1-2
z
Reducing Layer 2 broadcast packets, thus saving network bandwidth.
z
Enhancing the security of multicast traffic.
z
Facilitating the implementation of per-host accounting.
Basic Concepts in IGMP Snooping
IGMP Snooping related ports
As shown in
Figure 1-2
, Router A connects to the multicast source, IGMP Snooping runs on Switch A
and Switch B, Host A and Host C are receiver hosts (namely, multicast group members).
Figure 1-2
IGMP Snooping related ports
Router A
Switch A
Switch B
GE1/0/1
GE1/0/2
GE1/0/3
GE1/0/1
GE1/0/2
Receiver
Receiver
Host A
Host B
Host C
Host D
Source
Multicast packets
Router port
Member port
Ports involved in IGMP Snooping, as shown in
Figure 1-2
, are described as follows:
z
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.
z
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.
z
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.
z
Unless otherwise specified, router/member ports mentioned in this document include static and
dynamic ports.
z
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
ports.
