A friend of mine asked me to recommend him an open-source
VPN-server for Linux but unfortunately I never used one.
After some googling, I have found OpenVPN but do not know
if it is the best choice that suits his purposes, namely to access
local network that does not have its own fixed IP from the outside.
To be more precise: the local network to be accessed to from the
outside is part of another local network. The latter (outer) network
has its own fixed IP but the former (inner) network gets its IP via DHCP.
So, it is impossible to connect to a computer in the inner network
from the outside directly.
The computer in local network to be connected runs Windows.
The said friend of mine have tried to run some VPN server from
Windows but it somehow hangs the "inner" computer when
his "outer" computer has problems connecting to the Internet.
So, now his idea is
1) to run a virtual machine in the "inner" (Windows) computer,
2) to install into this virtual machine very lightweight Linux server
only to run in it a VPN-server that should help him to connect
from the outside to the "inner" host (Windows) computer, which
has its fixed IP within the inner local network.
Thank you for advance and sorry for a bit of offtopic.