How can I connect to my home computer from work?

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I have a couple of computers at home, running Windows XP Home and XP Pro. They are connected to the internet using a broadband router. I'd like to connect to them from my place of work. How do I do that?

Well, it may be possible, but there are several barriers in your way. It could get complicated, but we'll look at each of the barriers in turn, and consider ways to overcome them, if possible.

First, I'm going to assume that you want to connect using Remote Desktop. Using that, when you finally do connect, you'll have access to the remote computer almost as if you were sitting in front of it. The bad news here, is that Remote Desktop is a feature of Windows XP Pro, and is not present in XP Home. You'll only be able to access your XP Pro machines using Remote Desktop.

Our first barrier is your place of work. Depending on how they are connected to the internet, you simply may not be able to connect out. Larger corporations often restrict what protocols are allowed to access the internet. Quite often they restrict access to Web surfing and Email. If that's the case where you work, there's little recourse, other than pleading with your IT department to allow the Remote Desktop protocol (on port 3389) to reach the internet.

The next barrier, or at least point of confusion, is your IP address. The easiest scenario is if you have a static IP address at home. That way you'll always know what IP address to connect to. In fact, if you have a static IP, you can even register and assign a domain to it, so that you can access your home network by name - something like myhome.mydomain.com - rather than IP address.

If you have a dynamic IP address, you can still get to your network, you simply need to know what the current IP address is. There are several approaches, however none of them are really elegant. For example, you can call home and ask someone to visit a site such as Plot IP, which will display your IP, and then having them read it to you over the phone. If you have access to a web server's access logs, you can have your computer at home visit a specific web page periodically and retrieve the IP address from the logs. And finally there are tools that you can use to map a domain name - like myhome.mydomain.com - to a dynamic IP. These tools do require that you install software on your computer to detect IP address changes, and when a change occurs, it may take up to 48 hours for the DNS changes to make their way across the internet.

The good news about a dynamic IP is that if your router stays connected continuously, the IP address is actually not likely to change often.

The next barrier is your router. A router acts as a firewall, and prevents most connections coming in from the internet. Most people only connect out, to surf the web, download files or read email, so that's not a problem for them. But connecting from a remote location to your home is a connection coming in from the outside. The router needs to be configured to forward port 3389 (the Remote Desktop Protocol port) to the computer you want to connect to. Unfortunately exactly how that's done will vary depending on kind of router you have - you'll have to check the documentation.

Note that I said you need to configure it to forward to the computer you want to connect to. You can access only one of your computers directly through your router this way. (There are techniques where you can specify that Remote Desktop listen on ports other than 3389. Then by using a different such port for each computer, and forwarding each through the router to the appropriate computer you can connect directly to each. That's beyond the scope of this article, and more complex than most folks will want to deal with.)

My approach, for what it's worth, is to allow external remote access to only one machine on my network. Once connected to that machine I can if needed use remote desktop on it to connect to any other machine on my network. It can be a little confusing from a UI perspective, knowing which of the three machines connected in sequence my keystrokes are actually going to, but in practice I don't do it often.

Our final barrier is your IP address on your LAN. Your IP address on the internet, wether static or dynamic, is assigned by your ISP and really identifies only one device: your router. Within your local network, the router then typically assigns local IP addresses to all of your computers. The router then handles making sure that all the data traveling between the computers on your local network and the internet all go to the right computers.

Those local IP addresses never leave your network - the internet sees only your router's IP address. So when you configure your router to forward port 3389 to a computer, you need to select one of your local computers, and configure its IP address as the destination for Remote Desktop. Then, when the router receives a Remote Desktop request from the internet, it forwards that request to the computer whose IP address you configured.

The "problem" is that your local network is, more than likely, using dynamic IP addresses. That means that the IP address that are assigned to each computer could change over time. If you leave your computers on all the time, the addresses won't change, and you're probably OK configuring the router with the current IP address of the computer you want to access remotely. If it ever changes, you'll need to update your router's port forwarding configuration for port 3389.

If that's unacceptable or inconvenient, the only real solution is to configure one of your computers to have a static IP address, and then configure the router to forward to that one as the Remote Desktop target. Depending on your router it can be as easy as:

• Configuring the router to assign IP addresses from one range ... say 192.168.1.100 and up.
• Configuring the TCP/IP properties of one of your machines to be a static IP, and defining it with a value out of that range - say, 192.168.1.2 (normally 192.168.1.1 is reserved for the router itself).

In many cases that's enough. In cases where other machines on your network cannot "see" this one machine, it may be necessary add an entry to the "hosts" file on all the other machines that defines the static IP address for this one machine:

192.168.1.2 machinename

There's more on hosts in this article: Can I fake the DNS IP lookup to test my website?.

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As you can see, things get fairly complex fairly quickly. There are other solutions, but I've not tried any of them myself so I'm not qualified to comment on their suitability or their ease of setup:

• Commercial solutions such as PC Anywhere, or GoToMyPC.
• VNC (Virtual Network Computing) solutions that operate much like Remote Desktop. RealVNC is one example.
• VPN (Virtual Private Network) solutions that create a virtual connection to your entire local network. In recent years, some types of routers come with VPN support built in.

Perhaps some readers will chime in with their experiences with those, or other, solutions.

Related:

• Ask Leo! - How Can I access my Windows XP Machine Remotely?

• Ask Leo! - Can I fake the DNS IP lookup to test my website?.

• Ask Leo! - How can I connect using remote desktop to someone that has XP Home if I have XP Pro?

• Ask Leo! - How can I share my hard disk remotely?