Design Reference

All multicast streams are constrained within the level in which they originate, which is called the
scope level. In other words, if a sender transmits a multicast stream to a BEB on a C-VLAN with IP
multicast over SPBM enabled, only receivers that are part of the same Layer 2 VSN can receive that
stream. Similarly, if a sender transmits a multicast stream to a BEB on a VLAN that is part of the
Layer 3 VSN with IP multicast over SPBM enabled, only receivers that are part of the same Layer 3
instance can receive that stream.
IP multicast over SPBM uses BEBs to act as senders and receivers of data. After a BEB receives IP
multicast data from a sender, a BEB allocates a data I-SID in the range of 16,000,000 to 16,512,000
for the stream. The stream is identified by the S,G,V tuple, which is the source IP address, group IP
Address, and the stream is identified by the local VLAN on which the stream is received. The BEB
also sends a TLV update to its neighbors to inform them of the presence of an IP multicast stream,
along with identifying the sender. The BEB propagates the information through the SPBM cloud
through IS-IS TLV updates in LSPs that result in a multicast tree being created for that stream.
IGMP handles group membership registration to enable members to receive data. IGMP snooping
listens to conversations between hosts and routers, and maintains a table of links that require IP
multicast streams.
The BEBs also act as IGMP queriers and send out periodic IGMP queries. The IGMP querier
enables the creation of the link table. 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 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.
IS-IS acts dynamically using the TLV information it receives from BEBs that connect to the sender
and the receivers to create a multicast tree between them.
The following figure shows how multicast senders and receivers connect to the SPBM cloud using
BEBs.
SPBM design guidelines
88 Network Design Reference for Avaya VSP 4000 Series December 2014
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