IS
"A BGP router uses UDP based Hello messages to discover directly connected BGP neighbors over those interfaces enabled for Neighbor Discovery. The BGP Hello messages for the Neighbor Discovery procedure are used for link-locally signaling and hence MUST be addressed to the "all routers on this subnet" group multicast address (i.e., 224.0.0.2 in the IPv4 case and FF02::2 in the IPv6 case) and the TTL for the IP packets SHOULD be set to 1. The IP source address MUST be set to the address of the interface over which the message is sent out which would be the primary interface address or unnumbered address in the IPv4 case and the IPv6 link-local address on the interface in the IPv6 case."
https://tools.ietf.org/id/draft-xu-idr-neighbor-autodiscovery-12.html#:~:text=A%20BGP%20router,the%20IPv6%20case.