ASP how to detect actual URL for default page

Advert test
I would need to detect the actual URL in the browser window for the default page.
For instance, if the default page is index.asp I need to know if the browser reads or

Using Request.ServerVariables("URL") or Request.ServerVariables("SCRIPT_NAME") both return /index.asp in any case.

I have been asked to do so for SEO purposes to avoid content duplication. In my opinion thus, Google will know it is the same page and this is unlikely to lead to content duplication penalities, any though on this?