Routers - Introduction

Router is a networking device whose software and hardware are typically customized to the tasks of routing and forwarding information. For instance, on the Internet, information is directed to various paths by routers. Routers connect two or more logical subnets, which do not essentially map one-to-one to the physical interfaces of the router. It operates in two different planes:

1. Control plane: It is a plane in which the router learns the outgoing interface that is most appropriate for forwarding specific packets to specific destinations.
   
2. Forwarding plane: A plane which is responsible for the actual process of sending a packet received on a logical interface to an outbound logical interface.

Brief Description

In packet-switched networks like Internet, a router is a device or, in some cases, software in a computer which decides the next packet forwarding point in a network. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any gateway i.e. a point where one network meets another including each point-of-presence on the Internet. A router is often included as part of a network switch.

A router creates and maintains a table of the accessible routes and their conditions and makes use of this information along with distance and cost algorithms to establish the best route for a given packet. Normally, a packet travels through a number of network points with routers before arriving at its final destination. Routing is a function associated with the Network layer i.e. layer 3 in the Open Systems Interconnection (OSI) model (the standard model of network programming). A layer-3 switch is a switch that can perform routing functions.

Router Components