The present invention provides a method and apparatus for enabling a cluster of computers to appear as a single computer to host computers outside the cluster. A host computer communicates only with a gateway to access destination nodes and processes within the cluster. The gateway has at least one message switch which processes incoming and outgoing port type messages crossing the cluster boundary. This processing comprises examining certain information on the message headers and then changing some of this header information either to route an incoming message to the proper computer node, port and process or to make an outgoing message appear as if originated at the gateway node. The message switch uses a table to match incoming messages to a particular routing function which can be run to perform the changes necessary to correctly route different kinds of messages.