Dynamic DNS
Last updated on 8 Dec 2005 by David E. Smith <dave@technopagan.org>
Can there be only one?
Of course not. Here's a few other lists:
DNS? What's that?
You got to this Web page by looking up http://www.technopagan.org/dynamic/. DNS, the Domain Name Service, is responsible for the big part in the middle: www.technopagan.org. The Internet is divided into literally millions of domains; each one has its own name.
To a human, names like that (or ibm.com, or yahoo.com, or any of the other four million domain names registered) make perfect sense.
But not to the computer.
The computer doesn't have a clue. Computers work with numbers. Computers use IP addresses ("dotted quad" numbers like 10.20.30.255) to talk with each other on the Internet.
DNS is the middleman, translating domain names into numbers (and, occasionally, the other way around).
Great. But why "dynamic DNS?"
Glad you asked.
There's only so many numbers out there, at least as far as the computer is concerned. (Basically, each of the four parts in the "dotted quad" address can only be between 0 and 255.) Silly technical limitations eat up a lot of those addresses; historical design decisions eat up some more; and of course a LOT of them are already in use.
This means that Internet IP addresses are a finite, scarce resource, and have to be treated somewhat carefully.
Suppose you have a normal, $20 per month, Internet dialup account from "Some Local ISP, Inc." They have three thousand customers, but it's rare that all of them are online at the same time. (In fact, if they follow industry practice, they probably only have 500 or so phone lines anyway.) So that ISP may only have 600 or 700 IP addresses -- enough to provide one for each phone line, a few for internal use, a few for future growth, but nowhere near one for each of those 3000 customers.
Or maybe you have a cable modem, though "Big CableCo Inc." Whenever your cable modem goes online (when you first plug it in and turn it on), it broadcasts a request for an open address, and some computer in their office eventually answers. Cable modem addresses are usually assigned with "leases," which work just like the lease on an apartment - you're guaranteed to have that address for a certain time, but after that all bets are off. Your landlord (the cable company) might evict you, forcing you to move (get a new IP address) at the end of the lease. (These 'leases' usually only last for a few days, and sometimes only a few hours.) At the end of the lease, you may be able to negotiate a new lease, but you can't be sure of it.
So not everyone can have their own IP address. Your ISP, cable company, or whoever, might let you have a dedicated IP, but they'll probably charge you extra for it. It's more likely, though, that they can't or won't help you...
Imagine if the phone company changed your number twice a day -- people would have a hard time calling you.
Fortunately, most home users don't need to worry about all this "dynamic DNS" stuff. If you just want to get online, check your email, look at a few Web sites, maybe get in a quick game of Unreal Tournament 2003, your specific address doesn't matter. You'll get a fresh address every time you dial in, that's all yours for as long as you stay connected, and since other people aren't trying to connect to your computer, you're all set.
If you want to run a BBS, or Web server, or any number of other services, on your home computer, though, having your IP address change all the time is a real problem.
Enter Dynamic DNS services. They act like old-style phone operators: other users call the operator, and ask to speak to you, and magic happens. Every time your computer comes online, you tell the DDNS server what your current address is. Other users, through the magic of DNS, will be sent to the right place.
Sounds neat. Tell me more about how DNS works.
It gets a bit more technical here. If you just want to run a part-time Web server, or Shoutcast server, or something like that, you probably don't need to know most of this. But it may come in handy, and it's (I hope) interesting anyway. If you want to run a BBS, you'll almost certainly need to read on.
The most interesting, and useful, types of DNS records are A records, MX records, and CNAME records.
"A" records specify Addresses. An A record usually matches a single name to a single number. For instance, as I write this, it matches the domain name "technopagan.org" to the number "24.217.41.120". (Don't use that number for anything; I have a dynamically-assigned address too.) This mapping isn't always one-to-one, but for this discussion let's pretend they are.
"MX" stands for Mail eXchanger. MX records specify other computers that handle mail for a given domain. To continue the phone analogy: My primary MX is my home phone. If you can't reach me there, though, you might try my pager (a secondary MX) or my cell phone (another secondary). If a domain doesn't have an MX listed, the address from the A record will be used.
CNAME stands for Canonical Name. It specifies aliases - other names that a computer answers to. Suppose you want to look like a big company, running a Web server, FTP server, news, IRC, and other services too. But you can't afford to buy a dozen computers to run them all. So you set up a number of CNAMEs for your one computer: www.yourdomain.net, ftp.yourdomain.net, irc.yourdomain.net, bbs.yourdomain.net, and others. That one computer could run all those servers at once.
There are other DNS records, from the never used WKS, to PTR and HINFO, to the dreaded "in-addr.arpa" record. But they are beyond the scope of this document. For a good primer to DNS in general, see the Linux DNS HOWTO at http://www.ibiblio.org/pub/Linux/docs/howto/DNS-HOWTO.
If you're interested in running a DDNS service of your own (you brave soul, you), there are a couple things to do: Either write the software yourself (as the people at Dynup.net have done), or get a ready-made package from someplace (like CheapNet). The most important thing, though, is to email me when your service is up and running. :-)
I don't want this to become a list of "dynamic DNS software providers," but here's a (partial, incomplete) list of pre-made packages:
Okay, I'm sold. From whom can I get Dynamic DNS service?
Here's a small, partial, incomplete, and maybe out-of-date list of providers. (The date at the top of this document shows you when I last checked all these sites; then, at least, they all appeared to be in business and taking new customers. If things have changed since then, let me know via e-mail and I'll make the appropriate corrections.)
But first, let me explain the table.
"Subdomains" means you get a sub-domain of a name the company already owns. If your computer is named fred, and you buy this kind of service from "Some Big ISP," at somebigisp.net, your domain name will be fred.somebigisp.net.
"Domains" means you've purchased your own Internet domain name. This will be something like "yourdomain.com". There are literally hundreds of places that can sell dotcom names and others as well. I've gotten good prices and good results, both personally and professionally, from GoDaddy. The name is lame and cheesy, but for domain names starting at about seven bucks a year, the price is hard to beat.
The inevitable "?" means that the Web site in question doesn't list the information, or that it's sufficiently confusing that I gave up looking for it. (Usually, it means that you can only get the information if you sign up. I don't want to pollute all these different databases by creating accounts I'll never use, and I don't even know what I'd do with 100 extra domain names. :)
Web hosting ain't free. If this list was helpful, click that little button and make a donation to help keep this list running!Updated August 2006: Removed a whole bunch of dead providers.
And now, the standard disclaimers: I don't work for anyone on this page. I am a happy customer of a couple of these companies; if you know your way around DNS tools, you'll be able to figure out which ones. Though I try to keep this page up-to-date, I don't guarantee that anything on here is accurate. Including this disclaimer. Other users' opinions are their own, not mine. I try hard not to have opinions; makes life easier.
And if you've read this far: Wow! Feel free to link to this list, using the URL http://www.technopagan.org/dynamic/ -- it'll help boost my rankings in search engines, and help others find this list.
This list is © Copyright 1999-2004 David E. Smith. All rights reserved. All trademarks acknowledged.
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