Enhanced OISM with IGMPv2, IGMPv3, and IGMP snooping for IPv4 multicast traffic in EVPNVXLAN fabrics

We support an enhanced optimized intersubnet multicast (OISM) model with IGMPv2, IGMPv3, and IGMP snooping for IPv4 multicast traffic in EVPN-VXLAN edge-routed bridging (ERB) overlay fabrics. With enhanced OISM, on each device, you have the option to configure only the revenue VLANs that device hosts. You don't need to configure all revenue VLANs in the fabric on all OISM leaf devices as you do with the original OISM symmetric bridge domains model. This asymmetric bridge domains model enables OISM to scale well when your network has leaf devices that host a large number of different VLANs. 

Enhanced OISM operates similarly to the OISM symmetric bridge domains model, but with differences to account for the asymmetric bridge domains model, such as the following: 

The source devices forward east-west multicast traffic: 

• On the source VLAN to multihoming peer leaf devices. 
• On the OISM supplemental bridge domain (SBD) for all other destinations (whether they host the source VLAN or not). 

For north-south multicast traffic from external sources and to external receivers: 

• The border leaf PIM EVPN gateway (PEG) devices exchange EVPN Type 10 Selective PMulticast Service Interface (S-PMSI) Auto-Discovery (A-D) routes. 
• With the S-PMSI A-D routes, the PEG devices can reliably signal multicast (S,G) PIM registration to the external multicast rendezvous point (RP) only for sources within the fabric. You must configure: 
•  The enhanced-oism option instead of the oism option (both options are at the [edit forwardingoptions multicast-replication evpn irb] hierarchy level). 
•  Matching revenue VLANs on any OISM leaf devices that are multihoming peer devices.