Your NAT traversal strategy is limited by the type of NAT being employed. Traditionally, the worst case scenario for NAT traversal is "symmetric NAT." Symmetr

Your NAT traversal strategy is limited by the type of NAT being employed. Traditionally, the worst case scenario for NAT traversal is "symmetric NAT." Symmetric NAT means that each tuple of (source_ip, source_port, destination_ip, _destination_port) gets its own unique (external_ip, external_port) tuple. This is bad because it means that STUN is ineffective: your STUN server will see a different external port than what your actual destination would see. Mobile data networks are actually worse than symmetric NAT. Not only will your external port change based on your target, but your external IP likely will as well. This makes NAT traversal, AFAIK, basically impossible.