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Forum Replies

  1. Quick question Rene on this topic. The lab works fine as I followed along with my own topology. But I am just wondering why R2 should send the community only to R3? For example, you mentioned: “R2 sets the community so make sure that it advertises it to R3”… why should it not send the community to R4 as well. I know R4 is in another AS, but R4 would have filtered it out as well, wouldn’t it?

  2. Hi Mario,

    On R2 I configured the route-map inbound (facing R1) so that R2 sets the local AS community. Because of this, R2 will no longer advertise prefixes to R4 since it’s another sub-AS. R3 will still receive it since it’s in the same sub-AS as R2.

    To make sure R5 (and R4) learn anything through R3, we need to advertise the local AS community to R3.

    Rene

  3. Hi,

    I am confused about BGP selecting path.Here topology

    http://i65.tinypic.com/2r7n9t3.jpg

    R5 is in sub-AS 45.And advertise prefix 9.9.9.9/32.

    R5#sh ip bgp             
    BGP table version is 14, local router ID is 5.5.5.5
    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
    *> 9.9.9.9/32       0.0.0.0                  0         32768 i
    *> 192.168.12.0     2.2.2.2      
    ... Continue reading in our forum

  4. Hi Ler Sak,

    BGP doesn’t differentiate between confed-internal or confed-external. When the two paths are the same, it’s up to the router ID to decide which one will be selected.

    Here’s an example from the topology I used in this lesson:

    R4#show ip bgp 55.55.55.55/32
    BGP routing table entry for 55.55.55.55/32, version 5
    Paths: (2 available, best #1, table default)
    Flag: 0x800
      Not advertised to any peer
      Refresh Epoch 1
      (35)
        5.5.5.5 (metric 2) from 2.2.2.2 (2.2.2.2)
          Origin IGP, metric 0, localpref 100, valid, confed-internal, best
          rx pathid: 
    ... Continue reading in our forum

  5. Hi Rene,

    Thank you so much.

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