Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 734)

IGMP and IGMP Snooping Introduction
Software Reference for x310 Series Switches
30.8 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
Query Solicitation
Query Solicitation minimizes the loss of multicast data after a topology change on
networks that use EPSR or spanning tree (STP, RSTP, or MSTP) for loop protection. Without
Query Solicitation, when the underlying link layer topology changes, multicast data flow
can stop for up to several minutes, depending on which port goes down and how much of
the IGMP query interval remained at the time of the topology change. Query Solicitation
greatly reduces this disruption.
Query Solicitation operates without configuration in AlliedWare Plus
TM
switches running
STP, RSTP, MSTP or EPSR. However, you may find it useful to manually enable Query
Solicitation in loop-free networks running IGMP (see
Speeding up IGMP convergence in
a non-looped topology ) and networks where not all switches support Query Solicitation
(see Enabling Query Solicitation on multiple switches in a looped topology ).
How Query Solicitation Works
Query Solicitation monitors STP, RSTP, MSTP and EPSR messages for topology changes.
When it detects a change, it generates a special IGMP Leave message called a Query
Solicit. The switch floods the Query Solicit message to all ports in every VLAN that Query
Solicitation is enabled on. When the Querier receives the Query Solicit message, it sends
out a General Query and waits for clients to respond with Membership Reports. These
Reports update the snooping information throughout the network.
Query Solicit messages have a group address of 0.0.0.0.
Query Solicitation works 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 any
of the following events occur:
■ an STP BPDU packet with the Topology Change (TC) flag arrives at the root bridge
■ an STP port on a switch goes from a Discarding to Forwarding state
■ the FDB gets flushed by EPSR
If necessary, you can make clients respond more quickly to the General Query by tuning
the IGMP timers, especially the maximum response time advertised in IGMP queries using
the
ip igmp query-max-response-time command.
Query Solicitation Operation
When IGMP Snooping is enabled and EPSR or Spanning Tree changes the underlying link
layer topology, this can interrupt multicast data flow for a significant length of time. This is
because there is no way for switches in a network with interested clients to know where
the traffic is available, due to the change in network topology. This change in network
topology may take up to two IGMP Query intervals from the IGMP Querier, until the
switches will know where to forward membership reports received by client hosts. During
this time, those hosts will not receive multicast traffic.
Query solicitation prevents this by monitoring for any topology changes. When it detects
a change, it generates a special IGMP Leave message known as a Query Solicit, and floods
the Query Solicit message to all ports in every VLAN that query solicitation is enabled on.
When the IGMP Querier receives the message, it responds by sending a General Query,
which all IGMP listeners respond to. This refreshes snooped group membership
information in the network.