periodically sends IGMP host-query messages to discover which multicast groups
are present on attached networks. These messages are sent to the all-hosts
multicast group (188.8.131.52) with a time-to-live (TTL) of 1. The
sends host-query messages to refresh its knowledge of memberships present on
the network. If, after some number of queries, the software discovers that no
local hosts are members of a multicast group, the software stops forwarding
multicast packets to the local network from remote origins for that group and
sends a prune message upstream toward the source.
elects a PIM designated router (DR) for the LAN (subnet). The designated router
is responsible for sending IGMP host-query messages to all hosts on the LAN. In
sparse mode, the designated router also sends PIM register and PIM join
messages toward the RP router. With IGMPv2, the DR is the router or multilayer
with the highest IP address. With IGMPv1, the DR is elected according to the
multicast routing protocol that runs on the LAN.
This procedure is optional.