A router is a networking device whose software and hardware are usually tailored to the tasks of routing “ selecting paths in a network along which to send network traffic ” and forwarding information “relaying of packets from one network segment to another by nodes in a computer network“.

The router is the only device that sees every message sent by any computer on either of the networks .

Router is extremely useful in dealing with two separate computer networks. It joins the two networks, passing information from one to the other and, in some cases, performing translations of various protocols between the two networks. It also protects the networks from one another, preventing the traffic on one from unnecessarily spilling over to the other.

One of the tools a router uses to decide where a packet should go is a configuration table. A configuration table is a collection of information, including:

• Information on which connections lead to particular groups of addresses
• Priorities for connections to be used
• Rules for handling both routine and special cases of traffic

Configuration table is very useful that make sure :

• The router ensures that information doesn’t go where it’s not needed. This is crucial for keeping large volumes of data from clogging the connections of “innocent bystanders.”
• The router makes sure that information does make it to the intended destination.