Connecting two private LANs

This depends on exactly what you want to achieve. If I have read your message correctly, you are not interested in contacting the LAN behind your VPN server, but only in using it as a springboard to access the Internet (please correct me if I got this wrong).

If this is indeed the case, then there is no problem. All you have to do is to set up two separate routes, one for the subnet 10.x.x.x through the eth0 interface, and another one for your VPN router (let's say it has IP 10.0.0.1) through the interface ppp0/tun0/tap0, depending on the type of VPN you are using. This ought to be a route for a single IP address, 10.0.0.1/255.255.255.255. And that's all. This works because the routing table always applies first the most restrictive rules (and nothing can be more restrictive than a route for a single IP), then the more comprehensive ones.

If instead you are also interested in reaching the LAN behind your VPN router, the situation is more complex. It basically depends upon whether the two subnets, 10.x.x.x/mask1 and 10.y.y.y/mask2, overlap or not. To solve this case, you will have to post your routing table and ipconfig.

MariusMatutiae

Posted 2013-12-02T11:26:02.983

Reputation: 41 321

This is a paid for VPN service so I have no control over the routing tables on that side. Hopefully the diagram I just added will help to show what the setup looks like. – cogumel0 – 2013-12-02T19:22:12.640

But it is perfectly clear. The solution sketched above in fact is quite adequate. – MariusMatutiae – 2013-12-02T19:32:21.670

Can you explain how I would setup the two different routes directly on PC1 which is running Windows 7? Because that's where it would have to be done. Also bear in mind that the IP address given by the VPN service keeps changing. – cogumel0 – 2013-12-02T19:35:51.453

I looked at the routing table on the client and when the VPN connects it automatically creates a route for the single IP that I am given with a mask of 255.255.255.255. So if I do route add 10.0.0.0 mask 255.0.0.0 metric 50 if 11 that should route all requests that are going to 10.x.x.x and not caught by the more restrictive rules of the VPN to my router which in turn will route it to my VMs, whilst still routing all other non-internal traffic (192.168.1.x and 10.x.x.x) through the VPN, correct? – cogumel0 – 2013-12-02T20:42:57.773

Correct. That's the first solution I described in my answer. – MariusMatutiae – 2013-12-02T20:58:37.233

I knew what you meant, I just didn't know how to do it in Windows 7 :) – cogumel0 – 2013-12-02T21:30:27.783

Connecting two private LANs - issue with VPN

Answers