Netopia 3300 - Manual (Page 83)

System Configuration 3-39
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 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, Netopia Routers use a protocol for
for warding multicasting: Internet Group Management Protocol (IGMP).
Netopia Gateways suppor t IGMP Version 1, Version 2, or, beginning with Netopia Firmware Version 7.7,
Version 3. See
“Multicast For warding” on page 7-33 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 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 multicast 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 ticular 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.
To configure the IGMP options available in Netopia Routers, select IGMP (Internet Group Management
Protocol) and press Return.
The IGMP Setup screen appears.
You can set the following options:
IGMP Setup
IGMP Snooping: Off
Robustness: 2
Query Interval(s): 125
Query Response Interval(deci-sec): 100
Unsolicited Report Interval(s): 10
IGMP Querier Version: v3
V2/V3 Settings...
Return/Enter accepts * Tab toggles * ESC cancels.