Network Gateways

By Stephen Bucaro

When networks with different protocols, such as Ethernet and Token Ring need to be connected together, this requires reconstruction of the data packets. To do this, information from above the network layer is required. A gateway is a device that can function at all seven layers of the OSI model. A gateway can connect a LAN to a WAN, a LAN to a mainframe, translate protocols, or convert transmission media.

A router that connects a local subnet to other networks is called a "default gateway". A gateway that connects a LAN to the Internet is called a "proxy server" when it receives all requests for Internet access from the LAN and routes them to the Internet. A gateway that connects a LAN to the Internet is called a "firewall" when it provides security and protection against external intrusions.