IP Multicast over Fabric Connect supports Layer 2 VSN functionality where multicast traffic is bridged over the SPBM core infrastructure. An application for Layer 2 VSNs using IP Multicast over Fabric Connect is multicast traffic in data centers.
For more information on Layer 2 VSN configuration, see Layer 2 VSN Configuration.
After you configure ip igmp snooping on a VLAN that has an I-SID configured (a C-VLAN), that VLAN is automatically enabled for IP Multicast over Fabric Connect services. No explicit configuration exists separate from that to enable Layer 2 VSN IP Multicast over Fabric Connect.
Multicast traffic remains in the same Layer 2 VSN across the SPBM cloud for Layer 2 VSN IP Multicast over Fabric Connect. IP Multicast over Fabric Connect constrains all multicast streams within the scope level in which they originate. If a sender transmits a multicast stream to a BEB on a Layer 2 VSN with IP Multicast over Fabric Connect enabled, only receivers that are part of the same Layer 2 VSN can receive that stream.
After a BEB receives IP multicast data from a sender, the BEB allocates a data service instance identifier (I-SID) in the range of 16,000,000 to 16,512,000 for the multicast stream. The stream is identified by the S, G, V tuple, which is the source IP address, the group IP address and the local VLAN the multicast stream is received on. The data I-SID uses Tx/Rx bits to signify whether the BEB uses the I-SID to transmit, receive, or both transmit and receive data on that I-SID.
In the context of Layer 2 VSNs with IP Multicast over Fabric Connect, the scope is the I-SID value of the Layer 2 VSN associated with the local VLAN on which the IP multicast data was received.
This information is propagated through the SPBM cloud using IS-IS Link State Packets (LSPs), which carry TLV updates, that result in the multicast tree creation for that stream. For Layer 2 VSNs, the LSPs carry I-SID information and information about where IP multicast stream senders and receivers exist using TLV 144 and TLV 185.
IS-IS acts dynamically using the TLV information received from BEBs that connect to the sender and the receivers to create a multicast tree between them.
After a BEB receives an IGMP join message from a receiver, a BEB queries the IS-IS database to check if a sender exists for the requested stream within the scope of the receiver. If the requested stream does not exist, the IGMP information is kept, but no further action is taken. If the request stream exists, the BEB sends an IS-IS TLV update to its neighbors to inform them of the presence of a receiver and this information is propagated through the SPBM cloud.
For IGMP Snooping, ensure that the IGMP version used by multicast hosts and other devices in the network is the same as the IGMP version configured on the IGMP Snooping VLAN, or that you enable compatibility mode.