Netgear GS724TS-100NAS User Manual download pdf (Page 110)

110 | Chapter 3: Configuring Switching Information

GS716Tv2 and GS724Tv3 Software Administration Manual

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 unrequested 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.

IGMP Snooping Configuration

Use the IGMP Snooping Configuration page to configure the parameters for IGMP snooping,

which is used to build forwarding lists for multicast traffic.

To access the IGMP Snooping Configuration page, click Switching Multicast  IGMP

Snooping  IGMP Snooping Configuration.

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Netgear GS724TS-100NAS User Manual Page 110