Question

You are configuring eBGP between two directly connected routers, R1 and R2. R1 uses 'neighbor 10.1.1.2 remote-as 65002' pointing at R2's directly connected interface IP, and R2 uses 'neighbor 10.1.1.1 remote-as 65001'. However, an engineer changed R1 to peer with R2's Loopback0 address (192.168.2.2) instead, using 'neighbor 192.168.2.2 remote-as 65002' with a static route to reach the loopback. The session fails to establish. What is the MOST likely cause, and what corrects it?

Accepted Answer

eBGP packets are sent with a TTL of 1; peering to a loopback adds a hop, so 'neighbor 192.168.2.2 ebgp-multihop 2' (and matching update-source) is required

Answer

eBGP requires both peers to be in the same AS; change R2 to remote-as 65001 to match R1

Answer

eBGP does not support loopback peering under any circumstances; the only fix is to revert to the directly connected interface IPs

Answer

The loopback must be advertised via an IGP first; adding 'network 192.168.2.2' under BGP will restore the adjacency