Egress Multicast Groups; Egress Multicast Group Provisioning - Alcatel-Lucent 7750 SR OS Service Manual

Egress Multicast Groups

Efficient multicast replication is a method of increasing egress replication performance by
combining multiple destinations into a single egress forwarding pass. In standard egress VPLS
multicast forwarding, the complete egress forwarding plane is used per destination to provide
ACL, mirroring, QoS and accounting for each path with associated receivers. In order to apply the
complete set of available egress VPLS features, the egress forwarding plane must loop-back
copies of the original packet so that each flooding destination may be processed. While each
distributed egress forwarding plane only replicates to the destinations currently reached through
its ports, this loop-back and replicate function can be resource intensive. When egress forwarding
plane congestion conditions exist, unicast discards may be indiscriminate relative to forwarding
priority. Another by-product of this approach is that the ability for the forwarding plane to fill the
egress links is affected which could cause under-run conditions on each link while the forwarding
plane is looping packets back to itself.
In an effort to provide highly scalable VPLS egress multicast performance for triple play type
deployments, an alternative efficient multicast forwarding option is being offered. This method
allows the egress forwarding plane to send a multicast packet to a set (called a chain) of
destination SAPs with only a single pass through the egress forwarding plane. This minimizes the
egress resources (processing and traffic management) used for the set of destinations and allows
proper handling of congestion conditions and minimizes line under-run events. However, due to
the batch nature of the egress processing, the chain of destinations must share many attributes.
Also, egress port and ACL mirroring will be disallowed for packets handled in this manner.
Packets eligible for forwarding by SAP chaining are VPLS flooded packets (broadcast, multicast
and unknown destination unicast) and IP multicast packets matching an VPLS Layer 2 (s,g) record
(created through IGMP snooping).

Egress Multicast Group Provisioning

To identify SAPs in the chassis that are eligible for egress efficient multicast SAP chaining, an
egress multicast group must be created. SAPs from multiple VPLS contexts may be placed in a
single group to minimize the number of groups required on the system and to support multicast
VPLS registration (MVR) functions.
Some of the parameters associated with the group member SAPs must be configured with
identical values. The common parameters are checked as each SAP is provisioned into the group.
If the SAP fails to be consistent in one or more parameters, the SAP is not allowed into the egress
multicast group. Once a SAP is placed into the group, changing of a common parameter is not
permitted.
7750 SR OS Services Guide
Virtual Private LAN Services
Page 341