Egress multicast group policies
Overview
With standard egress multicasting, the entire egress forwarding plane is used on a per destination basis to provide ACL, mirroring, QoS, and accounting for each path with the associated receivers. This process is very resource intensive. Also, when congestion occurs at the egress forwarding plane, unicast discards may be indiscriminate of the forwarding priority.
The NFM-P provides an alternative egress multicasting method that increases egress replication performance and scalability by combining multiple destinations into a single egress forwarding pass as an egress multicast group (EMG). You specify the EMG requirements using a global EMG policy which defines the group destination SAPs in a chain. The chain receives a single multicast packet from the egress forwarding plane with only a single pass.
The EMG policy is applied to an L2 access interface that is created on an Ethernet port with null or dot1q encapsulation. SAP membership in an EMG policy has the following requirements:
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The L2 access interface egress ACL filter must match that of the EMG.
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The access port and the EMG must have the same encapsulation type.
When a SAP becomes a member of an EMG, the common parameters that it shares with other EMG members cannot be changed. On the other hand, a modification to an EMG common requirement changes that parameter in all SAPs in the chain. The same common required traits apply to egress filters: individual SAP filters cannot be changed, and any change to the EMG egress filter parameters affects the egress filters in all member SAPs. In addition, if an egress filter is not defined in the EMG common parameter requirements, a new member SAP cannot have an egress filter.
The following restrictions also apply to an EMG: