Easy RIP Question?

Discussion in 'Cisco' started by Darth Tyrannus, Jun 4, 2005.

  1. RIP uses a hold-down timer to make sure a route advertised with a
    higher metric is indeed valid. RIP will put a higher metric advertised
    route into hold-down for default 180 seconds, meaning it won't put this
    higher advertised metric into it's routing table for at least 180
    seconds as long as it keeps getting updates for the same metric.

    So what exactly happens with RIP split horizon poisoned reverse? If
    the router receives information that a network is unreachable through
    split horizon, and the route is already in it's table with a lower
    metric, wouldn't this route be eventually be replaced with an
    unreachable value?

    Wait...I just realized that this same router would obtain updates from
    another router with the lower metric for this route, so in essence,
    this route would be in hold-down for only as long as the next update is
    received advertising the lower metric.

    So, one router could advertise unreachable and another router could
    advertise 1, and the router inbetween would only be in hold-down for
    that route until it received the lower metric advertisement. Every
    time it received a split horizon unreachable on one interface it would
    go into hold-down. Then when the new update with the lower metric
    comes through the other interface the table is not updated, but the
    hold-down timer is reset.
    Darth Tyrannus, Jun 4, 2005
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