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Enabling Bulk Updates for Multicast Snooping

Whenever an individual interface joins or leaves a multicast group, a new next hop entry is installed in the routing table and the forwarding table. You can use the nexthop-hold-time statement to specify a time, from 1 through 1000 milliseconds (ms), during which outgoing interface changes are accumulated and then updated in bulk to the routing table and forwarding table. Bulk updating reduces the processing time and memory overhead required to process join and leave messages. This is useful for applications such as internet protocol television (IPTV), in which users changing channels can create thousands of interfaces joining or leaving a group in a short period. In IPTV scenarios, typically there is a relatively small and controlled number of streams and a high number of outgoing interfaces. Using bulk updates can reduce the join delay.

In this example, you configure a hold-time of 20 milliseconds for instance-type virtual-switch, using the nexthop-hold-time statement:

  1. Enable the nexthop-hold-time statement by configuring it under multicast-snooping-options, using 20 milliseconds for the time value:
    [edit routing-instances vs]multicast-snooping-options {nexthop-hold-time 20;}
  2. Use the show multicast snooping route command to verify that the bulk updates feature is turned on:

    user@host> show multicast snooping route instance vs
    Nexthop Bulking: ON
    Family: INET

You can include the nexthop-hold-time statement only for routing-instance types of virtual-switch or vpls at the following hierarchy level:

  • [edit routing-instances routing-instance-name multicast-snooping-options]

If the nexthop-hold-time statement is deleted from the router configuration, bulk updates are disabled.

Published: 2010-04-16

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