One computer on 2 networks with same IP ranges

Question

I have two networks:

Network A - 192.168.1.x with a router/gateway and cable modem Network B - 192.168.1.x with no gateway or internet acces

Both subnets are 255.255.255.0.

I have a computer with two network adapters - one connected to each of the networks (XP SP2). This computer runs an application that needs to use only the internet connection from network A and has to communicate with computers on network B.

Internet access seems to be unavailable when both adapters have a 192.168.1.x IP. I added a second router between the PC and network A's switch with an internal IP of 10.0.0.x and an external IP of 192.168.1.x.

This seems to be working Ok, but persistent connections sometimes drop. Is this an acceptable way to do this? Any way to eliminate the extra router?

Answer 1

You only have one network, which is 192.168.1.0 with netmask 255.255.255.0, this is classic Class C network (classfull), I think in your case may be happening ip duplicate, check the Ip's of your devices. Now would be good if you actually create another network, eg 192.168.10.0 with mask 255.255.255.0

Answer 2

Unfortunately, there isn't an easy way around this. If you have one host on each network that has the same IP as the other, how does your computer know which one it is to talk to?

Apart from changing the address range you could set up your router to do a 1 to 1 NAT.

The only other real option might be to use subnetting

Answer 3

You cannot - in principle - have two devices with the same IPv4 address reachable from a single machine unless you perform some kind of address translation. It may work from time to time, but will regularily break.

I strongly suggest that you simply move either network A or B to 192.168.2.0/24.

If you must use the same IP ranges on both machines, adjust the routing table as follows, assuming the internet router on network A has the IPv4 address 192.168.1.1:

192.168.1.1/32 device A
192.168.1.x/24 device B
0.0.0.0/0      gw 192.168.1.1

You will not be able to communicate with 192.168.1.1 on network B. However, while this setup is possible, it will be error-prone in the long term, and I see absolutely no reason why you shouldn't just pick a different address range for either network.