Computing | Networking 
Router: An Introduction
by Ruchi Gupta

If you have little idea about computer networks or even if you are using Internet, you must have come across the word “router”. Now the question arises what is “router” and of course what is “routing”?

We all know that in any computer network data is transported from one location to another location. This transportation of data is known as “routing”.

Internet is a worldwide network of computer networks. It is an interconnection of large and small networks around the globe. To connect one network to another we need some sort of linkage, this linkage provided by an electronic device, work of this device is to connect two or more networks and routes incoming data packets to the appropriate network.

The well known term for such device is “router”.

When we send any data across the network, it flows in the form of packet, besides containing data itself these packets contains two addresses. One which is assigned to the machine sending data i.e. source address and other assigned to the machine receiving data i.e. destination address. The addresses which we are talking about is known as IP addresses. IP stands for internet protocol. All computers across the internet are assigned a globally unique identifier called IP address. IP addresses are used as street addresses so other computers can locate them, these addresses takes the form of four numbers separated by dots e.g. 124.45.69.89. In future the IP numbers will be in the form of six numbers like 192.168.222.212.10.111

Function of router is to take out the destination IP address from the packet and determines the next network point to which a data packet should be forwarded towards its destination. Before reaching the destination from source, packet may have to follow a long path, in between it may go through many routers, like first router may send it to second and so on….number may rise up to 10 to 20 routers...or even more.

When ultimately packet reaches to the destination machine, that machine uses the source IP address of the packet to send to send acknowledgment indicating that packet has arrived.

This may also happen that packet may not arrive due to some reason, in that case error will be sent to the source machine.

One more very important function played by router is acting as “firewall”. Briefly I am explaining how it does so.

When our PC is directly connected to the internet, a unique address is assigned to our PC by the Internet Service Provider (ISP). For example, you are now connected to the internet, your PC will be having a globally unique IP address, this address is very public i.e. it can be known to anyone anywhere on the internet. In such cases, anyone can use the IP address of user machine to do some mischievous work, for example anyone can install some software to keep track of user activities. One of the software known as spyware can be installed in user machine that covertly gathers user information through the user’s internet connection without his or her knowledge.

In such cases router can act as hardware firewall, it does not allow computer’s IP address to directly expose to the internet.

Now the question arises how it does so?

What happens in such cases the IP address is assigned to the router by ISP (Internet Service Provider) and not to the PC, now it’s the work of router to assign private address to the PC. When we send any packet, router removes the source IP address and attaches its own public IP address, in turn stores the information about all the changes which were made. When any packet comes to the PC , router gets information which it has stored and accordingly routes the packet to the source machine. In this way our PC is not visible on the net, but our PC can see the internet……….isn’t it great

April 9, 2006

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