Question

Two directly connected routers, R1 (AS 65010) and R2 (AS 65020), are configured for eBGP peering using their physical interface IP addresses. The link is up and both routers can ping each other's interface, but the BGP session cycles between Idle and Active and never reaches Established. On R1 you see the neighbor configured with 'neighbor 10.0.0.2 update-source Loopback0'. R1's Loopback0 is 1.1.1.1/32 and R2 is peering to 10.0.0.1 (R1's physical interface). What is the most likely cause of the session failure?

Accepted Answer

R1 is sourcing BGP packets from Loopback0 (1.1.1.1), but R2 expects the session from 10.0.0.1, so the incoming packets do not match R2's configured neighbor address

Answer

eBGP requires the 'ebgp-multihop 2' command whenever routers are directly connected on the same subnet

Answer

The two routers are in different autonomous systems, which prevents any eBGP session from forming without a route reflector

Answer

BGP synchronization is enabled by default and must be disabled before the neighbor can reach Established