OSPF Routing loop?

Discussion in 'Cisco' started by Garry, Apr 23, 2005.

  1. Garry

    Garry Guest

    Somehow I must be going nuts ...

    I'm trying to set up a backup link. Currently, all traffic on the
    backbone is routed via OSPF-learned routes, which works fine. I have now
    added a backup line, which is also OSPF enabled. "show ip ospf nei"
    correctly shows all OSPF neighbors that should be there, none that
    shouldn't. Network looks something like this (simplified):

    R1----------R2
    | |
    | |
    | |
    R3----------R4

    R1-R2 and R3-R4 are 100M LAN links, R1-R3 is a POS, R2-R4 a 2M link.

    When R1-R3 goes down, it takes about three seconds for R1 to announce
    the loss of OSPF neighbor to R2. R2 then adjusts its routing to use
    R2-R4 for the link to the other side, and announces the routes. R1
    accepts the routing changes - then, R2 switches back to using R1 as
    gateway to the outside ... (whereas R1 still uses R2 as gateway to the
    outside).

    WTF is going on here? R1 is getting the route from R2, so why isn't R2
    using what it's announcing instead of switching back to R1???

    Hints appreciated!
    Garry, Apr 23, 2005
    #1
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  2. Garry

    Ivan Ostres Guest

    In article <d4eb63$ti6$>, says...
    > When R1-R3 goes down, it takes about three seconds for R1 to announce
    > the loss of OSPF neighbor to R2. R2 then adjusts its routing to use
    > R2-R4 for the link to the other side, and announces the routes. R1
    > accepts the routing changes - then, R2 switches back to using R1 as
    > gateway to the outside ... (whereas R1 still uses R2 as gateway to the
    > outside).
    >
    > WTF is going on here? R1 is getting the route from R2, so why isn't R2
    > using what it's announcing instead of switching back to R1???
    >


    This looks interesting. Can you please post 'show ip ospf database' from
    R1, R2 and R3 when POS link is down?

    --
    -Ivan.

    *** Use Rot13 to see my eMail address ***
    Ivan Ostres, Apr 23, 2005
    #2
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  3. Garry

    Garry Guest

    Ivan Ostres wrote:
    > This looks interesting. Can you please post 'show ip ospf database' from
    > R1, R2 and R3 when POS link is down?


    Slightly longer dumps --- what excerpts would be the most interesting?
    Garry, Apr 23, 2005
    #3
  4. Garry

    Ivan Ostres Guest

    In article <d4ejof$22$>, says...
    > Ivan Ostres wrote:
    > > This looks interesting. Can you please post 'show ip ospf database' from
    > > R1, R2 and R3 when POS link is down?

    >
    > Slightly longer dumps --- what excerpts would be the most interesting?
    >


    How many areas do you have? Where do you get your "outside" routes? Do
    you redistribute them? From where?


    --
    -Ivan.

    *** Use Rot13 to see my eMail address ***
    Ivan Ostres, Apr 24, 2005
    #4
  5. Garry

    Garry Guest

    Ivan Ostres wrote:
    > How many areas do you have? Where do you get your "outside" routes? Do
    > you redistribute them? From where?


    Just area 0.0.0.0 . Even tried adding IBGP on both routers with default
    announced from the other side. Still can't seem to get the one router to
    use the OSPF/BGP announced default route, but still sticks to the other
    route ... the crazy thing I can't understand is that the router right
    when the primary link goes down will use its backup connection,
    announces it to the local OSPF network, then seems to get it back from
    the other router and switches it over to the second even though its
    default is back to him ...

    What am I missing here?

    -garry
    Garry, May 7, 2005
    #5
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