Struggling with AS path filters and prepend

Discussion in 'Cisco' started by essenz, Dec 16, 2009.

  1. essenz

    essenz Guest

    OK... So after many days of struggling with this, its time to post.

    I have customer behind my router that does BGP and uses "me" as a BGP
    peer in addition to another carrier. Because he favor the carrier, on
    my BGP session he prepends a few times.

    I see his advertised routes, but my router is not advertising them out
    to my BGP upstreams (XO, Abovenet). My upstreams filter on prefix, but
    those filters have been updated to include the IPs that my customer
    announces off their router. And all of this works fine when the
    customer does not do the prepends.

    Here are my BGP settings:

    neighbor MY.DOWNSTREAM.CUST remote-as 33000
    neighbor MY.DOWNSTREAM.CUST ebgp-multihop 5
    neighbor MY.DOWNSTREAM.CUST update-source FastEthernet9/1
    neighbor MY.DOWNSTREAM.CUST next-hop-self
    neighbor MY.DOWNSTREAM.CUST send-community
    neighbor MY.DOWNSTREAM.CUST soft-reconfiguration inbound
    neighbor MY.DOWNSTREAM.CUST prefix-list AS33000-in in
    neighbor MY.DOWNSTREAM.CUST prefix-list AS33000-out out
    neighbor MY.DOWNSTREAM.CUST filter-list 1 out
    neighbor MY.ABOVE.NET remote-as 6461
    neighbor MY.ABOVE.NET ebgp-multihop 5
    neighbor MY.ABOVE.NET update-source GigabitEthernet3/8
    neighbor MY.ABOVE.NET next-hop-self
    neighbor MY.ABOVE.NET send-community
    neighbor MY.ABOVE.NET soft-reconfiguration inbound
    neighbor MY.ABOVE.NET filter-list 1 in
    neighbor MY.ABOVE.NET filter-list 15 out

    And here are the ACLs:

    ip as-path access-list 1 permit .*
    ip as-path access-list 15 permit ^$
    ip as-path access-list 15 permit ^(_33000)+$
    ip as-path access-list 15 permit ^(33000_)+$
    ip as-path access-list 15 permit 33000 33000 33000
    ip as-path access-list 15 permit ^(17000_)+$

    17000 is my ASN.

    AS 33000 is my customer and they prepend, here is the output of a sh
    ip bgp neighbor received-routes:

    Network Next Hop Metric LocPrf Weight Path
    * 100.100.242.0 5.5.49.194 0 33000 33000
    33000 i
    * 100.100.243.0 5.5.49.194 0 33000 33000
    33000 i
    * 100.100.244.0 5.5.49.194 0 33000 33000
    33000 i
    * 100.100.245.0 5.5.49.194 0 33000 33000
    33000 i
    * 100.100.252.0 5.5.49.194 0 33000 33000
    33000 i
    * 100.100.253.0 5.5.49.194 0 33000 33000
    33000 i
    * 100.100.254.0 5.5.49.194 0 33000 33000
    33000 i
    * 100.100.108.0 5.5.49.194 0 33000 33000
    33000 i


    The question is, are my problems due to filter syntax on the outbound
    as-path filter, OR is my upstream preventing routes with prepends?
     
    essenz, Dec 16, 2009
    #1
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