GE DS-82 - Manual (Page 112)

Chapter 4: Web-Based Management
108 GE-DS-82 and 82-PoE Ethernet Managed Switch User Manual
The Time-to-Live (TTL) field of query messages is set to 1 so that the queries will not
be forwarded to other sub networks.
IGMP version 2 introduces some enhancements such as a method to elect a
multicast queried for each LAN, an explicit leave message, and query messages that
are specific to a given group.
The states a computer will go through to join or to leave a multicast group are shown
below:
Figure 77: IGMP State Transitions
Leave Group
(Stop Timer)
Leave Group
Join Group
(Send Report
Start Timer)
Query Received
(Start Timer)
Report Received
(Stop Timer)
Timer Expried
(Send report)
Idle Member
Non-Member
Delaying Member
IGMP Querier
A router, or multicast-enabled switch, can periodically ask their hosts if 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 role of querying the LAN for group members. It then propagates the service
requests on to any upstream multicast switch/router to ensure that it will continue to
receive the multicast service.
NOTE: Multicast routers use this information, along with a multicast routing protocol
such as DVMRP or PIM, to support IP multicasting across the Internet.