Administrator Guide

Configuring the Switch as Querier
To configure 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 traffic is not routed and so there is no querier. Configure 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.
• Configure the switch to be the querier for a VLAN by first 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 configured 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-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
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Internet Group Management Protocol (IGMP)