Cisco Systems N3KC3048TP1GE, N3KC3064TFAL3 manual IGMPv1 and IGMPv2, IGMP Snooping Switch

Configuring IGMP Snooping

IGMPv1 and IGMPv2

The following figure shows an IGMP snooping switch that is located between the host and the IGMP router. The IGMP snooping switch snoops the IGMP membership reports and leave messages and forwards them only when necessary to the connected IGMP routers.

Figure 18: IGMP Snooping Switch

Note The switch supports IGMPv3 snooping based only on the destination multicast MAC address. It does not support snooping based on the source MAC address or on proxy reports.

The Cisco NX-OS IGMP snooping software supports optimized multicast flooding (OMF) that forwards unknown traffic to routers only and performs no data driven state creation. For more information about IGMP snooping, see http://tools.ietf.org/wg/magma/draft-ietf-magma-snoop/rfc4541.txt.

IGMPv1 and IGMPv2

Both IGMPv1 and IGMPv2 support membership report suppression, which means that if two hosts on the same subnet want to receive multicast data for the same group, then the host that receives a member report from the other host suppresses sending its report. Membership report suppression occurs for hosts that share a port.

If no more than one host is attached to each VLAN switch port, then you can configure the fast leave feature in IGMPv2. The fast leave feature does not send last member query messages to hosts. As soon as the software receives an IGMP leave message, the software stops forwarding multicast data to that port.

IGMPv1 does not provide an explicit IGMP leave message, so the software must rely on the membership message timeout to indicate that no hosts remain that want to receive multicast data for a particular group.

Note Cisco NX-OS ignores the configuration of last member query interval when you enable the fast leave feature because it does not check for remaining hosts.

	Cisco Nexus 3000 NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U3(1)
136	OL-26590-01