IP Multicast over Fabric Connect supports Layer 3 VSN functionality where multicast traffic is bridged over the SPBM core infrastructure. Layer 3 VSN using IP Multicast over Fabric Connect is helpful when you need complete security and total isolation of data. No one outside of the Layer 3 VSN can join or even see the Layer 3 VSN. Applications that can use Layer 3 VSN with IP Multicast over Fabric Connect include:
Configure the Layer 3 VSN (VRF) as a multicast VPN, and then enable IP Multicast over Fabric Connect on VRF VLANs to which IP multicast senders and receivers attach. This configuration automatically enables IGMP snooping and proxy on those VLANs. IGMPv2 at the VLAN level is the default setting, with no other configuration required. If you want to use IGMPv3, you must configure IGMPv3.
IP Multicast over Fabric Connect is only configured on BEBs.
Note
You do not need to enable IP Shortcuts to support multicast routing in the Layer 3 VSN using SPBM. IPVPN creation and I-SID assignment for the IPVPN is required, but you do not need to enable IPVPN.
If you only want to use IP Multicast over Fabric Connect, you do not need to enable the Layer 3 VSN or redistribute unicast routes into or out of IS-IS. IP Multicast over Fabric Connect routing does not depend on unicast routing for Layer 3 VSNs using VRFs, which allows you to more easily migrate from a PIM environment to IP Multicast over Fabric Connect. You can migrate a PIM environment to IP Multicast over Fabric Connect first and then migrate unicast separately or not at all.
If no IP interface exists on the VLAN, then you create one. (The IP interface must be the same subnet as the IGMP hosts that connect to the VLAN).
With Layer 3 VSN with IP Multicast over Fabric Connect, multicast traffic remains in the same Layer 3 VSN across the SPBM cloud. For a Layer 3 VSN, traffic can cross VLAN boundaries but remains confined to the subset of VLANs within the VRF that has IP Multicast over Fabric Connect enabled. If a sender transmits a multicast stream to a BEB on a Layer 3 VSN with IP Multicast over Fabric Connect enabled, only receivers that are part of the same Layer 3 VSN can receive that stream.
All or a subset of VLANs within a Layer 3 VSN can exchange multicast traffic. The BEB only sends out traffic for a multicast stream on which IGMP joins and reports are received.
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 3 VSNs with IP Multicast over Fabric Connect, the scope is the I-SID value of the Layer 3 VSN associated with the local VLAN that the IP multicast data was received on.
See TLVs.
After a BEB receives an IGMP join message from a receiver, the 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 requested 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.
On DvR Controllers in a DvR domain, you must manually configure IP multicast over Fabric Connect on Layer 3 VSNs (VRFs). This configuration is then automatically pushed to the Leaf nodes in the DvR domain.
For more information on DvR, see Distributed Virtual Routing.