A router is a device that forwards data packets between computer networks, creating an overlay internetwork.
A router is connected to two or more data lines from different networks.
The most familiar type of routers are home and small office routers that simply pass data, such as web pages and email, between the home computers and the owner's cable or DSL modem, which connects to the Internet through an ISP.
However more sophisticated routers range from enterprise routers, which connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone.
When multiple routers are used in interconnected networks, the routers exchange information about destination addresses, using a dynamic routing protocol.
A router has two stages of operation called planes: Routers may provide connectivity within enterprises, between enterprises and the Internet, and between internet service providers (ISPs) networks.
Smaller routers usually provide connectivity for typical home and office networks.
Distribution routers aggregate traffic from multiple access routers, either at the same site, or to collect the data streams from multiple sites to a major enterprise location.
In enterprises, a core router may provide a "collapsed backbone" interconnecting the distribution tier routers from multiple buildings of a campus, or large enterprise locations.
RFC 4098 standard defines the types of BGP-protocol routers according to the routers' functions: The very first device that had fundamentally the same functionality as a router does today, was the Interface Message Processor (IMP); IMPs were the devices that made up the ARPANET, the first packet network.
The idea for a router (called "gateways" at the time) initially came about through an international group of computer networking researchers called the International Network Working Group (INWG).
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