On Fri, Jan 28, 2011 at 10:07 AM, Ondrej Zajicek <santi...@crfreenet.org> wrote: > 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 Withdrawn prefix: 187.120.96.0 (187.120.96.0) 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 (causing him to switch to ibgp-route when ebgp-route was withdrawn and 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?
There is route detail: 187.120.96.0/23 via 81.xxx.yyy.190 on bond0.402 [casa190 04:45] * (100) [AS28202i] Type: BGP unicast univ BGP.origin: IGP BGP.as_path: 15685 29208 3549 4230 28202 BGP.next_hop: 81.xxx.yyy.190 BGP.local_pref: 700 BGP.community: via 109.xxx.yyy.10 on bond0.403 [r2 09:08] (100) [AS28202i] Type: BGP unicast univ BGP.origin: IGP BGP.as_path: 29208 3549 4230 28202 BGP.next_hop: 109.xxx.yyy.10 BGP.local_pref: 500 BGP.community: (2,100) (2,3549) (3549,4359) (3549,30840) (4230,21) (4230,30) (4230,31) (4230,131) (29208,3549) via 81.xxx.yyy.189 on bond0.402 [casa189 04:45] (100) [AS28202i] Type: BGP unicast univ BGP.origin: IGP BGP.as_path: 15685 29208 3549 4230 28202 BGP.next_hop: 81.xxx.yyy.189 BGP.local_pref: 700 BGP.community: But route list is probably affected by some experiments which i did on routers last night. I'm sure that ebgp routers send only one update/withdraw, i checked by tcpdump too. Switching sequence was on R3 and R4 too. But i found the problem is probably caused by local_pref settings. I did some experiments and found bird weird behaviour when i have identical bgp_local_pref value in import filter on both ibgp peers R3 & R4, like that: filter bgp_in_sitel { bgp_local_pref=500; accept; } protocol bgp r4 { # disabled; description "propoj s R4"; debug {events, states}; local as 35236; neighbor 109.xxx.yyy.12 as 35236; hold time 90; startup hold time 90; connect retry time 30; keepalive time 30; start delay time 5; error wait time 60, 300; error forget time 300; # disable after error; next hop self; path metric 1; default bgp_med 0; default bgp_local_pref 500; import filter bgp_in_sitel; export all; When i completely disabled import filter on both ibgp peers (set import all) and "default_bgp_local_pref" was identical on R3 & R4, bird behaviour was normal. When i enabled import filter on both sides, set different "bgp_local_pref" but "default bgp_local_pref" was identical, bird behaviour was still bad. When i enabled import filter on both sides, set different "bgp_local_pref" and set different "default bgp_local_pref" , bird behaviour was normal. Dan