bird route selection problem

[Daniel Rimal]

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Withdrawn prefix: 187.120.96.0 (187.120.96.0)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

which generates a lot of withdraw/updates messages between all routers
in my AS (288 times in this case):

14:19:26.018478 109.xxx.yyy.11  109.xxx.yyy.12  BGP     UPDATE Message
Withdrawn prefix: 187.120.96.0 (187.120.96.0)

14:19:26.018567 109.xxx.yyy.12  109.xxx.yyy.11  BGP     UPDATE Message
Withdrawn prefix: 187.120.96.0 (187.120.96.0)

14:19:26.018643 109.xxx.yyy.11  109.xxx.yyy.12  BGP     UPDATE Message
NLRI prefix: 187.120.96.0 (187.120.96.0)

14:19:26.018766 109.xxx.yyy.12  109.xxx.yyy.11  BGP     UPDATE Message
NLRI prefix: 187.120.96.0 (187.120.96.0)

If i undestant correctly, ebgp peer .189 withdraw this route, but
route is still
available via ebgp peer .190 and via ibgp peer and it looks bird don't
know which
path use. This is one concrete case, but i think, bird have this
behaviour with almost
of all bgp updates, which i can see in debug log.

Thanks for any help.

Dan Rimal