General BGP & OSPF Re-Distribution Question

Discussion in 'Cisco' started by Darren Green, Nov 16, 2009.

  1. Darren Green

    Darren Green Guest

    Hi,

    I set up a simple network in Dynamips. This was a triangle, R1, R2,
    R3. R1 is connected to R2 (serial) and to R3 (Serial). On the inside
    of R2 & R3 I use a switch to connect them together.

    R1
    / \
    R2 R3
    | |
    -------
    |
    R4

    I then added R4.

    On R1 I run ebgp (AS1), R2 ebgp (AS2), R3 ebgp (AS3). On this inside
    of R2, R3 & R4 I run OSPF. I then mutually re-distribute on R2 & R3
    the BGP into OSPF and vice versa. I added networks 10.0.2.0/24 and
    10.0.3.0/24 on R4 which get picked up in OSPF on R2 & R3 before being
    advertised out in BGP to R1.....everything works fine. (NB I don't
    have any filtering which I would normally add for best practice).

    I notice that when I shut say R3's LAN interface, the route to the R4
    networks are learned in BGP on R3 (AS Path is 1,2). This is of course
    because R2 advertises them onto R1 which then pushes the route in BGP
    to R3.

    When re-opening the LAN interface on R3, the BGP routes still stay's
    even when the OSPF neighborships come back up on the LAN side. I guess
    R3 sees the better AD and wont give it up even when the local route
    comes back.

    Can anyone comment on this and a suggested workaround.

    Regards

    Darren
     
    Darren Green, Nov 16, 2009
    #1
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