BGP Multipath
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Posted by Darren Green on September 25, 2008, 7:44 am
Please log in for more thread options I was able to create a Lab scenario where BGP was load balancing my traffic across equal cost paths. My lab network consisted of 2 x separate links (AS 65001) running to a non MPLS core in another AS. In the Core I effectively have a square, I will call these devices A, B, C and D. C---D | | A---B | | 1 2 (AS 65001) In my Lab when enabling BGP Multipath I saw routes learned for AS 65001 on C & D as equal cost paths, so far so good. In real life it turns out that the upstream Core uses route-reflectors not a full iBGP mesh. To this end the RR's (A, B & C only) don't seem to provide the same result. I found out that my connection from 1 goes into a 7600 router, this is a RR client of A. My connection from 2 goes directly into B which is a 7600 router that is not part of a RR cluster. Surely, using C as an example (a RR for other routers attached to it call them X + Y), C will receive equal cost BGP routes to 65001 via A and the link B--D--C (assuming equal metrics for AS-Path, Med etc). I believe that the RR will only advertise a single best path to it's clients X + Y but nonetheless can be configured to show 2 x routes in its IP routing table. This link provides more info: http://www.cisco.com/en/US/docs/ios/12_2t/12_2t11/feature/guide/ft11bmpl.html#wp1037704 It shows an example of how to achieve load sharing using RR's, unfortunately through I am not able to request that the RD is changed. A full iBGP mesh of the upstream Core for the VRF concerned is currently being considered. If anyone else has any other ideas though I would be happy to hear them. Regards Darren | ||||||||||
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| BGP Multipath | September 25, 2008, 7:44 am |