When examining routes advertised to BGP neighbor, notice some routes are tagged with “r”:
rtr1#sh ip bgp neighbor 10.11.19.21 advertised
BGP table version is 1735468, local router ID is 10.115.254.254
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, x best-external, f RT-Filter, a additional-path
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
r>i10.115.254.0/30 10.115.254.9 0 100 0 i
*> 10.115.254.0/23 10.115.254.9 21 32768 i
r>i10.115.254.4/30 10.115.254.9 0 100 0 i
r>i10.115.254.8/30 10.115.254.9 0 100 0 i
Note this is BGP “RIB-failure”, which indicates BGP fails to install the route in routing table. According to this link, the likely cause is the route is already installed by IGP which has a lower AD.
As shown, for routes already learned via OSPF, BGP encounters RIB-failure
rtr1#sh ip route 10.115.254.0
Routing entry for 10.115.254.0/30
Known via "ospf 100", distance 110, metric 21, type extern 1
Last update from 10.115.254.9 on Port-channel22, 2d09h ago
Routing Descriptor Blocks:
* 10.115.254.9, from 10.147.254.37, 2d09h ago, via Port-channel22
Route metric is 21, traffic share count is 1
What is the effect on BGP? BGP will not advertise “r” (RIB-failure) routes to peers. In other words, this may be the cause for BGP neighbor not learning networks as expected.
What is the work around? It is common for IGP to co-exist with BGP in an enterprise network, especially to learn certain internal networks via IGP, and use BGP to advertise those networks to other AS. As shown here, the RIB-failure behavior prevents advertisement out.
The solution is to use “network” statements with BGP to advertise. By using “network” statements, networks can be learned from connected routes, from dynamic routing, and from static route sources, BGP will advertise to peers.
router bgp 65000
network 10.115.254.0 255.255.255.252
Check routes advertised out again, RIB-failure is no longer showing for the network, it is now being advertised to BGP peers.