IP Address

On the Internet, the IP protocol defines the addressing mechanism to which all participating computers must conform. This standard specifies that each computer on the Internet be assigned a unique 32-bit number called Internet Protocol address, or in short, IP address. Each datagram traveling across the Internet contains the 32-bit address of the sender (source) as well as that of the recipient (destination). Therefore, to send any information, the sender must know the IP address of the recipient.

The IP address consists of three parts: a class, a prefix (or network number) and a suffix (or had number). This is done to make routing efficient. The prefix denotes the physical network to which the computer is attached. The suffix identifies an individual computer on that network. For this, each physical network on the Internet is assigned a unique network number this is the prefix portion of the IP address. Since no two network numbers across the Internet can be the same, assigning network numbers must be done at the global level, to ensure that there is no clash with another network number.

The network number is analogous to a street name and the host number is similar to a house number. For example, only one house can have number 56 on James Street. There is no confusion if we have a house number 56 on George Street in the neighborhood. Thus, across streets, the same house number can be repeated. But in a given street, it must be unique.

In this case, within a network (identified by network number), no two hosts can have the same host number. However, if their network numbers differ, the host numbers can be the same. For example, suppose the Internet consists of only three networks, each consisting of three computers. Then, we can number the networks as 1, 2 and 3. Within each network, the hosts could be numbered in the same way, i.e. 1, 2 and 3. Therefore, logically, the address of the second computer on the third network would be 3.2, where 3 is the network number and" 2 is the host number. The IP addressing mechanism works in a very similar fashion. Note that conceptually, this is very similar to the two part WAN addressing.

To summaries, the IP addressing scheme ensures the following:

• Each computer is assigned a unique address on the Internet.
• Although network addressing is done globally (worldwide), host addressing (suffixing) can be carried out locally without needing to consult the global coordinators.

Who Decides the IP Addresses?

To ensure that no two IP addresses are ever the same, there has to be a central authority that issues the prefix or network number portion of the IP addresses. Suppose an organisation wants to connect its network to the Internet. It has to approach one of the local Internet Service Providers (ISPs) for obtaining a unique IP address prefix. At the global level, the Internet Assigned Number Authority (IANA) allocates an IP address prefix to the ISP, which in turn, allocates the host numbers or suffixes to each different customer one by one. Thus, it is made sure that IP addresses are never duplicated.

Conceptually, we can consider that IANA is a wholesaler and an ISP is a retailer of IP addresses. The ISPs (retailers) purchase IP addresses from the IANA (wholesaler), and sell them to the individual customers.

Domain Name Search