Alcatel-Lucent 7750 SR OS Service Manual page 345

VPLS IGMP Snooping (s,g) Flooding List
When IGMP snooping is enabled on a VPLS context, a Layer 2 IP multicast record (s,g) is created
for each multicast stream entering the VPLS context. Each stream should only be sent to each SAP
or SDP binding where either a multicast router exists or a host exists that has requested to receive
the stream (known as a receiver). To facilitate egress handling of each stream, the IOM creates a
flooding list for each (s,g) record associated with the VPLS context. As with the BMU flooding
list, source and split horizon squelching is enforced by the egress forwarding plane.
As with the BMU VPLS flooding list, the egress multicast group SAPs that have either static or
dynamic multicast receivers for the (s,g) stream are chained into groups. The chaining is
independent of other (s,g) flooding lists and the BMU flooding list on the VPLS instance. As the
(s,g) flooding list membership is dynamic, the egress multicast group SAPs in chains in the list are
also managed dynamically.
Since all SAPs placed into the egress multicast group for a particular VPLS context are in the
same split horizon group, no special function is required for split horizon squelching.
MVR IGMP Snooping (s,g) Flooding List
When IGMP snooping on a SAP is tied to another VPLS context to facilitate cross VPLS context
IP multicast forwarding, a Layer 2 IP multicast (s,g) record is maintained on the VPLS context
receiving the multicast stream. This is essentially an extension to the VPLS IGMP snooped
flooding described in
considered to be owned by the VPLS context that the multicast stream will enter. Any SAP added
to the list that is outside the target VPLS context (using the from-vpls command) is handled as an
alien SAP. Split horizon squelching is ignored for alien SAPs.
When chaining the egress multicast group SAPs in an MVR (s,g) list, the IOM will keep the native
chained SAPs in separate chains from the alien SAPs to prevent issues with split horizon
squelching.
Mirroring and Efficient Multicast Replication
As previously stated, efficient multicast replication affects the ability to perform mirroring
decisions in the egress forwarding plane. In the egress forwarding plane, mirroring decisions are
performed prior to the egress chain replication function. Since mirroring decisions are only
evaluated for the first SAP in each chain, applying a mirroring condition to packets that egress
other SAPs in the chain has no effect. Also, the IOM manages the chain membership
automatically and the user has no ability to provision which SAP is first in a chain. Thus, in this
release, mirroring is not allowed for SAPs within a chain.
7750 SR OS Services Guide
VPLS IGMP Snooping (s,g) Flooding List on page
Virtual Private LAN Services
345. The (s,g) list is
Page 345