Motorola 3347 - Manual (Page 211)

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CONFIG Commands
IGMP Settings
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 ser vices 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 for warding device, Motorola Netopia®
Gateways use a protocol for for warding multicasting: Internet Group Management Protocol
(IGMP).
Motorola Netopia® Gateways suppor t IGMP Version 1, Version 2, or, beginning with Motor-
ola Netopia® Firmware Version 7.7, Version 3.
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 multicast 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 por t level for an IGMP
repor t. The switch then processes the IGMP repor t and star ts for warding the relevant mul-
ticast stream onto the host's por t. When the switch receives an IGMP leave message, it
processes the leave message, and if appropriate stops the multicast stream to that par tic-
ular por t. 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 suppor t was enabled.
IGMP Version 3 supports:
IGMP Source Filtering: the ability for group memberships to incorporate source address fil-
tering. This allows “Source-Specific Multicast” (SSM). By adding source filtering, a Gateway
that proxies IGMP can more selectively join the specific multicast group for which there are
interested LAN multicast receivers.
These features require no user configuration on the Gateway.
You can set the following options: