IETF RFC 8638 PDF

This document focuses on the IPv4-over-IPv6 scenario, as shown in the following diagram.

 In Figure 2, the E-IP client networks run IPv4, and the I-IP core runs IPv6.

Because of the much larger IPv6 group address space, the client E-IP tree can be mapped to a specific I-IP core tree. This simplifies operations on the AFBR because it becomes possible to algorithmically map an IPv4 group/source address to an IPv6 group/source address and vice versa.

The IPv4-over-IPv6 scenario is an emerging requirement as network operators build out native IPv6 backbone networks. These networks support native IPv6 services and applications, but, in many cases, support for legacy IPv4 unicast and multicast services will also need to be accommodated.