Netopia 3346N-ENT User Guide (en)

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3-36  Firmware User Guide
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 Routers can use either IGMP 
Version 1 or Version 2. IGMP for warding is enabled per IP Profile and WAN Connection Profile. See 
 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.
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 Snooping – toggling this option to On enables the Netopia Router to “listen in” to IGMP traffic. The 
Router discovers multicast group membership for the purpose of restricting multicast transmissions to only 
                                  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:              v2
         V2 Settings...
Return/Enter accepts * Tab toggles * ESC cancels.