BGP confusion

Danilo Dy · ‎03-07-2007

Hi,

I have three routers running iBGP, when I execute "show ip bgp regexp ^$" in one of them I get the output attached. What thus RIB-Failure mean and what causes it? Why the best (>) is the last two lines not the first?

Danilo Dy · ‎03-07-2007

Oop, here is the attached file

jarvar832004 · ‎03-07-2007

i have noticed this rib failure state to those routes, which are distributed into BGP but yet are not the best routes to be installed into the routing table. There might be better metric routes available through other routing protocols.

Jon Marshall · ‎03-07-2007

Hi

From the BGP FAQ

Q. What does r RIB-Failure mean in the show ip bgp command output?

R1> show ip bgp

BGP table version is 5, local router ID is 200.200.200.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

r> 6.6.6.0/24 10.10.13.3 0 130 0 30 i

*> 7.7.7.0/24 10.10.13.3 0 125 0 30 iWhen BGP tries to install the bestpath prefix into Routing Information Base (RIB) (for example, the IP Routing table), RIB might reject the BGP route due to any of these reasons:

Route with better administrative distance already present in IGP. For example, if a static route already exists in IP Routing table.

Memory failure.

The number of routes in VPN routing/forwarding (VRF) exceeds the route-limit configured under the VRF instance.

In such cases, the prefixes that are rejected for these reasons are identified by r RIB Failure in the show ip bgp command output and are not advertised to the peers. This feature was first made available in Cisco IOS Software Release 12.2(08.05)T.

HTH

Jon

Danilo Dy · ‎03-07-2007

Hi Jon,

Thanks for your reply. So if I advertised it to my eBGP neighbor what will happen, what is the impact? Will my eBGP neighbor still receive 192.168.0.0/20 or not at all?)

!

ip as-path access-list 1 ^$

!

neigbor 10.1.1.1 prefix-list 1 out

Jon Marshall · ‎03-08-2007

Hi

According to the FAQ, no. If the route has been marked with a rib failure then it will not get advertised to any peers. So your EBGP neighbor should not receive the 192.168.0.0/20 route at all.

HTH

Jon

Danilo Dy · ‎03-08-2007

Hi Jon,

That strange, my eBGP neighbor seems to be able to received it as when I look at the looking glass from RIPE NCC I can see 192.168.0.0/20 received from my eBGP neighbor. Will the FAQ pointing to BGP as a whole or just for iBGP and not eBGP?

Dandy

Jon Marshall · ‎03-08-2007

Hi

Yes that is a bit strange at first sight. The FAQ definitely states

"In such cases, the prefixes that are rejected for these reasons are identified by r RIB Failure in the show ip bgp command output and are not advertised to the peers."

I think the FAQ for this particular question was referring to BGP as a whole.

If i get a chance i will lab it up to see exactly what it is doing but may not be till next week.

Cheers

Jon

Danilo Dy · ‎03-08-2007

I've been trying to simulate the same error in the lab, no luck :)

Thanks Jon