Routers are the pieces of equipment responsible for making sure traffic between computers gets where it needs to go. They come in a variety of sizes from something you could hold in your hand to something too large for one person to lift. Routers choose the shortest path between computers using a complicated system of rules known as Routing Protocols. If you have an internet connection you probably have a router somewhere that your computer sends data to. This is the first router your computer will connect to in order to get to the internet. It is also known as a gateway (because it is your gateway to the internet). By convention the gateway has the lowest IP address (like a phone number for a computer) in the netblock (a group of addresses). Anytime you make a connection such as a connection to www.wikipedia.org your computer looks up the address using the global look-up service called DNS (Domain Name Service) Once the destination address has been found your computer connects to your gateway. The gateway then hands off data to a router at your ISP (Internet Service Provider) that router can be said to be part of the internet and connects to one or more other routers until the data reaches the destination.
In small networks such as homes, small businesses (including internet cafes) and small schools, the router also performs NAT (network address translation) which makes all outgoing connections appear to come from one address. Typically incoming connections are only allowed if they are replies to connections made by a computer inside the NAT.
A router is a computer whose software and hardware are usually customized to perform tasks of routing and forwarding information. Routers generally contain a specialized operating system, RAM, NVRAM, flash memory, and one or more processors, as well as two or more network interfaces.
Routers connect two or more logical subnets, which do not necessarily map one-to-one to the physical interfaces of the router.[1] The term layer 3 switch often is used interchangeably with router, but switch is really a general term without a precise technical definition; network switches are generally optimized for Ethernet LAN interfaces and may not have other physical interface types.
Routers operate in two different planes [2]:
Control Plane, in which the router learns the outgoing interface that is most appropriate for forwarding specific packets to specific destinations,
Forwarding Plane, which is responsible for the actual process of sending a packet received on a logical interface to an outbound logical interface.
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