IP Multicast over Fabric Connect within the GRT enables you to exchange IP multicast traffic with all or a subset of VLANs that are in the Global Routing Table (GRT). This restriction is called the scope level, which IP Multicast over Fabric Connect uses to constrain the multicast streams within the level in which they originate. For example, if a sender transmits a multicast stream to a BEB on a VLAN that is part of the GRT with IP Multicast over Fabric Connect enabled, only receivers that are part of the same GRT can receive that stream.
Applications that can use IP Multicast over Fabric Connect within the GRT include: Video surveillance, TV/Video/Ticker/Image distribution, VX-LAN.
Both IP Shortcuts and IP Multicast over Fabric Connect within the GRT use the GRT for the scope level to constrain multicast streams. However, they are separate features that work independently from each other.
Important
You do not have to enable IP Shortcuts to support IP Multicast over Fabric Connect within the GRT.
With IP Multicast over Fabric Connect within the GRT, routing of IP multicast traffic is allowed within the subset of VLANs in the GRT that have IP Multicast over Fabric Connect enabled. When you enable IP Multicast over Fabric Connect on a VLAN, the VLAN automatically becomes a multicast routing interface.
You must enable ip spb-multicast on each of the VLANs within the GRT that need to support IP multicast traffic. Enable IP Multicast over Fabric Connect on all VLANs to which IP multicast senders and receivers attach. IP Multicast over Fabric Connect is typically configured only on BEBs.
Note
If no IP interface exists on the VLAN, then you create one. (The IP interface must be in the same subnet as the IGMP hosts that connect to the VLAN).
Unlike IP Shortcuts with unicast, a data I-SID (for mac-in-mac encapsulation of the multicast traffic) is required for IP Multicast over Fabric Connect within the GRT. When the multicast stream reaches the BEB, the BEB assigns a data I-SID to the stream. 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.
Unlike Layer 2 VSNs and Layer 3 VSNs, IP Multicast over Fabric Connect within the GRT does not have a scope I-SID to determine the scope of the multicast traffic. Instead the scope is the Global Routing Table.
The scope and data I-SID information is propagated through the SPBM cloud using IS-IS Link State Packets (LSPs), which carry TLV updates, and result in the multicast tree creation for that stream. For IP Multicast over Fabric Connect within the GRT, the LSPs carry I-SID information and information about where IP multicast stream senders and receivers exist using TLV 144 and TLV 186.
After you configure ip spb-multicast enable, you cannot enable IGMP, IGMP Snooping, or IGMP proxy on the interface. If you try to enable IGMP Snooping or proxy on any interface where IP Multicast over Fabric Connect is enabled, an error message appears.
After you configure ip spb-multicast enable on each of the VLANs within the GRT that need to support IP multicast traffic, any IGMP functions required for IP Multicast over Fabric Connect within the GRT are automatically enabled. You do not need to configure anything IGMP related.
When you enable ip spb-multicast on the Controller nodes, the configuration is automatically pushed to all the Leaf nodes within the domain.
For more information on DvR, see Distributed Virtual Routing.