You need to ensure your have a IGMP subscription and that a IGMP query enable for that subent.
> if the iptv host is a unix box, the netstat -g cmd will show your subscriptions
[emnoc@venusfly ~]$ netstat -ng
IPv6/IPv4 Group Memberships
Interface RefCnt Group
--------------- ------ ---------------------
lo 1 224.0.0.1
eth0 1 224.0.0.251
eth0 1 224.0.0.1
lo 1 ff02::1
eth0 1 ff02::fb
eth0 1 ff02::1:ffc4:be1a
eth0 1 ff02::1
eth5 1 ff02::fb
eth5 2 ff02::1:ff40:8112
eth5 1 ff02::1
eth6 1 ff02::fb
eth6 1 ff02::1:ff40:80a5
eth6 1 ff02::1
eth7 1 ff02::fb
eth7 1 ff02::1:ff40:80a4
eth7 1 ff02::1
eth8 1 ff02::fb
eth8 1 ff02::1:ff40:80a7
eth8 1 ff02::1
> for windows, I don' t know of any reasonable way to find your subscriptions
Next,
To look for a igmp querier, execute the following;
tcpdump igmp
or for wireshark you can use a display filter of igmp also. I guess you could do the same on the diagnostic packet sniffer on the FGT and specify the lan interface where the IPTV host(s) sits.
btw: If you have no querier , than this is going to break your multicast_forwarder. Also, if you have a l2 switch that support igmp-snooping, this would break also.