Down the Rabbit Hole: The Making of Cloudflare Warp

In the real world, tunnels are often carved out from the mass of something bigger - a hill, the ground, but also man-made structures.

CC BY-SA 2.0 image by Matt Brown

In an abstract sense Cloudflare Warp is similar; its connection strategy punches a hole through firewalls and NAT, and provides easy and secure passage for HTTP traffic to your origin. But the technical reality is a bit more interesting than this strained metaphor invoked by the name of similar predecessor technologies like GRE tunnels.

Relics

Generic Routing Encapsulation or GRE is a well-supported standard, commonly used to join two networks together over the public Internet, and by some CDNs to shield an origin from DDoS attacks. It forms the basis of the legacy VPN protocol PPTP.

Establishing a GRE tunnel requires configuring both ends of the tunnel to accept the other end’s packets and deciding which IP ranges should be routed through the tunnel. With this in place, an IP packet destined for any address in the configured range will be encapsulated within a GRE packet. The GRE packet is delivered directly to the other end of the tunnel, which removes the encapsulation and forwards the original Continue reading