VPN - Accessing computer outside of network. Only works one way

Question

I could use some help here. My ideal goal is to create a VPN for 2 macs that are in different locations so that they can share each others screens and share files. I basically want to do what Logmein's Hamachi does, but without the 5 user limitation. I have set up the VPN on my Synology NAS at my house using the PPTP protocol. I could also use OpenVPN.

The good news is that I can use a laptop outside of my home network to access any computer on my network at my house.

The bad news is that I can not do the reverse. I want to use a computer in my home network (same network as the VPN server) to access a computer outside of my network (which is connected via VPN successfully).

My internal IP is 192.168.1.xxx

PPTP VPN assigns my laptop that is outside of my network with 192.168.5.xxx, but when I try to access it remotely either with afp://192.168.5.xxx or vnc://192.168.5.xxx I can't connect using either.

Is this something that I should be able to do or is VPN only one way? I've also tried openvpn with the same results.

Thanks for any help!

-Dan

Answer 1

Your VPN server is most likely acting as a router with NAT. When the VPN client tries to access a service on your home network the VPN server modifies the addresses so that client traffic appears to come from the VPN server. As a reslut of this translation replies will be delivered back to the VPN server which will perform the reverse translation and send them to the VPN client.

But clients on your home network have no idea how to reach 192.168.5.xxx so when they try to connect to a VPN client machine they send the packet out to their default gateway, your default gateway in turn has no idea on what to do with it so it sends the packet to the internet where sooner or later it gets dropped (possiblly with a "No route to host" ICMP error).

You may be able to add a route on your client machine with something like

route add 192.168.5.0/24 via <lan IP of vpn server>

(the exact syntax of the route command varies by platform, you may need to tweak this slightly but it should give you the idea of what you are trying to do)

In addition there may be firewall rules on the VPN server which may prevent traffic flowing from your LAN to the VPN. If so these will need to be altered.