We present the first formally-verified Internet router, which is part of the SCION Internet architecture. SCION routers run a cryptographic protocol for secure packet forwarding in an adversarial environment. We verify both the protocol's network-wide security properties and the low-level properties of its implementation. Namely, we develop a series of protocol models by refinement in Isabelle/HOL and we use an automated program verifier to prove that the router's Go code satisfies crash freedom, freedom from data races, and adheres to the most concrete model in our series of refinements. Both verification efforts are soundly linked together.