An interface device for interfacing between a networkable device such as a printer and a network, includes a hub and a circuit board, with the hub constructed with plural ports to repeat network transmissions received on one port to all other ports. An isolation switch is provided for controllably isolating the port to which the network is connected so that network transmissions are not repeated by the hub. The isolation switch is operated under control of the circuit board, which implements network functionality for the networkable device. For example, where the networkable device is a printer, the extended network functionality provided by the circuit board may relate to secure printing. The isolation switch can be operated so as to isolate the network from the printer, to permit the circuit board to transmit decrypted print jobs in clear text to the printer without danger of interception over the network.