Tuesday, October 11, 2011

BGP RIB Failure

When BGP tries to install the best-path prefix into the Routing Information Base (RIB), it might be rejected due to there is an IGP or static route with lower administrative distance already exists in the IP routing table.
A BGP route that is not being installed into the RIB is also known as an inactive route.
Note: Routing Information Base (RIB) is simply another name for the IP routing table.

The show ip bgp rib-failure EXEC command displays the BGP routes that failed to be installed into the RIB, but are installed into the BGP table as RIB-failure routes.
Note: The network topology that is used for this article is Page 223 - Advanced BGP Network.
RT2#sh ip bgp
BGP table version is 9, local router ID is 2.2.2.2
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
*> 192.168.1.0      1.1.1.1                  0             0 65001 i
*> 192.168.2.0      0.0.0.0                  0         32768 i
r>i192.168.3.0      3.3.3.3                  0    100      0 i
r>i192.168.4.0      4.4.4.4                  0    100      0 i
RT2#
RT2#sh ip route 192.168.0.0 255.255.0.0 longer-prefixes

Gateway of last resort is not set

B    192.168.1.0/24 [20/0] via 1.1.1.1, 00:00:55
C    192.168.2.0/24 is directly connected, Ethernet0/0
O    192.168.3.0/24 [110/20] via 23.23.23.3, 00:01:05, Ethernet0/2
O    192.168.4.0/24 [110/20] via 24.24.24.4, 00:01:05, Ethernet0/3
RT2#
RT2#sh ip bgp rib-failure
Network            Next Hop                      RIB-failure   RIB-NH Matches
192.168.3.0        3.3.3.3             Higher admin distance              n/a
192.168.4.0        4.4.4.4             Higher admin distance              n/a
RT2#

MISC notes for the output of the show ip bgp rib-failure EXEC command:
 An entry of 0.0.0.0 of the Next Hop column indicates that the router has some non-BGP routes to the particular network.
 The RIB-NH Matches column indicates whether the next hops of the BGP and IP routes are the same. It is valid (Yes / No) only when the Higher admin distance reason appears in the RIB-failure column and the bgp suppress-inactive BGP router subcommand is configured for the address family that is being used.
Yes The next hop of the route in the RIB is same as the next hop of the BGP route or recurses down to the same adjacency as the next hop of the BGP route.
No The next hop of the route in the RIB recurses down differently from the next hop of the BGP route. BGP route that has a different next hop than the next hop of the IP route will not be advertised to other BGP neighbors (both IBGP and EBGP) – it is being suppressed.
n/a bgp suppress-inactive is not configured for the address family that is being used.

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