Administrator’s Handbook
Link: IGMP (Internet Group Management Protocol)
Multicasting is a method for transmitting large amounts of information to many, but not all, computers over an internet. One common use is to distribute real time voice, video, and data services to the set of computers which have joined a distributed conference. Other uses include updating the address books of mobile computer users in the field, or sending out company newsletters to a distribution list.
Since a router should not be used as a passive forwarding device, Motorola Netopia® Gateways use a pro- tocol for forwarding multicasting: Internet Group Management Protocol (IGMP).
Motorola Netopia® Gateways support IGMP Version 1, Version 2, or, beginning with Motorola Netopia® Firmware Version 7.7, Version 3.
See the “Advanced” option in “LAN” on page 49 for more information.
IGMP “Snooping” is a feature of Ethernet layer 2 switches that “listens in” on the IGMP conversation between computers and multicast routers. Through this process, it builds a database of where the multi- cast routers reside by noting IGMP general queries used in the querier selection process and by listening to other router protocols.
From the host point of view, the snooping function listens at a port level for an IGMP report. The switch then processes the IGMP report and starts forwarding the relevant multicast stream onto the host's port. When the switch receives an IGMP leave message, it processes the leave message, and if appropriate stops the multicast stream to that particular port. Basically, customer IGMP messages although processed by the switch are also sent to the multicast routers.
In order for IGMP snooping to function with IGMP Version 3, it must always track the full source filter state of each host on each group, as was previously done with Version 2 only when Fast Leave support was enabled.
IGMP Version 3 supports:
IGMP Source Filtering: the ability for group memberships to incorporate source address filtering. This allows
These features require no user configuration on the Gateway.
To configure IGMP options available in Motorola Netopia® Gateways, click the IGMP link.
