This paper describes the hardware and software architecture of a gateway between an Ethernet-style local area network called Strathnet and an X.25 packet switched network (British Telecom's PSS). The hardware is based on a Motorola 68000 processor using the VME bus, and peripheral boards based on an 8-bit 68120/1 processor for the local network and the X.25 interfaces. The software is layered from the low-level executive, through the three X.25 levels and the transport layer, and through the corresponding layers on the local network side, to the bridging software itself. Both hardware and software are designed so that the system can be a general-purpose gateway: for example, the local area network peripheral board could be replaced by a ring type interface, and the software within the local network layers could similarly be replaced.