Universal Resource Locator (URL)

• URL shows the address of a resource on the Internet. It can refer to the website, some particular document, or an image.
• The Internet user just needs to insert URL into the location (Search) bar to find the needed website, document, folder, or image.
• A URL contains the following information:
  • The protocol used to a access the resource
  • The location of the server (whether by IP address or domain name)
  • The port number on the server (optional)
  • The location of the resource in the directory structure of the server
  • A fragment identifier (optional)
• The URLs of a file stored on the Internet are unique in nature.
• General syntax of URL: Protocol://Servername.domain/Directories/Subdirectories/Filename.filetype
• Example of URL:

Domain Name System (DNS)

• DNS is a hierarchical naming system built on a distributed database.
• This system transforms domain names to IP addresses, are the real URLs.
• But IP addresses are difficult for humans to remember, so alpha numeric addresses (URL) are introduced.
• Once DNS translate the URL into IP address, the web browsers can communicate with the web server and ask for the specified file.
• Commonly used Top-Level Domains(TLD) are .com, .edu, .net, .org, .gov etc. and some country specific domains are .in, .uk, .ca, .de, .jp etc.

How does DNS work?

• When user type a domain name (URL) such as google.com into browser using client computer operating system such as Windows or Apple OS.
• The client needs to find the IP address where google.com search engine is located on the earth (typically all websites are hosted in the Internet data center).
• Then browser will send this query to the operating system.
• Each operating system is configured to query certain DNS Servers. Typically users ISP or network administrator configures such DNS servers called Resolving Name Server.
• The resolving name server does not aware of the location of the google.com, but it does know where the root servers are located.

• Next, the resolving name server finds the location of the Top Level Domain (TLD) name server to send query for google.com. Each domain on the Internet has Authoritative Name Server.
• Finally, the authoritative name server will give user exact IP address of google.com. This information will come back to the resolving name server, which caches the information and send backs an answer (answer to user query what is IP address of google.com) on browser to the correct place. The end result user will see google search engine home page.