Allied Telesis AT-S63 - Manual (Page 227)

AT-S63 Management Software Features Guide
Section III: Snooping Protocols 227
Overview
Multicast routers are essential for IP multicasting. They send out the
queries to the network nodes to determine group memberships, route the
multicast packets across networks, and maintain lists of the multicast
groups and the ports where the members of the groups are located.
But if IP multicasting is restricted to a single LAN, without the need for
routing, IGMP snooping querier can be used in place of a multicast router.
It lets the switch mimic a multicast router by sending out general IGMP
queries for the nodes to respond to.
IGMP snooping querier supports both IGMP version 1 and version 2. The
switch sends version 2 messages unless it receives version 1 messages
from any of the nodes, in which case it sends version 1 queries. The
switch reverts back to version 2 queries if, after 400 seconds, no further
version 1 messages are received.
This feature has a number of requirements. There can be only one querier
on a LAN. The switch, if it receives a query from a multicast router or
another switch running IGMP snooping querier, immediately disables the
IGMP snooping querier. It reactivates the feature if it does not receive any
further queries for a period of 255 seconds.
The switch must be running IGMP snooping. The switch does not allow
you to enable IGMP snooping querier unless IGMP snooping is also
enabled.
To enable IGMP snooping querier, you apply it to the VLAN where it is to
send its queries. Allied Telesis recommends using the Default VLAN.
The switch must have an IP address to add to the queries as its source
address, and the address must be a member of the same network as the
host nodes and the multicasting source. You assign an IP address to the
switch by creating a routing interface in the VLAN.
Figure 25 is an example of IGMP snooping querier. It consists of a single
switch with just one VLAN, the Default VLAN, which has the VID 1. Both
IGMP snooping and IGMP snooping querier are enabled. A routing
interface has been assigned to the VLAN, with an IP address that is a
member of the same subnet as the multicast source and the host nodes.