[c-nsp] BGP - Older routes?

[Oliver Boehmer (oboehmer)]

Vincent De Keyzer <> wrote on Friday, February 01, 2008 4:22 PM:

> 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? How do I check this is indeed the
> cause? If it is, would a "soft in" clear be enough to fix the problem?

It does sound like the likely cause, you can paste a "show ip bgp
<prefix>" for one of the prefixes to make sure all decision steps up to
#10 return equal. Not sure if a "soft in" would help, maybe a
route-refresh ("clear ip bgp ... in") will.
If you require a deterministic decision, enable "bgp best path
compare-routerid" (as mentioned in the doc you've quoted)..

	oli