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Page 26 | AlliedWare™ OS How To Note: IGMP
Query solicitation (rapid recovery from topology changes) > How query solicitation works
Query solicitation (rapid recovery from topology
changes)
Query Solicitation minimises loss of multicast data after a topology change. It is a built-in
feature of Allied Telesis managed layer 3 switches since software versions 281-03 and 2.9.1
when running 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 timeout period was left (see "Why convergence takes so long without query
solicitation" on page 28). Query Solicitation greatly reduces this disruption.
Query Solicitation operates without configuration in networks of Allied Telesis managed
layer 3 switches running STP, RSTP, MSTP or EPSR. You may find it helpful to manually enable
it in the following other situations:
z loop-free networks running IGMP (see page 33)
z networks in which not all switches support Query Solicitation (see page 33)
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:
z an STP BPDU packet with the Topology Change (TC) flag arrives at the root bridge
z an STP port on a switch goes from a Discarding to Forwarding state
z 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 Query Response Interval—see page 77.