Distribute List Filtering


Ever since you were a child you wanted to be a trappist monk, the silence of the monastery and the science of trappist beer have been a part of your life as far as you can remember. Recently the monastery decided to cooperate with other monks to share information about the brewing process of trappist beer. One of the monks configured the routers and has setup redistribution between EIGRP and OSPF so there is full connectivity between the networks. However, your monastery holds some precious recipies that are not to be shared with everyone, you need to make sure access to these networks is filtered in the routing or redistribution process….Cheers!


  • All IP addresses have been preconfigured for you.
  • OSPF and EIGRP have been preconfigred for you on the corresponding routers.
  • Redistribution has been preconfigured for you on router Chimay.
  • Router Orval and Achel both have 2 loopback interfaces:
    Orval: L0: and L1:
    Achel: L0: and L1:
  • You are not allowed to make any changes to the network commands under the OSPF or EIGRP process.
  • Ensure router Chimay does not advertise the /24 network towards router Orval, use an access-list to accomplish this.
  • Ensure router Orval does not advertise the /24 network towards router Chimay, use a prefix-list to accomplish this.
  • Ensure router Chimay does not redistribute the network into OSPF, use a route-map to accomplish this.

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Distribute List Filtering

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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. About “Ensure router Achel does not advertise the /24 network towards router Chimay, use an access-list to accomplish this.”.
    Because of the OSPF logic, the topology database on all routers within an area must be identical, so you cannot filter advertisment of network on router Achel – filtering just don’t work, and the lab does not let you to play with network commands as well, so all you can do is to filter this route on Chimay router. Chimay router will still have this network in it’s topology database (it will see it as a stub network connected to Achel router), but it will be filtered from appearing in it’s routing table 🙂
    Maybe I’m wrong, then somebody please correct me 🙂

  2. Seems I wasn’t thinking when I chose the routing protocols ;D

    With OSPF it’s impossible to have an outgoing distribute-list, only method to do this is on an ASBR.

    So I changed the lab to remove this impossible task 😉


  3. Or on Chimay you may use distribute-list in to filter The choise depends on if you want Chimay to have a route for network in his routing table or you don’t. The lab task will be accomplished – Orval won’t hear about in any of those two cases 🙂

  4. Can someone please explain why the distribute list isn’t working with inbound @ f 0/0 on router Chimay?

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