Optimized Layer 2 Overlay Multicast functionality facilitates multicast traffic both at the access level and within the VXLAN fabric. Optimized Layer 2 Overlay Multicast is restricted to a Layer 2 Virtual Network Instance (L2VNI), wherein the source and receivers are within the same Layer 2 domain. Layer 2 multicast data traffic is not forwarded to a VTEP or a port that does not have a multicast router or receiver attached to it. Optimized Layer 2 Overlay Multicast supports both IPv4 and IPv6 multicast traffic in a Layer 2 EVPN VXLAN fabric.
Optimized Layer 2 Multicast in BGP EVPN VXLAN Layer 2 Overlay Optimized Layer 2 Overlay Multicast uses an EVPN instance (EVI) to build an IGMP or MLD overlay. When a VTEP receives an IGMP or MLD report from a host on the access link, it propagates this information to all other VTEPs in the same EVI, using EVPN Route Type 6 (RT6). Propagation of RT6 updates the multicast forwarding tree for the intra-VLAN multicast traffic in the fabric. If a host on a second VTEP sends multicast traffic to a group that already has receivers, traffic is forwarded in the established multicast forwarding tree.
Multicast traffic source and receiver, which are on the same VLAN but stretched across VTEPs in the BGP EVPN VXLAN fabric, can communicate with each other. Source and Receiver on Same VLAN, Connected to Different Layer 2 VTEPs Figure 1: Topology to show Layer 2 Overlay Multicast Traffic within a VLAN 1. Receiver R3 in VLAN 10 sends (*,G) IGMP Join to VTEP 2. (*,G) is created at VTEP 2. 2. VTEP 2 sends EVPN route type 6 to VTEP 1. (*,G) is created at VTEP 1. Configuring Optimized Layer 2 Overlay Multicast Optimized Layer 2 Multicast in BGP EVPN VXLAN Layer 2 Overlay Configuring Optimized Layer 2 Overlay Multicast 2