Simple QUIC holepunch demonstration
Usage:
// On computer 1
> go build ./client
> client.exe -msg "Hello from client 1"
Local address: ......
Your address is: <public IP:port>
Enter remote peer address (with port): <public IP:port of computer 2>
// On computer 2
> client.exe -msg "Hello from client 2"
Local address: ......
Your address is: <public IP:port>
Enter remote peer address (with port): <public IP:port of computer 1>The peers should exchange messages. You can then add more peers or simply disconnect.
I have tested this application using two computers: one connected to basic consumer internet (ATT), which is using Port Restricted Cone NAT (Endpoint-Independent Mapping, Address and Port Dependent Filtering). The second computer is connected to a LTE hotspot (T-Mobile), which is Port Restricted Cone NAPT, meaning the internal/external ports do not match.
Note that each computer needs to enter the others address within ~10-15 seconds of each other in order to successfully holepunch. In practice, it is better to use some sort of rendezvous point, but that requires a third party server, so I kept my implementation simple.
I have not tested this with Symmetric NAT, but I believe it should work, as long as one side has a NAT type that is less restrictive than Port Restrictive Cone NAT. The tool is flexible enough to work as long as at least one side makes a connection, as is the case when one side is Symmetric and the other is Full Cone/Restricted.
There was a tool called pwnat (http://samy.pl/pwnat) that was able to do this without even a rendezvous or any kind of client synchronization, but that no longer works.
chownat, made by the same author, does not work either anymore, rendering this approach impossible without some other way to signal peers.