VPN tunnel between two networks with the same ip address

Question

I'm trying to understand at a basic level networking. I've been asked the following question as a scenario for attempting to help me understand networking better. I've spent quite a bit of time researching this and haven't come up with a simple answer. Here's the scenario:

You have network 1 with an ip address of 192.168.0.x and it goes out through a router to another router and into another network with the same ip address 192.168.0.x. In this scenario, what would be the main or most simple reason, you would not be able to VPN from network 1 to network 2?

Answer 1

Do you mean you are trying to get two LANs of the same subnet to talk via a VPN? You use the term "192.168.0.x" so one would assume you are talking about a range of IPs within the given 192.168.0.x subnet.

The reason why you can't (and shouldn't) is due to the fact that a router's job is to route traffic from a known network to an unknown network.

When a computer in network A (192.168.0.2) tries to talk to, say, 192.168.0.3 the router will think this address is within the local network (A). It is saying "the address is within my LAN so don't route elsewhere (I.e. network B)". Thus computer .2 will either receive a response from the .3 on network A or - if .3 is only on the other network (B) - it will not make a connection and timeout.

If your network B was 192.168.1.x then the router WILL say "I don't look after 192.168.1.x addresses but (if a route to say that the VPN knows where to find the answer) I will send this over the VPN and see what response I get".

The router on network B does its job and sends the request to the correct workstation.

Source: I've recently had to do this so did my research ( mainly on the SE sites! )