IIS incoming request

Question

Hi, i have a IIS 6 server with clasic ASP and ASP.Net sites. I need that every incoming request to any clasic ASP sites be accesed only from a specific site, not that the user can access it directly.... is it possible ?

Example: principal site

other site 1 other site 2 other site 3

I need that only user can access to site 1,2,3 from principal site.

Important: i haven't the source code of web sites...

Thanks in advanced. Regina