Router |
: This article describes the computer networking device. A wood router is a kind of rotating cutting tool.
A router is a computer networking device that forwards data packets across an internetwork toward their destinations, through a process known as Routing. Routing occurs at layer 3 (the Network layer) of the OSI seven-layer model.
=What a Router Does=
In non-technical terms, a router acts as a junction between two networks to transfer data packets among them. A router is essentially different from a Network switch that connects devices to form a Local Area Network (LAN). One easy illustration for the different functions of routers and switches is to think of switches as neighborhood streets, and the router as the intersections with the street signs. Each house on the street has an address within a range on the block. In the same way, a switch connects various devices each with their own IP address on a LAN. However, the switch knows nothing about IP address except its own management address. Routers connect networks together the way that onramps or major intersections connect streets to both highways and freeways, etc. The street signs at the intersection (routing table) show which way the packets need to flow.
So for example, a router at home connects the Internet Service Provider s network (usually on an Internet address) together with the LAN in the home (typically using a range of Private IP address) and a single broadcast domain. The switch connects devices together to form the LAN. Sometimes the switch and the router are combined together in one single package sold as a multiple port router.
In order to route packets, a router communicates with other routers using routing protocols and using this information creates and maintains a routing table . The routing table stores the best routes to certain network destinations, the routing metrics associated with those routes, and the path to the next hop router. See the Routing article for a more detailed discussion of how this works.
Routing is most commonly associated with the Internet Protocol, although other less-popular routed protocols remain in use..
=Types of routers=
In the original era of routing (from the mid-1970s through the 1980s), general-purpose mini-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 DC power rather than line power (which can be provided from batteries in data centers), and using solid-state rather than magnetic storage for program loading. Large modern routers have thus come to resemble telephone switches, with whose technology they are currently converging and may eventually replace, whilst small routers have become a common household item.
A router that connects clients to the Internet is called an edge router . A router that serves solely to transmit data between other routers, e.g. inside the network of an Internet service provider, is called a core router .
A router is normally used to connect at least two computer networks, but 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.
In mobile ad-hoc networks every host performs routing and forwarding by itself, while in wired networks there is usually just one router for a whole broadcast domain.
In recent times many routing functions have been added to Local area network Network switch (a marketing term for high-speed Network bridge), 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 Digital Subscriber Line. These are routers in the true sense because they join two networks together - the Wide area network and the Local area network and have a routing table. Often these small routers support the Routing Information Protocol protocol, although in a home application the routing function does not serve much purpose since there are only two ways to go - the WAN and the LAN. In addition, these routers typically provide Dynamic Host Configuration Protocol, Network address translation, Demilitarized zone (computing) and Firewall services. Sometimes these routers can provide content filtering and Virtual private network. Typically they are used in conjunction with either a cable modem or Digital Subscriber Line modem, but that function can also be built-in.
=Manufacturers of routers=
There are several manufacturers of routers including:
= Software routers=
With the proper software, ordinary IBM PCs can be made into routers:
[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=
=External links=
*[http://www.bsdrouter.org www.bsdrouter.org] - website that covers router software based on Berkeley Software Distribution operating systems *[http://computer.howstuffworks.com/router.htm/printable HowStuffWorks: How Routers Work by Curt Franklin]|
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