Domain name servers, or DNS, are an incredibly important but completely hidden part of the Internet, and they are fascinating. The DNS system forms one of the largest and most active distributed databases on the planet. Without DNS, the Internet would shut down very quickly.
Each computer that is connected to the Internet needs to have a unique identification called an IP address. This is a numerical address with 10 digits, like this: 216.239.39.99, expressed as four "octets". But you don't type that in, you'd type www.google.com.
Every time you use a domain name, you use the Internet's domain name servers (DNS) to translate the human-readable domain name into the machine-readable IP address.
An IP address is not really the path for the rest of the world to follow directly to your PC, it's really the address to your ISP's server. Once the "visitor" reaches the ISP's server, the server takes over and directs the information to your website pages.
Every time that you visit a web site, send or receive an email or even share files with other PCs on your own home or business network, your computer is telling the other computer what its address is and how to find it on the internet.
Shared IP Addresses
As stated above, web servers have a static IP address that rarely changes. However, that does not necessarily mean that your site will have a unique or dedicated IP address!
If, like most people, you have opted for virtual hosting, your web site is stored on a computer along with several other sites.
Because of the relative scarcity of IP addresses, your web host may have assigned only one IP address to the server; this means your site shares the IP address of the server with the other sites stored on it.
Modern browsers send "header information" to the web server; it contains, among other things, the domain name of the requested site. Based on the header information, the web server is able to return the right data to the browser. (This is the "name-based virtual hosting" we referred to earlier.) Some web hosts offer a unique IP address as part of their hosting packages; so even if a web server hosts several sites, they will all have different IP addresses.
While some machines, such as network servers and web servers usually keep their same IP address for life, your PCs own IP address may change regularly. Most home PC users don't have any way of assigning their PCs an IP address. Instead, they "borrow" one from their Internet Service Provider (ISP) every time that they log onto the Internet. This is almost always true for services such as AOL, and less true for broadband users who may keep the same IP address for months if not forever.
When you get your IP number from your ISP an interesting thing happens. Your IP address is not really the path for the rest of the world to follow directly to your PC, it's really the address to your ISP's server. Once the "visitor" reaches the ISP's server, the server takes over and directs the information to your PC's front door. This allows the ISP to change your IP address every minute if it wants to while keeping a static IP address out there for the world to find you at. Sound confusing? It is. In fact there is a lot of sophisticated machinery at work whose only job is to keep this all in order and working more or less flawlessly.
Whenever you type http://www.Google.com into your browser, the browser sends a query off to a big telephone book in the sky and asks "Hey, what's the IP address for Google.com?". This big telephone book, more commonly called a "Domain Name Server" or DNS for short, returns 216.239.39.99 to your browser. Your browser then heads off to Google's web site using the IP address as a map..
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