I believe I'm on the right track, but have stumble across something with advertising BGP prefixes to neighbors. I am wonder how if I have a single ASN with multiple prefixes ( and with multiple upstream ISPs. How do I send BGP attributes to these upstreams to influence how ingress traffic would go to which router. See picture. enter image description here

As you can see this is a GNS3 lab I put together. I have an ASN#99 with 2(two) prefixes ( and I also have two ISP neighboring routers. Tier3-1 and Tier3-2. I am trying to get from Tier1's perspective, the best path for prefix is through Tier3-1 and the best paht for prefix prefix is through Tier3-2.

Keep in mind, I cannot touch Tier3-1 or Tier3-2.

This is probably something simple I am missing. Appreciate everyones help.

  • 1
    Have you tried AS-Path prepending? When you advertise a prefix to the ASN that you least want traffic for that prefix, prepend your AS number to the path multiple times, and don't do that for the prefix for which you do want traffic. – Ron Maupin Aug 25 '15 at 20:34
  • I've added a route-map for with set as-path prepent 99 99 99 – Jim Aug 26 '15 at 12:55
  • I've added a route-map for with set as-path prepent 99 99 99, but the show ip bgp on Tier1 still shows Site 1 as the best path for both prefixes. – Jim Aug 26 '15 at 13:05
  • After you set up the prepending, did you restart BGP? If ASN#1 has two paths to from both ASN#31 and ASN#32, and it has one AS hop through ASN#31 and 3 AS hops through ASN#32, under normal circumstances, it will chose the path through ASN#31. You can try to influence which path another AS chooses to your site, but you have no control over the path. – Ron Maupin Aug 26 '15 at 13:18
  • Would it be better to just Advertise one prefix out of site 1 and the other out of site 2, rather than both and try to influence it. – Jim Aug 26 '15 at 13:30

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