Specifying a Port as Connected to a Multicast Router
To statically specify or view a port in a VLAN, use the following commands.
• Statically specify a port in a VLAN as connected to a multicast router.
INTERFACE VLAN mode
ip igmp snooping mrouter
• View the ports that are connected to multicast routers.
EXEC Privilege mode.
show ip igmp snooping mrouter
Conguring the Switch as Querier
To congure the switch as a querier, use the following command.
Hosts that do not support unsolicited reporting wait for a general query before sending a membership report. When the multicast source
and receivers are in the same VLAN, multicast trac is not routed and so there is no querier. Congure the switch to be the querier for a
VLAN so that hosts send membership reports and the switch can generate a forwarding table by snooping.
• Congure the switch to be the querier for a VLAN by rst assigning an IP address to the VLAN interface.
INTERFACE VLAN mode
ip igmp snooping querier
IGMP snooping querier does not start if there is a statically congured multicast router interface in the VLAN.
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-specic query out of the ports specied 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.
• Adjust the last member query interval.
INTERFACE VLAN mode
ip igmp snooping last-member-query-interval
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Internet Group Management Protocol (IGMP)
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