Link-Local Next Hop Capability for BGP

To support IPv6 [RFC4291] reachability, BGP [RFC4271] relies on the Multiprotocol Extensions as defined in [RFC4760]. [RFC2545] defines the structure of IPv6 next hops. These IPv6 next hops may contain a Global IPv6 address, and optionally can contain an IPv6 Link-Local address when the BGP peer is directly attached and shares a common subnet with the IPv6 Global address. This document updates [RFC2545] to clarify the encoding of the BGP next hop when the advertising system is directly attached and only an IPv6 Link-Local address is available. A new BGP Capability [RFC5492] is defined to signal support for this updated encoding. This clarification applies specifically to IPv6 Link-Local addresses and does not pertain to IPv4 Link-Local addresses as defined in [RFC3927].