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December 09, 2007

Do You Need a Permanent IP Address?

This post is NOT for nerds: you already know about permanent IP addresses and what they’re used for; but you can tag along and kibitz if you’d like.

When your computer is connected to the Internet, it has an Internet Protocol (IP) address. It looks like this: 192.168.0.11. Actual numbers will differ but there are always four “octets” (numbers between zero and 255) separated by periods. When you send a request to a web site, your request contains the IP address as a return address so that, whatever you requested, can be sent back to your computer (kibitzing nerds be quiet; I know this is oversimplified and will elaborate later).

In the old days of dialup you got a different address each time you connected to the Internet. Didn’t cause any confusion because, each time you request something, you send whatever your current IP address happens to be and replies come to that. Now that our computers are connected for long periods, the IP address generally stays the same at least for the length of a single connection. However, if you sign off and then on again, your IP address may change. NOT having a permanent IP address makes it a little less easy to target your computer with nasty things and gives you some measure of privacy since websites and snoops can’t use an IP address which keeps changing to track your habits.

So why would you want a permanent IP address, one that is the same every time you connect to the Internet? The only reason you might is so that you or someone else can access your computer from somewhere else.

Suppose you have a desktop computer which you use at home and a laptop you use when you travel. You may want to have access to the files on the desktop computer from the laptop when you’re in a hotel room somewhere. There are several programs which support this kind of remote access; but all of them require that the laptop know what the IP address of the desktop computer is so that it can direct requests to it. If your desktop computer has an IP address which is always changing, your laptop doesn’t know where on the Internet to go to get your information even though you know that, in real life, the desktop is in the study in your house.

Another reason that you might want a permanent IP address is that you want the computer in your house to be a web server which people outside can access. If this is the case, you’ll want not just a permanent IP address but also a domain address – something like www.mydomainaddress.com.  In fact, the domain address is just a slightly better way for people to access your website than by its IP address. When someone types your domain address into their browser, it is promptly translated into your IP address by a domain name server (DNS) somewhere out on the Internet. Twofold purpose for this: 1) it’s easier for people to remember and type names than numbers; 2) even a “permanent” IP address can change; if this happens, it doesn’t affect users who are using the domain name so long as DNS has been properly updated (which is not always immediate).

Third reason you might want a permanent IP address is so that you can get to other IP services in your house while you travel. For example, I can access my home security system, check status, reset codes, even change the thermostats while I’m away. Other people have webcams in or on their house that they want to be able to see while they’re away.

Note that we’ve now sneaked in a little complexity. If you have more than one computer in your house or IP devices other than your computer, it’s probably your house rather than your computer which has an IP address which is either permanent or changeable as far as the outside world is concerned. That IP address belongs to your cable, dsl, or wireless modem and is inherited by your router. Each device in the house has its own IP address but these are assigned by the router and almost always start with 192.168. These addresses are NOT visible outside the house. The router does some trickery we won’t talk about to decide which computer or device gets which outside query and to make sure that when you request a web page from your computer, the page comes back to you and not to your spouse (bet you didn’t even know to worry about that).

Some ISPs (but not many) automatically give you a permanent IP address; others charge you an extra amount each month if you want one. $5/month is a usual, fair and reasonable charge for this; there is a cost to the ISP. But you have to check with your ISP on their policy. Some keep the price pretty high because they don’t want you to be running a web service at consumer access rates. Business Internet access almost always comes with a permanent IP address.

One note of caution: you DO want a firewall in your router if you have a permanent IP address and probably want to run some firewall program on each PC. These are good practices anyway but especially important with the extra exposure a permanent address implies.

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