IPv6 routers within the link-local scope
FF02::5 All OSPFv3 routers within the link-local scope
FF02::6 All OSPFv3 designated routers within the link-local scope
FF02::9 All RIPng routers within the link-local scope
FF02::A All EIGRP routers within the link-local scope
FF02::D All PIM routers within the link-local scope
FF02::1:2 All DHCPv6 agents (servers and relays) within the link-local scope
FF05::2 All IPv6 routers within the site-local scope
FF02::1:FF00:0/104 IPv6 solicited-node multicast address within the link-local scope

Question 3

Refer to the exhibit. Routers R1 and R2 are IPv6 BGP peers that have been configured to support a neighbor relationship over an IPv4 internetwork. Which three neighbor IP addresses are valid choices to use in the highlighted section of the exhibit? (Choose three)

IPv6toIPv4_tunnel

A – ::0A43:0002
B – 0A43:0002::
C – ::10.67.0.2
D – 10.67.0.2::
E – 0:0:0:0:0:0:10.67.0.2
F – 10.67.0.2:0:0:0:0:0:0

 

Answer: A C E

Explanation

The automatic tunneling mechanism uses a special type of IPv6 address, termed an “IPv4-compatible” address. An IPv4-compatible address is identified by an all-zeros 96-bit prefix, and holds an IPv4 address in the low-order 32-bits. IPv4-compatible addresses are structured as follows:

ipv6toIPv4structure

Therefore, an IPv4 address of 10.67.0.2 will be written as ::10.67.0.2 or 0:0:0:0:0:0:10.67.0.2 or ::0A43:0002 (with 10[decimal] = 0A[hexa] ; 67[decimal] = 43[hexa] ; 0[hexa] = 0[decimal] ; 2[hexa] = 2[decimal])

Question 4

Refer to the exhibit. The 6to4 overlay tunnel configuration has been applied on each router to join isolated IPv6 networks over a IPv4 network. Which statements regarding the 6to4 overlay tunnel is true?

Automatic_6to4_Tunnels

A -The least significant 32 bits in the address referenced by the ipv6 route 2002::/16 Tunnel0 command will correspond to the interface E0/0 IPv4 address
B – The least significant 32 bits in the address referenced by the ipv6 route 2002::/16 Tunnel0 command will correspond to the IPv4 address assigned to the tunnel source
C – The configuration is invalid since the tunnel source command must be configured with an IPv6 address
D – This is actually a configuration example of an IPv4-compatible tunnel and not a 6to4 tunnel
E – This is actually a configuration example of an ISATAP overlay tunnel and not a 6to4 tunnel

Answer: B

Explanation

6to4 tunnels use IPv6 addresses that concatenate 2002::/16 with the 32-bit IPv4 address of the edge router, creating a 48-bit prefix. The tunnel interface on R1 has an IPv6 prefix of 2002:4065:4001:1::/64, where 4065:4001 is the hexadecimal equivalent of 64.101.64.1, the IPv4 address of its interface in the IPv4 network. The tunnel interface on R2 has an IPv6 prefix of 2002:4065:4101:1::/64, where 4065:4101 is the hexadecimal equivalent of 64.101.65.1, the IPv4 address of its interface in the IPv4 network.

When R1 receives a packet with IPv6 destination address of 2002:4065:4101:1:: (from the left IPv6 network, for example) R1 will:

* Take the IPv6 destination address of that packet (2002:4065:4101:1::) and convert it into an IPv4 address. In this case, the IPv4 address is 40.65.41.01 in hexa, which is 64.101.65.1 in decimal format.
* R1 encapsulates the IPv6 packet in an IPv4 packet with a destination address of 64.101.65.1; the packet is routed normally through the IPv4 network to R2
* R2 receives the IPv4 packet, decapsulates and routes it normally to its final IPv6 destination.

Question 5

What will occur when an IPv6 enabled router running 6to4 must transmit a packet to a remote destination and the next hop is the address of 2002::/16 ?

A – The IPv6 packet has its header removed and replaced with an IPv4 header
B – The IPv6 packet is encapsulated in an IPv4 packet using an IPv4 protocol type of 41
C – The IPv6 packet is dropped because that destination is unable to route IPv6 packets
D – The packet is tagged with an IPv6 header and the IPv6 prefix is included

 

Answer: B

Question 6

What are three IPv6 transition mechanisms? (Choose three)

A – 6to4 tunneling
B – VPN tunneling
C – GRE tunneling
D – ISATAP tunneling
E – PPP tunneling
F – Teredo tunneling

 

Answer: A D F

Explanation

Below is a summary of IPv6 transition technologies:

6 to 4 tunneling: This mechanism allows IPv6 sites to communicate with each other over the IPv4 network without explicit tunnel setup. The main advantage of this technology is that it requires no end-node reconfiguration and minimal router configuration but it is not intended as a permanent solution.

ISATAP tunneling (Intra-Site Automatic Tunnel Addressing Protocol): is a mechanism for transmitting IPv6 packets over IPv4 network. The word “automatic” means that once an ISATAP server/router has been set up, only the clients must be configured to connect to it.

Teredo tunneling: This mechanism tunnels IPv6 datagrams within IPv4 UDP datagrams, allowing private IPv4 address and IPv4 NAT traversal to be used.

In fact, GRE tunneling is also a IPv6 transition mechanism but is not mentioned in ROUTE so we shouldn’t choose it (there are 4 types of IPv6 transition mechanisms mentioned in ROUTE; they are: manual, 6-to-4, Teredo and ISATAP).

IPv6 Questions 2

May 1st, 2014 digitaltut No comments

Here you will find answer to IPv6 Questions – Part 2

Question 1

Refer to the exhibit. In the show ipv6 route output, what would the metric be for a summary route that summarizes all three OSPFv3 routes displayed?

show_ipv6_route.jpg

 

A. 20
B. 40
C. 100
D. 120
E. 140
F. 160

 

Answer: C

Explanation

The metric of a summary route is the highest cost of the routes being summarized. Therefore when summarizing three routes above the highest cost (100) will be chosen.

Question 2

Which statement is true concerning 6to4 tunneling?

A. IPv4 traffic is encapsulated with an IPv6 header.
B. The edge routers can use any locally configured IPv6 address.
C. Hosts and routers inside a 6to4 site will need a special code.
D. An edge router must use IPv6 address of 2002: :/16 in its prefix.

 

Answer: D

Explanation

6to4 tunnels use IPv6 addresses that concatenate 2002::/16 with the 32-bit IPv4 address of the edge router, creating a 48-bit prefix.

Question 3

Which two statements are true about using IPv4 and IPv6 simultaneously on a network segment? (Choose two)

A. Hosts can be configured to receive both IPv4 and IPv6 addresses via DHCP.
B. Host configuration: options for IPv4 can be either statically assigned or assigned via DHCP. Host configuration: options for IPv6 can be statically assigned only.
C. IPv6 allows a host to create its own IPv6 address that will allow it to communicate to other devices on a network configured via DHCP. IPv4 does not provide a similar capability for hosts.
D. IPv4 and IPv6 addresses can be simultaneously assigned to a host but not to a router interface.
E. IPv6 provides for more host IP addresses but IPv4 provides for more network addresses.

 

Answer: A C

Question 4

Which statement describes the difference between a manually configured IPv6 in IPv4 tunnel versus an automatic 6to4 tunnel?

A. A manually configured IPv6 in IPv4 tunnel allows multiple IPv4 destinations.
B. An automatic 6to4 tunnel allows multiple IPv4 destinations.
C. A manually configured IPv6 in IPv4 tunnel does not require dual-stack (IPv4 and IPv6) routers at the tunnel endpoints.
D. An automatic 6to4 tunnel does not require dual-stack (IPv4 and IPv6) routers at the tunnel endpoints.

 

Answer: B

Explanation

An automatic 6to4 tunnel allows isolated IPv6 domains to be connected over an IPv4 network to remote IPv6 networks. The key difference between automatic 6to4 tunnels and manually configured tunnels is that the tunnel is not point-to-point; it is point-to-multipoint -> it allows multiple IPv4 destinations -> B is correct.

A is not correct because manually 6to4 is point-to-point -> only allows one IPv4 destination.

Configuring 6to4 (manually and automatic) requires dual-stack routers (which supports both IPv4 & IPv6) at the tunnel endpoints because they are border routers between IPv4 & IPv6 networks.

(Reference: http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-tunnel_ps6441_TSD_Products_Configuration_Guide_Chapter.html#wp1055515)

Question 5

You need to explain the differences between an IPv4 header and an IPv6 header. In this comparison, which three statements are true? (Choose three)

A. An IPv6 header is half the size of an IPv4 header.
B. An IPv4 header includes a checksum. However, an IPv6 header does not include one.
C. A router has to recompute the checksum of an IPv6 packet when decrementing the TTL.
D. An IPv6 header is simpler and more efficient than an IPv4 header.
E. The 128-bit IPv6 address makes the IPv6 header more complicated than an IPv4 header.
F. An IPv6 header has twice as many octets as an IPv4 header.

 

Answer: B D F

Explanation

The image below shows the differences between an IPv4 header and an IPv6 header:

IPv6_header_compare_IPv4_header.jpg

(Reference and a good resource, too: http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_9-3/ipv6_internals.html)

Question 6

What are two rules for compacting IPv6 addresses? (Choose two)

A. The maximum number of times a double colon can replace a 16-bit segment that consists of all zeroes is two.
B. The leading zeroes in any 16-bit segment do not have to be written.
C. Every 16-bit segment that consists of all zeroes can be represented with a single colon.
D. The trailing zeroes in any 16-bit segment do not have to be written.
E. Any single, continuous string of one or more 16-bit segments that consists of all zeroes can be represented with a double colon.
F. Two zeroes in the middle of any 16-bit segment do not have to be written.

 

Answer: B E

Explanation

These rules are very popular for compacting IPv6 addresses, if you are not sure about them please read my IPv6 tutorial.

Question 7

How is authentication handled with OSPFv3?

A. OSPFv3 for IPv6 authentication is supported by SHA-1 authentication.
B. OSPFv3 for IPv6 authentication is supported by MD5 authentication.
C. OSPFv3 for IPv6 authentication is supported by IPv6 IPsec.
D. OSPFv3 for IPv6 authentication is supported by IPv4 IPsec.

 

Answer: C

Question 8

sing the rules for IPv6 addressing, how can the address 2031:0000:240F:0000:0000:09C0:123A:121B be rewritten?

A. 2031:0:240F::09C0:123A:121B
B. 2031::240F::09C0:123A:121B
C. 2031::240F::9C0::123A:121B
D. 2031::240F:::09C0:123A:121B

 

Answer: A

Question 9

Refer to the exhibit. What is required to complete the IPv6 routing configurations shown?

Router1#
interface S1/1
ipv6 address 2001:410:FFFF:1::1/64
ipv6 ospf 100 area 0

interface S2/0
ipv6 address 3FFE:B00:FFFF:1::2/64
ipv6 ospf 100 area 1

ipv6 router ospf 100
router-id 10.1.1.3

Router2#
interface S3/0
ipv6 address 3FFE:BOO:FFFF:1::1/64
ipv6 ospf 100 area 1

ipv6 router ospf 100
router-id 10.1.1.4

A. Interface authentication must be configured.
B. The routing processes must be configured with an area ID.
C. IP unicast routing must be enabled.
D. IPv4 addresses must be applied to the interfaces.

 

Answer: C

Question 10

When implementing OSPFv3, which statement describes the configuration of OSPF areas?

A. In interface configuration mode, the OSPFv3 area ID combination assigns interfaces to OSPFv3 areas.
B. In router configuration mode, the network wildcard area ID combination assigns networks to OSPFv3 areas.
C. In interface configuration mode, the IPv6 OSPF process area ID combination assigns interfaces to OSPFv3 areas.
D. In router configuration mode, the IPv6 OSPF interface area ID combination assigns interfaces to OSPFv3 areas.

 

Answer: C

IPv6 Questions 3

May 1st, 2014 digitaltut 5 comments

Here you will find answers to IPv6 Questions – Part 3

Question 1

During the IPv6 autoconfiguration, what does the device append to the 64-bit prefix that it receives from the router to create its IPv6 address?

A. a pseudorandom generated number
B. its locally configured IPv4 address
C. the DHCP-supplied device ID
D. its MAC address

 

Answer: D

Explanation

The automatic configuration is a great feature of IPv6. Imagine you have to manually configure an IPv6 address with 128-bit long, what a pain! With this feature, it is no longer necessary to configure each host manually. But notice that host only autonomously configures its own Link-local address (the IP address used on a LAN). The Link-local address can be created automatically using a link-local prefix of FE80::/10 and a 64-bit interface identifier (based on 48-bit MAC address).

For example, if your MAC address is 00:12:34:56:78:9a, your 64-bit interface identifier is 0012:34FF:FE56:789a (16-bit FFFE is inserted in the middle). And notice that the notation has been changed because IPv6 addresses require 16-bit pieces to be separated by “:”.

Then, according to the RFC 3513 we need to invert the Universal/Local bit (“U/L” bit) in the 6th position of the first octet (start counting from 0). The “u” bit is set to 1 to indicate Universal, and it is set to zero (0) to indicate local scope. In this case we set this bit to 1 because the MAC address is universally unique. Thus the result is: 0212:34FF:FE56:789a (0012 = 0000 0000 0001 0010 -> turn on 6th bit we get 0000 0010 0001 0010 which is 0212).

Finally, add the link-local prefix FE80 to create the full IPv6 address: FE80:0:0:0:0212:34FF:FE56:789a (or FE80::212:34FF:FE56:789a, in short form).

Note: The reason for inverting the “U/L” bit is to allow ignoring it for short values in the manual configuration case. For example, you can manually assign the short address fc80::1 instead of the long fc80:0:0:0:0200::1.

Question 2

Which three are characteristics of IPv6? (Choose three)

A. An IPv6 address is 128 bits long.
B. An IPv6 header is 20 bits long.
C. An IPv6 header contains the next header field.
D. An IPv6 header contains the protocol field.
E. IPv6 routers send RA messages.
F. An IPv6 header contains the header checksum field.

 

Answer: A C E

Explanation

A & C are obviously correct based on the theory of IPv6.

When a client sends a Router Solicitation (RS) message, router responds with a Router Advertisement (RA) message which includes prefix, default route and lifetime (how long the host should retain information about the router) -> E is correct.

Question 3

When an IPv6 enabled host boots, it sends a router solicitation (RS) message. An IPv6 router responds with a router advertisement (RA). Which two items are contained in the RA? (Choose two)

A. IPv6 address for the host
B. lifetime of the prefix
C. prefixes for the link
D. keepalive timers
E. request for the local host IP address
F. any route advertisements it has received

 

Answer: B C

Question 4

What is IPv6 router solicitation?

A. a request made by a node to join a specified multicast group
B. a request made by a node for its IP address
C. a request made by a node for the IP address of the DHCP server
D. a request made by a node for the IP address of the local router

 

Answer: D

Question 5

Which statement is true about IPv6?

A. Only one IPv6 address is assigned per node.
B. Only one IPv6 address can be assigned to each interface.
C. Each host can autoconfigure its address without the aid of a DHCP setver.
D. IPv6 hosts use anycast addresses to assign IP addresses to interfaces.

 

Answer: C

Question 6

What does the command clear ipv6 ospf process accomplish?

A. The OSPF adjacencies are cleared and initiated again.
B. The route table is cleared. Then the OSPF neighbors are reformed.
C. The shortest path first (SPF) algorithm is performed on the LSA database.
D. The OSPF database is repopulated. Then the shortest path first (SPF) algorithm is performed.

 

Answer: D

Explanation

The command “clear ipv6 ospf” will clear the present routing table and force the OSPFv3 process to build a new one. This command is often used when something in the network was changed or for debugging purpose.

When the “process” keyword is added, which means “clear ipv6 ospf process”, the OSPF database is cleared and repopulated then the SPF algorithm is performed.

Question 7

Which statement is true about the command ipv6 ospf 1 area 0?

A. It must be issued in router global configuration mode to enable the OSPF process for IPv6.
B. It must be issued in interface configuration mode to enable the OSPF process for IPv6.
C. It must be issued before the network command to enable the OSPF process for IPv6.
D. It must be issued after the network command to enable the OSPF process for IPv6.

 

Answer: B

Question 8

Your trainee asks you, in the context of IPv6 and OSPF, what best describes a type 9 LSA? What should you tell her?

A. Link LSA
B. Interarea prefix LSA for ABRs
C. Router LSA
D. Switch LSA
E. Intra-area prefix LSA
F. None of the above

 

Answer: E

Question 9

You have been tasked with setting up OSPF on an existing router using IPv6. Which command enables OSPF for IPv6 on a router?

A. ipv6 router ospf process-id
B. router ospf process-id
C. router ospf ipv6 process-id
D. ipv6 ospf process-id area-id
E. None of the above

 

Answer: A

Explanation

The command “ipv6 router ospf process-id” is used to enable an OSPF process on the router. For example:

Router(config)#ipv6 router ospf 1

Note: This command is used in global configuration mode.

Question 10

Which statement is true about the implementation of IPv6 in an already existing IPv4 network?

A. IPv6 can be routed using the same routing protocol versions as IPv4
B. A router routing for IPv6 and IPv4 must convert IPv4 packets to IPv6 packets to route them.
C. IPv4 and IPv6 networks can be routed simultaneously.
D. Only OSPF version 3 can be utilized for routing IPv4 and IPv6.

 

Answer: C

Explanation

There are many techniques to run implement IPv6 in an already existing IPv4 network. Maybe answer C wants to mention about “dual-stacking” technique. This is the most common technique which only requires edge routers to run both IPv4 and IPv6 while the inside routers only run IPv4. At the edge network, IPv4 packets are converted to IPv6 packets before sending out.

Question 11

Refer to the exhibit. Which statement about this neighbor of R1 is true?

show_ipv6_neighbor_ICMP.jpg

A. OSPFv3 adjacency has been lost, which causes the neighbor to be considered Stale.
B. Aggregate global addresses are always used between IPv6 neighbors.
C. OSPFv3 adjacency will not work between link-local addresses.
D. R1 used ICMP to learn about this neighbor.

 

Answer: D

Explanation

The “show ipv6 neighbor” command is used to display IPv6 neighbor discovery cache information. We notice that the neighbor IPv6 address is a Link Local address (in the range of FE80::/10) so this neighbor was discovered via the neighbor discovery process. The IPv6 neighbor discovery process uses ICMP messages and solicited-node multicast addresses to determine the link-layer address of a neighbor on the same network (local link), to verify the reachability of the neighbor, and to keep track of neighboring routers.

The STALE state indicates more than ReachableTime milliseconds have elapsed since the last positive confirmation was received that the forward path was functioning properly. While in stale state, the device takes no action until a packet is sent.

Note: Nodes on a local link use link-local addresses and do not require globally unique addresses to communicate. IPv6 routers do not forward packets with link-local source or destination addresses to other links.

Question 12

Which IPv6 address correctly compresses the IPv6 unicast address 2001:0:0:0:0DB8:0:0:417A?

A. 2001:0DB8:417A
B. 2001::0DB8::417A
C. 2001:::0DB8::417A
D. 2001:0DB8:0:0:417A
E. 2001::DB8:0:0:417A
F. 2001:::0DB8:0:0:417A

 

Answer: E

IPv6 Questions 4

May 1st, 2014 digitaltut No comments

Here you will find answers to IPv6 questions – part 4

Question 1

Which IPv4-mapped IPv6 address is equivalent to IPv6 address ::ffff:AC11:AC11?

A. ::ffff:10.12.10.12
B. ::ffff:10.14.10.14
C. ::ffff:44.49.44.49
D. ::ffff:161.193.161.193
E. ::ffff:172.17.172.17
F. ::ffff:193.11.193.11

 

Answer: E

Explanation

The IPv4-mapped IPv6 addresses are regular IPv4 addresses that have been mapped into the IPv6 address space. The range of this kind of IP address is 0:0:0:0:0:FFFF/96 (or ::FFFF/96). They have a set of 16 ones after the initial string of 80 zeroes, and then the IPv4 address. For example, if an IPv4 device has the address 172.17.172.17, it would be represented as 0:0:0:0:0:FFFF:172.17.172.17, or ::FFFF:172.17.172.17. To convert this address to IPv6 address, just write the IPv4 part in binary form and convert a group of four bits into a hexadecimal digit. For example: 172 = 1010 1100 = AC.

Question 2

Which command must be globally enabled on a Cisco router to support IPv6?

A. ip routing ipv6
B. ipv6 unicast-routing
C. ipv6 routing
D. ip classless
E. ipv6 cef

 

Answer: B

Question 3

What number is a valid representation for the 200F:0000:AB00:0000:0000:0000:0000/56 IPv6 prefix?

A. 200F:0:0:AB/56
B. 200F:0:AB00::/56
C. 200F::AB00/56
D. 200F:AB/56

 

Answer: B

Question 4

An enterprise has plans to start adding IPv6 support. The initial deployment requires support from some IPv6-only devices that need to access servers that support only IPv4. Which of the following tools would be most appropriate?

A. Native IPv6
B. Point-to-point tunnels
C. Multipoint tunnels
D. NAT-PT

 

Answer: D

Explanation

The Network Address Translator – Protocol Translator (NAT-PT) defines a set of network-layer translation mechanisms designed to allow nodes that only support IPv4 to communicate with nodes that only support IPv6, during the transition to the use of IPv6 in the Internet.

NAT-PT provides IPv4/IPv6 protocol translation. It resides within an IP router, situated at the boundary of an IPv4 network and an IPv6 network. By installing NAT-PT between an IPv4 and IPv6 network, all IPv4 users are given access to the IPv6 network without modification in the local IPv4-hosts (and vice versa). Equally, all hosts on the IPv6 network are given access to the IPv4 hosts without modification to the local IPv6-hosts. This is accomplished with a pool of IPv4 addresses for assignment to IPv6 nodes on a dynamic basis as sessions are initiated across IPv4-IPv6 boundaries.

(Reference: http://www.ietf.org/rfc/rfc4966.txt and http://www.cisco.com/en/US/prod/collateral/iosswrel/ps8802/ps6969/ps1835/prod_white_paper09186a008011ff51_ps6640_Products_White_Paper.html)

Question 5

Using the rules for IPv6 addressing, how can the address 2031:0000:240F:0000:0000:09C0:123A:121B be rewritten?

A. 2031:0:240F::09C0:123A:121B
B. 2031::240F::09C0:123A:121B
C. 2031::240F:9C0::123A:121B
D. 2031::240F:::09C0:123A:121B

 

Answer: A

Question 6

Which of the following address types are associated with IPv6? (Choose three)

A. Unicast
B. Private
C. Broadcast
D. Public
E. Multicast
F. Anycast

 

Answer: A E F

Question 7

Which three IPv6 notations represent the same address? (Select three)

A. 2031::130F::9C0:876A:130B
B. 2031:0000:130F:0000:0000:09C0:876A:130B
C. 2031:0:130F:::9C0:876A:130B
D. 2031::130F:0::9C0:876A:130B
E. 2031:0:130F:0:0:09C0:876A: 130B
F. 2031:0:130F::9C0:876A:130B

 

Answer: B E F

Question 8

An IPv6 overlay tunnel is required to communicate with isolated IPv6 networks across an IPv4 infrastructure. There are currently five IPv6 overlay tunnel types. Which three IPv6 overlay tunnel statements are true? (Choose three)

A. Overlay tunnels can only be configured between border routers capable of supporting IPv4 and IPv6.
B. Overlay tunnels can be configured between border routers or between a border router and a host capable of supporting IPv4 and IPv6.
C. Cisco IOS supports manual, generic, routing encapsulation (GRE), IPv6-compatible. 4to6, and multiprotocol Label Switching (MPLS) Overlay tunneling mechanism.
D. Cisco IOS supports manual, generic routing encapsulation (GRE), IPv4-compatible, 6to4, and Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) overlay tunneling mechanisms.
E. A manual overlay tunnel supports point-to-multipoint tunnels capable of carrying IPv6 and Connectionless Network Service (CLNS) packets.
F. Overlay tunneling encapsulates IPv6 packets in IPv4 packets for delivery across an IPv4 infrastructure.

 

Answer: B D F

Question 9

What is the benefit of deploying IPv6 in a campus network using dual stack mode?

A. Dual Stack Mode takes advantage of IPv6 over IPv4 tunnel within a network.
B. IPv4 and IPv6 run alongside one another and have no dependency on each other to function
C. IPv4 and IPv6 share network resources.
D. IPv6 can depend on existing IPv4 routing, QoS, security, and multicast policies.

 

Answer: B

Question 10

Refer to the exhibit. Which two statements are true about the router configuration? (Choose two)

ipv6 unicast routing
interface fastethernet 0/0
ip address 192.168.200.1 255.255.255.0
ipv6 address 3ffe:b00:c18:1::3/127

A. This configuration allows applications on the same segment to communicate via IPv4 or IPv6.
B. This configuration is referred to as a dual-stack 6to4 tunnel.
C. This configuration is referred to as a dual stack.
D. This configuration will attempt to route packets using IPv4 first, and if that fails, then IPv6.

 

Answer: A C

IPv6 Questions 5

May 1st, 2014 digitaltut 1 comment

Here you will find answers to IPv6 questions – Part 5

Question 1

IPv6 host wants to communicate with IPv4 host, what will occur?

IPv6_IPv4_NAT_PT_IP_determine.jpg

A. router will determine IPv4 address
B. host itself has IPv6-IPv4 mapping
C. IPv6 host can use DNS server to find out IPv4 address
D. ICMP can be used to discover right address

 

Answer: A

Question 2

What is the difference between the IPv6 addresses ::/0 and ::/128?

A. /0 is the unspecified address, and ::/128 is the multicast address.
B. /0 is the unicast address, and ::/128 is the anycast address.
C. /0 is the unicast address, and ::/128 is the multicast address.
D. /0 is the anycast address, and ::/128 is the multicast address.
E. /0 is the default route, and ::/128 is the unspecified address.
F. /0 is the anycast address, and ::/128 is the default address.

 

Answer: E

Operations Questions

April 30th, 2014 digitaltut No comments

Here you will find answers to Operation questions

Question 1

Which three route filtering statements are true? (Choose three)

A – After the router rip and passive-interface s0/0 commands have been issued, the s0/0 interface will not send any RIP updates, but will receive routing updates on that interface.
B – After the router eigrp 10 and passive-interface s0/0 commands have been issued, the s0/0 interface will not send any EIGRP updates, but will receive routing updates on that interface
C – After the router ospf 10 and passive-interface s0/0 commands have been issued , the s0/0 interface will not send any OSPF updates, but will receive routing updates on that interface
D – When you use the passive-interface command with RIPv2, multicasts are sent out the specified interface
E – When you use the passive-interface command with EIGRP, hello messages are not sent out the specified interface
F – When you use the passive-interface command with OSPF, hello messages are not sent out the specified interface

Answer: A E F

Explanation

Passive-interface command is used in all routing protocols to disable sending updates out from a specific interface. However the command behavior varies from o­ne protocol to another”

– In RIP, this command will not allow sending multicast updates via a specific interface but will allow listening to incoming updates from other RIP speaking neighbors. This means that the router will still be able to receive updates o­n that passive interface and use them in its routing table.

In EIGRP and OSPF the passive-interface command stops sending outgoing hello packets, hence the router can not form any neighbor relationship via the passive interface. This behavior stops both outgoing and incoming routing updates.

Question 2

Which functionality is required within an IP router that is situated at the boundary of an IPv4 network and an IPv6 network to allow communication between IPv6-only and IPv4-only nodes?

A. Autoconfiguration
B. Automatic 6to4 Tunnel
C. Automatic 6to4 Relay
D. Network Address Translator-Protocol Translator (NAT-PT)
E. Intrasite Automatic Tunnel Address Protocol (ISATAP)

 

Answer: D

Explanation

The Network Address Translator – Protocol Translator (NAT-PT) defines a set of network-layer translation mechanisms designed to allow nodes that only support IPv4 to communicate with nodes that only support IPv6, during the transition to the use of IPv6 in the Internet.

NAT-PT provides IPv4/IPv6 protocol translation. It resides within an IP router, situated at the boundary of an IPv4 network and an IPv6 network. By installing NAT-PT between an IPv4 and IPv6 network, all IPv4 users are given access to the IPv6 network without modification in the local IPv4-hosts (and vice versa). Equally, all hosts on the IPv6 network are given access to the IPv4 hosts without modification to the local IPv6-hosts. This is accomplished with a pool of IPv4 addresses for assignment to IPv6 nodes on a dynamic basis as sessions are initiated across IPv4-IPv6 boundaries

(Reference: http://www.ietf.org/rfc/rfc4966.txt and http://www.cisco.com/en/US/prod/collateral/iosswrel/ps8802/ps6969/ps1835/prod_white_paper09186a008011ff51_ps6640_Products_White_Paper.html)

Question 3

Which DSL encapsulation method requires client software running on the end-user PC that is directly connected to a DSL modem?

A. PPPoA
B. PPPoE
C. PPP
D. L2TP
E. ATM

 

Answer: B

Question 4

What is the purpose of configuring the router as a PPPoE client?

A. to provide VPN access over L2TP
B. to enable PPP session from the router to the termination device at the headend for metro Ethernet connectivity
C. for DSL connectivity and removing the need for the end-user PC to run the PPPoE client software
D. for connecting the router to a cable modem, which bridges the Ethernet frames from the router to the cable modem termination system

 

Answer: C

Question 5

What is the international standard for transmitting data over a cable system?

A. PPPoE
B. DOCSIS
C. CMTS
D. AAL5

 

Answer: B

Explanation

Data Over Cable Service Interface Specifications (DOCSIS) is a method for transporting data over a cable (CATV) plant utilizing QAM and/or QPSK RF modulatio. DOCSIS specifies modulation schemes and the protocol for exchanging bidirectional signals over cable. The DOCSIS has been approved as an international standard for transmitting data over cable systems.

Question 6

Under which circumstance will a branch ISR router contain interface vlan configurations?

A. performing inter-VLAN routing
B. performing 802.1Q trunking
C. performing ISL trunking
D. Ethernet Switch Module installed
E. ADSL WIC installed
F. running Call Manager Express

 

Answer: D

Explanation

An Integrated Services Router(ISR) router can be implemented an Ethernet Switch Module to perform both IP routing and inter-VLAN routing. With this module, an ISR router will contain interface vlan configurations.

Question 7

Which of the following are true? (choose three)

A. For Frame Relay point-to-point interfaces, set the bandwidth to the CIR.
B. For Frame Relay point-to-point interfaces set the bandwidth to the sum of all CIRs.
C. For Frame Relay multipoint connections, set the bandwidth to the sum of all CIRs.
D. For generic serial interfaces such as PPP and HDLC, set the bandwidth to match the line speed.
E. For Frame Relay multipoint connections, set the bandwidth to the CIR.

 

Answer: A C D

Question 8

Refer to the exhibit. What is the correct configuration to enable router R4 to exchange RIP routing updates with router R1 but not with router R3?

RIP_routing_updates_passive_interface.jpg

A.
R4(config)# interface fa0/0
R4(config-if)# neighbor 192.168.10.3
R4(config-if)# passive-interface fa0/0

B.
R4(config)# router rip
R4(config-router)#neighbor 192.168.10.3
R4(config-router)#passive-interface fa0/0

C.
R4(config)# interface fa0/0
R4(config-if)# neighbor 192.168.10.3
R4(config-if)# passive-interface 192.168.10.34

D.
R4(config)# router rip
R4(config-router)# neighbor 162.168.10.34 no broadcast
R4(config-router)#passive-interface fa0/0

 

Answer: B

Explanation

The “neighbor 192.168.10.3” command in RIP will make that router to send unicast update to 192.168.10.3 while the “passive-interface …” command is used to disable sending multicast or broadcast updates out of a specific interface. The key point here is the “passive-interface” still allows to send unicast update so it can be used along with the “neighbor …” command.

Question 9

Refer to exhibit. RA (DR) failed, and after 10 minutes it came back. Which two statements are true? (Choose two)

DR_DOTHER.jpg

A. RA is a DR
B. RA is a BDR
C. RA is a DROTHER
D. RB is a DR
E. RB is a BDR
F. RC is a DROTHER

 

Answer: C D(?)

Explanation

This question is missing some information. We don’t know before RA failed, who the BDR was. Suppose RB was the BDR before RA failed then RB would be the DR even when RA comes back. When RA comes back, its segment has both DR and BDR elected so RA will take the DROTHER role -> C is correct but D is missing information.

Question 10

A router has been configured to filter routes. Which of the following are reasons to control routing updates via route filtering? (Choose three)

A. to hide certain networks from the rest of organization
B. for easier implementations
C. to control network overhead on the wire
D. for simple security
E. to prevent adjacencies from forming

 

Answer: A C D

Operations Questions 2

April 30th, 2014 digitaltut No comments

Here you will find answers to Operation questions

Question 1

The Cisco ASA 500 Series Security Appliances are built specifically for businesses with less than 100 employees. What are three important benefits of this device? (Choose three)

A. business-grade firewall
B. premium support via SMART net
C. site-to-site VPN for remote offices
D. Cisco IOS software-based
E. email security
F. XML support

 

Answer: A C E

Question 2

Refer to the exhibit. Which interoperability technique implemented on the router would allow Host-1 to communicate with Host-2?

IPv6_IPv4_NAT_PT.jpg

A. Dual Stack
B. NAT-PT
C. 6to4 tunnel
D. GRE tunnel
E. ISATAP tunnel

 

Answer: B

Question 3

Which of the following NSAP addresses is a private, locally administered address?

A. 39.0f01.0002.0000.0c00.1111.00
B. 48.0f01.0002.0000.0c00.1111.00
C. 49.0004.30ac.0000.3090.c7df.00
D. 52.0f01.0002.0000.0c00.1111.00

 

Answer: C

Explanation

Network Service Address Point (NSAP) address is the equivalent of an IP address for an OSI network; A NSAP address is a hexadecimal address with a length of up to 40 hexadecimal digits. NSAP addresses are used in ATM and IS-IS.

Note: NSAP addresses are not present anymore in ROUTE exam, only old BSCI exam had it so we will not mention them much here. Maybe this question is old and you will not see it in ROUTE exam.

Question 4

How is network layer addressing accomplished in the OSI protocol suite?

A. Internet Protocol address
B. Media Access Control address
C. Packet Layer Protocol address
D. Network Service Access Point address
E. Authority and Format Identifier address

 

Answer: D

Explanation

Network Service Address Point (NSAP) address is the equivalent of an IP address for an OSI network; A NSAP address is a hexadecimal address with a length of up to 40 hexadecimal digits. NSAP addresses are used in ATM and IS-IS.

Question 5

Which routing protocol will continue to receive and process routing updates from neighbors after the passive-interface router configuration command is entered?

A. EIGRP
B. RIP
C. OSPF
D. IS-IS

 

Answer: B

Explanation

Unlike OSPF and EIGRP, RIP still receives and proceeds routing updates from neighbors even if the “passive-interface” command is configured on that router.

Question 6

Given the network diagram, which address would successfully summarize only the networks seen?

summarize_all_networks.jpg

A. 192.168.0.0/24
B. 192.168.8.0/20
C. 192.168.8.0/21
D. 192.168.12.0/20
E. 192.168.16.0/21
F. These networks cannot be summarized.

 

Answer: C

Distribute List Questions

April 29th, 2014 digitaltut No comments

Here you will find answers to Distribute List questions

Question 1

Refer to the exhibit. R1 and R2 belong to the RIP routing domain that includes the networks 10.20.0.0/16 and 10.21.0.0/16. R3 and R4 are performing two-way route redistribution between OSPF and RIP. A network administrator has discovered that R2 is receiving OSPF routes for the networks 10.20.0.0/16 and 10.21.0.0/16 and a routing loop has occurred.
Which action will correct this problem?

redistribute_RIP_OSPF_routing_loop.jpg

A. Apply an inbound ACL to the R2 serial interface.
B. Change the RIP administrative distance on R3 to 110.
C. Configure distribute-lists on R3 and R4.
D. Set the OSPF default metric to 20.
E. Change the OSPF administrative distance on R3 to 110.

 

Answer: C

Question 2

Refer to the exhibit. Which one statement is true?

distribute_list_traffic_blocked.jpg

A. Traffic from the 172.16.0.0/16 network will be blocked by the ACL.
B. The 10.0.0.0/8 network will not be advertised by Router B because the network statement for the 10.0.0.0/8 network is missing from Router
C. The 10.0.0.0/8 network will not be in the routing table on Router B.
D. Users on the 10.0.0.0/8 network can successfully ping users on the 192.168.5.0/24 network, but users on the 192.168.5.0/24 cannot successfully ping users on the 10.0.0.0/8 network.
E. Router B will not advertise the 10.0.0.0/8 network because it is blocked by the ACL.

 

Answer: E

Question 3

Based on the information in the exhibit, which statement is true?

distribute_list_access-list_routing_table.jpg

A. RTC will be able to access the 10.0.0.0 network.
B. RTC will not have the 10.0.0.0 network in its routing table.
C. RTC will not have the 192.168.10.0 network in its routing table.
D. RTB will not have the 10.0.0.0 network in its routing table.
E. RTB and RTC will not have the 10.0.0.0 network in their routing tables.

 

Answer: B

Explanation

The distribute list only permits network 192.168.10.0/24 to be sent out of interface S0/0 so RTC only receives advertisement of this network -> 10.0.0.0 network will not exist in the routing table of RTC.

Question 4

Study this exhibit below carefully. What is the effect of the distribute-list command in the R1 configuration?

distribute-list

A – R1 will permit only the 10.0.0.0/24 route in the R2 RIP updates
B – R1 will not filter any routes because there is no exact prefix match
C – R1 will filter the 10.1.0.0/24 and the 172.24.1.0/24 routes from the R2 RIP updates
D – R1 will filter only the 172.24.1.0/24 route from the P4S-R2 RIP updates

 

Answer: C

Explanation

The command “distribute-list 10 in Serial0” will create an incoming distribute list for interface serial 0 and refers to access list 10. So it will permit routing updates from 10.0.x.x network while other entries (in this case the 10.1.0.0/24 and 172.24.1.0/24 networks) will be filtered out from the routing update received on interface S0.

Question 5

Router RTA is configured as follows:
RTA (config)#router rip
RTA(config-router)#network 10.0.0.0
RTA(config-router)#distribute-list 44 in interface BRIO
RTA(config-router)#exit
RTA(config)#access-list 44 deny 172.16.1.0 0.0.0.255
RTA(config)#access-list 44 permit any

distribute_list_2

What are the effects of this RIP configuration on router RTA? (Choose two)

A – no routing updates will be sent from router RTA on interface BRIO to router RTX
B – router RTA will not advertise the 10.0.0.0 network to router RTX
C – the route to network 172.16.1.0 will not be entered into the routing table on router RTA
D – user traffic from the 172.16.1.0 network is denied by access-list 44
E – the routing table on router RTA will be updated with the route to router RTW

 

Answer: C E

Explanation

Distribute list are used to filter routing updates and they are based on access lists. In this case, an access list of 44 was created to deny the route from network 172.16.1.0/24 so this route will not be entered into the routing table of RTA. But the route from RTW can be entered because it is not filtered by the access list

A and B are not correct because the distribute list is applied to the inbound direction of interface BRI0 so outgoing routing updated will not be filtered.

D is not correct because distribute list just filters routing updates so user traffic from network 172.16.1.0 will not be denied.

IPSec and GRE

April 28th, 2014 digitaltut No comments

Here you will find answers to IPSec and GRE questions

Question 1

What two features are benefits of using GRE tunnels with IPsec over using IPsec tunnel alone for building site-to-site VPNs? (Choose two)

A. allows dynamic routing securely over the tunnel
B. IKE keepalives are unidirectional and sent every ten seconds
C. reduces IPsec headers overhead since tunnel mode is used
D. supports non-IP traffic over the tunnel
E. uses Virtual Tunnel Interface (VTI)to simplify the IPsec VPN configuration

 

Answer: A D

Explanation

A drawback of IPSec is it does not support multicast traffic. But most popular routing protocols nowadays rely on multicast (like OSPF, EIGRP, RIP… except BGP) to send their routing updates. A popular solution to this is using GRE tunnels. GRE tunnels do support transporting IP multicast and broadcast packets to the other end of the GRE tunnel -> A is correct.

Non-IP traffic (such as IPX, AppleTalk) can be wrapped inside GRE encapsulation and then this packet is subjected to IPSec encapsulation so all traffic can be routed -> D is correct.

Question 2

Which statement is true about an IPsec/GRE tunnel?

A. The GRE tunnel source and destination addresses are specified within the IPsec transform set.
B. An IPsec/GRE tunnel must use IPsec tunnel mode.
C. GRE encapsulation occurs before the IPsec encryption process.
D. Crypto map ACL is not needed to match which traffic will be protected.

 

Answer: C

Explanation

When running GRE tunnel over IPSec, a packet is first encapsulated in a GRE packet and then GRE is encrypted by IPSec -> C is correct.

Question 3

Which of the following is a GRE Tunnel characteristic?

A. GRE impose more CPU overhead than IPSec on VPN gateways
B. GRE tunnels can run through IPsec tunnels.
C. GRE Tunnel doesn’t have support for IPv6
D. GRE consists of two sub-protocols: Encapsulated Security Payload (ESP) and Authentication Header (AH).

 

Answer: B

 

Question 4

What is a key benefit of using a GRE tunnel to provide connectivity between branch offices and headquarters?

A. authentication, integrity checking, and confidentiality
B. less overhead
C. dynamic routing over the tunnel
D. granular QoS support
E. open standard
F. scalability

 

Answer: C

Explanation

GRE tunnel provides a way to encapsulate any network layer protocol over any other network layer protocol. GRE allows routers to act as if they have a virtual point-to-point connection to each other. GRE tunneling is accomplished by creating routable tunnel endpoints that operate on top of existing physical and/or other logical endpoints. Especially, IPsec does not support multicast traffic so GRE tunnel is a good solution instead (or we can combine both).

Question 5

What are the four main steps in configuring a GRE tunnel over IPsec on Cisco routers? (Choose four)

A. Configure a physical interface or create a loopback interface to use as the tunnel endpoint.
B. Create the GRE tunnel interfaces.
C. Add the tunnel interfaces to the routing process so that it exchanges routing updates across that interface.
D. Add the tunnel subnet to the routing process so that it exchanges routing updates across that interface.
E. Add all subnets to the crypto access-list, so that IPsec encrypts the GRE tunnel traffic.
F. Add GRE traffic to the crypto access-list, so that IPsec encrypts the GRE tunnel traffic.

 

Answer: A B D F

Explanation

Four steps to configure GRE tunnel over IPsec are:

1. Create a physical or loopback interface to use as the tunnel endpoint. Using a loopback rather than a physical interface adds stability to the configuration.
2. Create the GRE tunnel interfaces.
3. Add the tunnel subnet to the routing process so that it exchanges routing updates across that interface.
4. Add GRE traffic to the crypto access list, so that IPsec encrypts the GRE tunnel traffic.

An example of configuring GRE Tunnel is shown below:

interface Tunnel0
ip address 192.168.16.2 255.255.255.0
tunnel source FastEthernet1/0
tunnel destination 14.38.88.10
tunnel mode gre ip

Note: The last command is enabled by default so we can ignore it in the configuration)

(Reference: CCNP Routing and Switching Quick Reference)

Question 6

A network administrator uses GRE over IPSec to connect two branches together via VPN tunnel. Which one of the following is the reason for using GRE over IPSec?

A. GRE over IPSec provides better QoS mechanism and is faster than other WAN technologies.
B. GRE over IPSec decreases the overhead of the header.
C. GRE supports use of routing protocol, while IPSec supports encryption.
D. GRE supports encryption, while IPSec supports use of routing protocol.

 

Answer: C

Question 7

Refer to the exhibit. A new TAC engineer came to you for advice. A GRE over IPsec tunnel was configured, but the tunnel is not coming up.
What did the TAC engineer configure incorrectly?

GRE_over_IPsec_isakmp.jpg

A. The crypto map is not configured correctly.
B. The crypto ACL is not configured correctly.
C. The crypto map is not applied to the correct interface.
D. The OSPF network is not configured correctly.

 

Answer: B

Explanation

The access-list must also support GRE traffic with the “access-list 102 permit gre host 192.168.1.1 host 192.168.2.1” command -> B is correct.

Below is the correct configuration for GRE over IPsec on router B1 along with descriptions.

Configure_GRE_tunnel_over_IPsec.jpg

The interface tunnel configuration is rather simple so I don’t post it here.

Question 8

Refer to the exhibit. A new TAC engineer came to you for advice. A GRE over IPsec tunnel was configured, but the tunnel is not coming up.
What did the TAC engineer configure incorrectly?

GRE_over_IPsec_isakmp_2.jpg

A. The crypto isakmp configuration is not correct.
B. The crypto map configuration is not correct.
C. The interface tunnel configuration is not correct.
D. The network configuration is not correct; network 172.16.1.0 is missing

 

Answer: A

Explanation

The address of the crypto isakmp key should be 192.168.1.2, not 172.16.1.2 -> A is correct.

Question 9

Refer to the exhibit. A new TAC engineer came to you for advice. A GRE over IPsec tunnel was configured, but the tunnel is not coming up.
What did the TAC engineer configure incorrectly?

GRE_over_IPsec_isakmp_3.jpg

A. The crypto isakmp configuration is not correct.
B. The crypto map configuration is not correct.
C. The network 172.16.1.0 is not included in the OSPF process.
D. The interface tunnel configuration is not correct.

 

Answer: D

Explanation

The “tunnel destination” in interface tunnel should be 192.168.1.2, not 172.16.1.2 -> D is correct.

Question 10

For a GRE tunnel to be up between two routers, which of the following must be configured?

A. Loopback interface
B. IP reachability between the loopback interfaces
C. Dynamic Routing between routers.
D. Tunnel interfaces must be in the same subnet.

 

Answer: D

Question 11

Which two methods use IPsec to provide secure connectivity from the branch office to the headquarters office? (Choose two)

A. DMVPN
B. MPLS VPN
C. Virtual Tunnel Interface (VTI)
D. SSL VPN
E. PPPoE

 

Answer: A C

Explanation

The Dynamic Multipoint VPN (DMVPN) feature allows users to better scale large and small IPSec VPNs by combining generic routing encapsulation (GRE) tunnels, IPSec encryption, and Next Hop Resolution Protocol (NHRP) to provide users with easy configuration through crypto profiles, which override the requirement for defining static crypto maps, and dynamic discovery of tunnel endpoints.

(Reference: http://www.cisco.com/en/US/tech/tk583/tk372/technologies_configuration_example09186a008014bcd7.shtml)

The use of VTI greatly simplifies the configuration process when you need to configure IPsec. A major benefit associated with IPsec VTIs is that the configuration does not require a static mapping of IPsec sessions to a physical interface.

OSPF LSA Types Lab

April 27th, 2014 digitaltut 25 comments

In this lab we will learn when different types of LSA will be created. The main topic of this lab is LSA Types 1, 2, 3, 4, 5, 7. If you need to review your OSPF LSA Types knowledge, we recommend you to read our OSPF LSA Types Tutorial first.

Lab topology

OSPF_LSA_Types_Topology.jpg

You can download the initial configuration file of this lab here: http://www.digitaltut.com/download/OSPF_LSA_Types_Initial.zip.

Read more…

6to4 Tunnel

April 27th, 2014 digitaltut 4 comments

Here you will find answers to 6to4 Tunnel questions

Question 1

Refer to the exhibit. Which interoperability technique implemented on the dual-stack routers would allow connectivity between IPv6 sites across automatic created tunnels using the 2002::/16 prefix?

dual_stack_routers_6to4_tunnel.jpg

A. Dual Stack

B. NAT-PT

C. 6to4 tunnel

D. GRE tunnel

E. ISATAP tunnel

 

Answer: C

Explanation

6to4 tunnel is a technique which relies on reserved address space 2002::/16 (you must remember this range). These tunnels determine the appropriate destination address by combining the IPv6 prefix with the globally unique destination 6to4 border

router’s IPv4 address, beginning with the 2002::/16 prefix, in this format:

2002:border-router-IPv4-address::/48

For example, if the border-router-IPv4-address is 64.101.64.1, the tunnel interface will have an IPv6 prefix of 2002:4065:4001:1::/64, where 4065:4001 is the hexadecimal equivalent of 64.101.64.1.

Question 2

To configure 6to4 on a dual-stack edge router. Which three of the following are valid in 6to4 Tunneling configuration? (Choose three)

A. IPv4 Tunnel IP address

B. Tunnel mode (6to4)

C. Tunnel Keepalives

D. IPv4 Tunnel Destination

E. IPv4 Tunnel Source

F. 6to4 IPv6 address (within 2002::/16)

 

Answer: B E F

Question 3

Which three techniques can be used to transition from IPv4 to IPv6? (Select three)

A. Dual stack

B. NAT

C. Flow label

D. Mobile IP

E. 6to4 tunneling

F. Anycast

G. MBGP

 

Answer: A B E

Explanation

Dual stack is the most common technique which only requires edge routers to run both IPv4 and IPv6 while the inside routers only run IPv4. At the edge network, IPv4 packets are converted to IPv6 packets before sending out.

The Network Address Translator – Protocol Translator (NAT-PT) defines a set of network-layer translation mechanisms designed to allow nodes that only support IPv4 to communicate with nodes that only support IPv6, during the transition to the use of IPv6 in the Internet.

NAT-PT provides IPv4/IPv6 protocol translation. It resides within an IP router, situated at the boundary of an IPv4 network and an IPv6 network. By installing NAT-PT between an IPv4 and IPv6 network, all IPv4 users are given access to the IPv6 network without modification in the local IPv4-hosts (and vice versa). Equally, all hosts on the IPv6 network are given access to the IPv4 hosts without modification to the local IPv6-hosts. This is accomplished with a pool of IPv4 addresses for assignment to IPv6 nodes on a dynamic basis as sessions are initiated across IPv4-IPv6 boundaries

(Reference: http://www.ietf.org/rfc/rfc4966.txt and http://www.cisco.com/en/US/prod/collateral/iosswrel/ps8802/ps6969/ps1835/prod_white_paper09186a008011ff51_ps6640_Products_White_Paper.html)

6to4 tunnel is a technique which relies on reserved address space 2002::/16 (you must remember this range). These tunnels determine the appropriate destination address by combining the IPv6 prefix with the globally unique destination 6to4 border

router’s IPv4 address, beginning with the 2002::/16 prefix, in this format:

2002:border-router-IPv4-address::/48

For example, if the border-router-IPv4-address is 64.101.64.1, the tunnel interface will have an IPv6 prefix of 2002:4065:4001:1::/64, where 4065:4001 is the hexadecimal equivalent of 64.101.64.1.

Question 4

Which two statements about 6to4 tunneling are accurate? (Choose two)

A. Prepending a reserved IPv6 code to the hexadecimal representation of 192.168.0.1 facilitates 6to4 tunneling

B. Each 6to4 site receives a /48 prefix in a 6to4 tunnel

C. 2002::/48 is the address range specifically assigned to 6to4

D. Prepending 0x2002 with the IPv4 address creates an IPv6 address that is used in 6to4 tunneling

E. 6to4 is a manual tunnel method

 

Answer: B D

Explanation

6to4 tunnel is a technique which relies on reserved address space 2002::/16 (you must remember this range). These tunnels determine the appropriate destination address by combining the IPv6 prefix with the globally unique destination 6to4 border

router’s IPv4 address, beginning with the 2002::/16 prefix, in this format:

2002:border-router-IPv4-address::/48

Because the border-router-IPv4-address is added, we will have a /48 prefix (we all know an IPv4 address consists of 32 bits). An example of a 6to4 address with the border-router-IPv4-address of 192.168.1.2 is 2002:C0A8:01:02::/48.

Question 5

Which two statements are true about 6to4 tunnels? (Choose two)

A. In a 6to4 tunnel, the first two bytes of the IPv6 address will be 0x2002 and the next four bytes will be the hexadecimal equivalent of the IPv4 address.

B. In a 6to4 tunnel, the first two bytes of the IPv6 address will be locally derived and the next two bytes will be the hexadecimal equivalent of the IPv4 address.

C. In a 6to4 tunnel, the IPv4 address 192.168.99.1 would be converted to the 2002:c0a8:6301::/48 IPv6 address.

D. In a 6to4 tunnel, the IPv4 address 192.168.99.1 would be converted to the 2002:c0a8:6301::/16 IPv6 address.

E. In a 6to4 tunnel, the IPv4 address 192.168.99.1 would be converted to the 2002:1316:4463:1::/64 IPv6 address.

 

Answer: A C

Explanation

6to4 tunnel is a technique which relies on reserved address space 2002::/16 (you must remember this range). These tunnels determine the appropriate destination address by combining the IPv6 prefix with the globally unique destination 6to4 border

router’s IPv4 address, beginning with the 2002::/16 prefix, in this format:

2002:border-router-IPv4-address::/48

For example, if the border-router-IPv4-address is 64.101.64.1, the tunnel interface will have an IPv6 prefix of 2002:4065:4001:1::/64, where 4065:4001 is the hexadecimal equivalent of 64.101.64.1.

Question 6

When implementing a 6to4 tunnel, which IPv6 address is the correct translation of the IPv4 address 192.168.99.1?

A. c0a8:6301:2002::/48

B. 2002:c0a8:6301::/48

C. 2002:c0a8:6301::/8

D. 2002::/16

 

Answer: B

Question 7

Refer to the exhibit. If R1 is configured for 6to4 tunneling, what will the prefix of its IPv6 network be?

6to4_tunneling_IPv6_prefix.jpg

A. 1723:1100:1::/48

B. FFFF:AC1F:6401::/16

C. AC1F:6401::/32

D. 2002:AC1F:6401::/48

E. 3FFE:AC1F:6401::/32

 

Answer: D

Multicast Questions

April 26th, 2014 digitaltut No comments

Here you will find answers to Multicast questions

Question 1

A network administrator assigns a multicast address of 239.255.8.5 to an application running on a device with an Ethernet MAC address of 01.b2.7d.05.f1.80. Which Layer 2 multicast address will this device use?

A. 01.00.5e.7F.08.05
B. 01.b2.7d.05.f1.80
C. 01.b2.7d.0a.08.05
D. 01.00.5e.05.f1.80
E. ff.ff.ff.ff.ff.ff

 

Answer: A

Explanation

+ First convert the IP multicast address 239.255.8.5 to binary form:
1110 1111.1111 1111.0000 1000. 0000 0101

+ Next we separate the 23 low-order binary bits from the converted address:
1110 1111.1111 1111.0000 1000. 0000 0101

+ Drop other bits:
111 1111.0000 1000. 0000 0101

+ Convert these bits to hexadecimal:7F.08.05

+ We knew that the first 24 bits of this MAC address always begin with 01.00.5e (the organizationally unique identifier or OUI). So we just need to append the converted result with 01.00.5e to get the result:01.00.5e.7F.08.05. That is the official way to convert multicast IP address to multicast MAC address.

There is a shorter way to do this:
+ Convert 3rd and 4th octet directly to hex.
+ If the decimal value of 2nd octet is great than 128 then subtract it with 128 and convert it to hex. If not, convert it directly to hex.
+ Append your results with 01.00.5e.

Question 2

Which three statements are true about IP multicast configuration? (Choose three)

A. PIM sparse-dense mode and PIM dense mode require an RP on the network.
B. PIM sparse mode and PIM dense mode require an RP on the network.
C. PIM sparse mode interfaces are always added to the multicast routing table in a router.
D. PIM sparse mode and PIM sparse-dense mode require an RP on the network.
E. PIM dense mode interfaces are always added to the multicast routing table in a router.
F. PIM sparse-dense mode acts as PIM dense mode if an RP is not known.

 

Answer: D E F

Explanation

A rendezvous point (RP) is required only in networks running Protocol Independent Multicast sparse mode (PIM-SM) -> A & B are not correct.

In PIM-SM, only network segments with active receivers that have explicitly requested multicast data will be forwarded the traffic. This method of delivering multicast data is in contrast to the PIM dense mode (PIM-DM) model. In PIM-DM, multicast traffic is initially flooded to all segments of the network. Routers that have no downstream neighbors or directly connected receivers prune back the unwanted traffic -> C is not correct

In populating the multicast routing table, dense-mode interfaces are always added to the table. Sparse-mode interfaces are added to the table only when periodic join messages are received from downstream routers, or there is a directly connected member on the interface -> E is correct.

An interface configured in sparse-dense mode is treated in either sparse mode or dense mode of operation, depending on which mode the multicast group operates. If a multicast group has a known RP, the interface is treated in sparse mode. If a group has no known RP, the interface is treated in dense mode and data will be flooded over this interface -> F is correct.

In fact answer D and F seem to contradict with each other. But if we have to choose 3 answers, D is the best option left after eliminating the three other answers.

(Reference: Cisco IOS 12.0 Solutions for Network Protocols, Volume 1)

Policy Based Routing Lab

March 24th, 2014 digitaltut 12 comments

In this lab we will learn how to use Policy Based Routing to send traffic via the route we want.

Policy_Based_Routing_Topology.jpg

IOS used: c3640-jk9s-mz.124-16.bin

Tasks
+ Enable OSPF on all interfaces of R2, R3, R4, R5 using only one command on each router.
+ Create Policy Based Routing on R2 so that traffic from R1 to the Loopback interface of R5 (5.5.5.5) must go through R3 (the less optimal path).

You can download the Initial Config Lab here: http://www.digitaltut.com/download/Policy_Based_Routing_Lab_Initial.zip.

Read more…

Auto and Manual Summary Routes to Null0 with EIGRP

October 21st, 2012 digitaltut 5 comments

In this small lab we are going to see and learn about the Null0 when a summarized route is created. The topology is simple with only two routers.

Auto_Manual_Summary_Routes_Null0_topology.jpgThe purpose of this lab is to summarize all Loopback interfaces on R2 via auto and manual summarization and advertise it to R1.

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OSPF EIGRP Redistribute Lab

October 1st, 2012 digitaltut 14 comments

In this GNS3 lab we will learn how to redistribute from EIGRP into OSPF and vice versa. Below is the topology used in this lab:

OSPF_EIGRP_Redistribute_topology.jpg

The purposes of this sim are:
+ Redistribute from EIGRP to OSPF and vice versa.
+ Traffic from R1 to R4 must go through the best path (after redistribution, traffic from R1 will go R1 -> R2 -> R4; this is not the most optimal path as it must go through 2 serial links. The best path is R1 -> R2 -> R3 -> R4 and we have to configure the routers to complete this task.)

You can download the initial configuration of this lab here: http://www.digitaltut.com/download/EIGRP_OSPF_Redistribute_initial_configs.zip.

Initial Configurations (which have not had the redistribute command yet):

R1(config)#interface s0/0
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no shut
R1(config-if)#exit
R1(config)#router eigrp 100
R1(config-router)#network 192.168.1.0
R2(config)#interface s0/1
R2(config-if)#ip address 192.168.1.2 255.255.255.0
R2(config-if)#no shut
R2(config-if)#interface f1/0
R2(config-if)#ip address 192.168.2.2 255.255.255.0
R2(config-if)#no shut
R2(config-if)#interface s0/0
R2(config-if)#ip address 192.168.3.2 255.255.255.0
R2(config-if)#no shut
R2(config-if)#exit
R2(config)#router eigrp 100
R2(config-router)#network 192.168.1.0
R2(config-router)#network 192.168.2.0
R2(config-router)#exit
R2(config)#router ospf 1
R2(config-router)#network 192.168.3.0 0.0.0.255 area 24
R3(config)#interface f0/0
R3(config-if)#ip address 192.168.2.3 255.255.255.0
R3(config-if)#no shut
R3(config-if)#interface f1/0
R3(config-if)#ip address 192.168.4.3 255.255.255.0
R3(config-if)#no shut
R3(config-if)#exit
R3(config)#router eigrp 100
R3(config-router)#network 192.168.2.0
R3(config-router)#exit
R3(config)#router ospf 1
R3(config-router)#network 192.168.4.0 0.0.0.255 area 34

R4(config)#interface s0/0
R4(config-if)#ip address 192.168.3.4 255.255.255.0
R3(config-if)#interface f1/0
R3(config-if)#ip address 192.168.4.4 255.255.255.0
R4(config-if)#no shut
R3(config-if)#interface loopback0
R3(config-if)#ip address 172.16.100.1 255.255.255.0
R4(config-if)#exit
R4(config)#router ospf 1
R4(config-router)#network 192.168.3.0 0.0.0.255 area 24
R4(config-router)#network 192.168.4.0 0.0.0.255 area 34
R4(config-router)#network 172.16.100.0 0.0.0.255 area 0

After finishing the initial commands above, the routing tables of each router are shown below:

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BGP Route map and MED – GNS3 Lab

March 21st, 2012 digitaltut 6 comments

In this lab we will learn how to use Route map to set MED attribute to tell which path the neighbor should choose to a specific network.

Topology:

BGP_Route_map_MED_topology.jpg

IOS used in this lab: c3640-jk9s-mz.124-16.bin

Tasks in this lab:

1) Set up basic IBGP & EBGP
2) Advertise loopback 1 & loopback 10 on R1
3) Use route-maps on R2 & R3 to set MED for only 192.168.1.0, verify on R6 and will R6 see network 192.168.10.0?

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BGP Summary Route

March 4th, 2012 digitaltut 4 comments

In this lab we will learn how to aggregate (summarize) small networks into a bigger one. Below is the topology used in this GNS3 lab.

BGP_aggregate_topology.jpg

IOS used: c3640-jk9s-mz.124-16.bin

Task: Summary networks 10.10.10.0/24 & 10.10.20.0/24 into 10.10.0.0/16

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Use Distribute-list to filter Routing Updates in BGP

March 2nd, 2012 digitaltut 5 comments

In this lab we will learn how to use distribute-list to filter unwanted routes in BGP. Below is the topology of this lab:

BGP_community_topology.jpg

IOS used in this lab: c3640-jk9s-mz.124-16.bin

Objectives of this lab:
+ Task 1: Configure EBGP on AS 1, AS 23, AS 4 and configure IBGP between R2 & R3 (AS23), also advertise loopback 0 interface on R1 so that all the routers learn about this network.
+ Task 2: Use a distribute-list to filter out network 1.1.1.0

Let’s start our lab!

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BGP next-hop-self, community no-export & send-community – GNS3 Lab

February 29th, 2012 digitaltut 5 comments

In this GNS3 lab we will learn how to establish neighborship between routers running BGP and use BGP attributes to control how a route is advertised to its neighbors. In this lab I wish to show how to create a basic “BGP network” and explain about next-hop-self, community no-export & send-community features in BGP. Below is the topology of this lab:

BGP_community_topology.jpg

IOS used in this lab: c3640-jk9s-mz.124-16.bin

Objectives of this lab:
+ Task 1: Configure EBGP on AS 1, AS 23, AS 4 and configure IBGP between R2 & R3 (AS23)
+ Task 2: Advertise loopback0 on R1 to R4 and make sure R4 can ping to that loopback interface (AS23 becomes a transit AS)
+ Task 3: Make AS 23 not a transit AS by using the feature “community no-export”

Read more…

Redistribute EIGRP and OSPF – GNS3 Lab

January 18th, 2012 digitaltut 2 comments

In this GNS3 lab we will learn how to redistribute from EIGRP into OSPF and vice versa. Below is the topology used in this lab:

Redistribute_EIGRP_OSPF_Topology.jpg

First we assign IP addresses to all interfaces on the routers. Notice the 4th octet of the IP address of each router has the same value of the name of that router (for example R2 has 2 interfaces 12.12.12.2 & 23.23.23.2; R3 has 2 interfaces 23.23.23.3 & 34.34.34.3…)

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Configure Static Route – GNS3 Lab

October 1st, 2010 digitaltut 1 comment

In this tutorial we will connect two routers via static route with GNS3.

Static route and Dynamic route

Static route tells the device exactly where to send traffic, no matter what. Static route is often used when your network has only a few routers or there is only one route from a source to a destination. Dynamic routes, on the other hand, use a routing protocol to determine the best path and the routes can be changed depending on specific parameters (like bandwidth, delay, cost…). With dynamic routes, routers can communicate with each other to exchange routing information. In ROUTE 642-902 you will learn about dynamic routing protocols such as OSPF, EIGRP and BGP (RIP is also a dynamic routing protocol but it is not mentioned in ROUTE).

The simple syntax of static route:

ip route <destination><subnet mask><next hop IP address or outbound interface>

Now we consider a real-world example of static routing. Suppose that your company has 2 branches located in New York and Chicago. As the administrator of the network, you are tasked to connect them so that employees in the two LANs can communicate with each other. After careful consideration you decided to connect them via static route.

Configure_Static_Route_topology.jpg

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Configure Cisco Router Passwords – GNS3 Lab

September 23rd, 2010 digitaltut 2 comments

In this tutorial we will use GNS3 to do a very basic task to secure your routers – apply a password so that users will be asked for this password when try to enter the privileged mode. For example:


Router>enable
Password: ******* (enter that password here)
Router# (this is the privileged mode)

Now let’s start!

First launch the GNS3, for this tutorial I use the IOS c2600-bin-mz.123-6f.bin but this is a very fundamental lab so you can use any IOS you have.

1. Drag the Router c2600 the place it onto the right-side box,
2. Click the Start button (the green triangle button)
3. Click the Telnet to all IOS button (the black button) to open the Telnet command line interface (CLI).

Configure_Password1.jpg

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