IP Routing

A large portion of the world is now on broadband. And an increasing number of those people are getting routers in their home to facilitate home networking.
But what is a router? What does a router do? And how does this magic device actually work?

Routing And Routers

Routing is the process of moving a packet of data from one network to another network based on the destination IP address. The Internet uses routing to move data from your computer, across several networks, to reach a final destination, like a website. Specialized computer devices that perform this routing function are referred to as routers. Routers use the information contained in a route to make decisions about which network interface to forward a packet through in order to reach the destination address in the packet. Routers maintain a list of routes which is often referred to as a routing table.

Routers look up routes in the routing table to figure out how to move data from one network to another network. Routes are simply the signposts that tell a router which network interface to forward a packet through in order to reach the packet's intended destination.

There are two basic kinds of routes: static or dynamic.

How Routers Work ?

A router is a piece of hardware used to route and forward information from one location to another. In companies and large corporations, a central computer system acts as a router to connect all of the company's computers to one network. This allows group participation and collaboration on large projects or just to connect all of the company's resources at one central location. It also aids in reliable communication between employees working on different floors in the building or in different countries.

For the Internet, a router allows the sending and receiving of data quickly. Downloading and uploading web pages and files are also handled by a router. Consumers become more and more dependent on the Internet, but didn't know what made it possible to access their favorite sites to shop online, send email, or to run their online business.

Routing Emails
There are many fascinating things that happen behind the scenes when sending and receiving email. After a sender clicks the "send" button on her email client, a router gets that information and sends it to the desired location using the different parts of the email address. Because routers can communicate with one another no matter what network it is on, messages are able to be sent to any email address in the world.

Directing Traffic
It is a router's job to direct email and web traffic. To do this it uses the configuration table to decipher where they should go. A configuration table is the data needed for transmission. The data included in the configuration table is the group of addresses for each connection, the connections' priority order and the traffic rules for regular and special connections. Depending on the size of the router and network, the size of the configuration table varies. So, using the information from the configuration table, the router makes sure the data packets go to the correct location in a timely and accurate manner.

Transmitting Packets
The Internet is many networks working together to make up one massive network. For information to move in and between networks it is sent in data packets. The system that data travels through is called a "packet-switching network." To make sure that the data is able to travel through the networks, it is broken down into smaller packets before being sent. A wrapper is placed around each packet to keep the group together so they end up in the same and correct location. The addresses of the sender and receiver, plus the packet's predefined place in the collection, are the information that is contained in the wrapper. The router uses this information to deliver the packets. Directing traffic and transmitting packets are the router's main responsibilities.

IP Routing

Routing is the process of moving data from one network to another by forwarding packets via gateways. With IP based networks, the routing decision is based on the destination address in the IP packet's header.

IP Routing is an umbrella term for the set of protocols that determine the path that data follows in order to travel across multiple networks from its source to its destination. Data is routed from its source to its destination through a series of routers, and across multiple networks. The IP Routing protocols enable routers to build up a forwarding table that correlates final destinations with next hop addresses.

These protocols include:

BGP - Border Gateway Protocol
IS-IS - Intermediate System - Intermediate System
OSPF - Open Shortest Path First
RIP - Routing Information Protocol.

When an IP packet is to be forwarded, a router uses its forwarding table to determine the next hop for the packet's destination (based on the destination IP address in the IP packet header), and forwards the packet appropriately. The next router then repeats this process using its own forwarding table, and so on until the packet reaches its destination. At each stage, the IP address in the packet header is sufficient information to determine the next hop; no additional protocol headers are required.

http://gallery.techarena.in/data/519...ip-routing.jpg

The Internet, for the purpose of routing, is divided into Autonomous Systems (ASs). An AS is a group of routers that are under the control of a single administration and exchange routing information using a common routing protocol.

Can anybody please tell me that,

why do we need routers?
Can't computer just send the information directly?

No :no: , your computer can't do this directly. Because of IP addresses and subnet masks, your computer only knows about things that exist on its own subnet and therefore can only communicate directly with devices on that subnet. That's where routing comes in. A router can also be known as a gateway (think default gateway). A gateway is a portal from one location to another. And that's what a router is, a portal from one subnet to another. The router will have known "Routes" for different subnets. These routes can be manually or dynamically assigned in various ways and through various protocols (Google routing protocols). These routes are like road maps that tell your router where to send traffic. Most routes in a router actually point to a different router on a different subnet. If you ever look at your route tables in your router you'll see a route that's similar to 0.0.0.0 with a netmask of 0.0.0.0 pointing to another IP address (that address is usually going to be your internal router, but if you look at the route tables on your modem, then that IP address would be your ISPs router). This is known as a default route. This route tells your router to forward any unknown traffic on to the next router who probably knows the route to the final destination. By using routing tables in this way your network can connect to a network with a different IP structure and establish communication.