Interlogix GE-DS-242-PoE - Manual (Page 100)

Chapter 4: Web-Based Management
96 GE-DS-242-PoE Managed Ethernet Switch User Manual
IGMP Snooping
Theory
The Internet Group Management Protocol (IGMP) lets host and routers share
information about multicast groups memberships. IGMP snooping is a switch
feature that monitors the exchange of IGMP messages and copies them to the
CPU for feature processing. The overall purpose of IGMP Snooping is to limit the
forwarding of multicast frames to only ports that are a member of the multicast
group.
About the Internet Group Management Protocol (IGMP) Snooping
Computers and network devices that want to receive multicast transmissions
need to inform nearby routers that they will become members of a multicast
group. The Internet Group Management Protocol (IGMP) is used to communicate
this information. IGMP is also used to periodically check the multicast group for
members that are no longer active. In the case where there is more than one
multicast router on a sub network, one router is elected as the 'queried'. This
router then keeps track of the membership of the multicast groups that have
active members. The information received from IGMP is then used to determine
if multicast packets should be forwarded to a given sub network or not. The
router can check, using IGMP, to see if there is at least one member of a
multicast group on a given subnet work. If there are no members on a sub
network, packets will not be forwarded to that sub network.