How to create this type of subdomain on the fly like Blogger.com

Sometime ago I asked this question and I was told that the entry has to be made in DNS etc. I was not sure whether all this is really required or not. The kind of feature that I am looking for is shown in the screenshot below:

As you can see blogger lets the user choose the subdomain for his blog. How can we achieve this? I am basically developing in asp.net C#. How 开发者_JS百科can I allow my users to choose subdomains like this once I have my top level domain. Currently I am developing on localhost.

---

Use a wild card domain in IIS so it traps every request to the top level domain and under.

In asp.net: Create an HttpModule... this will run for every request and you can check the domain name, etc and pull in user information based on the sub-domain. An example httpmodule can be found at URL Rewriting in ASP.NET via HttpModule.

In asp.net mvc: Create a custom RouteHandler (custom based on interface IRouteHandler). Look at RouteHandler vs ControllerFactory question for an example.

---

You need to add a wildcard DNS mapping that maps *.example.com to your webserver, and a wildcard hostname mapping telling IIS to send all subdomains to your ASP.Net website.

You can then check Request.Hostname in server-side code and use the appropriate content (or error message)