Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 737)

IGMP and IGMP Snooping Introduction
Software Reference for x310 Series Switches
C613-50046-01 REV A AlliedWare Plus TM Operating System - Version 5.4.4C 30.11
Speeding up IGMP convergence in a non-looped
topology
For loop-free networks running IGMP, where it may take up to two minutes for
multicasting to recover in a non-looped topology after a port comes back up, you can
speed up convergence by enabling RSTP using the
spanning-tree mode and spanning-
tree enable commands.
RSTP enables the network to use Query Solicitation by default, and means that
multicasting should resume within seconds, not minutes, of the link coming up.
Enabling Query Solicitation on multiple switches
in a looped topology
On networks that use spanning tree or EPSR, Query Solicitation is not normally required
on switches other than the STP root bridge or EPSR master node. Therefore, it is only
enabled by default on the root bridge and the master node.
However, in some networks you may need to turn on Query Solicitation on all switches -
for example, if the network includes other switches that do not support Query Solicitation
and therefore the STP root bridge may be a switch that does not send Query Solicit
messages. To enable Query Solicitation, use the
ip igmp snooping tcn query solicit
command.
Every switch that has Query Solicitation enabled sends a Query Solicit message when it
detects a topology change. Enabling it on multiple switches means you get multiple
messages, but has no other disadvantage.
The following figure shows the packet flow for a four-switch network with Query
Solicitation enabled on all the switches.