A network extension device comprising a CPU, memory, protected I/O connectable to local controls and peripherals, external communications port, a trusted device connected to the CPU such that it can provide attestation of the network extension device's trusted operation to a connected known external network, and a protected interface connected to at least one network extension module that includes a local network communications port. Optionally, a traffic encryption module may be provided, and the trusted device's attestation may include a check of its operation. Also, a method comprising connecting the network extension device to an external network, performing an operating mode check, causing the network extension device to operate in a mode and perform a security check that correspond to the result, causing the trusted device to attest trusted operation to the external network and thereafter causing the CPU to function fully and permitting access to the external network.