Chapter 4: Web-Based Management

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

Non-Member

Leave Group

(Stop Timer) Join Group

(Send Report

Start Timer)

Leave Group

 

Query Received

 

 

 

 

Delaying Member

(Start Timer)

Idle Member

Report Received

 

 

(Stop Timer)

Timer Expried

(Send report)

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.

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

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GE GE-DS-82, 82-POE user manual Igmp Querier, Igmp State Transitions