Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) User Manual
Page 735
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
30.9
Query solicitation reduces downtime to a negligible amount by triggering on topology
changes. The generation of query solicitation messages in the network causes the IGMP
Querier to send an IGMP Query immediately following a topology change. This enables
the switches to know where to look for the traffic and thus to send reports to the correct
switch upstream. This allows the multicast data traffic to be recovered instantly.
Query solicitation functions by default (without you enabling it) on all VLANs on the root
bridge in an STP instance and on all data VLANs on the master node in an EPSR instance.
By default, the root bridge or master node always sends a Query Solicit message when the
topology changes.
If you have multiple STP or EPSR instances, query solicitation only sends Query Solicit
messages on VLANs in the instance that experienced a topology change.
In switches other than the STP root bridge or EPSR master node, query solicitation is
disabled by default, but you can enable it by using the
command.
If you enable query solicitation on a switch other than the STP root bridge or EPSR master
node, both that switch and the root or master send a Query Solicit message.
Once the Querier receives the Query Solicit message, it sends out a General Query and
waits for responses, which update the snooping information throughout the network.
The
command can be configured on the IGMP Querier. This
command introduces a brief delay between when the IGMP Querier receives the query
solicit, and when it sends out the general query. Although this slightly reduces the speed
with which the network recovers from the topology change, its does guard against a DoS
(Denial of Service) attack. Without this delay, a malign host sending a stream of query
solicits could cause the IGMP Querier to flood the network with IGMP Queries.
To get the network to converge faster, use the
ip igmp query-max-response-time
command and set a low response time value, such as one or two seconds, so that the
clients will respond immediately with a report as a response to the IGMP Queries
On switches other than the STP root bridge or the EPSR master node, you can disable
query solicitation by using the no variant of the
ip igmp snooping tcn query solicit
command. In addition, on all switches, you can disable query solicitation on a per-vlan
basis using the no variant of the
ip igmp snooping tcn query solicit
command in
Interface Configuration mode, after specifying a VLAN first in Interface Configuration
mode.
To see whether query solicitation is on or off, check the Query Solicitation field in output
of the
command. You can view running and startup
configurations with
commands to see if
Query Solicitation is enabled.
The following figure shows how Query Solicitation works when a port goes down.