Configuring The Switch As Querier; Fast Convergence After Mstp Topology Changes - Dell S6100 Configuration Manual

• 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

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

When a port transitions to the Forwarding state as a result of an STP or MSTP topology change, Dell Networking OS 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.
Internet Group Management Protocol (IGMP) 363