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 configure IGMP Snooping on a GS-23xx series switch.


  • LCOS SX as of version 3.32 Rel (download latest version)
  • Any web browser for accessing the webinterface
  • Configured and functional VLANs


1) Connect to the switch via the webinterface and go to the menu Configuration → IGMP Snooping → Basic Configuration

2) Modify the following parameters:

  • Activate the option Snooping Enabled.
  • Make sure, that the option Unregistered IPMCv4 Flooding Enabled is deactivated, as otherwise unknown streams would be forwarded to all ports. 

3) Activate the option Router Port for the port, where the Multicast sender is connected to and click Apply.

If there are additional switches in the scenario, the uplink port to the next switch with the Multicast sender also has to be set to Router Port

4) Go to the menu Configuration → IGMP Snooping → VLAN Configuration, enter the VLAN ID for the desired network and click Add.

5) Modify the following parameters and click Apply:

  • Activate the option Snooping Enabled for the VLAN, where Multicast should be used.
  • Make sure, that the option IGMP Querier is active in every 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) With the configuration complete, go to the menu Maintenance → Save/Restore → Save Start and click Save so that the configuration is saved as a 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.