Okay i tried to debug this but failed miserably x)
Test setup was 2 networks.
No forwarding allowed between them.
I tried vlc streaming feature to test -> legacy udp to a multicast address.
I tested some addresses but nope nothing works.
First i could not get igmpproxy to show any routes in its verbose log.
But the firewall log shows hits for the igmp input rules.
So maybe its a problem of igmpproxy that is shipped with openwrt.
I compiled the new version. Still no go.
No routes in igmpproxy verbose log. ip mroute shows also nothing.
Hmm. Maybe it is a problem of the igmp snooping feature.
So disabled that.
And indeed on the green zone network. igmpproxy now showed my desired route.
But it still didn't work.
My client on the red zone could not retrieve any multicast stream.
So i tried some manual firewall rules. input rules for igmp and udp multicast. also tested forward rules.
Nothing works. Only the igmp input rules showed hits.
Also the firewall log doesn't show any dropped packets.
So yeah im a bit lost. Hmm
I will test it tomorrow again. when i have more time. I also only have one wifi android phone to test from the red zone. So yeah...
//edit
Forgot to add ttl increase rule was also used.