CLI Guide

Layer 2 Switching Commands 530
User Guidelines
It is preferable to configure mrouter ports for IGMP snooping as opposed to
configuring a static MAC address entry for the router. A static MAC address
entry is tied to a specific port whereas an mrouter configuration will
dynamically learn the MAC address of the router. Multiple mrouter ports may
be configured for a VLAN.
IGMP snooping will consider that an mrouter is active if an mrouter port is
defined in the VLAN, regardless of whether the mrouter port is up or not. If
an mrouter port is defined, IGMP snooping will not flood unregistered
multicast packets received in the VLAN. This behavior can be used to ensure
that IGMP snooping will selectively forward IPv4 multicast data traffic in a
VLAN even if no dynamically discovered IPv4 multicast router has been
discovered.
Multicast data plane traffic from multicast sources in a VLAN is always
forwarded to the mrouter ports in the VLAN. Multicast control plane packets
(those addressed to the reserved 224.0.0.X address) are always flooded to all
ports in the VLAN, regardless of whether an mrouter port is defined or not.
Example
console(config)#ip igmp snooping vlan 10 mrouter interface Gi1/0/2