Home > EIGRP Stub Sim

EIGRP Stub Sim

May 8th, 2014 in Lab Sim, LabSim Go to comments


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


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

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

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 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, 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 is a summary…) then we should use the command ip summary-address eigrp 123 so that all the ping can work well.

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

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

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 “ is a summary,….Null0” then you need to summary using the network with the command “ip summary-address eigrp 123” . 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 OSPF Redistribution Sim

IPv6 OSPF Virtual Link Sim

EIGRP Simlet
Policy Based Routing Sim

Comment pages
1 2 3 30
  1. L.A
    September 30th, 2018

    I tried this on GNS3 it works both either /16 summarization or

  2. HansPeru
    October 12th, 2018

    Dear Guys,
    Yesterday I passed with 8XX the exam 300-101!! and this question was in the exam, regards from Peru.

  3. ddowner
    October 18th, 2018

    I have this loaded in GNS3 & I never only get two subnets on R3. Here’s the output of the on R3: is variably subnetted, 3 subnets, 3 masks
    D [90/2170112] via, 00:00:15, Serial1/0
    C is directly connected, Serial1/0
    L is directly connected, Serial1/0 is variably subnetted, 2 subnets, 2 masks
    C is directly connected, GigabitEthernet4/0
    L is directly connected, GigabitEthernet4/0

  4. Anonymous
    October 22nd, 2018

    Why “R4(config-if)#ip summary-address eigrp 123”??

    I think “R4(config-if)#ip summary-address eigrp 123”

  5. BROS
    November 1st, 2018

    Anonymous October 22nd, 2018
    Why “R4(config-if)#ip summary-address eigrp 123”??

    I think “R4(config-if)#ip summary-address eigrp 123”
    Dude this is totally wrong, you are making a route summery with is supposed to put all the subnets in two,

  6. Anonymous
    November 2nd, 2018

    Today’s exam 834 score, Lab eigrp – ospf – redistribute-Drag – Drops Frame-Relay – GRE – Trafic

    R4(config-if)#ip summary-address eigrp 123 correto

  7. Ahmed
    November 3rd, 2018

    @BROS agreed with you this command ip summary-address eigrp 123” may advertised the lab requirement but maybe you will not get full marks command should be ip summary-address eigrp 123” to get your full marks .

  8. Sorlags
    November 14th, 2018

    We have not a problem with the ip ? This IP is on port S0/1, not S0/0 like all the other.

    After the summary the ip route table have the same IP directly connected but on s0/1. I think is right, but I don’t understand.

  9. Sorlags
    November 15th, 2018


    I have exacly this lab on the exam today and the summary /20 don’t works. With the /16 it’s was Ok.

    And there is not other serial interface on R1

  10. NetIng
    November 24th, 2018

    I had this question on my exam this week and I was using the /20 mask for summarization but the command did not work.

  11. Django
    November 25th, 2018

    @ddowner the objective is to have just two “” subnets in the IP routing table. You have 3, so You are probably not summarizing properly.

  12. Djason
    November 28th, 2018 is a host, not a subnet, so it doesn’t count. The question requests 2x *subnets* in the routing table. The reason why it appears is that newer IOSes (>15.0) show the local interface IPs as /32 hosts and their subnets as separate entries in the routing table.

    The summary subnet mask shouldn’t matter *in theory* as long as it covers all the loopback IPs from R4. As a general thumb of rule, in a real environment I would use the most specific mask, which is /20, not /16.

  13. Danish
    December 1st, 2018

    Probably reason for multiple sub nets is you are configuring it on different router, you have to configure it on R4.

Comment pages
1 2 3 30
  1. No trackbacks yet.