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Forum Replies

  1. system says:

    Hi Rene,

    Good lesson. Just two points in your text:

    "This is what makes EIGRP a FAST routing table…"
    Shouldn’t be a fast routing protocol?

    "Next step is to fill in the feasible successors"
    I believe here that you wanted to say feasible distances


  2. Hi Rene,

    This is all I have to say, THANK YOU! :clap::clap::clap:

    Complicated concepts, made very objective.

  3. Hello Dennis

    Yes, what you’re saying is correct.

    1. R1 will advertise a distance of 25 to the destination to R3 because it learned this distance from R2.
    2. Similarly, R1 will advertise a distance of 12 to the destination to R2 because it learned this from R3.

    So, R1 will always give the distance to the destination to each router that it did not learn from that particular router.

    I hope this has been helpful!


  4. Hello Ziad

    R3 will share its own advertised distance to the destiation with R4 and not the advertised distance reported by R1 and R2. So R3 will share an AD of 9 to the destination with R4.

    In general, in EIGRP a router will share its own AD with other routers and the the AD reported by other routers.

    I hope this has been helpful!


  5. Hi Ziad,

    In reality, when R3 receives an update from R1 or R2 about the destination behind R4, it won’t install them since these don’t pass the feasibility condition (AD of the feasible successor has to be lower than FD of successor).

    R3 will only advertise its successor route to other neighbors. In this topology, R4 is the successor route so normally R3 would advertise this route to R4. However, because of split horizon (don’t advertise a route to a neighbor if you learned that route from the neighbor)…this route is not advertised.

    It might be helpful to see all of this in action. Connect four routers like in the topology picture, then load these four configs:

    R1-show-run-2018-01-17-15-58-39-clean.txt (270 Bytes)
    R2-show-run-2018-01-17-15-58-43-clean.txt (270 Bytes)
    R3-show-run-2018-01-17-15-58-46-clean.txt (366 Bytes)
    R4-show-run-2018-01-17-15-58-50-clean.txt (261 Bytes)

    If you want to see the EIGRP updates, you can start Wireshark and use this filter:

    eigrp.opcode == 1

    It will show you the route that is advertised and the metric.

    Seeing this in action probably makes it easier to understand.


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