Sudarsan Reddy

Author Archives: Sudarsan Reddy

Getting Cloudflare Tunnels to connect to the Cloudflare Network with QUIC

Getting Cloudflare Tunnels to connect to the Cloudflare Network with QUIC
Getting Cloudflare Tunnels to connect to the Cloudflare Network with QUIC

I work on Cloudflare Tunnel, which lets customers quickly connect their private services and networks through the Cloudflare network without having to expose their public IPs or ports through their firewall. Tunnel is managed for users by cloudflared, a tool that runs on the same network as the private services. It proxies traffic for these services via Cloudflare, and users can then access these services securely through the Cloudflare network.

Recently, I was trying to get Cloudflare Tunnel to connect to the Cloudflare network using a UDP protocol, QUIC. While doing this, I ran into an interesting connectivity problem unique to UDP. In this post I will talk about how I went about debugging this connectivity issue beyond the land of firewalls, and how some interesting differences between UDP and TCP came into play when sending network packets.

How does Cloudflare Tunnel work?

Getting Cloudflare Tunnels to connect to the Cloudflare Network with QUIC

cloudflared works by opening several connections to different servers on the Cloudflare edge. Currently, these are long-lived TCP-based connections proxied over HTTP/2 frames. When Cloudflare receives a request to a hostname, it is proxied through these connections to the local service behind cloudflared.

While our HTTP/2 protocol mode works great, we’d like to improve a Continue reading