This article describes the computer networking device. A wood router is also a kind of rotating cutting tool.

A router is a computer networking device that forwards data packets toward their destinations, 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 remain 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 both common routing functions such as packet forwarding and specialised functions such as IPSec encryption .

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 networks, 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.

In recent times many routing functions have been added to LAN switches, creating "Layer 2/3 Switches" which route traffic at near wire speed.

Routers are also now being implemented as Internet gateways, primarily for small networks like those used in homes and small offices. This application is mainly where the Internet connection is an always-on broadband connection like cable modem or DSL. These are not "routers" in the true sense, but the terminology has been confused with network address translation.

There are several manufacturers of routers including:

• 3Com (www.3com.com)
• Cisco Systems, Inc. (www.cisco.com)
• D-Link Systems (www.dlink.com)
• Enterasys Networks (www.enterasys.com)
• Juniper Networks (www.juniper.net)
• Linksys (www.linksys.com)
• Mikrotik (www.mikrotik.com)
• Netgear (www.netgear.com)
• Nortel (www.nortelnetworks.com)
• Pivotal Networking (www.pivnet.com)
• SMC Networks (www.smc.com)
• Tellabs (www.tellabs.com)

With the proper software, ordinary PCs can be made into routers:

• fdgw
• FREESCO
• GNU Zebra ( www.zebra.org )
• IPCop ( www.ipcop.org )
• SmoothWall ( smoothwall.org )
• The Linux Router Project^[1]

^[1]Most Unix-like operating systems include all necessary software to perform routing; the Linux Router Project is an example of a Linux distribution that specialises in routing.

See also: flapping router, network address translation

External links

• http://www.bsdrouter.org/ - Website that covers router software based on BSD operating systems