13
Configuring IGMP snooping
Overview
IGMP snooping runs on a Layer 2 device as a multicast constraining mechanism to improve
multicast forwarding efficiency. It creates Layer 2 multicast forwarding entries from IGMP packets
that are exchanged between the hosts and the router.
As shown in
, when IGMP snooping is not enabled, the Layer 2 switch floods multicast
packets to all hosts in a VLAN or VSI. When IGMP snooping is enabled, the Layer 2 switch forwards
multicast packets of known multicast groups to only the receivers.
Figure 11 Multicast packet transmission without and with IGMP snooping
IGMP snooping ports
As shown in
, IGMP snooping runs on Switch A and Switch B, and Host A and Host C are
receivers in a multicast group. IGMP snooping ports are divided into member ports and router ports.
Multicast packet transmission
without IGMP snooping
Source
Multicast router
Host A
Receiver
Host B
Host C
Receiver
Multicast packets
Layer 2 switch
Multicast packet transmission
when IGMP snooping runs
Source
Multicast router
Host A
Receiver
Host B
Host C
Receiver
Layer 2 switch