Hi Quinn, so I got the application to successfully establish the QUIC connection via AWDL from iPhone to iPad, thank you for your time and input and for pointing me into the right direction. I used the POSIX getifaddrs call to get the IP addresses of the iPad and printed them. Then I put the IPv6 address of the awdl0 interface into the client. It's needless to say that this solution is technically not beautiful. Any ideas on how to improve this?

Hi Quinn, thanks for replying. I have used the sec_protocol_options_set_verify_block method form the post you pointed out. When using localhost (on my iPad) the closure is called and the certificates get compared correctly. Thanks for this input. Unfortunately I am still having another problem which might have something to do with your "one more thing" but sadly I don't quite get what you mean or I may have not described my situation precise enough. I am trying to use AWDL between my iPhone and my iPad. Since Bonjour can only advertise TCP and UDP services, I chose to hardcode a port number into my application where the QUIC Service is listening. When connecting to my iPad I try to rely on the DNS cache the Bonjour service figured out and call NWConnection(host: "iPad.local.", port: Config.quicPort, using: transportProtocol.parameters) so I am not using Bonjour directly with QUIC in my understanding and it doesn't throw a DNS error so I assumed it works. Unfortunately it is still stuck in preparing state and the sec_protocol_options_set_verify_block closure is not even called on the iPhone. So what do you mean with DNS name endpoint? Can I approach this differently? How can I connect to the iPad service without being able to advertise it? I assume sending the IP address and port number of the iPads QUIC listener (without the hard coded port number, let the OS allocate a port) via the TCP connection to let the iPhone know the address of the service would work, but I would like to save this additional effort if it works in another way.