User’s Manual of GSD-800S / GSD-802S / GSD-802PS

A host will never send a report when it wants to leave a group (for version 1).

A host will send a “leave” report when it wants to leave a group (for version 2).

Multicast routers send IGMP queries (to the all-hosts group address: 224.0.0.1) periodically to see whether any group members exist on their sub networks. If there is no response from a particular group, the router assumes that there are no group members on the network.

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:

Non-Member

Leave Group

 

Leave Group

(Stop Timer)

Join Group

 

 

 

(Send Report,

 

 

 

Start Timer)

 

 

 

 

 

 

Query Received

 

Delaying Member

(Start Timer)

Idle Member

Report Received

 

 

 

(Stop Timer)

 

 

Timer Expried

 

 

(Send report)

 

IGMP State Transitions