Inside the Post Office

So our routers just behave like post offices , just sending packets from one post office to another , till it reaches the destination.
To do this forwarding, the routers take the help of the routing table. Based on the entry in routing table, the router decides where to send the packet.In the end , router is just a machine. And any machine cant have information by itself? So , who or what makes the routing table in the machine called the router?
The answer to this two fold:
1. A person mananging the router, normally referred to as the administrator
2. Automatic applications, called Routing Protocols
Route entries made using approach 1 are called static routes. Route entries made using approach 2 are called dynamic routes.
Static routes are well static. Once they are made, they will not be removed unless the administrator removes them . Dynamic routes are learned automatically by the interaction of routing protocols. They are added dynamically at run time and they may be removed dynamicaly too. Dynamic routes are required because, in general, the entire network topology is not known before-hand.
We have said that dynamic routes are added by Routing Protocol. Routing Protocol is an application which runs on the routers and whose responsibility is to exchange network topology information(in other words, routes :-) ) with corresponding routign protocols running on other routes. In other words, it is just an intelligent piece of software which has the capability of discovering the network topology information, sending it to other routers as well as the capability to process such information recived from other routers.
To take the analogy with the post office setup further, static routes are well known routes, which dont change. Dynamic routes are routes which depend on the road/traffic condition :) Routing protocols are like dedicated professionals in the post office whose responsibility is to find out about the neighboring roads/routes and send to the corresponding professional in another post office. These professional's job is to ensure that any change in road conditions in their vicinity is conveyed to other post offices asap, so that no letters are lost.

With this, we close a very very high-level overview of how packets are sent from source to destination. At the end of this, you should be able the foll questions:
1. What is the role of IP Address ?
2. What is a packet ?
3. What is a routing table ?
4. What does a routing protocol do ?

The next series will be a bit more tech, carrying on from where this series has left. The aim will be to introduce the elements of any typical network topology. At the end of the next series, you will be able to answer questions like:
1. What is a subnet?
2. What is MAC address?
3. What packet enters a router and what leaves, whats the diff in the two packets?
4. When does a packet not reach a destination ?
and some more