Hello all, I'm having a curious problem relating to how IBGP transfers routing information. Here is the scenery:
- 2 Routers belonging to the same AS using IBGP to interact
- Each router communicates with a different ISP trough EBGP
- Router A communicates with ISP A and has a higher Local Preference than Router B (150 and 50)
ISP A --- ROUTER A ---- ROUTER B --- ISP B
Configuration:
ROUTER A configuration
router bgp MY-AS no synchronization bgp router-id ROUTER-A bgp default local-preference 150 network zzz.zzz.zzz.zzz neighbor ISP-A remote-as ISP-A-AS neighbor ISP-A soft-reconfiguration inbound neighbor ROUTER-B remote-as MY-AS neighbor ROUTER-B soft-reconfiguration inbound
ROUTER B configuration
router bgp MY-AS no synchronization bgp router-id ROUTER-B bgp default local-preference 50 network vvv.vvv.vvv.vvv neighbor ISP-B remote-as ISP-B-AS neighbor ISP-B soft-reconfiguration inbound neighbor ROUTER-A remote-as MY-AS neighbor ROUTER-A soft-reconfiguration inbound
After issuing: SH IP BGP SUMMARY
ROUTER A #sh ip bgp summary ... Neighbor PfxRcd ISP A 164428 ROUTER B 996
ROUTER B #sh ip bgp summary ... Neighbor PfxRcd ISP B 164394 ROUTER A 164394
So the resulting SH IP BGP shows the following:
ROUTER B#sh ip bgp BGP table version is 5700819, local router ID is ROUTER B Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
- X.0.0.0 xxx.xxx.xxx.xxx 0 aaaa fghh wer i
*>i yyy.yyy.yyy.yyy 0 150 0 bbbb jfgj erttt ytuty i
- Y.0.0.0 xxx.xxx.xxx.xxx 0 aaaa ewerwwe jbvn i
*>i yyy.yyy.yyy.yyy 0 150 0 bbbb fsdff ghjt i ...
ROUTER A#sh ip bgp BGP table version is 8295544, local router ID is ROUTER A Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>X.0.0.0 xxx.xxx.xxx.xxx 0 aaaa fggg wer i
*>Y.0.0.0 xxx.xxx.xxx.xxx 0 aaaa sfdfg fghh whhf i ...
As you can see the ROUTER A doesn't have all the alternative routes that should be accessed through Router B in case ISP A connectivity fails. So the ROUTER B has all the alternatives, and ROUTER A doesn't. In other words, if ROUTER A has connectivity loss with ISP A, there will be some major time delay to establish all the connectivity through ISP B in ROUTER B. All processes had the time to stabilize and converge their routing information. Can someone explain-me why this happens?
Cheers