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Forum Replies

  1. Good to hear you like it! I think that’s one of the things that is important to know, most people assume EIGRP will just summarize anything when you use auto-summary.

  2. Hi Rene

    Thank you that was a useful lesson.
    There is an important thing that you didn’t explicitly mention and is important.

    • The eigrp router will only announce an auto-summary out an interface if the classful network of the interface is different from the classful network of the interface it learnt the network from. In other words if it has 2 interfaces and both are in the same network class, it will never send an auto summary out (this is how I understood the cisco info, haven’t labbed it).
      Cisco says it this way "When a router has multiple working interfaces, and those interfaces use IP addresses in different classful networks, the router advertises a summary route for each classful network on interfaces attached to a different classful network.

    What I took away from the lesson is:
    -A router will only send out auto-summaries of connected networks (never learnt)
    -A router will only auto-summarize between network classes.


  3. Hi Rene
    I got this "EIGRP auto-summary will only create summary routes for directly connected networks, not for routes you learn from other EIGRP routers."
    But what about OSPF auto-summary route. Does it do the same thing ?
    Thank you so much .

  4. Hi guys,

    so can we say that the auto-summary command is the same for EIGRP and RIP?
    When enabled, routes will be summarized to the class A, B or C network and no mask will be send with the update message?


  5. Hello florian

    Essentially, yes, that is correct. However, EIGRP unlike RIP will automatically install a discard route in the local routing table. The discard route is one that has as an exit interface the Null0 interface.

    I hope this has been helpful!


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