Access device from internet on internal IP with RT-AX86U

[asus_pi]

I have the following configuration, with internet access, but without external IP.
Internet > ISP device (local IP range) > my RT-AX86U (Merlin 388) > Air Conditioning with own IP

I need to expose the AC to the outside temporary, so it's available for someone in another location.
I know I can expose PC using Hamachi, but AC can't do it.

Is it possible? What will be the easiest way to give access to the AC?

 

[bbunge]

I have the following configuration, with internet access, but without external IP.
Internet > ISP device (local IP range) > my RT-AX86U (Merlin 388) > Air Conditioning with own IP

I need to expose the AC to the outside temporary, so it's available for someone in another location.
I know I can expose PC using Hamachi, but AC can't do it.

Is it possible? What will be the easiest way to give access to the AC?

Always risky giving someone you do not know access to your LAN.
With that said you could port forward the ISP router to the AX86U then port forward that to the AC.
Another way would be to set up TeamViewer on a PC then give them access to that so they can run the web browser to control the AC. TeamViewer can be run from the install file without actually installing and it has a built in password you can give the other party. But, be at the PC when they are controlling it and be ready to "pull the plug" (power or ethernet cable) if they start to do something fishy

 

[asus_pi]

It's supposed to be only AC access, single IP and port, could be in guest network, it only accept API requests.
ISP router doesn't have external IP either.
Teamviewer can't be option here, as need a bit of environment for debugging.

I thought there's a way to expose single device to the outside, maybe some kind of VPN connection from third party, exactly what's Hamachi is doing, but couldn't find a way how to combine Asus with it, or any alternative.