Finding Out Who Owns a Domain Name
A simple search of the ownership details of any of the currently-registered 43-million-odd domain names in the world can be conducted through a 'whois' search via any of the ICAAN registrars for the area in which the website is owned, for example at whois.melbourneIT.com. for Australian records.
When such a search returns a result, you are seeing details of the A-Record or Address Record for a DNS entry. This will contain contact information for the domain owner, in addition to the all-important Name Server record which directs browsers to the appropriate Domain Name Server when a Web Address is entered.
DNS Tricks and Techniques
The structure of DNS allows for a lot of flexibility in the way websites are hosted. For example, a virtual web server can accomodate any number of Domain Names on a computer with one IP address. Many hosting services exploit this principle to host multiple sites on their machines.
Conversely, one domain name may map against a number of IP addresses which is useful for fail-safe and load-distribution purposes.
DNS also includes:
- MX Records, for Mail Exchange, used for specifying how domain email should be routed
- CNAME record or canonical name record makes one domain name an alias of another. The aliased domain gets all the subdomains and DNS records of the original
- NS record or name server record maps a domain name to a list of DNS servers for that domain
- SOA or Start of Authority record for specifying the DNS server and providing authoritative information about an Internet domain
(This is not an exhaustive list.)
Zone Record
The extent of the Domain is indicated by a Zone Record, which may sub-divide the Domain into several zones or against a number of IP addresses.
DNS and the URL
We have already seen how a web address is resolved against an IP address by DNS. However in many cases a Web address will contain an additional layer of detail to the right of the basic Web address, separated by a '/'.
This indicates a URL, or Universal Resource Locater. Essentially a URL is a request for a particular file, directory, or process, on a named server.The URL is simply the web address in question, along with an indicator of the particular file on the server.
At its simplest, a URL simply fetches a file in a named location, for example, the URL that fetches the file you are reading is <lc.netcomm.com.au/DNS_2.htm>
If you enter a web address/directory name in your web browser, the browser will generally attempt to find and display a file called 'index.html' or 'default.html' located within the directory. If it can't find one, it will display an error message.
An URL can also be 'active' for example when it includes a procedure to execute an Active Server Page [.asp] or .php script. In these cases, the webserver does more than serve a web-page - it executes a 'server-side' process which may interogate a database and return a record, update a user registration, or any number of other processes.
Conclusion
This brief article is by no means comprehensive, however if you read it in conjunction with the Intro to TCP/IP, you will get a very good idea of the main technologies underlying the amazing diversity of the Internet.