Reference 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.
• Adjust the last member query interval.
INTERFACE VLAN mode
ip igmp snooping last-member-query-interval
Fast Convergence after MSTP Topology Changes
The following describes the fast convergence feature.
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
To designate an interface as a multicast router interface, use the following 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.
• Designate an interface as a multicast router interface.
ip igmp snooping mrouter interface
356