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Originally Posted by finalight
if i use computer as host, can my domain be words instead of ip address?
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This is sort of a rather simplified, inaccurate, and unnecessary expanation of how DNS works... even so, it still manages to be difficult to understand.
Anyway, DNS is how those names you type are able to take you to actual computers. All computers have IP addresses. When you type in a name like
www.google.com, you ask a DNS server what the IP address for
www.google.com is and it tells you.
The Internet has thousands of DNS servers running on it. At the top are the DNS servers for com, edu, gov, jp, au, etc. the toplevel domains. These servers are handled by ICANN (the people who are in charge of domain names and IP addresses).
When you want to see a site, say bob.localdomain.com... Your request is sent to one of these DNS servers at the top. In this case, the one handling com domains.
Then this DNS server looks to see if there's a DNS server registered as handling localdomain.com. It then sends the request to that DNS server if it exists. If it doesn't exist, the domain name is invalid.
Then the DNS server for localdomain.com looks up the IP address of bob.localdomain.com and tells what it is. This DNS server is owned by the person who owns localdomain.com. Some domain name resellers provide DNS servers for you, since setting them up can be complicated.
So in order for your computer to have a name of some sort, a DNS server has to have your IP address listed for that name. It also has to be accessible from right to left...
That is, if you set up your own DNS server that said you were bob.ngemu.com, it wouldn't work unless the com DNS server for com domains handled by ICANN has your DNS server listed for ngemu.com. They will only do this if you buy a domain name.
What dyndns.org does is let you choose a subdomain (e.g. mysite.dyndns.org), and they add that name to their DNS server, and have it point to your IP address. So then your computer has a name. If you happen to own your own Domain name, they'll also let you use their DNS server to use it.
This isn't exactly necessary though. What matters is that the user has an easy to remember name they can type at any time and get to your site with. Because of this, a service such as cjb.net that is a redirection service (they have a page at the subdomain whatever.cjb.net that tells the browser to go to where the site really is) can work just as well. While your computer won't have a name, users can type in a name that takes them to your computer. This is just as good as DNS if you just have a web server on that computer.