A hack to BGP and MPLS

Discussion in 'Cisco' started by tuancao, Feb 18, 2008.

  1. tuancao

    tuancao

    Joined:
    Feb 14, 2008
    Messages:
    2
    HI guys,

    Could you please help me whether we can achieve this or not?

    We have the following network:

    R0 ---- R1---- ..... ----R5---- R6.

    R0 belongs to AS 1.
    (R1,...,R6) belong to AS2.

    Router R6 learned a prefix, say 170.168.0.0/16, from router R0.

    R0's ip address is : 198.18.1.200.

    From R6:
    R6#show ip bgp
    BGP table version is 10, local router ID is 6.6.6.6
    Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
    r RIB-failure, S Stale
    Origin codes: i - IGP, e - EGP, ? - incomplete

    Network Next Hop Metric LocPrf Weight Path
    * i170.168.0.0 198.18.1.200 0 100 0 1 i


    R6#show mpls forwarding-table
    Local Outgoing Prefix Bytes tag Outgoing Next Hop
    tag tag or VC or Tunnel Id switched interface
    26 26 198.18.1.200/32 0 Gi0/1 198.18.1.189


    If I send a packet to 170.168.0.1 the I would like to have the following effect.
    It looks at the BGP forwarding table , see the next hop is : 198.18.1.200.
    It then checks the mpls forwarding table, see that there is an entry for 198.18.1.200, it put up a label, 26 in this case, to that packet and send the labeled packet to the next hop, say 198.18.1.189.

    But I can not achieve it because the router always checks mpls forwarding table first and then check bgp forwarding table.

    So, in my case, it looks at the mpls forwarding table, no entry for 170.168.0.1, then it checks the BGP forwarding table, find an entry for 170.168.0.1, but then it could not forward packet since it does not know how to reach 198.18.1.200.

    it will be great if it can lookup the mpls forwarding table again.

    Do you know how to *tell* the router to looup the mpls forwarding table again?

    Many thanks.
     
    Last edited: Feb 18, 2008
    tuancao, Feb 18, 2008
    #1
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