Routing/Default Gateways/WAN down.

Discussion in 'Cisco' started by Edwin Davidson, May 10, 2004.

  1. I have multiple routers.

    (WAN) Router one has a default gateway that gets it to our (Lan)
    router two, which in turn has a default gateway that gets it to an
    (internet) router three that connects to yet another (internet) router
    four., etc on out to the internet.

    The clients on our LAN have default gateways that point to a few of
    these routers that route traffic to our WAN locations. By having a
    default gateway on these WAN routers that points to the internet
    router three (above) any traffic can be routed by our WAN routers beit
    directly or with ICMP redirects.

    The problem is that when these remote WAN locations are shut down, the
    DEFAULT GATEWAY side of these Cisco routers direct all this WAN
    traffic over to internet router three. Internet router three has
    static routes to the WAN locations via the LAN router two.

    So we end up with a routing loop. This drains router two and router
    three's resources.

    How do I configure the Cisco router two so that if the WAN link isn't
    down it doesn't pass that traffic off to the default gateway? I still
    want unknown traffic to get ICMP redirects. Just now the WAN

    To add to this, there are three LAN->WAN (not internet) routers setup
    like this, which all are a part of a IGRP group.

    I'm not the Networking guy - I am the guy in the router 3 portion of
    this mix, where router 3 is an antivirus gateway.


    Edwin Davidson
    Edwin Davidson, May 10, 2004
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  2. Set up a floating static route for the WAN subnets that points to the
    Null0 interface:

    ip route <subnet> <mask> Serial0/1
    ip route <subnet> <mask> Null0 250

    As long as Serial0/1 is up, the WAN traffic will be sent to it. When
    the WAN link is down the interface with shut down, and then the Null0
    route will be used.
    Barry Margolin, May 10, 2004
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