Configuring IGMP Snooping
D-Link
Unified Wired and Wireless Access System
Oct. 2015
Page 213
D-Link UWS User Manual
Configuring IGMP Snooping
Internet Group Management Protocol (IGMP) Snooping is a feature that allows a switch to forward multicast
traffic intelligently on the switch. Multicast IP traffic is traffic that is destined to a host group. Host groups are
identified by class
D IP addresses, which range from 224.0.0.0 to 239.255.255.255. Based on the IGMP query
and report messages, the switch forwards traffic only to the ports that request the multicast traffic. This
prevents the switch from broadcasting the traffic to all ports and possibly affecting network performance.
A traditional Ethernet network may be separated into different network segments to prevent placing too many
devices onto the same shared media. Bridges and switches connect these segments. When a packet with a
broadcast or multicast destination address is received, the switch will forward a copy into each of the
remaining network segments in accordance with the IEEE MAC Bridge standard. Eventually, the packet is
made accessible to all nodes connected to the network.
This approach works well for broadcast packets that are intended to be seen or processed by all connected
nodes. In the case of multicast packets, however, this approach could lead to less efficient use of network
bandwidth, particularly when the packet is intended for only a small number of nodes. Packets will be flooded
into network segments where no node has any interest in receiving the packet. While nodes will rarely incur
any processing overhead to filter packets addressed to un-requested group addresses, they are unable to
transmit new packets onto the shared media for the period of time that the multicast packet is flooded. The
problem of wasting bandwidth is even worse when the LAN segment is not shared, for example in Full Duplex
links.
Allowing switches to snoop IGMP packets is a creative effort to solve this problem. The switch uses the
information in the IGMP packets as they are being forwarded throughout the network to determine which
segments should receive packets directed to the group address.
Summary of Contents for DWL-8600AP
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