A host sends an IGMP
“report”
to join a group
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
Delaying Member
Idle Member
Leave Group
Leave Group
(Stop Timer)
Join Group
(Send Report,
Start Timer)
Query Received
(Start Timer)
Report Received
(Stop Timer)
Timer Expried
(Send report)
IGMP State Transitions
IGMP Snooping Configuration
The default status of the IGMP Snooping function is disabled. To turn on the IGMP Snooping, select
“Enable”
of
the
IGMP Snooping Status
field and click on the
“OK”
button to save.
