GatewayA gateway is a program or service converts input from one system type to another. A gateway can also function as an access portal from one system to another.
Often gateways are used to connect outside LANs and WANs to the Internet. Gateways can be configured so that only users on the attached LAN can bring information across the gateway from the Internet. Gateways are also used to restrict the access and the transfer of information to or from the Internet. For example, the gateway linking CompuServe to the Internet allows e-mail and Web documents to transmit across the gateway but not binaries. Gateways are also referred to as firewalls when they are used to enforce strict security measures.