FUJITSU PSWITCH User’s Guide
92 December/2018
of IGMP must support all earlier versions.
The following list describes the basic operation of IGMP, common to all versions. A
multicast router can act as both an IGMP host and an IGMP router and as a result
can respond to its own IGMP messages. The software implementation of IGMPv3
supports the multicast router portion of the protocol (that is, not the host portion).
It is backward compatible with IGMPv1 and IGMPv2.
One router periodically broadcasts IGMP Query messages onto the network.
Hosts respond to the Query messages by sending IGMP Report messages
indicating their group memberships.
All routers receive the Report messages and note the memberships of hosts on
the network.
If a router does not receive a Report message for a particular group for a period
of time, the router assumes there are no more members of the group on the
network.
All IGMP messages are raw IP data grams and are sent to multicast group
addresses, with a time to leave (TTL) of 1. Since raw IP does not provide reliable
transport, some messages are sent multiple times to aid reliability.
3.1.3.6. MLD (Multicast Listener Discovery) v1/v2
Multicast Listener Discovery (MLD) protocol enables IPv6 routers to discover the
presence of multicast listeners, the nodes who wish to receive the multicast data
packets on its directly attached interfaces. On IPv6 multicast routers, MLD replaces
the functionality performed by IGMP on IPv4 networks.
MLD discovers which multicast addresses are of interest to its neighboring nodes
and provides this information to the active multicast routing protocol that makes
decisions on the flow of multicast data packets.
The software implementation of MLD v2 supports only the multicast router portion
of the protocol and not the listener portion. It is backward-compatible with MLD v1.
3.1.3.7. DVMRP (Distance Vector Multicast Routing Protocol)
Distance Vector Multicast Routing Protocol (DVMRP) is a dense mode multicast
protocol and is most appropriate for use in networks where bandwidth is relatively
plentiful and there is at least one multicast group member in each subnet. DVMRP
assumes that all hosts are part of a multicast group until it is informed of multicast
group changes. When the dense-mode multicast router is informed of a group
membership change, the multicast delivery tree is pruned. DVMRP uses a
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