IGMP v1 - Internet Group Management Protocol

Switches record SRC MAC/interface to reduce the flooding of packets to all ports. Broadcast and multicast packets do not have a source MAC address, so by default are flooded out of all ports.

Static MAC table entries, Cisco Group Management Protocol (CGMP), and IGMP snooping are solutions to prevent the requirement to flood packets out of all ports. Performance improvements.

IGMP is a protocol that allows router/switch to determine a multicast group is being used, and to enable the switch to only forward packets to the interfaces wishing to recieve packets to that multicast group.

First phase is for the clients to identify themselves to the router, so that they can join the multicast group. In IGMP v1 this is via a membership report sent by the client to the destination mutlicast group, and intercepted by the router.

The router on each segment sends a query to the all hosts address 224.0.0.1, if it recieves one or more responses, the group is maintained, if not the group is removed.

In IGMP v1 there is no function to allow a host to remove its self from a group, it must 'age-out'.