This document discusses bridges and gateways. It defines a bridge as a connecting device with its own processor and memory that uses two network interface cards to connect two portions of a network at the physical and data link layers. Bridges are used to divide large networks into smaller subnetworks and connect two local area networks. The document also defines a gateway as a device that connects two networks using different protocols by operating at all seven layers of the OSI model and translating between different frame formats and protocols. Gateways are more powerful than bridges and used to connect incompatible networks.