Networking Basic Questions

Posted on 2007-07-22
Last Modified: 2010-04-17
I got a question about networking.

Anyone know how to make a loop of length 4 in RIP, even if one uses split horizon with poisonous reverse?
Question by:geoffryf
    LVL 50

    Accepted Solution

    First of all, split horizons and poison reverse accomplish the same thing. Some vendors use one, some use the other.

    So you want to make a routing loop even though split horizons or poison reverse are being used?

    It's possible...But it requires a network going down and some real specific timing.

    Put the four routers in a loop.

    |              |

    If R1 loses a path to a network that is not reachable through R2, 3 or 4 (say a directly connected network). It will notify R2 and R3 that the network is down. If (and here's the tricky timing part) R4 sends out an update BEFORE it learns that the network is down from R2 and R3, then it will notify those two neighbors that the network is still reachable.

    Of course, if hold down timers are used, this won't happen.

    Author Comment

    Thank you. That clearifies my concept about RIP and Split Horizon

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