IETF RFC 9625 PDF

Ethernet VPN (EVPN) provides a service that allows a single Local Area Network (LAN), comprising a single IP subnet, to be divided into multiple segments. Each segment may be located at a different site, and the segments are interconnected by an IP or MPLS backbone. Intra-subnet traffic (either unicast or multicast) always appears to the end users to be bridged, even when it is actually carried over the IP or MPLS backbone. When a single tenant owns multiple such LANs, EVPN also allows IP unicast traffic to be routed between those LANs. This document specifies new procedures that allow inter-subnet IP multicast traffic to be routed among the LANs of a given tenant while still making intra-subnet IP multicast traffic appear to be bridged. These procedures can provide optimal routing of the inter-subnet multicast traffic and do not require any such traffic to egress a given router and then ingress that same router. These procedures also accommodate IP multicast traffic that originates or is destined to be external to the EVPN domain.