SMC Networks TigerSwitch SMC6948L2, Management Manual

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the group registration information, and configures multicast filters
accordingly. IGMP Snooping generates no additional network
traffic, allowing you to significantly reduce the multicast traffic
passing through your switch.
IGMP Protocol
The Internet Group Management Protocol (IGMP) runs between
hosts and their immediately neighboring multicast router/switch.
IGMP is a multicast host registration protocol that allows any host
to inform its local router that it wants to receive transmissions
addressed to a specific multicast group.
A router, or multicast-enabled switch, can periodically ask their
hosts is they want to receive multicast traffic. If there is more than
one router/switch on the LAN performing IP multicasting, one of
these devices is elected “querier” and assumes the responsibility of
querying the LAN for group members.
Based on the group membership information learned from IGMP, a
router/switch can determine which (if any) multicast traffic needs
to be forwarded to each of its ports. At Layer 3, multicast routers
use this information, along with a multicast routing protocol such
as DVMRP, to support IP multicasting across the Internet.
Note that IGMP neither alters nor routes any IP multicast packets.
A multicast router/switch must be used to deliver IP multicast
packets across different subnetworks.