How to configure access to a computer behind a VPN?

Question

Computer networks

On one of the computers in the local area there is a VPN network in which a computer with an information system hanging on port 80 is available. Previously, in order to access this system from LAN, I forwarded port 80 on the first computer. Now, on the first computer, a similar system was installed on the same port 80 and port 80 can no longer be forwarded to the VPN.
I tried to configure the first computer to listen on port 7777 and forward from it to port 80 of the computer behind the VPN.
The VPN login page opens at COMP1:7777/login.aspx, but after you enter the login with a password, it removes the specified port and tries to open COMP1/main.aspx and gets into the local system.
How now to configure access to both systems, taking into account the fact that ports cannot be changed and I do not have access to computer settings for VPN.

Answer 1

Everything was resolved - both information systems are the same and run on IIS. I looked at the settings of my system - by default, IIS responds not only on port 80, but also on ports 90 inclusive. On my server, I removed the response to port 88 and forwarded this port to the computer behind the VPN.
Now if you do not specify the port, then my system opens, and if you specify 88, then the system is behind a VPN.

Answer 2

You need a so-called. your computer1 raise the so-called. "reverse proxy" like nginx. There are a lot of articles on this configuration on the Internet.

Answer 3

ports cannot be changed and I do not have access to computer settings for VPN

cooperate with those who have access to a computer for vpn, otherwise nothing