To Documents

Domain Name System

• DNS stands for Domain Name System or Domain Name Server (depending on whom you ask).

• The Domain Name System (DNS) translates a logical URL into an IP address.
   
• Example: http://www.depaul.edu
  is translated to
  http://140.192.23.180
  
   
  
• Here are three DOS commands for determining IP addresses. Open a DOS Command Prompt window
   
  
  1. To determine the local IP address of your PC:
      
     
     > ipconfig /all
     
     
  2. To determine the IP addresses and port numbers of all active connections to your PC:
      
     
     > netstat -n
     
     
  3. To determine the IP address of a URL, use the ping command, for example:
      
     
     > ping www.depaul.edu
     
     The ping command is supposed to send an IP packet to another IP address and wait for it to return. However, if the destination website is behind a firewall, the ping may not be completed and time out.
      
• The parts of this logical Uniform Resource Locator (URL):
  http://www.depaul.edu
  

  http	Protocol
  edu	Top level domain (TLD)
  depaul	Second level domain
  www	Web server name

  
   
  
• Some common TLDs:
  
  com    edu    gov    mil    net    org
   
   
  
• Many countries have their own TLD:
  
  au    ca    de    fr    uk
   
   
  
• More URLs:
  

  www.yahoo.com	A famous search engine site
  encarta.msn.com	A Web server that does not start with www
  www.bbc.co.uk	A name using four parts rather than three
  ftp.microsoft.com	An FTP server rather than a Web server

  
   
  
• Steps to display a web document in a browser:
  
  • User enters URL of web document in browser.
  • Browser gets IP address of server from DNS.
  • Browser gets web document from server.
  • Browser displays web document.
     
    
• If a submit button is clicked on an HTML form, the page is sent back to the server. Values in controls on a form on the page can then be read by the server.