Tunnels & encapsulation
Magic Transit uses tunnels to transmit packets from Cloudflare’s edge to your origin network. Cloudflare sets up GRE tunnel endpoints on edge servers inside your network namespace, and you on routers at your data center.
This diagram illustrates the flow of traffic with Magic Transit.
In the diagram below, Magic Transit encapsulates packets at the Cloudflare edge and transmits them to a customer’s — Acme for example — tunnel endpoint router.
This works because the GRE protocol is stateless—each packet is processed independently and does not require any negotiation or coordination between tunnel endpoints. Tunnel endpoints are technically bound to IP addresses but do not need to be bound to specific devices. Any device that can strip off the outer headers and then route the inner packet can handle any GRE packet sent over the tunnel.
Cloudflare’s Anycast GRE architecture provides a conduit to your GRE tunnel for every server in every data center on Cloudflare’s global edge network as shown in the image below.