Gateways, Routers, Firewalls, Proxy Server, Bridges . . .
A gateway is a hardware device that acts as a “gate” between two networks. It may be a router, firewall, server, or other device that enables traffic to flow in and out of the network.
While a gateway protects the nodes within network, it also a node itself. The gateway node is considered to be on the “edge” of the network as all data must flow through it before coming in or going out of the network. It may also translate data received from outside networks into a format or protocol recognized by devices within the internal network. This is why the gateway is found at the top of the OSI model.
A router is a common type of gateway used in home networks. It allows computers within the local network to send and receive data over the Internet (therefore translation happens)
A firewall is a more advanced type of gateway, which filters inbound and outbound traffic, disallowing incoming data from suspicious or unauthorized sources. One can program sets of rules into the firewall defining what and what not may be allowed through based on the user’s profile e.g. the boss can have access to FaceBook whereas his personal assistent may not.
A proxy server is another type of gateway. A proxy as an intermediary for requests from clients seeking resources from servers usually outside of their LAN. For example, a proxy server may only allow local computers to access a list of authorized websites. It can also keep “copies” of websites that are often visited by people on the LAN. Often companies have a duplicate copy of their main database on the proxy server; changes are made to the duplicate copy first before the main database is updated.
A bridge is a node that provides interconnectivity with other networks that use the same protocol (no translation necessary).