GE 82-POE 用户手册

 

Chapter 4: Web-Based Management 

GE-DS-82 and 82-PoE Ethernet Managed Switch User Manual 

105 

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. 

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that are no longer active.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.