Ip Address

TOPIC:IP ADDRESS

AUTHOR-Rameshwar Prasad Srivastava

MS ( Cyber Law & Information Security)

Indian Institute of Information Technology ,Allahabad

The address of a computer on the Internet is commonly referred to as the IP Address (Internet Protocol). It's a 32 bit (4 bytes) number normally written as follows:

xxx.xxx.xxx.xxx

Since a byte can represent any number from zero to 255, the least and the maximum IP address possible are:

0.0.0.0 to 255.255.255.255

Understanding IP Addresses

Understanding IP Addressing is necessary, since all applications on the Internet

generate logs, wherein IP Addresses of all interacting computers are recorded. The logs from a basis for investigation by investigating officers. The IP address has two parts - Network number and the Host number. Whereas the Network Number is assigned by an International Body interNIC, the host Number or Host ID is assigned by the Network System's administrator. For convenience we shall address the four bytes as follows

Class A network

These are among the biggest networks in the world. If the numeric value of the first byte is between 1 and 127, it indicates that the IP Address belongs to a A Class network. For such addresses the 1st byte represents the network number 2nd, 3rd and the 4th byte represent the host number. Thus for the IP Address 98.124.103.45 the network number is 98; and the host number is 124.103.45. As is evident there can only be 127 Class A networks, and each of them can support (256x256x256) about 1,67,77,000 terminals.

Class B network

If the numeric value of the first byte is between 128 and 191, it indicates that the IP Address belongs to a B Class network. For such addresses 1st and 2nd byte represents the network number, and the 3rd and the 4th byte represent the host number. Thus for the IP Address 156.124.103.45 the network number is 156.124 and the host number is 103.45. As is evident there can only be 16,384 (64x256) Class B networks, and each of them can support (256x256) about 65,536 terminals.

Class C network

If the numeric value of the first byte is between 192 and 223, it indicates that the IP Address belongs to a C Class network. For such addresses 1st, 2nd and the 3rd byte represents the network number, and the 4th byte represent the host number. Thus for the IP Address 196.124.103.45 the network number is 196.124.103 and the host number is 45. As is evident there can only be 20,97,152 (32x256x256) Class B networks, and each of them can support 256 terminals.

Class D and E networks

These networks are not available for commercial use. Their IP addresses start from 224.0.0.0. onwards. These networks are used for multicast groups or for research purposes. The four byte IP Address does not follow the above scheme of addressing. As is evident from above, there is a finite number of computers that can be on the Internet at given point of time. Each IP Address is valued. Hence casual users of the Internet are not given a permanent IP Address.

Static IP Address

Under this scheme, Computers are assigned a permanent IP Address. The address remains the same when ever the computer logs on to the Internet.

Dynamic IP Address

Casuals users of the Internet are assigned IP Addresses as and when they log on. In such cases the ISP(Internet Service Provider) provides an available IP address for the session (till the user logs off or connection is broken) as soon as the user logs on. Next time, when the user logs in again, he may be assigned a different IP address for that session. This becomes a challenge for investigating officer, to trace the user. The ISP maintains a log of the phone number from where the user has logged on, the MAC (media access code) of the computer through which the internet was accessed, the time of start and end of session, and finally the dynamic IP address allocated for that session. This could help in tracing the user.

Domain Names

It is difficult to remember the IP Address. As a solution, computers can be addressed by names correlated to the organization they are owned by, called Fully Qualified Domain Names (FQDN). There is no relation between an IP address and the FQDN. They are somewhat related as the name of a person, and his telephone number. A list of IP Addresses and their corresponding Domain names is kept in servers called the Domain name service Servers - DNS Server. A Domain name has four parts:

1) Computer Name, or the host machine name

2) Organization Name

3) Internet Top Level Domain

a. This give information regarding the nature of the organization. gov, com, edu, mil, net etc representing Government, commercial, educational, military, network provider organization respectively.

4) Countries name - usually the first two letters of the name of the country

A typical domain name appears as follows:

adohare.svpnpa.gov.in

indicating that the name of the host machine is adohare, on a network called svpnpa, which is a government organization in India.

Universal Resource Locator URL

Programs on the computer are identified uniquely by URL's. An URL specifies exactly where on a system to go. It has six parts:-

1. Protocol/Information service : type http, ftp, NNTP.

2. Domain name of the server

3.