ARRIS 2247-N8-10NA (v9.1.x) Admin Handbook - Manual (Page 47)

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IP IGMP commands
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 com-
puter 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 gateways use a protocol for for-
warding multicasting: Internet Group Management Protocol (IGMP).
Motorola gateways support IGMP Version 1, Version 2, or 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 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
“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:
‹ IGMP Snooping – enables the 2247-N8 to “listen in” to IGMP traffic. The 2247-N8 discovers multicast group
membership for the purpose of restricting multicast transmissions to only those ports which have requested
them. This helps to reduce overall network traffic from streaming media and other bandwidth-intensive IP
multicast applications.
‹ Robustness – a way of indicating how sensitive to lost packets the network is. IGMP can recover from
robustness minus 1 lost IGMP packet. The default value is 2.
‹ Query Interval – the amount of time in seconds between IGMP General Query messages sent by the querier
gateway. The default query interval is 125 seconds.
‹ Query Response Interval – the maximum amount of time in tenths of a second that the IGMP gateway
waits to receive a response to a General Query message. The default query response interval is 10 seconds
and must be less than the query interval.
‹ Unsolicited Report Interval – the amount of time in seconds between repetitions of a particular computer’s
initial report of membership in a group. The default unsolicited report interval is 10 seconds.