TTL for BGP packets

By default, an eBGP message has IP TTL of 1. When neighbors do not have a common network, or an eBGP router uses its loopback interface as an update source, the TTL value needs to be adjusted.

(config-router)# bgp neighbor IP_ADDR ebgp-multihop TTL_VALUE

In contrast, iBGP message has TTL of 255, and there is no need for extra configuration when using a loopback interface as an update source.

eBGP OPEN Message

iBGP OPEN Message