HostOnNet.com

melbin · Posted: Mon Feb 19, 2007 8:05 am Post subject: How Domains Work

The Basics

When you use the Web or send an e-mail message, you use a domain name to do it. For example, the URL "http://www.hostonnet.com" contains the domain name hostonnet.com. So does the e-mail address "someone@hostonnet.com."

Human-readable names like "hostonnet.com" are easy for people to remember, but they don't do machines any good. All of the machines use names called IP addresses to refer to one another. For example, the machine that humans refer to as "www.hostonnet.com" has the IP address 72.36.192.82. 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. During a day of browsing and e-mailing, you might access the domain name servers hundreds of times!

Domain name servers translate domain names to IP addresses. That sounds like a simple task, and it would be -- except for five things:

*There are billions of IP addresses currently in use, and most machines have a human-readable name as well.
*There are many billions of DNS requests made every day. A single person can easily make a hundred or more DNS requests a day, and there are hundreds of millions of people and machines using the Internet daily.
*Domain names and IP addresses change daily.
*New domain names get created daily.
*Millions of people do the work to change and add domain names and IP addresses every day.

The DNS system is a database, and no other database on the planet gets this many requests. No other database on the planet has millions of people changing it every day, either. That is what makes the DNS system so unique!

melbin · Posted: Mon Feb 19, 2007 8:10 am Post subject:

IP Addresses

To keep all of the machines on the Internet straight, each machine is assigned a unique address called an IP address. IP stands for Internet protocol, and these addresses are 32-bit numbers normally expressed as four "octets" in a "dotted decimal number." A typical IP address looks like this:

72.36.192.82

The four numbers in an IP address are called octets because they can have values between 0 and 255 (28 possibilities per octet).

Every machine on the Internet has its own IP address. A server has a static IP address that does not change very often. A home machine that is dialing up through a modem often has an IP address that is assigned by the ISP when you dial in. That IP address is unique for your session and may be different the next time you dial in. In this way, an ISP only needs one IP address for each modem it supports, rather than for every customer.

If you are working on a Windows machine, you can view your current IP address with the command WINIPCFG.EXE (IPCONFIG.EXE for Windows 2000/XP). On a UNIX machine, type nslookup along with a machine name (such as "nslookup www.hostonnet.com") to display the IP address of the machine (use the command hostname to learn the name of your machine).

As far as the Internet's machines are concerned, an IP address is all that you need to talk to a server.

melbin · Posted: Mon Feb 19, 2007 8:14 am Post subject:

Domain Names

If we had to remember the IP addresses of all of the Web sites we visit every day, we would all go nuts. Human beings just are not that good at remembering strings of numbers. We are good at remembering words, however, and that is where domain names come in. You probably have hundreds of domain names stored in your head. For example:

*www.hostonnet.com - a typical name
*www.yahoo.com - the world's best-known name
*www.mit.edu - a popular EDU name
*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

The COM, EDU and UK portions of these domain names are called the top-level domain or first-level domain. There are several hundred top-level domain names, including COM, EDU, GOV, MIL, NET, ORG and INT, as well as unique two-letter combinations for every country.
Within every top-level domain there is a huge list of second-level domains. For example, in the COM first-level domain, you've got:

hostonnet
yahoo
msn
microsoft
plus millions of others...

Every name in the COM top-level domain must be unique, but there can be duplication across domains. For example, www.hostonnet.com and www.hostonnet.net are completely different machines.
In the case of bbc.co.uk, it is a third-level domain. Up to 127 levels are possible, although more than four is rare.

The left-most word, such as www or encarta, is the host name. It specifies the name of a specific machine (with a specific IP address) in a domain. A given domain can potentially contain millions of host names as long as they are all unique within that domain.

melbin · Posted: Mon Feb 19, 2007 8:16 am Post subject:

Distributing Domain Names

Because all of the names in a given domain need to be unique, there has to be a single entity that controls the list and makes sure no duplicates arise. For example, the COM domain cannot contain any duplicate names, and a company called Network Solutions is in charge of maintaining this list. When you register a domain name, it goes through one of several dozen registrars who work with Network Solutions to add names to the list. Network Solutions, in turn, keeps a central database known as the whois database that contains information about the owner and name servers for each domain. If you go to the whois form, you can find information about any domain currently in existence.

While it is important to have a central authority keeping track of the database of names in the COM (and other) top-level domain, you would not want to centralize the database of all of the information in the COM domain. For example, Microsoft has hundreds of thousands of IP addresses and host names. Microsoft wants to maintain its own domain name server for the microsoft.com domain. Similarly, Great Britain probably wants to administrate the uk top-level domain, and Australia probably wants to administrate the au domain, and so on. For this reason, the DNS system is a distributed database. Microsoft is completely responsible for dealing with the name server for microsoft.com -- it maintains the machines that implement its part of the DNS system, and Microsoft can change the database for its domain whenever it wants to because it owns its domain name servers.

Every domain has a domain name server somewhere that handles its requests, and there is a person maintaining the records in that DNS. This is one of the most amazing parts of the DNS system -- it is completely distributed throughout the world on millions of machines administered by millions of people, yet it behaves like a single, integrated database!