so easy to loop ?

Discussion in 'Cisco' started by Yannick CHAMPS, Aug 6, 2004.

  1. Hi,

    2 routers running ospf over wan.
    Router A redistribute a static route pointing to router B.
    Router B get this ospf update and install a route pointing back to router A.
    Easy loop created !
    Is there no loop prevention mecanism ?

    Yannick.
     
    Yannick CHAMPS, Aug 6, 2004
    #1
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  2. Yannick CHAMPS

    JNCIP#0136 Guest

    Yes, that can easily happen if the next-hop of static route is NOT covered
    by "network" statement
    on Router A and then Router A creates LSA Type 5 with forwarding address
    0.0.0.0 (means self).
    Router B accepts this LSA and installs OSPF route with next-hop pointing to
    Router A assuming
    the AD of this route is most preferred.
    Make sure You always specify OSPF network with correct wildcard mask and/or
    double-check and redefine
    AD on Router B.
    Or get rid of static routes altogether :)
    HTH,
    Cheers
    Alex

    "Yannick CHAMPS" <> wrote in message
    news:...
    > Hi,
    >
    > 2 routers running ospf over wan.
    > Router A redistribute a static route pointing to router B.
    > Router B get this ospf update and install a route pointing back to router

    A.
    > Easy loop created !
    > Is there no loop prevention mecanism ?
    >
    > Yannick.
     
    JNCIP#0136, Aug 6, 2004
    #2
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  3. Yannick CHAMPS

    Martijn Guest

    (Yannick CHAMPS) wrote in message news:<>...
    > Hi,
    >
    > 2 routers running ospf over wan.
    > Router A redistribute a static route pointing to router B.
    > Router B get this ospf update and install a route pointing back to router A.
    > Easy loop created !
    > Is there no loop prevention mecanism ?
    >
    > Yannick.


    Yannick,

    If the static route on router A is pointing to a subnet directly
    connected to router B, then there should be no loop since the metric
    for a directly connected networks is lower. The only exception is when
    the subnetmask configured in the static route is smaller ("most
    specific route").

    Regards, Martijn
     
    Martijn, Aug 6, 2004
    #3
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