BGP - Missing Routes

Question 1

Missing BGP Routes

Answer 1

Reasons that route advertisement fails between BGP peers:

• Next-Hop Check Failure
• Bad Network Design
• Validity Check Failure
• BGP Communities
• Mandatory EBGP Route Policy for IOS XR
• Route filtering

Question 2

Adj-RIB-In

Answer 2

The Loc-RIB table contains only valid routes that passed the
router’s inbound route policies.

Examining the Adj-RIB-in table verifies whether the peer received the NLRI.
If the peer received it, the local inbound route policy prevents the route from installing
into the Loc-RIB table.

Inbound Soft Configuration is required to view the Adj-RIB-in table, because the table
is purged by default after all inbound route-policy processing has occurred.

# show bgp afi safi neighbor ip-address [prefix/prefix-length] received-routes

Question 3

Loc-RIB

Answer 3

Just because a route is missing from the Global RIB, it does not mean
the route did not make it into the router’s BGP table.

Examine the Loc-RIB table to see if the prefix exists in the BGP table. It is possible
that the route installed in the BGP table but did not install into the RIB.

Viewing the local BGP table is the first step in troubleshooting any missing route.
Examining a specific prefix provides the reason a route was not installed into the RIB.

# show bgp afi safi [prefix/prefix-length]

Question 4

Adj-RIB-Out

Answer 4

Viewing the Adj-RIB-out table on the advertising router verifies that the
route was advertised and provides a list of the BGP PAs that were included with the route.

In the event that the route is not present in the advertising router’s Adj-RIB-out
table, check the advertising router’sLoc-RIB table to verify the prefix exists there.

Assuming the prefix is in the Loc-RIB table, but not in the Adj-RIB-out table,
then the outbound route policies are preventing the advertisement of the route.

# show bgp afi safi neighbor ip-address [prefix/prefix-length] advertised-routes