At ingress, CFHP output traffic is automatically mapped to a unicast or multipoint queue in to reach the correct switch fabric destinations. To manage this automatic queuing function, a shared queue policy has been created or exists by default and is named policer-output-queues.
The unicast queues in the policy are automatically created on each destination switch fabric tap and ingress CFHP unicast packets automatically map to one of the queues based on forwarding class and destination tap. The multipoint queues within the policy are created on the IOM3-XP’s 16/IMM or XMA multicast paths; 16 multicast paths are supported by default with 28 on 7950 XRS systems and the 7750 SR 12-e systems, with the latter having setting ‟tools perform the system set-fabric-speed fabric-speed-b.” The multicast paths represent an available multicast switch fabric path; the number of each being controlled using the command:
configure mcast-management bandwidth-policy policy-name t2-paths secondary-path
— number-paths number-of-paths [dual-sfm number-of-paths]
For ingress CFHP multicast packets (Broadcast, Unknown unicast, or Multicast—referred to as BUM traffic), the system maintains a conversation hash table per forwarding class and populates the table’s forwarding class hash result entry with the one of the multicast paths. Best-effort traffic uses the secondary paths, and expedited traffic uses the primary paths. When a BUM packet is output by ingress CFHP, a conversation hash is performed and used along with the packet’s forwarding class to select a hash table entry to derive the multicast path to be used. Each table entry maintains a bandwidth counter that is used to monitor the aggregate traffic per multicast path. The process can be optimized by enabling IMPM on any forwarding complex, which allows the system to redistribute this traffic across the IMPM paths on all forwarding complexes to achieve a more even capacity distribution. Be aware that enabling IMPM causes routed and VPLS (IGMP and PIM) snooped IPv4 multicast groups, and routed and PIM snooped (with sg-based forwarding) IPv6 multicast groups to be managed by IMPM.
Any discards performed in the ingress shared queues are reflected in the ingress child policer's discard counters and reported statistics, assuming a discard counter capable stat-mode is configured for the child policer.