Changes to routing table with multilink PPP

Discussion in 'Cisco' started by John Caruso, Mar 28, 2006.

  1. John Caruso

    John Caruso Guest

    I've converted a T1 connection between two sites to use multilink PPP,
    in preparation for putting in a second T1 between the sites. As part of
    this change I moved the IP address (172.29.1.25, with a /30 netmask) from
    the serial line (serial1/0) to the multilink interface (multilink1).

    This caused a change in the routing table that I didn't expect. Before
    the multilink config, the relevant routing table entries looked like this:

    172.29.0.0/30 is subnetted, 9 subnets
    C 172.29.1.24 is directly connected, Serial1/0

    The other 8 subnets on 172.29.0.0 were also /30s. But after the switching
    to the multilink the routing table now looks like this:

    172.29.0.0/16 is variably subnetted, 10 subnets, 2 masks
    C 172.29.1.24/30 is directly connected, Multilink1
    C 172.29.1.26/32 is directly connected, Multilink1

    So apparently what's happening is that not only is the route for the
    network on the multilink interface itself being added to the routing table
    (as I expected), but also another route for the IP address of the router
    on the *other side* of the multilink interface (172.29.1.26).

    Is this expected behavior? This is on IOS 12.3(17a), by the way. If it's
    not expected behavior, any ideas why it would be happening?

    - John
     
    John Caruso, Mar 28, 2006
    #1
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  2. John Caruso

    Merv Guest

    this is default behaviour for PPP IPCP.

    to disable this behaviour:

    int <>
    no peer neighbor-route
     
    Merv, Mar 28, 2006
    #2
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  3. John Caruso

    John Caruso Guest

    Yes, that was it, thanks. I see a lot of references to it now that I know
    what to look for (so often the case with Cisco).

    One point for anyone reading this in the future: adding these statements
    to the config is not enough to get rid of the peer's /32 route once it's
    infested your routing table--you have to bounce the interface.

    - John
     
    John Caruso, Mar 28, 2006
    #3
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