the problem is that I can't connect to VPN through the internet connection, but it works on the local network.
I use no-ip.com service to connect to the first router, then It should allow me to connect to VPN on router 2 to access files from a computer on router 1 network.
All PCs from router 1 and 2 networks have no problem with connecting to VPN.
The first router is D-Link DWR-921 and it is 192.168.20.1 IP
The second router is ASUS RT-AC51U and it is 192.168.21.1 IP
For some reason, the first router can't access the second network, but second can access first.
EDIT:
Computer I want to connect to ip is: 192.168.20.3 and mask is 255.255.255.0, for now I've abandoned no-ip and using external ip to try and connect to vpn.