Multicast Group Registration - Hirschmann MACH 4000 User Manual

Multicast Routing

9.2 Multicast Group Registration

The Internet Group Management Protocol (IGMP) describes the distribution
of Multicast information between routers and terminal devices on Layer 3.
Routers with an active IGMP function periodically send queries to find out
which IP Multicast group members are connected to the LAN, or to find out
who is interested in becoming a group member.
Multicast group members reply with a Report message. This Report
message contains all the parameters required by the IGMP. The router
records the IP Multicast group address from the Report message in its
routing table. The result of this is that it transfers frames with this IP Multicast
group address in the target address field only in accordance with the routing
table.
Devices which no longer want to be members of a Multicast group can
cancel their membership by means of a Leave message (from IGMP
version 2), and they do not transmit any more Report messages. The router
removes the routing table entry if it does not receive any Report messages
within a specified period of time (aging time).
If there are multiple routers with an active IGMP function in the subnetwork,
then
for IGMP version 1, all routers in this subnetwork periodically send
queries
for IGMP versions 2 and 3, the routers decide which router takes over the
query function (Querier Election).
Protocol Standard
IGMP v1 RFC 1112
IGMP v2 RFC 2236
IGMP v3 RFC 3376
Table 13: Standards which describe the Multicast Group Membership Discovery
An advantage that IGMP version 2 has over IGMP version 1 is that a
Multicast recipient can cancel his membership in a Multicast group,
thus freeing up his bandwidth more quickly. Another advantage is the
introduction of the Querier Election.
Routing L3P
Release 4.0 11/07
9.2 Multicast Group Registration
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