bird route selection problem

[Ondrej Zajicek]

On Thu, Jan 27, 2011 at 05:50:42PM +0100, Daniel Rimal wrote:
> Hello,
> 
> i have little weird problem with route selection in bird. A have four
> routers in
> my AS, routers called R1 and R2 is running guagga, routers called R3 and R4
> is running bird 1.2.5. I have configured full mesh between all of them.
> 
> IP 81.xxx.yyy.189 and 81.xxx.yyy.190 is ebgp peers. Both,
> R3 and R4 running bird have established peer with both ebgp routers.
> 
> IP 109.xxx.yyy.11 and 109.xxx.yyy.12 is IP on R3 respectively R4
> (ibgp interconnection)
> 
> After receive this withdraw from ebgp peer 81.xxx.yyy.189 by R3 for example:
> 14:19:23.930683 81.xxx.yyy.189  81.x.yyy.185    BGP     UPDATE Message
> Withdrawn prefix: 187.120.96.0 (187.120.96.0)
> 
> bird do this: - switch route between ebgp and ibgp peer very fast -
> 288 times (in one second) in this case:
> 14:19:25 <TRACE> kernel1 < replaced 187.120.96.0/23 via 81.xxx.yyy.190
> on bond0.402
> 14:19:25 <TRACE> kernel1 < replaced 187.120.96.0/23 via 109.xxx.yyy.12
> on bond0.403
> 14:19:25 <TRACE> kernel1 < replaced 187.120.96.0/23 via 81.xxx.yyy.190
> on bond0.402

This is really strange - if R3 has a route from 81.xxx.yyy.190, that
route should be preferred. One possible explanation is that ebgp peer
81.xxx.yyy.190 also sent that sequence of updates and withdraws to R3
(causing him to switch to ibgp-route when ebgp-route was withdrawn and
swich back when it reappears). Are you sure that it is not the case?

The switching sequence was on both R3 and R4?

Could you also send me an output of 'show route 187.120.96.0/23 all'
on R3 and R4?

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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