Reducing Layer 2 broadcast packets, thus saving network bandwidth.
Enhancing the security of multicast traffic.
Facilitating the implementation of per-host accounting.
Basic Concepts in IGMP Snooping
IGMP Snooping related ports
As shown in
and Switch B, Host A and Host C are receiver hosts (namely, multicast group members).
Figure 1-2 IGMP Snooping related ports
Ports involved in IGMP Snooping, as shown in
Router port: A router port is a port on an Ethernet switch that leads switch towards a Layer 3
multicast device (DR or IGMP querier). In the figure, GigabitEthernet 1/0/1 of Switch A and
GigabitEthernet 1/0/1 of Switch B are router ports. The switch registers all its local router ports in its
router port list.
Member port: A member port is a port on an Ethernet switch that leads the switch towards multicast
group members. In the figure, GigabitEthernet 1/0/2 and GigabitEthernet 1/0/3 of Switch A and
GigabitEthernet 1/0/2 of Switch B are member ports. The switch registers all the member ports on
the local device in its IGMP Snooping forwarding table.
Whenever mentioned in this document, a router port is a port on the switch that leads the switch to
a Layer 3 multicast device, rather than a port on a router.
Unless otherwise specified, router/member ports mentioned in this document include static and
An IGMP-snooping-enabled switch deems that all its ports on which IGMP general queries with the
source IP address other than 0.0.0.0 or PIM hello messages are received to be dynamic router
1-2, Router A connects to the multicast source, IGMP Snooping runs on Switch A
1-2, are described as follows: