I am always hesitating to write an article because after I have found the solution I cannot beleive how hard was to find it. But it is over I must write it down.
I decided to implemet two IIS servers in my network but I have only one public IP address. I think everyone has figured out what was the trouble with this implementation. If do not I tell it.
The main issue with this that I could not reach both servers because of the only one public IP address therefore I have had to implement a router (and of course a NAT device (actually it is only one device)). In this case I can do a port forwarding for port 80 but I can do this for one IP address.