Multicast traffic is usually sent to the entire network. The disadvantage of this is that participants receive this data traffic even if they do not need it. This increases the base load on the network. Using IGMP snooping, it is possible to restrict multicast data traffic to certain switch ports and thus reduce the number of network participants affected.  

This article describes how to set up IGMP snooping on a GS-3xxx series switch.


  • LCOS SX as of version 4.00 Rel (download latest version)
  • Any web browser for access to the web interface
  • VLANs that are already set up and functional


1) Connect to the device's web interface and switch to the menu System → IP Address → Advanced Settings and click Add interface to assign an IP address to a VLAN.

2) Modify the following parameters and then click Apply:

  • VLAN: Enter the VLAN ID of the network where multicast should be used.
  • IPv4 Address: Enter an IP address from the network where multicast should be used.
  • IPv4 Mask Length: Enter the subnet mask in CIDR (Classless Inter Domain Routing) notation.

3) Change to the menu Multicast → IGMP Snooping → Basic Configuration and modify the following parameters:

  • Activate IGMP snooping by moving the slider for Snooping Enabled to On.
  • Deactivate the option Unregistered IPMCv4 Flooding Enabled to prevent unknown streams from being forwarded to all ports. 

4) For the port that the multicast source is connected to, activate the option Router Port

For any further switches in the scenario, the uplink port to the next switch must also be set as Router Port.

5) Navigate to the menu Multicast → IGMP Snooping → VLAN Configuration, modify the following parameters, and click Apply:

  • For the VLAN where multicast should be used, activate the option Snooping Enabled.
  • Be sure that the option Querier Election is activated for each VLAN where multicast should be used.

In order for IAPP messages (Inter Access Point Protocol) to be transmitted with active IGMP Snooping, the parameter Compatibility has to be set to the option Forced IGMPv3 for the respective VLAN. However it is not practical to always use this setting as otherwise IGMPv1 and IGMPv2 messages would not be transmitted. Therefore the option Forced IGMPv3 should only be selected for a VLAN, where access points have to exchange IAPP messages.

6) When you are finished, click the disk icon in the top right corner to save the configuration as the start configuration.

The start configuration is retained even if the device is restarted or there is a power failure.

7) This concludes the configuration of IGMP snooping. Repeat these steps for further switches in the scenario, if applicable.