Enabling fast convergence

In addition to periodically sending general queries, an active (querier) device sends out general queries
when it detects a new port. However, since it does not recognize the other device port-up event, the
multicast traffic might still use the query-interval time to resume after a topology change. Configuring
fast-convergence allows the device to listen to topology change events in Layer 2 protocols, such as
spanning tree, and send general queries to shorten the convergence time.
If the Layer 2 protocol is unable to detect a topology change, the fast-convergence feature may not
work. For example, if the direct connection between two devices switches from one interface to another,
the rapid spanning tree protocol (802.1w) considers this an optimization action, rather than a topology
change. In this case, other devices will not receive topology change notifications and will be unable to
send queries to speed up the convergence. The original spanning tree protocol does not recognize
optimization actions, and fast-convergence works in all cases.
To enable fast-convergence, enter commands such as the following.
device(config)#vlan 70
device(config-vlan-70)#multicast6 fast-convergence
Syntax: [no] multicast6 fast-convergence
Displaying MLD snooping information
You can display the following MLD snooping information:
• MLD snooping error information
• Group and forwarding information for VLANs
• Information about MLD snooping mcache
• MLD memory pool usage
• Status of MLD traffic
• MLD information by VLAN

Displaying MLD snooping error information

To display information about possible MLD errors, enter the following command.
device#show ipv6 multicast error
snoop SW processed pkt: 173, up-time 160 sec
Syntax: show ipv6 multicast error
The following table describes the output from the show ipv6 multicast error command.
Field Description
SW processed pkt The number of IPv6 multicast packets processed by MLD snooping.
up-time The MLD snooping up time.

Enabling fast convergence

FastIron Ethernet Switch IP Multicast Configuration Guide 55
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