Layer 3 Multicast
Cisco Multi-Site Layer 3 multicast is enabled or disabled at three levels, the VRF, the bridge domain (BD), and any EPGs that have multicast sources present.
At the top level, multicast routing must be enabled on the VRF that has any multicast-enabled BDs. On a multicast-enabled VRF, there can be a combination of multicast-enabled BDs and BDs where multicast routing is disabled. Enabling multicast routing on a VRF from the Cisco Nexus Dashboard Orchestrator GUI enables it on the APIC sites where the VRF is stretched.
Once a VRF is enabled for multicast, the individual BDs under that VRF can be enabled for multicast routing. Configuring Layer 3 multicast on a BD enables protocol independent multicast (PIM) routing on that BD. By default, PIM is disabled in all BDs.
If a source belonging to a specific site-local EPG sends multicast traffic to a remote site, the Nexus Dashboard Orchestrator must create a shadow EPG and program the corresponding subnet route(s) on the remote site for the source EPG. In order to limit the configuration changes applied to the remote Top-of-Rack (TOR) switches, you are required to explicitly enable Layer 3 multicast on the local EPGs that have multicast sources present, so that only the configuration necessary for those EPGs is pushed to the remote sites. EPGs with multicast receivers do not require enabling Layer 3 multicast.
Multi-Site supports all of the following Layer 3 multicast source and receiver combinations:
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Multicast sources and receivers inside ACI fabric
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Multicast sources and receivers outside ACI fabric
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Multicast sources inside ACI fabric with external receivers
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Multicast receivers inside ACI fabric with external sources