D-Link DES-3326 User Manual page 124

24-port NWay Ethernet Switch User's Guide
response from a particular group, the router assumes
that there are no group members on the network.
Note: The TTL field of query messages is set to 1 so that
the queries do not get forwarded to other subnetworks.
Based on the reports a router receives from the hosts it can
decide whether to forward a multicast packet on a particular
interface or not.
IGMP Version 2 is and enhancement to the original IGMP and
includes a few extensions such as a procedure for the election of
the multicast querier for each LAN, explicit leave messages for
faster pruning , and group-specific query messages. The router
with the lowest IP address is elected as the querier. The explicit
group leave message is added to decrease the latency of the
protocol, and routers can ask for reports on a particular group
ID. IGMP Version 3 is in preliminary stage, makes it possible for
a host to join a group and specify a set of sources of that group
from which it wants to receive multicast messages. Similarly,
leave group messages of Version 2 has been enhanced to support
group-source leave messages.
The transition states a host will go through to join or leave a
multicast group are shown in the diagram below.
108 Switch Management and Operating Concepts