Concept Guide

Disabling Multicast Flooding
If the switch receives a multicast packet that has an IP address of a group it has not learned (unregistered frame), the switch oods that
packet out of all ports on the VLAN.
When you congure the no ip igmp snooping flood command, the system drops the packets immediately. The system does not
forward the frames on mrouter ports, even if they are present. Disable Layer 3 multicast (no ip multicast-routing) in order to
disable multicast ooding.
• Congure the switch to only forward unregistered packets to ports on a VLAN that are connected to mrouter ports.
CONFIGURATION mode
no ip igmp snooping flood
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 interface interface
– For a 10-Gigabit Ethernet interface, enter the keyword TenGigabitEthernet then the slot/port information.
– For a 40-Gigabit Ethernet interface, enter the keyword fortyGigE then the slot/port information.
– For a Port Channel interface, enter the keywords portchannel then a number.
• 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.
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Internet Group Management Protocol (IGMP)