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EIGRP Stub Sim

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

Question

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

EIGRPStubSim

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

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

Answer and Explanation:

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

EIGRPStubSim_show_running_config_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

EIGRPStubSim_show_ip_route_R3_no-summary.jpg

 

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:

EIGRPStubSim_show_ip_route_R3_final_no_summary.jpg

(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

Comments
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  1. Anonymous
    February 8th, 2017

    I don’t understand the mask used for summarization. As many have said, I think it should be 255.255.240.0 If you breakdown the third octet in the networks you see in R3’s route table, you have:

    2-0000 0010
    3-0000 0011
    4-0000 0100
    5-0000 0101
    6-0000 0110
    7-0000 0111
    8-0000 1000
    9-0000 1001

    So, the first three bits of that 3rd octet are what’s in common. That gives you a /20 and .240 for those four bits. Can anyone explain why this answer says it’s 255.255.0.0 and not 255.255.240.0???

  2. Anonymous
    February 8th, 2017

    Even this online calculator confirms this:

    https://nubem.com/ip-summarization-tool/

    The summary is 10.2.0.0 /20

  3. Anonymous
    February 8th, 2017

    Just proved what many have been saying. I had misconfigure the summary address with a mask of 255.255.255.240. It should be 255.255.240.0 Here’s my config under R4 s1/0 (for the summary address):

    interface Serial1/0
    ip summary-address eigrp 123 10.2.0.0 255.255.240.0 5

    Now I see just two entries for the 10.x.x.x network:

    R3#sh ip route | b Gate
    Gateway of last resort is not set

    172.16.0.0/24 is subnetted, 1 subnets
    C 172.16.1.0 is directly connected, FastEthernet0/0
    10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
    D 10.2.0.0/20 [90/2195456] via 10.2.3.4, 00:02:15, Serial1/0
    C 10.2.3.0/24 is directly connected, Serial1/0
    R3#

    Bam! mic drop :)

  4. Martin
    February 9th, 2017

    Yes, the proper summarization of the range 10.2.2.0 – 10.2.9.0 is 10.2.0.0 /20

    Therefore, the command “ip summary-address eigrp 123 10.2.0.0 255.255.0.0” is wrong.
    It should be “ip summary-address eigrp 123 10.2.0.0 255.255.240.0”.

    However, the exam simulator probably checks *how many* 10.x.x.x entries are in the routing table and since the two commands have the same effect in that regard you’ll probably won’t lose points by using a /16 mask. Regardless, I’d use /20 just to play safe.

  5. Mythili
    February 10th, 2017

    Can someone tell if 149+41+15 dumps are valid?

  6. PassCCNP
    February 11th, 2017

    it is valid 149+41+15

  7. Anonymous
    February 11th, 2017

    Hi PassCCNP

    Could u plz sent to me 149+41+15 Dump. hunter_korn49(at)hotmail.com

  8. Gerardo Mejia
    February 13th, 2017
  9. BugHumNoi
    February 15th, 2017

    Thx very much @Gerardo Mejia

    I’m passed exam by your kindness.
    “15 New Question” Appear all and LAB
    – OSPF Totally Stubly Area
    – EIGRP NSSA and summary ip address
    – OSPFv3 Virtual Link
    – PBR
    – OSPF EIGRP Redistribute

    Thx so much.

  10. Mandark
    February 17th, 2017

    Yes 149 + 41 + 15 are still valid. Passed Route on 11/02/2017
    SIM: OSPFv3, OSPF, PBR, EIGRP/OSPF Redistribution, OSPF Evaluation SIM. I passed with 8xx/1000. Was very happy using Digital Tut.

    Preparing for SWITCH next month.

  11. mutt
    February 24th, 2017

    hi to all

    may i have 15q please

    merter.metro (at) gmail . com

  12. Anonymous
    February 24th, 2017

    Anyone tried 10.2.2.0 255.255.254.0 as the summary address?

  13. nic
    February 25th, 2017

    Anyone tried 10.2.2.0 255.255.254.0 as the summary address?=>
    Host Address Range 10.2.2.1 – 10.2.3.254

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