This report discusses some of the problems and limitations in existing internetwork design for the connection of packet-switching networks of different technologies and presents an algorithm that has been shown to be suitable for internetworks of unbounded size. Using a new form of address and a flat routing mechanism called Cartesian routing, this algorithm is designed to solve three problems: (1) overhead that increases with size and thus limits expansion; (2) an inability to allow mobile hosts free movement throughout the internetwork; and (3) routing and packet processing requiring large tables or substantial computation per packet. It also retains two desirable attributes of current algorithms: robustness in the presence of link and router failures, and the use of short paths. This report discusses (1) routing and addressing problems in large metropolitan scale internetworks; (2) Cartesian routing; (3) heuristic modifications; (4) congestion control; (5) applying Cartesian routing to a metropolitan region; (6) host mobility; and (7) simulating Cartesian routing. A model for minimizing hop counts in point-to-point networks is appended and 25 references are provided. (RP)