GE ML1200 instruction manual Igmp

IGMP CHAPTER 15: IGMP

zero. On the other hand, a transient group is dynamically assigned an address when the group is created, at the request of a host. A transient group ceases to exist, and its address becomes eligible for reassignment, when its membership drops to zero.

The creation of transient groups and the maintenance of group membership is the responsibility of “multicast agents”, entities that reside in internet gateways or other special-purpose hosts. There is at least one multicast agent directly attached to every IP network or sub-network that supports IP multicasting. A host requests the creation of new groups, and joins or leaves existing groups by exchanging messages with a neighboring agent.

The Internet Group Management Protocol (IGMP) is an internal protocol of the Internet Protocol (IP) suite. IP manages multicast traffic by using switches, multicast routers, and hosts that support IGMP (in the MultiLink ML1200 Managed Field Switch implementation of IGMP, a multicast router is not necessary as long as a switch is configured to support IGMP with the querier feature enabled). A set of hosts, routers, and/or switches that send or receive multicast data streams to or from the same source(s) is termed a multicast group, and all devices in the group use the same multicast group address. The multicast group running version 2 of IGMP uses three fundamental types of messages to communicate:

•Query: A message sent from the querier (multicast router or switch) asking for a response from each host belonging to the multicast group. If a multicast router supporting IGMP is not present, then the switch must assume this function in order to elicit group membership information from the hosts on the network (if you need to disable the querier feature, you can do so using the IGMP configuration MIB).

•Report: A message sent by a host to the querier to indicate that the host wants to be or is a member of a given group indicated in the report message.

•Leave Group: A message sent by a host to the querier to indicate that the host has ceased to be a member of a specific multicast group. Thus, IGMP identifies members of a multicast group (within a subnet) and allows IGMP-configured hosts (and routers) to join or leave multicast groups.

When IGMP is enabled on the MultiLink ML1200 Managed Field Switch, it examines the

IGMP packets it receives to:

•Learn which ports are linked to IGMP hosts and multicast routers/queriers belonging to any multicast group.

•Become a querier if a multicast router/querier is not discovered on the network.

Once the switch learns the port location of the hosts belonging to any particular multicast group, it can direct group traffic to only those ports, resulting in bandwidth savings on ports where group members do not reside. The following example illustrates this operation.

15–2 MULTILINK ML1200 MANAGED FIELD SWITCH – INSTRUCTION MANUAL