ROUTE 642-902 Training

(Reference: http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-tunnel_ps6441_TSD_Products_Configuration_Guide_Chapter.html#wp1055515)

Policy Based Routing Sim

OSPF Questions

digitaltut — Wed, 20 Jul 2011 08:12:19 +0000

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?

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?

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?

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?

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?

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

digitaltut — Tue, 19 Jul 2011 09:18:02 +0000

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?

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?

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 R3 has been configured as a stub for Area 5. This will drop down the neighbor relationship between R3 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.

OSPF Questions 3

digitaltut — Mon, 18 Jul 2011 10:13:17 +0000

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:

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?

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

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.

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.

OSPF Questions 4

digitaltut — Sun, 17 Jul 2011 16:42:07 +0000

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)

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?

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 OSPF routers 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

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:

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?

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

digitaltut — Sat, 16 Jul 2011 14:07:18 +0000

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?

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 not 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?

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?

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: 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.

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?

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?

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

digitaltut — Fri, 15 Jul 2011 06:38:53 +0000

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?

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?

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

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)

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?

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)

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?

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:

+ 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):

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:

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)

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

digitaltut — Thu, 14 Jul 2011 13:33:45 +0000

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?

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?

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

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)

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:

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

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:

Question 6

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

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?

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?

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?

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 3 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)

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)

Answer: A D

BGP Questions

digitaltut — Sun, 10 Jul 2011 08:09:47 +0000

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)

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?

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?

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 bettwe 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)

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 can not 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

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

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)

Redistribute Questions

digitaltut — Sat, 09 Jul 2011 13:54:55 +0000

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 0.0.0.0 255.255.224.0 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)

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?

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)

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?

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)

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

digitaltut — Fri, 08 Jul 2011 13:07:44 +0000

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?

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?

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?

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)

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?

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?

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?

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)

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

digitaltut — Thu, 07 Jul 2011 15:43:00 +0000

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?

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?

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?

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?

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

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)

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

+ 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?

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.

IPv6 Questions

digitaltut — Fri, 01 Jul 2011 08:05:19 +0000

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)

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:

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?

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

digitaltut — Thu, 30 Jun 2011 14:32:02 +0000

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?

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.

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:

(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

digitaltut — Tue, 28 Jun 2011 05:32:28 +0000

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.

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.

Operations Questions

digitaltut — Fri, 24 Jun 2011 07:57:59 +0000

Here you will find answers to Operation questions

Question 1

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

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 2

Study this exhibit below carefully. What is the effect of the distribute-list command in the R1 configuration?

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 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 s0/0 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 4

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

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.

Question 5

Look at the following exhibit. Which of the following correctly states the routes to be redistributed into OSPF? (Choose two)

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

Configure Static Route – GNS3 Lab

digitaltut — Fri, 01 Oct 2010 09:58:44 +0000

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

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.

In GNS3, place 2 routers and connect them as the image below, I used IOS c2600-bin-mz.123-6f.bin to save some RAM (only require 64MB/router). We will use two loopback interfaces to simulate two Ethernet LANs.

Configuring interfaces on R0

R0(config)#interface s0/0
R0(config-if)#ip address 12.12.12.1 255.255.255.0
R0(config-if)#no shutdown
R0(config-if)#interface lo0
R0(config-if)#ip address 10.0.0.1 255.0.0.0
R0(config-if)#exit

Configuring interfaces on R1

R0(config)#interface s0/0
R0(config-if)#ip address 12.12.12.2 255.255.255.0
R0(config-if)#no shutdown
R0(config-if)#interface lo0
R0(config-if)#ip address 172.16.0.1 255.255.0.0
R0(config-if)#exit

Now if we check the routing table of R0 & R1 by the command show ip route on both R0 and R1

On R0:
R0# show ip route

The letter “C” means “connected” or “directly connected”. So there are 2 networks that are directly connected to R0: 10.0.0.0/8 and 12.12.12.0

On R1

R1# show ip route

Configuring static route on R0

R0(config)#ip route 172.16.0.0 255.255.0.0 12.12.12.2

Configuring static route on R1

R1(config)#ip route 10.0.0.0 255.0.0.0 12.12.12.1

Notice that static route works one-way. It means we have to add static route to both R0 and R1 so that R0 and R1 can communicate.

Now try to ping each far end network

(Note: In fact, R0 can successfully ping R1 right after adding the static route to R0)

Administrative distance of a static route.

After adding two static routes in R0 & R1 routers, the routing tables of two routers contain these lines:

S 10.0.0.0/8 [1/0] via 12.12.12.1 (on R1)
S 172.16.0.0/16 [1/0] via 12.12.12.2 (on R0)

The “S” letter tells us this is a static route. The networks 10.0.0.0/8 and 172.16.0.0/16 are the destinations of this static route and if the routers want to reach them they must send packets to 12.12.12.1 (on R1) and 12.12.12.2 (on R2). These parameters are straightforward and easy to understand. But what is [1/0]? Well, 1 is the administrative distance (AD) and 0 is the metric of that static route.

The administrative distance is a measure of trustworthiness where lower numbers are considered to be more trustworthy than higher numbers. The route with the lowest administrative distance value is the preferred route that the router selects. Administrative distance is the value from 0 to 255.

Directly connected routes have an administrative distance of 0. Static routes have an administrative distance
of 1 so in the outputs above you will see the administrative distance of both static routes are 1.

The router treats a static route pointing to an interface the same as a connected interface so the its AD is 0. If you configure a static route pointing to an exiting interface (for example: “ip route 172.16.0.0 255.255.0.0 s0/0” on R0) then the AD will not be shown.

(For your information, EIGRP has an administrative distance of 90. IGRP has an administrative distance of 100. OSPF has an administrative distance of 110. And RIP has an administrative distance of 120)

Configure Cisco Router Passwords – GNS3 Lab

digitaltut — Thu, 23 Sep 2010 09:17:28 +0000

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).

The CLI window will appear, asking “Would you like to enter the initial configuration dialog? [yes/no]:”. Type n here as we want to configure this router manually.

Wait for a few seconds and now the router will be ready for the configuration.

Router>enable
Router#configure terminal (or type conf t as a shortcut)
Router(config)#enable password digitaltut
Router(config)#exit (or press Ctrl-Z)
Router#exit (to exit privileged mode)

We logged out the router, notice that you will see two lines “Router con0 is now available” and “Press RETURN to get started.” Press Enter to enter the user mode (a line Router> will appear)

Now we can test if the password is working. Log in the privileged mode with the enable command

Router>enable

Now we can see the router is asking for a password. Type “digitaltut” as its password here and we can log in to the privileged mode

Notice that we with the “enable password” command, the router will save our password in plain text. It means if someone types show running-config on our router, they can see our password.

Router#show running-config (or show run)

This is a thing we don’t want as our router is not secured completely. In fact, most of the administrators use the “enable secret” command nowadays. To do it, in the privileged mode type the following commands:

Router#config terminal
Router(config)#enable secret digitaltutSecret (notice the letter “S” is capital)
Router(config)#exit
Router#exit

Now try to log in the privileged mode again (type enable in the user mode). First, try the password digitaltut again; the router will not accept this password anymore. Now type digitaltutSecret and we can login! (make sure you capitalize the letter S).

So notice that if you configure the enable secret command, it takes precedence over the enable password command. The two commands cannot be in effect simultaneously.

The enable secret command will encrypt the password so no one can see the password with the show running-config command. We can check it.

Router#show running-config

We can also set the password for console and vty (telnet) login with these commands:

Set console password:
Router#config terminal
Router(config)#line console 0
Router(config-line)#password cisco
Router(config-line)#login
Router(config-line)#exit

Set vty (virtual terminal lines) password:
Router#config terminal
Router(config)#line vty 0 4
Router(config-line)#password cisco
Router(config-line)#login
Router(config-line)#exit

By default, a Cisco router supports 5 simultaneous telnet sessions. By using the command line vty 0 4, the configuration below will be applied to all 5 sessions (line 0 to line 4).

Notice these passwords are not encrypted and we can see them with the “show running-config” command. We can encrypt all the passwords with the service password-encryption command in global configuration mode

Router(config)# service password-encryption

Another notice is that we can’t login to a Cisco router via telnet if we don’t set a vty line password for it.

EIGRP OSPF Redistribution Sim

digitaltut — Sat, 31 Jul 2010 20:19:00 +0000

Question: (Hope someone will contribute the detailed requirement of this sim!)

Some information I have gathered so far:

R2 is an ASBR for EIGRP 100 and OSPF AREA 24

R3 is an ASBR for EIGRP 100 and OSPF AREA 34

[note: so there are TWO separate areas on TWO separate ASBRS

thus you need to do redistribution on R2 and R3

R1 is ONLY in EIGRP 100, and is THE ONLY router you can ping from. R4 has a loopback interface that must be pinged from R1.

R4 is running OSPF and has redundant link to EIGRP network over R3 router.

Notice: You should make a ping from R1 to 172.16.100.1 network to make sure everything is working correctly.

Answer and Explanation:

Thanks to POONAM who send us the topology and configuration. He got 100% on EIGRP-OSPF lab so this solution is perfect! Please say thank to him and others who contribute this lab-sim!

SOLUTION from POONAM

First we need to find out 5 parameters (Bandwidth, Delay, Reliability, Load, MTU) of the s0/0/0 interface (the interface of R2 connected to R4) for redistribution :

R2#show interface s0/0/0

Write down these 5 parameters, notice that we have to divide the Delay by 10 because its metric unit is tens of microsecond. For example, we get Bandwidth=1544 Kbit, Delay=20000 us, Reliability=255, Load=1, MTU=1500 bytes then we would redistribute as follows:

R2#config terminal

R2(config)# router ospf 1

R2(config-router)# redistribute eigrp 100 metric-type 1 subnets

R2(config-router)#exit

R2(config-router)#router eigrp 100

R2(config-router)#redistribute ospf 1 metric 1544 2000 255 1 1500

(Notice: In fact, these parameters are just used for reference and we can use other parameters with no problem. Also, a candidate said that the simulator didn’t accept the Bandwidth of 1544; in that case, we can use a lower value, like 128.

If the delay is 20000us then we need to divide it by 10, that is 20000 / 10 = 2000)

For R3 we use the show interface fa0/0 to get 5 parameters too

R3#show interface fa0/0

For example we get Bandwidth=10000 Kbit, Delay=1000 us, Reliability=255, Load=1, MTU=1500 bytes

R3#config terminal

R3(config)#router ospf 1

R3(config-router)#redistribute eigrp 100 metric-type 1 subnets

R3(config)#exit

R3(config-router)#router eigrp 100

R3(config-router)#redistribute ospf 1 metric 10000 100 255 1 1500

Finally you should try to “show ip route” to see the 172.16.100.1 network (the network behind R4) in the routing table of R1 and make a ping from R1 to this network.

Maybe the “copy running-config startup-config” command will not work in this lab so don’t worry, just skip it.

WISH U A VERY BEST GUYS………..

GO ROCK…

Other lab-sims on this site:

EIGRP Simlet

Policy Based Routing Sim

digitaltut — Sat, 31 Jul 2010 08:40:45 +0000

Question

Company Acan has two links which can take it to the Internet. The company policy demands that you use web traffic to be forwarded only to Frame Relay link if available and other traffic can go through any links. No static or default routing is allowed.

Answer and Explanation:

Notice: The answer and explanation below are from PeterPan and Helper.Please say thank to them!

All the HTTP traffic from the EIGRP Network should go through Frame Relay link if available and all the other traffic should go through either link.
The only router you are able to administrate is the Border Router, from the EIGRP Network you may only send HTTP traffic. As the other people mentioned, actually it is not a BGP lab. You are not able to execute the command “router bgp 65001″

1) Access list that catches the HTTP traffic:
BorderRouter#access-list 101 permit tcp any any eq www

Note that the server was not directly connected to the Border Router. There were a lot of EIGRP routes on it. In the real exam you do not know the exact IP address of the server in the EIGRP network so we have to use the source as “any” to catch all the source addresses.

2) Route map that sets the next hop address to be ISP1 and permits the rest of the traffic:
BorderRouter(config)#route-map pbr permit 10
BorderRouter(config-route-map)#match ip address 101
BorderRouter(config-route-map)#set ip next-hop 10.1.101.1
BorderRouter(config-route-map)#exit
BorderRouter(config)#route-map pbr permit 20

(Notice: the route-map pbr permit 20 line allows other traffic than HTTP to be routed. Otherwise, other traffic will be dropped)

3) Apply the route-map on the interface to the server in the EIGRP Network:
BorderRouter(config-route-map)#exit
BorderRouter(config)#int fa0/0
BorderRouter(config-if)#ip policy route-map pbr
BorderRouter(config-if)#exit
BorderRouter(config)#exit

4) There is a “Host for Testing”, click on this host to open a box in which there is a button named “Generate HTTP traffic”. Click on this button to generate some packets for HTTP traffic. Jump back to the BorderRouter and type the command “show route-map”.

BorderRouter#show route-map

In the output you will see the line “Policy routing matches: 9 packets…”. It means that the route-map we configured is working properly.

Other lab-sims on this site:

EIGRP Simlet

IPv6 OSPF Virtual Link Sim

digitaltut — Sat, 31 Jul 2010 08:35:27 +0000

Question

Acme is a small export company that has an existing enterprise network that is running IPv6 OSPFv3. Currently OSPF is configured on all routers. However, R4′s loopback address (FEC0:4:4) cannot be seen in R1′s IPv6 routing table. You are tasked with identifying the cause of this fault and implementing the needed corrective actions that uses OSPF features and does no change the current area assignments. You will know that you have corrected the fault when R4′s loopback address (FEC0:4:4) can be seen in the routing table of R1.

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:

To troubleshoot the problem, first issue the show running-config on all of 4 routers. Pay more attention to the outputs of routers R2 and R3

The output of the “show running-config” command of R2:

The output of the “show running-config” command of R3:

We knew that all areas in an Open Shortest Path First (OSPF) autonomous system must be physically connected to the backbone area (Area 0). In some cases, where this is not possible,we can use a virtual link to connect to the backbone through a non-backbone area. The area through which you configure the virtual link is known as a transit area. In this case, the area 11 will become the transit area. Therefore, routers R2 and R3 must be configured with the area area-id virtual-link neighbor-router-id command.

+ Configure virtual link on R2 (from the first output above, we learned that the OSPF process ID of R2 is 1):

R2>enable
R2#configure terminal
R2(config)#ipv6 router ospf 1
R2(config-rtr)#area 11 virtual-link 3.3.3.3

(Notice that we have to use neighbor router-id 3.3.3.3, not R2′s router-id 2.2.2.2)

+ Configure virtual link on R3 (from the second output above, we learned that the OSPF process ID of R3 is 1 and we have to disable the wrong configuration of “area 54 virtual-link 4.4.4.4″):

R3>enable
R3#configure terminal
R3(config)#ipv6 router ospf 1
R3(config-rtr)#no area 54 virtual-link 4.4.4.4
R3(config-rtr)#area 11 virtual-link 2.2.2.2

We should check the configuration on R4:

R4>enable
R4#show running-config

You will see a wrongly configured virtual-link command. To get full mark we have to disable this command:

R4#configure terminal
R4(config)#ipv6 router ospf 1
R4(config-rtr)#no area 54 virtual-link 3.3.3.3

After finishing the configuration don’t forget to ping between R1 and R4 to make sure they work well!

Now all the configuration was done. It is weird that we can’t ping the IPv6 loopback interface of R4 (with the ping or ping ipv6 command) but we can check by using the command show ipv6 route on R1

The copying running-config startup-config command will not work but don’t worry, just skip it.

Notice: If you issue the command “show running-config” on R1, you will see these two lines:

passive-interface default
no passive-interface fa0/0 (fa0/0 is the interface connecting with R2)

These two lines make all the interfaces of R1 become passive interfaces except interface fa0/0. They are correctly configured so don’t try to disable them.

Other lab-sims on this site:

EIGRP Simlet
Policy Based Routing Sim

EIGRP Stub Sim

digitaltut — Sat, 31 Jul 2010 08:24:30 +0000

Question

By increasing the first distant office, JS manufactures has extended their business. They configured the remote office router (R3) from which they can reach all Corporate subnets. In order to raise network stableness and lower the memory usage and broadband utilization to R3, JS manufactures makes use of route summarization together with the EIGRP Stub Routing feature. Another network engineer is responsible for the implementing of this solution. However, in the process of configuring EIGRP stub routing connectivity with the remote network devices off of R3 has been missing.

Presently JS 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:

First we have to figure out why R3 and R4 can not communicate with each other. Use the show running-config command on router R3

Notice that R3 is configured as a stub receive-only router. The receive-only keyword will restrict the router from sharing any of its routes with any other router in that EIGRP autonomous system. This keyword will also prevent any type of route from being sent.

Therefore we will remove this command and replace it with the eigrp stub command:

R3#configure terminal
R3(config)#router eigrp 123
R3(config-router)#no eigrp stub receive-only
R3(config-router)#eigrp stub
R3(config-router)#end

Now R3 will send updates containing its connected and summary routes to other routers. Notice that the eigrp stub command equals to the eigrp stub connected summary because the connected and summary options are enabled by default.

Next we will configure router R3 so that it has only 2 subnets of 10.0.0.0 network. Use the show ip route command on R3 to view its routing table

R3#show ip route

Because we want the routing table of R3 only have 2 subnets so we have to summary sub-networks at the interface which is connected with R3, the s0/0 interface of R4.

There is one interesting thing about the output of the show ip route shown above: the 10.2.3.0/24, which is a directly connected network of R3. We can’t get rid of it in the routing table no matter what technique we use to summary the networks. Therefore, to make the routing table of R3 has only 2 subnets we have to summary other subnets into one subnet.

In the output if we don’t see the summary line (like 10.0.0.0/8 is a summary…) then we should use the command ip summary-address eigrp 123 10.2.0.0 255.255.0.0 so that all the ping can work well.

In conclusion, we will use the ip summary-address eigrp 123 10.2.0.0 255.255.0.0 at the interface s0/0 of R4 to summary.

R4>enable
R4#configure terminal
R4(config)#interface s0/0
R4(config-if)#ip summary-address eigrp 123 10.2.0.0 255.255.0.0

Now we jump back to R3 and use the show ip route command to verify the effect, the output is shown below:

(But please notice that the ip addresses and the subnet masks in your real exam might be different so you might use different ones to solve this question)

But in your real exam, if you see the line “10.0.0.0/8 is a summary,….Null0″ then you need to summary using the network 10.0.0.0/8 with the command “ip summary-address eigrp 123 10.0.0.0 255.0.0.0″ . This configuration is less optimize than the first but it summaries into 2 subnets as the question requires (maybe you will not see this case, don’t worry!).

The command “copy running-config startup-config” will not work so try using this command; just skip if it doesn’t work.

Other lab-sims on this site:

EIGRP Simlet
Policy Based Routing Sim

OSPF Sim

digitaltut — Sat, 31 Jul 2010 08:20:45 +0000

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.

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:

First, we configure Portland’s S0/0 interface so that it belongs to Area 1. So, we have to find out which sub-network the IP address 192.168.4.5/30 (the IP of interface S0/0 of Portland) belongs to. This address belongs to a subnetwork which has:

Increment: 4 (/30 = 255.255.255.252 or 1111 1111.1111 1111.1111 1111.1111 1100)
Network address: 192.168.4.4 (because 4 = 4 * 1 and 4 < 5)
Broadcast address: 192.168.4.7 (because 7 = 4 + 4 – 1) (It is not necessary to find out the broadcast address but we should know it)

The question requires that only Portland’s S0/0 and Amani’s S0/1 could be in Area 1, therefore we must use a wildcard of 0.0.0.3 (this wildcard is equivalent with a subnet mask of /30) so that there are only 2 IP addresses can participate in area 1 (they are 192.168.4.5 & 192.168.4.6). The full command we use here is network 192.168.4.4 0.0.0.3 area 1

The question also requires that “Area 1 should not receive any external or inter-area routes (except the default route)”. Recall that if we don’t want the router to receive external routes, we have to stop LSA Type 5. And if we don’t want to receive inter-area routes, we have to stop LSA Type 3 and Type 4. Therefore we have to configure area 1 as a totally stubby area. For your information, here is the definition of a totally stubby area:

“Totally stubb area – This area does not accept summary LSAs from other areas (types 3 or 4) or external summary LSAs (Type 5). Types 3,4 and 5 LSAs are replaced by the Area Border Router(ABR) with a default router. Totally stubby areas protect internal routers by minimizing the routing table and summarizing everything outside the area with a default route.” (CCNP BSCI Official Exam Certification Guide, Fourth Edition)

In conclusion, we have to configure area 1 as a totally stubby area. We do that by configuring Portland as stub and configuring Amani (ABR router) as a stub + “no-summary”suffix.

+ Configure Portland router as a stub:

Portland#configure terminal
Portland(config)#router ospf 1

Allow network 192.168.4.4/30 to join Area 1, notice that you have to convert subnet mask into wildcard mask:

Portland(config-router)#network 192.168.4.4 0.0.0.3 area 1

Configure Portland as a stub:

Portland(config-router)#area 1 stub

Portland(config-router)#end
Portland#copy running-config startup-config

+ Configure Amani router as a “totally stub”:

Amani#configure terminal
Amani(config)#router ospf 1
Amani(config-router)#network 192.168.4.4 0.0.0.3 area 1

Make area 1 become a totally stubby area, notice that we can only use this command on ABR router:

Amani(config-router)#area 1 stub no-summary

Amani(config-router)#end
Amani#copy running-config startup-config

Other lab-sims on this site: