@Napsterbater Yeah, considering I'm stuck and even though it seems that pfSense does pass the zero-checksum packet, VoWiFi still does not work, which makes me thing you might be right and it's HOW it passes it. So far I can't get it to work when using pfSense NAT64 setup...

@IonutIT Check "NAT64 Prefix Override" on System > Advanced, Firewall/NAT

Hey, ich habs jetzt hinbekommen, also nicht selber :/. Mein Freund hat mir geholfen und es geht jetzt. Vielen dank für die ganze Hilfe. LG Mathias

@jwt Definetly looking forward to it and be glad to test it out in first snapshots/betas that will have it. We can easily hook up an v6 only network in the lab (there should already be one) and give it a spin :)