User`s guide

AT-S45 User’s Guide
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IGMP Snooping Overview
The Internet Group Management Protocol (IGMP) enables routers to
create lists of nodes that are members of multicast groups. (A multicast
group is a group of end 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 report, 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 enables the switch 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-S45 software supports both IGMP version 1 and version 2.