Advertising IPv4 Prefixes Over an IPv6 BGP Peering
Creating an IPv6 BGP peering to advertise IPv4 prefixes is a feasible network configuration. However, a common challenge faced in this setup is the complexity associated with handling IPv4 next hops when the network's underlay is IPv6-only. Typically, IPv4 routes can have unreachable IPv4 next hops in such a case because the next hop is an IPv6 address.
RFC 5549 addresses this issue by providing a standard method for BGP to advertise IPv4 routes with an IPv6 next-hop. This removes the need for IPv4 addresses in the control plane between BGP peers. This approach is often used by networks transitioning from IPv4 to IPv6.
Links
https://networklessons.com/bgp/multiprotocol-bgp-mp-bgp-configuration