Users Guide

The switch may lose the querier election if it does not have the lowest IP address of all potential queriers on the subnet.
When enabled, IGMP snooping querier starts after one query interval in case no IGMP general query (with IP SA lower than
its VLAN IP address) is received on any of its VLAN members.
Adjusting the Last Member Query Interval
To adjust the last member query interval, use the following command.
When the querier receives a Leave message from a receiver, it sends a group-specific query out of the ports specified in the
forwarding table. If no response is received, it sends another. The amount of time that the querier waits to receive a response
to the initial query before sending a second one is the last member query interval (LMQI). The switch waits one LMQI after the
second query before removing the group-port entry from the forwarding table. The last member query interval is the maximum
response time inserted into Group-Specific queries sent in response to Group-Leave messages.
• Sets the last member query interval in milliseconds on the specified VLAN.
INTERFACE VLAN mode
ip igmp snooping last-member-query-interval milliseconds
milliseconds — Enter the interval in milliseconds. The range is from 100 to 65535. The default is 1000 milliseconds.
Fast Convergence after MSTP Topology Changes
When a port transitions to the Forwarding state as a result of an STP or MSTP topology change, the system 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
To designate an interface as a multicast router interface, use the following command.
The system 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.
• Designate an interface as a multicast router interface.
ip igmp snooping mrouter interface
Internet Group Management Protocol (IGMP) 408