Configuring Layer 2 Multicast Layer 2 Multicast
Configuration Guide
215
Demonstrated as below:
Figure 1-1 IGMP Snooping
Source
IGMP Querier
Snooping Switch
Router Port
Member Port
Member Port
Host A Host B Host C
Receiver Receiver
Multicast packets transmission
with IGMP Snooping
Source
IGMP Querier
Non-Snooping Switch
Host A Host B Host C
Receiver
Receiver
Multicast packets transmission
without IGMP Snooping
Multicast packets
The following basic concepts of IGMP Snooping will be introduced: IGMP querier, snooping
switch, router port and member port.
IGMP Querier
An IGMP querier is a multicast router (a router or a Layer 3 switch) that sends query
messages to maintain a list of multicast group memberships for each attached network,
and a timer for each membership.
Normally only one device acts as querier per physical network. If there are more than
one multicast router in the network, a querier election process will be implemented to
determine which one acts as the querier.
Snooping Switch
A snooping switch indicates a switch with IGMP Snooping enabled. The switch maintains a
multicast forwarding table by snooping on the IGMP transmissions between the host and
the querier. With the multicast forwarding table, the switch can forward multicast data only
to the ports that are in the corresponding multicast group, so as to constrain the flooding
of multicast data in the Layer 2 network.
Router Port
A router port is a port on snooping switch that is connecting to the IGMP querier.
Member Port
A member port is a port on snooping switch that is connecting to the host.
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