Layer 2 Multicast Features
For information about configuring L2 multicast features, see "Configuring L2
Multicast Features" on page 713.
MAC Multicast Support
Multicast service is a limited broadcast service that allows one-to-many and
many-to-many connections. In Layer 2 multicast services, a single frame
addressed to a specific multicast address is received, and copies of the frame
to be transmitted on each relevant port are created.
Internet Group Management Protocol (IGMP) Snooping is a feature that
allows a switch to forward multicast traffic intelligently on the switch.
Multicast IP traffic is traffic that is destined to a host group. Host groups are
identified by class D IP addresses, which range from 184.108.40.206 to
220.127.116.11. Based on the IGMP query and report messages, the switch
forwards traffic only to the ports that request the multicast traffic. This
prevents the switch from broadcasting the traffic to all ports and possibly
affecting network performance.
IGMP Snooping Querier
When Protocol Independent Multicast (PIM) and IGMP are enabled in a
network with IP multicast routing, the IP multicast router acts as the IGMP
querier. However, if the IP-multicast traffic in a VLAN needs to be Layer 2
switched only, an IP-multicast router is not required. The IGMP Snooping
Querier can perform the IGMP snooping functions on the VLAN.
In IPv4, Layer 2 switches can use IGMP Snooping to limit the flooding of
multicast traffic by dynamically configuring Layer 2 interfaces so that
multicast traffic is forwarded to only those interfaces associated with IP
In IPv6, MLD snooping performs a similar function. With MLD snooping,
IPv6 multicast data is selectively forwarded to a list of ports intended to
receive the data (instead of being flooded to all of the ports in a VLAN). This
list is constructed by snooping IPv6 multicast control packets.