Alcatel-Lucent 7750 SR Manual page 752

Virtual Private LAN Services
dest-chain-limit
Syntax dest-chain-limit destinations per pass
no dest-chain-limit
Context config>service>egress-multicast-group
Description This command defines the maximum length of an egress forwarding plane efficient multicast
replication chain for an egress-multicast-group. Varying the maximum length of chains created for an
egress multicast group has the effect of efficient multicast batched chain replication on other packets
flowing through the egress forwarding plane. While replicating for the SAPs within a replication
chain, other packets are waiting for the forwarding plane to finish. As the chain length increases,
forwarding latency for the other waiting packets may increase. When the chain length decreases, a
loss of efficiency in the replication process will be observed.
The no form of the command restores the default value.
Default
16
Parameters
destinations per pass — This parameter must be specified when executing the dest-chain-limit
sap-common-requirements
Syntax sap-common-requirements
Context config>service>egress-multicast-group
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command. When executed, the command will use the number-of-destinations parameter to
reorganize all efficient multicast SAP chains that contain members from the egress-multicast-
group.
The destinations per pass parameter can be modified at any time. Be aware that when changing
the maximum chain length, the system will rebuild the chains according to the new limit. When
this happens, it is possible that packets will not be replicated to a destination while it is being
reorganized in the flooding list's chains. Only the chains associated with the egress-multicast-
group context the command is executed in will be affected by changing the parameter.
It is expected that the optimal replication chain length will be between 10 and 16. Since so many
variables affect efficient multicast (i.e. ingress packet rate, number of chains, size of replicated
packets), only proper testing in the environment that replication will be performed will identify
the best dest-chain-limit value for each Egress Multicast Group.
Setting the destinations per pass parameter to a value of 0 has the effect of removing from all
egress forwarding planes all chains with members from the egress-multicast-group. Replication
to each destination SAP from the group is performed using the normal method (non-efficient
replication). The value 0 is not considered a normal value for dest-chain-limit and is provided for
debugging purposes only. Setting the value to 0 is persistent between reboots of the system.
Setting the destinations per pass parameter to a value of 1 has the effect of placing each egress-
multicast-group member SAP into a chain with a single SAP. The value 1 is not considered a
normal value for the dest-chain-limit and is provided for debugging purposes only. Setting the
value to 1 is persistent between reboots of the system.
Values 1 — 30
7750 SR OS Services Guide