The purpose of this lab is to summarize all Loopback interfaces on R2 via auto and manual summarization and advertise it to R1.

In this topology R2 has three loopback interfaces. Instead of advertising all we will summarize these loopback interfaces before sending out to R1. And we will test the effect with auto summarization and manual summarization on R2.

First I listed the initial configuration on both routers, including IP address assignments and EIGRP configuration:

Auto summarization

By default, the “auto-summary” command is enabled on R2 so R2 will summarize the loopback interfaces’ networks and advertise to R1 as 10.0.0.0/8 because it goes cross a different major network 192.168.1.0/24. Therefore in the routing table of R1 we only see 1 summarized route:

Now on R2 we can see the Null0 has been created:

So, why is a route to Null0 created? Now let’s take an example to understand the importance of this route. We suppose the “10.0.0.0/8 is a summary… Null0″ line does not exist in the routing table of R2 and R1 needs to send traffic to 10.4.0.1. It looks up its routing table and see that the route to 10.0.0.0/8 is advertised via Fa0/0 (from R2) so it just forwards packets to R2. Although R2 advertised a summary of 10.0.0.0/8 but it does not have a route to 10.4.0.1 and R2 will drop this packet. That’s the lucky circumstance.

Suppose R1 is the only router connecting to the Internet so maybe on R2 the administrator wants to add a default route to R1 for Internet traffic. Something like this:

R2(config)#ip route 0.0.0.0 0.0.0.0 192.168.1.1

(or a more preferred way is to configure the “ip default-network network-connected-to-Internet” command on R1)

Now, if R2 receives traffic to 10.4.0.1 it will forward that traffic to the default network. That means the 10.4.0.1 traffic will go back to R1 and a routing loop occurs! This is the time when the “Null0″ interface comes into play!

With the summarized route 10.0.0.0/8 pointed to Null0, traffic to 10.4.0.1 will not be sent back to R1, it is sent to Null0 interface instead. And packets sent to Null0 are simply dropped without creating a routing loop.

Well, you understood why the Null0 interface is created and its purpose. Now we will explore how to create the Null0 interface with a summary route.

In fact, in the above configuration you saw a summary route pointed to Null0 created with the auto-summary feature of EIGRP. To make sure that route is created via “auto-summary”, we will try turning it off.

R2(config)#router eigrp 100
R2(config-router)#no auto-summary

After the neighbor relationship of R1 & R2 is reset, the summarized route to Null0 disappears.

Of course, if we enable “auto-summary” and shut down all three loopback interfaces, the summarized route to Null0 will not exist in the routing table of R2 and it will not be advertised to R1 either (even we do have a “network 10.0.0.0″ under EIGRP mode).

Manual summarization

First we must turn off the auto summarization with the “no auto summary” command on R2 so that it will not cause any effect on the manual summarization.

R2(config-router)#no auto-summary

Also, if you turned off loopback interfaces, make sure to turn it on again.

Next, add the manual summarization command under Fa0/0 interface of R2:

R2(config-router)#exit
R2(config)#int f0/0
R2(config-if)#ip summary-address eigrp 100 10.0.0.0 255.0.0.0

Let’s check the routing table of R2 now:

A summarized route is also created like in the case of Auto Summarization for preventing routing loop. R1 also receives the summarized route to 10.0.0.0/8 only.

So now if we turn off all the loopback interfaces, will the summarized route exist in the routing table of R2? The answer is no.

R2 will not advertise the summarized route to R1 either so R1′s routing table does not have this route:

In conclusion, a summarized route to Null0 interface is created along with the summarization of that route. If the summarizing router does not have a specific route for a subnet of that summarized route, it will send packets to Null0, sometimes called a “black hole”. This helps prevent routing loop and reduce unnecessary traffic. We can summarize a route via auto or manual summarization. Both methods require at least one related route of the summarized route to exist in the routing table before the summarized route is advertised.

The purposes of this sim are:
+ Redistribute from EIGRP to OSPF and vice versa.
+ Traffic from R1 to R4 must go through the best path (after redistribution, traffic from R1 will go R1 -> R2 -> R4; this is not the most optimal path as it must go through 2 serial links. The best path is R1 -> R2 -> R3 -> R4 and we have to configure the routers to complete this task.)

Initial Configurations (which have not had the redistribute command yet):

After finishing the initial commands above, the routing tables of each router are shown below:

R1:

R2:

R3:

R4:

First on R2 we will redistribute routes from EIGRP to OSPF:

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

We can see two “O E1″ routes that are being redistributed into OSPF. Now we will redistribute OSPF to EIGRP on R2:

R2(config)#router eigrp 100
R2(config-router)#redistribute ospf 1 metric 1544 2000 255 1 1500

The routing table of R1 is now learned routes to networks 172.16.100.0/24, 192.168.4.0/24 & 192.168.3.0/24 which are advertised by OSPF:

Note: The routing table of R3 is still the same because R3 had all routes advertised by OSPF. Also, R1 can now ping 172.168.100.1 successfully.

Let’s do redistribution on R3:

Redistribute EIGRP to OSPF on R3:

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

Now the routing table of R4 changes a bit:

As you can see, now the external routes 192.168.1.0 & 192.168.2.0 are learned via 192.168.4.3, not 192.168.3.2.

The last thing we do is to redistribute OSPF to EIGRP on R3:

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

Now R2 (and R1) will use which route to go to 172.16.100.1? Let’s check the routing table of R2:

So R2 still sends traffic to 172.16.100.1 via the serial link between R4 & R2. This link is less optimal than the Ethernet link between R2 and R3. If we wish R2 to send traffic via the Ethernet link between R2 and R3, use this command:

R2(config-router)#distance eigrp 90 105

This command sets the Administrative Distance of EIGRP external route to 105, which is smaller than an OSPF route (110) so the Ethernet link between R2 and R3 will be preferred to the link between R2 & R4.

After that, the route to 172.16.100.1 is re-learned via 192.168.2.3 as an EIGRP external route.

A traceroute command on R1 also confirms this:

First we really want to say thanks to all who are reading digitaltut.com. Thank for the time you spent with us, your comments and opinions.

Our team had a conversation about digitaltut.com. We all love to write tutorials, explanations and answer questions from our readers. We love to support you to achieve your targets but our time is limited. So recently new questions, tutorials have not been added to digitaltut. It is sad to say but if we keep this situation, digitaltut cannot develop anymore. After that talk, we decide that digitaltut should have a premium membership part to fully support you.

We really hope to continue bringing you amazing stuffs in the networking field. But without the fund, digitaltut and other sites cannot operate. With your support, we can continue offering ROUTE tutorials and questions more frequently. We also try our best to keep the fee as small as possible (currently $9 a month) while bringing you our best support.

Become premium member allows you to access:

+ Flash-based questions to check your knowledge before each topic of ROUTE.
+ Flash-based questions on all topics of ROUTE to help you fully prepare for the ROUTE exam. See example.
+ Popular lab Simulators
We wish you to understand our situation now.

If you have any questions, don’t hesitate to comment here or contact us at support@digitaltut.com.

Thanks and regards,

Digitaltut team.

Note: The Premium Membership on this site is dedicated for the ROUTE exam.

Topology:

IOS used in this lab: c3640-jk9s-mz.124-16.bin

Tasks in this lab:

1) Set up basic IBGP & EBGP
2) Advertise loopback 1 & loopback 10 on R1
3) Use route-maps on R2 & R3 to set MED for only 192.168.1.0, verify on R6 and will R6 see network 192.168.10.0?

Basic Configuration – IP Assignments

1) Set up IBGP & EBGP connections

Note: The use of a loopback interface to define neighbors is common with iBGP, but is not common with eBGP. Normally, you use the loopback interface to make sure that the IP address of the neighbor stays up and is independent of hardware that functions properly. In the case of eBGP, peer routers frequently have direct connection, and loopback does not apply.

2) Advertise networks 192.168.1.0 & 192.168.10.0 on R1:

On R1 we advertise two networks 192.168.1.0/24 & 192.168.10.0/24:

Now check on both R2 & R3 to see both networks are advertised

Also on EBGP neighbors, these networks are also advertised (you have to wait a moment for BGP updates)

On R6 networks 192.168.1.0 & 192.168.10.0 are learned via both R4 & R5:

Note: the path via R4 (46.46.46.4) are chosen for both networks as the best path because of lower router-ID on R4)

3) Use route-maps on R2 & R3 to set MED for 192.168.1.0 to 150 & 170, respectively:

Now R6 only receives updates about 192.168.1.0. The metric advertised by R3 is lower so it is chosen as the best path to 192.168.1.0 (marked with “>”).

Notice that updates for 192.168.10.0 have been filtered out because there is an implicit “deny all” statement at the end of each access-list.

IOS used: c3640-jk9s-mz.124-16.bin

Task: Summary networks 10.10.10.0/24 & 10.10.20.0/24 into 10.10.0.0/16

Basic IP address Assignments

Establish BGP neighbors

Notice that the BGP tables are still empty now.

Advertise loopback0 interfaces on R1 & R2

Check the BGP table to see our loopback interfaces have been advertised

On R1 we see the next hop of 10.10.10.0/24 is 0.0.0.0 -> the network originated by a “network” command has the next-hop of 0.0.0.0.

Now we want to summary two networks 10.10.10.0/24 & 10.10.20.0/24 into one network 10.10.0.0/16

Notice that after being summarized, the “Next Hop” of summarized network is 0.0.0.0 -> the network originated via an “aggregate” command will have a next hop of 0.0.0.0.

Also a rule of aggregation is “Aggregation applies only to routes that exist in the BGP routing table. An aggregated route is forwarded if at least one more specific route of the aggregation exists in the BGP routing table”. That means the aggregated network 10.10.0.0/16 is only forwarded if the BGP table of R3 has at least 10.10.10.0/24 or 10.10.20.0/24.

Check the BGP table of R4 to see our aggregated network has been advertised.

Although the summarized network was created but two more specific networks are still there. If you want to advertise the summarized network only, use the command:

The BGP table of R3 still shows these routes but they are marked as suppressed (s>)

Now R3 only advertises summarized route so the BGP table of R4 does not display these suppressed networks

But let’s check the BGP table of R1 or R2.

Wow! The summarized route is also advertised back to R2 as if it were learned from R3 (next hop 23.23.23.3). So if R2 receives a packet destined to a subnet of 10.10.0.0/16 (10.10.30.0 for example) it will send to R3 but R3 does not have more specific route -> it will drop that packet, this creates a black hole. To avoid this problem, append the keyword “as-set” to ask the router to send the information about all the Autonomous Systems it has passed:

Now the path information in R4 changes to 3 {1,2}. This set indicates the aggregate route summarizes routes that have passed through AS 1 & AS 2 and is advertised through AS 3.

The as-set information is very important in the avoidance of routing loops. Let’s see the BGP table of R2:

When receiving this advertisement, R2 will not accept this route anymore because R2 sees its AS in the AS-Path. Notice before the “as-set” keyword is used, R2 only sees this advertisement comes from AS 3 and accepts it.

Note: If you wish to ping from R4 to loopback of R1 (or R2), you have to advertise the network 34.34.34.0 on R4 so that the ICMP Reply from R1 knows where to go (use the “network 34.34.34.0 mask 255.255.255.0 on R4).

IOS used in this lab: c3640-jk9s-mz.124-16.bin

Objectives of this lab:
+ Task 1: Configure EBGP on AS 1, AS 23, AS 4 and configure IBGP between R2 & R3 (AS23), also advertise loopback 0 interface on R1 so that all the routers learn about this network.
+ Task 2: Use a distribute-list to filter out network 1.1.1.0

Let’s start our lab!

Task 1 has been mentioned in detail in BGP next-hop-self, community no-export & send-community Lab so I just post the configuration here:

Configure IP addresses on all interfaces

Configure EBGP & IBGP

Advertise loopback0 on R1 to other routers

Now we can see 1.1.1.0/24 on all routers. For example on R4 we see:

Task 2: Use distribute-list to filter out network 1.1.1.0

On R2 configure an access-list and apply it in the distribute-list under BGP mode.

Now network 1.1.1.0 disappears in both BGP routing table and routing table of R4

You can check to see the access-list 1 has been matched with the “show access-list 1″ command:

Another way to complete this task is to apply the distribute-list on R3

In practical we should apply the distribute-list on R2 so that routers in our company don’t need to learn about that route.

IOS used in this lab: c3640-jk9s-mz.124-16.bin

Objectives of this lab:
+ Task 1: Configure EBGP on AS 1, AS 23, AS 4 and configure IBGP between R2 & R3 (AS23)
+ Task 2: Advertise loopback0 on R1 to R4 and make sure R4 can ping to that loopback interface (AS23 becomes a transit AS)
+ Task 3: Make AS 23 not a transit AS by using the feature “community no-export”

First we will configure all IP addresses of this lab and turn on all the interfaces:

Configure IP addresses on all interfaces

Task 1: Configure EBGP & IBGP

Now we should check to make sure each BGP speaker (router running BGP) learn about their neighbors with the “show ip bgp summary” command:

Note: At this time, the “show ip bgp” commands on all routers show nothing and the “show ip route” commands only show directly connected networks. For example on R4:

Task 2: Advertise loopback0 on R1 to R4 and make sure R4 can ping to that loopback interface

First, create loopback 1.1.1.1/24 on R1 and advertise it

Now we can see that route in both the routing table and BGP routing table of R2.

By the way, let’s have a look of the output of the “show ip bgp” command on R3 at this time

Please notice the “Next Hop” field from the output above. We can see that although the loopback0 of R1 is learned from R2 (so the next hop field should be the fa1/0 interface of R2) but here the “Next Hop” field here is an interface on R1 (12.12.12.1). The reason is:
“For EBGP, the next hop is always the IP address of the neighbor specified in the neighbor command. For IBGP, the protocol states that the next hop advertised by EBGP should be carried into IBGP“. In this case, the next hop of EBGP (R1 on AS 1) will be installed into BGP of R3.

Therefore R3 needs an IGP (like OSPF, EIGRP…) to reach that EBGP router, if not it will drop all packets destined for network 1.1.1.0/24. In this case no IGP has been configured so a ping to 1.1.1.1 from R3 will surely fail because R3 doesn’t know how to reach 12.12.12.1.

Also, we can see that R3 can’t reach 1.1.1.0/24 with the “show ip bgp 1.1.1.0/24″ command

This route is “inaccessible” so R3 will not advertise this route to R4 -> no network 1.1.1.0/24 is installed in the BGP routing table of R4

To overcome this problem, we can declare the “next-hop-self” on the edge router (R2). With this command, R2 will send its own IP address as the next hop instead of sending the EBGP next hop.

Now the Next Hop field will be an interface on R2 (23.23.23.2):

And network 1.1.1.0/24 is also installed in the BGP routing table of R4 because the route is now accessible and R3 advertises it to R4

Notice that although the network 1.1.1.0/24 exists in the BGP routing table but R4 still can’t ping to it

Check the BGP routing table of R1 we will see that R1 does not know how to reach 34.34.34.0 network -> R1 does not know how to send the “ping reply” (ICMP response) to R4.

To make a successful ping from R4, we must advertise network 34.34.34.0 on R4.

Now R1 has learned about network 34.34.34.0/24

Maybe we can now ping from R4 to loopback0? The answer is still no! Although the ping can reach loopback0 but the reply packets can’t reach R4 because there is a mistake on the BGP routing table of R2

As you can guess, the same problem “next hop advertised by EBGP should be carried into IBGP” occurs so we need to use the command:

Now we can ping from R4 to loopback0 on R1

Task 3: Make AS 23 not a transit AS

This is an important problem in real life. Suppose your company (with R2 & R3 routers) wants the connection to the Internet must be available in any time so your administrators hired two internet lines from two separate ISPs (R1 & R4). But improper configuration can make traffic flow from R1 -> R2 -> R3 -> R4 and your company becomes a transit AS. Surely your company does not want to receive this traffic as it takes much bandwidth of the company. We need to filter out this type of traffic.

The purpose of this task is opposite to task 2. We will make AS 23 not a transit AS by not advertising network 1.1.1.0 to R4. To do this, we will create a route-map for 1.1.1.0/24 and set the “no-export” attribute to this route:

The “no-export” means “do not advertise this route to any EBGP peers” and this attribute is set to network 1.1.1.0/24 before entering R3 (because we apply this route-map on inbound direction to R3). Therefore R3 will understand “do not advertise 1.1.1.0/24 to any EBGP neighbor”, in this case EBGP neighbor is R4.

Also on R4 the 1.1.1.0/24 network disappears.

Another way to achieve the same result as above is configuring a route-map and apply it on the outbound direction of R2 (to R3):

For your information, we can use the “community no-export” on R1 on outbound direction to achieve the same result but notice you have to add the “send-community” feature so that the community attribute on R1 is sent to R2 because even if you set the community attribute on R1, this attribute does not transmit to BGP neighbors by default.

Now on R2 you will see

Also add “neighbor … send-community” command on R2 to propagate community attribute to R3

Now both R2 & R3 receive community attribute on R1

R3 knows network 1.1.1.0/24 is not allowed to advertise to R4 (R4 is an EBGP) so R4 does not have this route in its BGP routing table (note: we don’t need to set the “send-community” on R3 because R3 understands this route should “not be advertised to any peer”).

This is the end of this lab. I don’t upload the configuration files because I wish you to do it by yourself (I am sorry).

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.

The requirement of this sim is traffic from R1 should go to the most optimal route to reach 172.16.100.0/24 network

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. She 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 the metric unit is in 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)

Note: “usec” here does not mean microsecond (which is 1/1000 milliseconds) but means millisecond. In short usec = msec. I don’t know why they use the word “usec” here but just think it is “msec” (According to this link: http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml#eigrpmetrics: “The delay as shown in the show ip eigrp topology or show interface commands is in microseconds”)

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.

Note: If the link between R2 and R3 is FastEthernet link, we must put the command below under EIGRP process to make traffic from R1 to go through R3 (R1 -> R2 -> R3 -> R4), which is better than R1 -> R2 -> R4.

R2(config-router)# distance eigrp 90 105

This command sets the Administrative Distance of all EIGRP internal routes to 90 and all EIGRP external routes to 105, which is smaller than the Administrative Distance of OSPF (110) -> the link between R2 & R3 will be preferred to the serial link between R2 & R4.

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

Note: Please check the OSPF process numbers first before typing these commands. Maybe they are not “ospf 1″ like above.

If you want to have a closer look at this sim and understand more about the “distance eigrp” command, please read my OSPF EIGRP Redistribute Lab in GNS3.

Other lab-sims on this site:

EIGRP Stub Sim

OSPF Sim

IPv6 OSPF Virtual Link Sim

EIGRP Simlet

Policy Based Routing Sim

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

(Update: We don’t need the last command route-map pbr permit 20 to permit other traffic according to Cisco:

“If the packets do not meet any of the defined match criteria (that is, if the packets fall off the end of a route map), then those packets are routed through the normal destination-based routing process. If it is desired not to revert to normal forwarding and to drop the packets that do not match the specified criteria, then interface Null 0 should be specified as the last interface in the list by using the set clause.”

Reference: http://www.cisco.com/en/US/products/ps6599/products_white_paper09186a00800a4409.shtml)

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 Stub Sim

OSPF Sim

EIGRP OSPF Redistribution Sim

IPv6 OSPF Virtual Link Sim

EIGRP Simlet

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 Stub Sim

OSPF Sim

EIGRP OSPF Redistribution Sim

EIGRP Simlet
Policy Based Routing Sim

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:

OSPF Sim

EIGRP OSPF Redistribution Sim

IPv6 OSPF Virtual Link Sim

EIGRP Simlet
Policy Based Routing Sim

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.

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

Note: Make sure to check the OSPF process ID before typing your configuration. Maybe it is not OSPF process 1 like the configuration above.

Other lab-sims on this site:

EIGRP Stub Sim

EIGRP OSPF Redistribution Sim

IPv6 OSPF Virtual Link Sim

EIGRP Simlet
Policy Based Routing Sim

First we assign IP addresses to all interfaces on the routers. Notice the 4th octet of the IP address of each router has the same value of the name of that router (for example R2 has 2 interfaces 12.12.12.2 & 23.23.23.2; R3 has 2 interfaces 23.23.23.3 & 34.34.34.3…)

Assign IP addresses to interfaces:

Turn on EIGRP on R1, R2, R3, R4 and turn on OSPF on R4, R5, R6:

We should check the routing table of R4 (the border router) to make sure all the routes are learned:

Redistribute EIGRP into OSPF

The routing table of R4 contains all the routes in the topology so now we will redistribute EIGRP into OSPF with the command:

After entering these commands we will see a warning from R4

Ok, maybe our EIGRP routes have been redistributed so we should check the routing table of R5:

What? We don’t see anything we expect in the output of R5. No redistributed routes here. All are only directly connected routes!

Wait a minute! We have been warned that “only classful networks will be redistributed”. We wish to see networks 12.12.12.0/24, 23.23.23.0/24 & 34.34.34.0/24 redistributed into OSPF but they are subnets, not “classful” networks. Please notice that a “classful” network here means network with the default major subnet mask (for example: 1.0.0.0/8; 175.10.0.0/16; 200.200.0.0/24…). To prove this, we will create loopback0 interface on R2 with the IP address 2.2.2.2/8:

Now we check the routing table of R5 again, the 2.0.0.0/8 network has been redistributed successfully with a O E2 (by default, a route redistributed into OSPF will have type E2 with a default metric of 20):

It is not necessary but we can check the OSPF database of R5, notice that we only see a redistributed route (Type-5) of 2.0.0.0

Therefore if we want to redistribute all subnets into OSPF, use the command:

(The keyword subnets is only used when we redistribute from another routing protocol into OSPF)

Now all the routes appear in the routing table of R5

Ok, R5 got all the routes in EIGRP domain so we may want to ping them to test the connection. So we ping from R5 to R1:

Now the ping is not successful. We can check where the packets have been dropped with the traceroute command:

The last good router is R4, which is the border router for redistribution. Therefore we can realize that the ping is not successful because OSPF knows how to route packets but EIGRP routers don’t know where to send reply to -> We need to redistribute OSPF to EIGRP.

Redistribute OSPF into EIGRP

Unlike OSPF, we must specify five metrics when redistributing into EIGRP: bandwidth, delay, reliability, load, and MTU, respectively. Therefore our redistribute command will be like this:

Now R1 has all the OSPF routes and they are marked with D EX:

Now all routers can ping each other.

In conclusion, from this lab we learned:
+ We should use the keyword “subnets” when redistributing into OSPF; otherwise only classful networks will be redistributed.
+ The ping will not work if we only redistribute “one-way” because the reply packets can not be sent.
+ Redistribution into EIGRP requires the metrics to be defined. The only exception is when redistributing between IGRP & EIGRP, we don’t need to assign the metrics because the metrics of these 2 routing protocols are the same.

Question 1

Drag each item to its proper location

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

Answer:

Question 2

Place the BGP commands to the proper locations

Answer:

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

Question 3

Place the EIGRP commands to the proper locations

Answer:

Sources of routes information: show ip eigrp neighbor

What being learned: show ip eigrp topology

What actually being used: show ip route eigrp

Verify eigrp information for each network: show ip interface eigrp

Question 4

Place the EIGRP terms to the proper locations

Answer:

lists adjacent routers: Neighbor table

route entries for all destinations: Topology table

primary route to destination: Successor

best routers to destinations: Routing table

backup route to destination: Feasible successor

Question 5

Place the EIGRP packets to the proper locations

Answer:

Neighbor discovery/recovery mechanism: Hello

Indicate receipt of any EIGRP packet: Acknowledgement

Convey reachability of destinations: Update

Provides specific and reliable information of neighbors: Query

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

Question 1

Answer:

Identifies the source of the packet: Router ID

Identifies the area to which the packet belongs: Area ID

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

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

Contains authentication information: Authentication

Contains encapsulated upper-layer information: Data

Question 2

Answer:

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

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

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

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

Question 3

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

Answer:

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

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

The address boundaries must be extremely clear: Hybrid VPN

Question 4

IPv6 to IPv4 transition methods

Answer:

NAT-PT

6 to 4 tunnels

GRE tunnels

ISATAP tunnels

Question 5

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

Answer:

The correct order is:

Explanation

The structure of a normal IPv6 packet is:

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

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

Question

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

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

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

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

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

Answer: F

Explanation

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

Question 2

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

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

Answer: C

Explanation

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

Question 3

The log of d1 reports the following:

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

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

Answer: E

Explanation

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

Question 4

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

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

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

Answer: G

Explanation

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

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

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

Question 1

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

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

Answer: B, C, F

Question 2

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

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

Answer: B

Explanation

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

Question 3

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

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

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

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

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

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

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

Answer: C

Explanation

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

Question 4

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

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

Answer: A

Explanation

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

Question 5

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

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

Answer: D

Explanation

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