Reference Guide

362 | Internet Group Management Protocol (IGMP)
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Fast Convergence after MSTP Topology Changes
When a port transitions to the Forwarding state as a result of an STP or MSTP topology change, FTOS
sends a general query out of all ports except the multicast router ports. The host sends a response to the
general query and the forwarding database is updated without having to wait for the query interval to
expire.
When an IGMP snooping switch is not acting as a Querier, it sends out the general query, in response to the
MSTP triggered link-layer topology change, with the source IP address of 0.0.0.0, to avoid triggering
Querier election.
Designating a Multicast Router Interface
You can designate an interface as a multicast router interface with the ip igmp snooping mrouter interface
command. FTOS also has the capability of listening in on the incoming IGMP General Queries and
designate those interfaces as the multicast router interface when the frames have a non-zero IP source
address. All IGMP control packets and IP multicast data traffic originating from receivers is forwarded to
multicast router interfaces.
Debugging IGMP
Use any of the commands in EXEC Privilege mode to enable IGMP debugging.
FTOS displays debug messages on the console. To view which debugging commands are enabled, use the
show debugging command in EXEC Privilege mode.
Use the keyword no followed by the debug command To disable a specific debug command. For example,
to disable debugging of IGMP updates, enter
no debug ip igmp command.
Use
no debug ip igmp to disable all IGMP debugging.
Use
undebug all to disable all debugging.
Command Syntax Command Mode Purpose
debug ip igmp [ip-address | fortyGigE |
Gigabitethernet | port-channel |
Tengigabitethernet | vlan]
EXEC Privilege View all information on IGMP, including query,
report and leave.