IFS NS3601-24P/4S GE-DSSG-244 and 244-POE User Manual
132
following outlines what is communicated between a multicast router and a multicast group member using IGMP.
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:
Figure 4-8-4
IGMP State Transitions
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.
Multicast routers use this information, along with a multicast routing protocol such as
DVMRP or PIM, to support IP multicasting across the Internet.
Summary of Contents for GE-DSSG-244
Page 1: ...P N 1072570 REV 00 10 ISS 13JUN13 IFS NS3601 24P 4S GE DSSG 244 GE DSSG 244 POE User Manual ...
Page 10: ......
Page 38: ...IFS NS3601 24P 4S GE DSSG 244 and 244 POE User Manual 36 ...
Page 132: ...IFS NS3601 24P 4S GE DSSG 244 and 244 POE User Manual 130 Figure 4 8 1 Multicast Service ...