A router consists of a computer networking device that determines the next network point to which to forward a data packet toward its destination, a process known as routing. Routing occurs at layer 3 of the OSI seven-layer model.
Routing is most commonly associated with the Internet protocol, although other less-popular routed protocols continue in use.
In the original 1960s-era of routing, general-purpose computers served as routers. Although general-purpose computers can perform routing, modern high-speed routers are highly specialised computers, generally with extra hardware added to accelerate the common routing functions, such as packet forwarding.
Other changes also improve reliability, such as using battery rather than mains power, and using solid-state rather than magnetic storage. Modern routers have thus come to resemble telephone switches, whose technology they are currently converging with and may eventually replace.
The first modern (dedicated, standalone) routers were the Fuzzball routers.
A router must be connected to at least two networkss, or it will have nothing to route. A special variety of router is the one-armed router used to route packets in a virtual LAN environment. In the case of a one-armed router the multiple attachments to different networks are all over the same physical link.
A router creates and/or maintains a table, called a "routing table" that stores the best routes to certain network destinations and the "routing metrics" associated with those routes.
See the routing article for a more detailed discussion of how this works.
There are several manufacturers of routers including: