EIGRP Auto Summarization


Working as a freelance network engineer you have some strange customers. One of them is a scatterbrain inventor who claims to work on a ‘world-changing’ machine. He has problems with his network and is currently unable to upload some schematics. The routing protocol of choice is EIGRP (Enhanced Interior Gateway Routing Protocol) and since you are an expert you should be able to fix his problems….back to the labs!


  • All IP addresses have been preconfigured for you.
  • EIGRP AS123 has been preconfigured for you and is advertising all networks.
  • You are not allowed to disable EIGRP auto-summarization.
  • When you try to reach the networks on the loopback interfaces from router Delorean you have reachability problems, solve this problem.
  • When you send a ping from router McFly’s loopback0 interface to router Brown’s loopback0 interface you have reachability problems, solve this problem.
  • Ensure there is full reachability for all networks.

It took me 1000s of hours reading books and doing labs, making mistakes over and over again until I mastered all the protocols for CCNA.

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You will learn all the secrets about EIGRP, summarization and more.

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EIGRP Auto Summarization Network Topology

Video Solution:

Configuration Files

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Once you are logged in you will find the configuration files right here.

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Written by René Molenaar - CCIE #41726

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About the Author: Rene Molenaar

René - CCIE #41726 is the creator of GNS3Vault.com where he shares CCNA, CCNP and CCIE R&S labs. He also blogs about networking on http://networklessons.com


  1. Hmmm… this is a tricky one….
    since we cannot disable auto-summarization, are we allowed to make changes to the network design?

  2. the lab says “You are not allowed to disable EIGRP auto-summarization.”
    Comment above makes me think we can do turn off auto summarization?

    Please clarify

  3. Nope… it means that you are not supposed to use “no auto-summary” command in the eigrp process…

  4. MCFLY#show running-config interface fastEthernet 0/0
    Building configuration…

    Current configuration : 154 bytes
    interface FastEthernet0/0
    ip address
    ip summary-address eigrp 123 5
    duplex auto
    speed auto


    BROWN#show running-config interface fastEthernet 0/0
    Building configuration…

    Current configuration : 154 bytes
    interface FastEthernet0/0
    ip address
    ip summary-address eigrp 123 5
    duplex auto
    speed auto


  5. Deep,

    Why do you configure summary on the fastethernet interfaces isntead of doing it on the loopback?

  6. É o seguinte…

    tem que configurar resumo de rota nos routers: McFly e Brown:
    ip summary-address eigrp 123
    ip summary-address eigrp 123

    Por que?
    Pois por padrão as rotas classfull são sumarizadas automaticamente com o comando auto-summary habilitado. O AD(distancia administrativa) de uma rota sumarizada é 5. Fazendo também a sumarização de rotas pelos comandos acima, o que vai prevalecer para o router é a rota sumarizada mais específica. Correto?

  7. I think I remember that from my CCNA !! If you can’t disable auto-summarization the only alternative is static routes,however redistributing this creates an exterior EX route which doesn’t seem to get summarized.

  8. I put a static route and redistributed it into EIGRP with the same metrics as the interface, is this correct because it works?

  9. Hi Oliver,

    Static routes and redistribution will work but you can also fix this one by creating a summary. Even if auto-summarization is enabled for EIGRP you can still create summaries with a subnet mask, this can solve your problem here.

    The video solution is on youtube, i’ll add the config here within 24 hours.


  10. I downloaded the ZIP file and I do not believe the ip address and anything is pre-configured.

  11. First of all, nice work and thanks for everything! In this lab I just create static routes on all 3 routers and everything seems to work properly. I mean, do we need the ip summary-address commands or just adding static routes is enough?
    Best regards.

    1. the static route is not good reply.
      another waaaaaaaaaaayyyyyyyyyyy 😉

  12. Please let me know, how to download IOS image and install in GS3?

    1. gns3 latest is free in website, pay 25$ and get an even better but buggy version, ios, just torrent it, its easy

      and starting up gns is always messy, try and google the problems, almost all problems you have someone else have already had it before

  13. Hey Rene,
    I did the same thing as you did on the video solution, however, i didn’t understand why did you disable CEF ????

    And also, when before solving the problem, my ping’s from DELOREAN never reached the neighbors, it was U.U.U. I expected a couple of packets to make it in either direction since eigrp was doing load balancing.

    Never mind, i achieved full connectivity with the manual summarization.
    Just explain to me the CEF thing ???


  14. Hi Rene

    Simple lab but very useful ……I never thought of this before

    Always we solve this problem by no auto command ….but its great to know the different solution …..

    Thank a lot

  15. Hi – I have a problem with all labs, No router configs are loaded, just empty routers. I have edited the topology file. Im using a 3725 IOS image as I dont have the 3640. Is this the reason ?

    1. Hey Nikolaisen,

      I believe your problem is the way you have configured GNS3, it could be the location were you have the Images or projects, look were have you decompress the lab config (it should be under the Projects folder) and were do you have this folder set on gns3, also check where you have placed your IOS images.

      e.g on OS X

      IOS Images and hypervisors

      Projects and Images locations

      If this do not work try checking on GNS3 Preferences, where do you have set the Dynamips path. (Very Importat)

      Executable Path to Dynamips:

      If nothing of this works i would suggest to re-install GNS3 and to read the step-by-step guide.

      kind Regards,

  16. Hello Rene,

    I add myself to the previous questions from Masaya and Nipun, why do you need to disable CEF ?

    I could also achieve this without disabling it

    Thanks for the labs

  17. yes my question is also about the cef, thing, what was the benefit of it,

    maybe its a good practice in industry can you give us a sneak peek

    thanks for all the effort.

  18. thanks , but please describe the cef table and difference between “ip cef” and “no ip cef”

  19. Hello Rene,
    Quick question is there any way to download your gns3 topologies and go straight to the configs without having to build the entire topology, connecting cables, etc?

Comments are closed.