A device or set of devices that interconnect two or more networks,
enabling data transfers to be made between them. When the networks offer similar
services, a gateway may simply serve to route packets or messages from one
network to another. When the networks differ (i.e. in packet size, connection
service, etc.), a gateway performs extensive protocol translation services as
well. The word bridge is sometimes used to describe a gateway whose presence is
invisible to hosts on the connected networks.
The bridge receives all the packets that are addressed to hosts on other
networks, and forwards them appropriately. Thus only the bridges need to have
their routing tables changed when a host moves from one network to another, or
when internetwork connectivity changes. Within a particular protocol domain
there may be a specific definition of the term gateway and the services that one
provides. Many gateways participate in an intergateway status check and routing
update protocol. Some gateways also provide secondary services such as current
date and time, or host name to address conversion. See also internetworking.