What happens when you request a web page
Introduction
Here is a description of exactly what happens when you request a web page?
Requesting a web page and the role of the DNS server
You can request a web page in two ways. You can click on a link (called a 'hot link') on a page you are already on or you can type in an address (called a URL or Uniform Resource Locator) into your web browser. When you first connected to the Internet, your ISP (Internet Service Provider) sent you some information that told your computer which DNS (Domain Name System) server to use when you request web pages. Your web browser will contact that DNS server first when you want a web page. The DNS server will look up the human-readable form of the web page you want and get back the IP address for that web page. If that DNS server can't find a particular IP address then it will ask another DNS server that is higher up in importance to it, and then another one even higher up, until it either finds the IP address that corresponds to the web page you want, or it returns a message to you that it doesn't exist or can't be found. DNS servers are essentially ordered like a family tree, and you start at the bottom of the tree, working your way up the tree to ever more important DNS servers if an IP address can't be found.
What happens when the IP address is returned by the DNS server?
Your web browser uses the IP address sent back to you to visit the web server that holds the page that you want and it does this using the TCP/IP protocol on port number 80. The web server will go and find the requested web page and send back the HTML codes (called 'tags') that make up that page to your browser. Your browser then goes through each HTML code and each piece of information in turn and displays it (or 'marks it up') in accordance with the HTML codes used. The connection with the web server for that web page will end when you either close the browser or move to a different web page.