The kernel has very specific rules correlating file type with comment type, and also SPDX identifiers can't be merged with other comments.
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Sep 19, 2018
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== NAT Hole Punching Example == This code should never be used, ever. But, it's a nice demonstration of how to punch holes and have two NAT'd peers talk to each other. Compile with: $ gcc nat-punch-client.c -o client -lresolv $ gcc nat-punch-server.c -o server Server is 220.127.116.11 and is on the public internet accepting UDP:49918. Client A is NAT'd and doesnt't know its IP address. Client B is NAT'd and doesnt't know its IP address. Server runs: $ ./server Client A runs: # ip link add wg0 type wireguard # ip addr add 10.200.200.1 peer 10.200.200.2 dev wg0 # wg set wg0 private-key ... peer ... allowed-ips 10.200.200.2/32 # ./client 18.104.22.168 wg0 # ping 10.200.200.2 Client B runs: # ip link add wg0 type wireguard # ip addr add 10.200.200.2 peer 10.200.200.1 dev wg0 # wg set wg0 private-key ... peer ... allowed-ips 10.200.200.1/32 # ./client 22.214.171.124 wg0 # ping 10.200.200.1 And voila! Client A and Client B can speak from behind NAT. ----- Keep in mind that this is proof-of-concept example code. It is not code that should be used in production, ever. It is woefully insecure, and is unsuitable for any real usage. With that said, this is useful as a learning example of how NAT hole punching might work within a more developed solution.