To be reachable, each computer on the Internet must have a unique identifying address referred to as the IP address. IP stands for the Internet Protocol which is the protocol responsible for delivering data from the source computer to the destination computer and expectedly it does so using the destination computer’s IP address. The IP address is made of 4 bytes (32 bits). It is usually expressed in the dotted-decimal notation where each of the four bytes is expressed in decimal and dots separate the four decimal values. People prefer names to numbers. Therefore, some computers are also uniquely identified by names referred to as domain names.

Domain names are expressed as a number of labels separated by dots. Each domain name corresponds to an IP address. For instance, the name www.sol.net.eg corresponds to the address 63.170.73.70. Domain names are grouped based upon the type of the organization to which computers belong, or based upon country where computers reside, or based upon both. The Internet has thousands of name servers running. A name server is responsible for translating a domain name given by a name client to the corresponding IP address. A name server is also called a DNS server, where DNS stands for Domain Name System which is the protocol defining the rules that govern the operation and interaction of name clients and servers.