On Feb 1, 2008 9:22 AM, Vincent De Keyzer <[EMAIL PROTECTED]> wrote: > Hello list, > > I have a BGP router with 2 eBGP peers (upstreams). This morning one of > the two upstreams (say A) had a scheduled maintenance, and most of the > outgoing traffic went to B. But when A came back up 4 hours longer, > outgoing traffic mostly kept going through B, and traffic towards A did > not reach back its previous level. As a consequence, there currently is > now too much traffic going to B (given the current CDR). > > I have no reason to believe that A has made any configuration change; so > I believe this behaviour is due to "older route first" criterium of the > BGP route selection algorithm (as described in step 10 of > http://www.cisco.com/warp/public/459/25.shtml). > > Does that sound like a reasonable?
Yep, very much so. I've seen this before many times. If both your eBGP upstreams are of the same tier level, more than likely this is it. >How do I check this is indeed the > cause? show ip bgp nei <x.x.x.x> Check the remote router-id of both peers. Bet you a dollar the preferred route has a lower RID (assuming it's two different upstream provider AS's). >If it is, would a "soft in" clear be enough to fix the problem? I believe you have to hard clear to have the BGP RIB re-learn that same prefix and rerun the path selection process. Even so, it'll still come back at the next peering flap, so that's not a good solution. You should probably set up policy for your learned routes to avoid this in the future. _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
