BGP Peering
BGP assumes that external neighbors are directly connected and that they
are peering with the IP address of the directly connected interface of their
neighbor. If not, you must tell BGP to look more than one hop away for its
neighbor, with the neighbor ip-address ebgp-multihop number-of-hops
command. You might use this command if you are peering with loopback
interface IP addresses, for instance. BGP assumes that internal neighbors
might not be directly connected, so this command is not needed with IBGP.