page client port

[Mark]

Hi,

I have ASP.NET application. In IIS application port is set to 80, but
for the world it is redirected to port 8001.

I build url adress :
String str = HttpContext.Current.Request.Url.Port + ":" +
HttpContext.Current.Request.ApplicationPath.ToString() + "/" + link;

But the variable:
HttpContext.Current.Request.Url.Port is equal 80,because server
doesn't see that the page is redirected to 8001.

How can I detect the client seen port ?

Thanks for help
Mark