IIS anonymous access
anonymous access is one of the authentication method that IIS follows to authentiate any user who visit your site. In this method IIS allows everybody to visit the public areas of your site. anonymous users are assigned by default to the IUSR_MachineName account, which is a valid Windows account that is a member of the Guests group.
how to set this access method for a site.
Go to IIS –> Virtual Directory –> right click (select properties) –> click directory security tab

Here you can set the anonymous access.
Now comes the point of controlling it from my .NET application.
We have an element in the web.config file called IDENTITY to control this.
identity impersonate=”true|false”
userName=”domain\username”
password=”password”/>
Now if i say impersonate = true and give any USerName and password, it is same as we do in the above figure.
The behaviour of your site differs with each combination of this element with authentication mode (windows/forms).