OSPF LSA Type 5 summarization


As the junior network engineer for a large cartoon network you are asked to look at the OSPF configuration of the network. Some external networks are redistributed into OSPF and your boss asks you if you can summarize them so the routing table stays small. Your colleague tried some summary commands but couldn’t get it working…see if you can fix it!


  • All IP addresses have been preconfigured for you.
  • Configure OSPF on all routers. Advertise all physical interfaces.
  • Router Sam has a number of loopback interfaces. Redistribute them in OSPF so they show up as external routes on router Jack.
  • Configure OSPF so there are two summaries for the loopback interfaces of router Sam. Use the most optimal summaries.

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

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OSPF LSA Type 5 Summarization Network Topology

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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. Hey Rene got a quick question for you. In regards to this summarized and the Type 3 tutorial you use two different methods to advertise the summarized subnet. I know there are instances where there are multiple ways to accomplish the same goal. Could I use the summarize method from the type 5 tutorial for type 3. Let me know if needs more specifics.

    1. Need specifics. For LSA5 summarization you’d generally use summary-address versus area X range.

  2. Hi, (This is my first post on gns3vault)

    Firstly great work Rene, your Labs are great!!!! Learning lots..Much appreciated!

    One of the objectives are to set up two optimal summaries on router SAM (as follows).

    Aside of the objective is there any reason(s) the below summary won’t work? (Best practice? etc)

    Thanks for your help in advance 😉

  3. Nicholas,
    Thanks for your response. Just wanted to confirm the methods to summarize routes for LSA 5 (summary-adress) differ from LSA 3(area).

  4. Hi Guys,

    I tried it myself to use the area range command instead of summary-address command to see if it works, but area range command didn’t work.

    Can someone please explain, why it didn’t work? is it because we redistributed it into OSPF?


    1. Yes. Area range applies to LSA3 only while summary-address applies to LSA5/7. You can only go summarization at ABRs and ASBRs (of note, you can summarize LSA7s on an ABR if it’s the 7to5 translator).

  5. hi Rene.

    In your ccnp book you say:

    So far so good? Excellent! One more thing we can do with OSPF and summarization which is
    external route summarization. This is where we summarize the type 5 external LSAs.
     You can create the summary on the ABR or ASBR.
     A null0 entry will be created in the routing table for the summary route.

    But from Cisco are saying that i can do it only on the ASBR.


    I have tried it on the ABR and no luck. Why is that?


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