Getting Cloudflare Tunnels to connect to the Cloudflare Network with QUIC

Sudarsan Reddy, a developer working on Cloudflare Tunnel, recently experienced an interesting connectivity issue while trying to get the service to connect using UDP protocol QUIC. The problem was unique to UDP and required debugging beyond firewalls. The solution involved setting the source address explicitly in the application to avoid relying on kernel heuristics. This was achieved by using recvmsg and sendmsg system calls, which allow passing additional out-of-band data including source addresses. A minor bug in the library used for this task was also discovered and fixed. The updated version of Cloudflare Tunnel now supports UDP (QUIC) connectivity to the Cloudflare network from anywhere in the world.