UNDERSTANDING IP ADDRESSES

An IP ADDRESS is the address of a computer on the network which means a computer is recognized through it's IP ADDRESS.

What is IP?
INTERNET PROTOCOL or IP is a unique number assigned to each computer on a network. It is this unique address which represents the system on the network. Generally the IP of a particular system changes each time you log on to the network by dialing to your ISP(Internet Service Provider) and it is assigned to you by your ISP. IP of a system which is always on the network remains generally the same.

Lets take the example of the following IP address: 209.144.49.110 Now the first part, the numbers before the first decimal i.e. 209 is the Network number or the Network Prefix.. This means that it identifies the number of the network in which the host is. The second part i.e. 144 is the Host Number that is it identifies the number of the host within the Network. This means that in the same Network, the network number is same. In order to provide flexibility in the size of the Network, here are different classes of IP addresses:



Address Class Dotted Decimal Notation Ranges:

Class A ( /8 Prefixes) 1.xxx.xxx.xxx through 126.xxx.xxx.xxx

Class B ( /16 Prefixes) 128.0.xxx.xxx through 191.255.xxx.xxx

Class C ( /24 Prefixes) 192.0.0.xxx through 223.255.255.xxx

These classes will be clearer after reading the next few lines.

Each Class A Network Address contains a 8 bit Network Prefix followed by a 24-bit host number. They are considered to be primitive. They are referred to as "/8''s" or just "8's" as they have an 8-bit Network prefix.

In a Class B Network Address there is a 16 bit Network Prefix followed by a 16-bit Host number. It is referred to as "16's".

A class C Network address contains a 24-bit Network Prefix and a 8 bit Host number. It is referred to as
"24's" and is commonly used by most ISP's.


Due to the growing size of the Internet the Network Administrators faced many problems. The Internet routing tables were beginning to grow and now the administrators had to request another network number from the Internet before a new network could be installed at their site. This is where sub-netting came in.

Now if your ISP is a big one and if it provides you with dynamic IP addresses then you will most probably see that whenever you log on to the net, your IP address will have the same first 24 bits and only the last 8 bits will keep changing. This is due to the fact that when sub-netting comes in then the IP Addresses structure becomes:

xxx.xxx.zzz.yyy

where the first 2 parts are Network Prefix numbers and the zzz is the Subnet number and the yyy is the host number. So you are always connected to the same Subnet within the same Network. As a result the first 3 parts will remain the same and only the last part i.e. yyy is variable.
For Example, if say an ISP xyz is given the IP: 203.98.12.xx Network address then you can be awarded any IP, whose first three fields are 203.98.12.

So, basically this means that each ISP has a particular range in which to allocate all its subscribers. Or in other words, all subscribers or all people connected to the internet using the same ISP, will have to be in this range. This in effect would mean that all people using the same ISP are likely to have the same first three fields of their IP Addresses.

This means that if you have done a lot of of research, then you could figure out which ISP a person is using by simply looking at his IP.
For e.g say in a country,there are three main ISP’s:

ISP Name - Network Address Allotted
ISP I - 203.94.47.xx
ISP II - 202.92.12.xx
ISP III - 203.91.35.xx

Now if anyone sends me a mail from 203.94.47.23 then i can easily tell that he/she belongs to ISP I and where do he/she lives. I can tell that because i have done research from various sources. You gotta do the same.