The IGMP Proxy (Services > IGMP Proxy) will, as the name implies, proxy IGMP traffic between network segments. Currently defined interfaces are listed on the main page, and the entries can be managed from there.
In order for the IGMP proxy to work properly an upstream interface and one or more downstream interfaces must be defined. Only one upstream interface may be defined.
When adding an IGMP Proxy interface, choose the Interface (eg WAN), enter a Description, select the Type (either Upstream or Downstream), and optionally enter a Threshold for the TTL to help avoid looping.
Network(s) must also be defined to specify what is allowed to communicate via the IGMP proxy. Add a new subnet by clicking , then type in an IP address and select a CIDR mask. To delete an existing subnet, click .
A firewall rule is also required on the downstream side (typically LAN) that matches/passes this traffic which has the Advanced Options checked to Allow packets with IP Options.