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Getting to know IP address - Vol 1

Posted by Aravin on September 4, 2012 at 4:40 AM

This article is contributed by Mr. Lee Heng Wai

Basic IPv4 Address


Why we need IP address?

According TCP/IP model, network layer try to guide the packet from source all the way to the destination


How to achieve it?

Network layer must know topology of network.


Through internet, a computer somewhere in the world needs to communicate with another computer some else in the world.


In order to implement this, the computers have to be connected to the Internet, and we need a global addressing scheme, so that computers able to identify their locations.


In order to let computers can talk to another computer, the IP addressing schema must have those characteristic.

1) Unique: In order to connect to Internet, you have must have one and only one IP address.

2) Universal: This addressing scheme must be well accepted by any host.


Here, we will discuss about IP addressing scheme which based on RFC791, Internet Protocol. The version discussed is IP version 4. We have another new version which is IPv6, we will not discuss here.


What is IP address?


IPv4 has 32bit, which is something like this

11000000101010000011100 01000101 (all in binary terms)


This 32 bit binary numbers are understandable by computer easily.

Problem is we as human being, and we are not going to memorise these numbers (unless you are a genius).


So what we need to do is convert to certain format by dividing those numbers into 8 bit per chunks. Each chunk is separated by dot notation.


This 8bit per chunks, the highest value is 128 and the lowest value is 1. And we have to convert those 8 bit into decimal value, so the range is 0~255.

After we convert, we will get this result:

This format is much easier and readable compare to binary numbers.


The IPv4 decimal notation format as below:


where X has range from 0 to 255.


IP address has 2 part. One is network part, or NetID or Prefix, another part is host part or HostID, or suffix.

So what is NetID and HostID?

You can imagine house is HostID, each house has house number.

House 101 ‘s neighbour is House 102. Both of them located on a street name 100, this is NetID.

So people in the house 101 want to talk to people in house 102, he just directly walk to house 102.

Look at this example:

So people in the house 101 want to talk to people in the house 202, so what he need to do is he have go out to street 100 then pass the junction which is connected to street 200. From the street 200, then he can go to house 202.

So, let say you have cross a junction something like below, so how do you know which street you need to go? This can be solved by so called Street Sign. In IP world, we called it IP routing table, which contained inside a special device, called Router.


In human world, our home address may consist of country, city, postcode, street name, and house number. But, for IP, it is very special, it just contain only street name and house number. Street name is NetworkID, house number is HostID. Few houses may locate on the same street, same thing to PC. Few PCs may have the same network segment. When across the street, you need to pass the junction first, or PCs in different network segment to be communicated, they are interconnected through router.


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