Question

A service provider establishes an EBGP session between two routers, R1 (AS 65001) and R2 (AS 65002), that are directly connected via a single physical link. The engineer configures the peering using each router's loopback interface address as the neighbor and update source. Static routes to reach the remote loopbacks are in place, and the loopbacks are reachable via ping. However, the EBGP session remains stuck in Active/Idle. What must be configured to bring this session up?

Accepted Answer

Add 'ebgp-multihop 2' (or 'neighbor ... ttl-security') on both routers so the EBGP TTL check does not drop the packets sourced from the loopbacks

Answer

Change the peering to use the directly connected interface addresses instead, because EBGP cannot use loopback interfaces under any circumstance

Answer

Enable 'next-hop-self' on both neighbors so the loopback next hop is rewritten to the connected interface

Answer

Configure BFD on the link, since EBGP loopback peering requires BFD to establish adjacency