My work and home computers have the same IP address, how do I fix that?

Yes, “The Rule” is that no two computers can have the same IP
address.

Except that the rule is incomplete. It’s actually very common for
two computers to have the same IP address. In fact, I’ll bet that
thousands of computers around the world have the same IP address as the
very computer I’m typing on.

I’ll explain how.

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The full text of the rule should read like this:

No two computers can have the same IP address on the same network.

That phrase at the end makes all the difference.

The internet is one giant network of computers, and it’s absolutely true that no two computers on the internet can have the same IP address. It’s the IP address that tells one computer from another on a network.

But if you’re behind a router, you’re not actually directly on the internet. You’ve set up a separate, local network that is connected to the internet through your router.

What that means is that the IP address of a machine on your local network is assigned separately and independently from the internet, and from all the other local networks around the world. My IP address is 192.168.1.5 on my local network, and it’s likely that the same IP address is used on many other machines on many other local networks.

When you communicate to the internet from your machine, it crosses your router which performs what’s called “Network Address Translation” – converting your local IP address to the internet IP address that has been assigned to the router’s internet connection. Your local IP address is never seen on the internet.

So the question is if the local IP address of the machine you want to connect to is never seen on the internet … how do you connect to it?

There are several ways, include configuring the router to route certain types of connections to a specific IP address on the local networking, through something called “port forwarding”. So, to oversimplify in English, the router might be instructed: “when you get a connection request on your internet side that is for the remote desktop protocol, send that connection to IP address 192.168.1.1 on your local network side”. This means that remote desktop connections can be made from the outside to the one computer the router has been instructed to send them too.

While workable, this approach has problems:

• If you’re trying to connect to your work computer, then it’s the workplace router you need to configure, and you may not have access to it.

• You probably need to take additional steps to ensure that your IP address on your local network does not change. It typically can.

• It’s easy(ish) to configure this to access one of your computers on your local network remotely. If you want to also be able to access another of your local machines, it’s still possible, but slightly more difficult.

My preferred approach is to set up what’s called a “virtual private network”, and I happen to really like using Hamachi to do it.

A VPN creates a virtual network that ignores the entire local/internet/local structure of the physical network layout. It’s as if the two (or more) machines running Hamachi were all on the same network – which, in fact they then are. VPNs do this by assigning additional IP addresses to all the machines connected to the VPN. These addresses are once again unique; no two machines can have the same IP address on the same network, and a VPN is one network.

Which solution is appropriate for you depends on your need, and to be honest, exactly what your company’s IT department (or person) will let you do. I’d certainly recommend checking with them first.