IP Addressing

• The IP address system is in transition as of the date of publication. The address that has lasted from the creation of the Internet is a 32-digit binary number. The 32 bits are organized into four bytes. Each byte is translated into a digital number, and then the four numbers are separated by a dot. This is called dot notation and is meant to make IP addresses easier for people to understand. However, an address like “123.234.12.23” is not very memorable. The number of addresses in the current IP address scheme has run out, and so a new address format has been created which has 128 bits. This is even harder for people to remember.
  
  

Domain Names

• The Domain Name System is one of the three technologies that created the World Wide Web, the other two being HTML and HTTP. HTML is the Hypertext Markup Language. It is the format in which all Web pages are written. HTTP is the Hypertext Transfer Protocol, which is the format all Web transfers follow. The Domain Name System creates an addressing system that overlays the IP addresses of the Internet and creates human-friendly addresses that use meaningful words.
  
  

DNS Query

• A DNS query has two parts. A PC-based application, such as a Web browser or mail client, first sends a DNS query to a DNS resolver. The DNS resolver may be resident on the local computer, somewhere on the network or may be provided by a server contactable over the Internet. The resolver saves regularly accessed addresses and so may be able to return the IP address for a given domain. If not, it has to perform its own DNS query by accessing a DNS server.
  
  

DNS Server Query

• The DNS resolver makes the same DNS query it received from an application to a DNS server. The last part of a domain name, the “.com,” “.org,” “.co.uk,” etc, is called the domain and a different DNS server serves each. The domain resolver does not need to know the address of all of these. It can go to any DNS server, and then the DNS server delivers the required IP address, if it is the DNS server for that domain. If it is not, it either sends a query itself for the domain name and then returns that to the resolver, or it replies to the resolver with the address of the correct DNS server and the resolver then has to contact that server directly. Once the resolver has the IP address, it returns it to the browser or mail client as a response to the original DNS query.