Allied Telesis AT-8350GB - Manual (Page 40)

Product Description
40
The QoS feature was designed to address this problem. With it, Ethernet
frames can be assigned different priorities. The switch uses the priorities
when determining which frames to forward first. Frames from end-
nodes running time-critical applications can be given a high priority, so
that they will be forwarded by the switch ahead of less time-critical
frames.
IGMP Snooping The Internet Group Management Protocol (IGMP) enables routers to
create lists of nodes that want to receive multicast packets from a
multicast application. The router creates a multicast membership list by
periodically sending out queries to the local area networks connected to
its ports. A node wanting to become a member of a particular multicast
group responds to a query by sending a report. Nodes that join a
multicast group are referred to as host nodes.
Once the router has received a request from a host node to join a
multicast group, it notes the multicast group that the host node wants
to join and the port on the router where the node is located. Any
multicast packets belonging to that multicast group are then forwarded
by the router out the port. If a particular port on the router has no nodes
that want to be members of multicast groups, the router does not send
multicast packets out the port. This improves network performance by
restricting multicast packets only to router ports where host nodes are
located.
The IGMP snooping feature on the AT-8350GB switch enables the unit to
monitor the flow of queries from the router and reports from the host
nodes to build its own multicast membership lists. It uses the lists to
forward multicast packets only to switch ports where there are host
nodes that are members of multicast groups. This improves switch
performance and network security by further restricting the flow of
multicast packets only to those switch ports connected to host nodes.
Without IGMP snooping, the switch would flood all multicast packets
out all of its ports, except the port on which it received the packet. Such
flooding of packets can negatively impact switch and network
performance.
Note
By default, IGMP snooping is disabled on the switch.
Note
The AT-S41 software supports both IGMP version 1 and version 2.