what is a computer router

what is a computer router

A Router is a usually a device, but can be a piece of software running on a computer, that transmits data between two networks that without the router, would not know how to communicate with each other.

When a computer needs to send data to a destination which is not parts of its same network of computers, the sending computer transmits that data to a router. When the router receives that data it then looks at a table of possible routers that it knows about and forwards the data to the router it feels would be best suited to deliver the data to its ultimate destination.

For home users, a router is a device that you would plug your cable or dsl modem into the back of, and connect your computer to. This router would then enable you to have a small network of computers at home that would share the same Internet Connection. The theory discussed above would still apply to this scenario. When one of your home computers send information to a computer that is not on your home network, it will send that data to your router. Your router will receive that data and look at its table of known routers to send the data to. As it only know the router for your ISP, it will forward that data on to them.

At the Edge and In Between:Most routers in the world sit in homes and small offices and do nothing more than direct traffic from the network to the Internet. Sitting at the edge of the network, they may also contain a built-in firewall for security, and the firewall serves all users in the network without requiring a personal firewall in each computer. See firewall and personal firewall.

However, in the larger company, routers are also used to separate local area networks (LANs) into subnetworks (subnets) in order to balance traffic within workgroups and to filter traffic for security purposes and policy management.

Routers in the Core:Within a large enterprise, routers serve as an internet (lower case "i") backbone that connects all internal networks, in which case they are typically connected via Ethernet. Within the global Internet (upper case "I"), routers do all the packet switching between the backbones and are typically connected via T3, ATM or SONET links.

Routable Protocols:Routers route messages transmitted only by a routable protocol such as IP "or" IPX. Multiprotocol routers support more than one; for example, IP "and" IPX. Messages in non-routable protocols, such as NetBIOS and LAT, cannot be routed, but they can be transferred from LAN to LAN via a bridge.

Because routers have to inspect the network address in the packet, they do more processing and add more overhead than a bridge or switch. Routers work at the network layer (layer 3) of the protocol, whereas bridges and switches work at the data link layer (layer 2), also known as the "MAC layer." See OSI model.

Specialized Machines or Regular PCs:Most routers are specialized computer-based devices optimized for communications; however, router functions can also be implemented by adding software to a server. For example, the NetWare operating system includes software to route packets from one subnetwork to another if each is connected to a separate network adapter (NIC). The major router vendors are Cisco Systems and Nortel Networks.

Router Terminology:Routers used to be called "gateways," which is why the term "default gateway" means the router in your network (see default gateway). In older Novell terminology, routers were also called "network-layer bridges." For more details on the routable protocol layer (network layer 3), see OSI model and TCP/IP abc's. See layer 3 switch, route server, router cluster and routing protocol.