author here. NAT traversal definitely still works, but it's very situational. I'd estimate the simple techniques get you successful p2p in 90% of cases, but tho

author here. NAT traversal definitely still works, but it's very situational. I'd estimate the simple techniques get you successful p2p in 90% of cases, but those 90% are unevenly distributed: for a particular pair of endpoints, the success rate is either 100% or 0%, and it's little consolation to the 0% folks to know that they're the exception :) The paper you linked seems to have reasonably modern techniques for UDP traversal, so it should work. One thing that paper doesn't make clear, IMO, is that you need to STUN on both ends to discover your WAN ip:port, and you need to run the STUN traffic from the same socket as the one you're using for the NAT traversal. If you have Tailscale, you can run `tailscale netcheck` to characterize your network a little bit, which might give you some answers as to why the traversal doesn't work. Successful traversal depends on the properties of both endpoints, so you'd want to netcheck from both ends. The usual culprit is MappingVariesByDestIP=true, which indicates a hard NAT.