how many possible internet addresses are there? i know email addresses (at least the ones @juno.com) can have up to 21 characters in them; is it the same for internet addresses? about the longest one i can think of off the top of my head is www.myrtlebeachhelpwanted.com (21 letters).
Permitted domain name length is between 3 and 63 characters (not including extension)
Letters a through (no accents of any kind) - not case sensitive.
The numbers 0 - 9
The hyphen character (but not as the first character)
Actually, that 63 character limit might just specific to my ISP
DANG!!!
There are several extensions to the current domain name alphabet in the works. There will be (or already is) extensions for other European alphabets. The Cyrillic is going to be fun. Did you notice that odd little letter in the “safe looking” URL before you clicked on it? You may not end up at the site you expected, entering passwords or credit card nos.
Asian countries are hoping to get their alphabets okayed real soon. Since there is no “byte limit” on symbol encoding in some of those, let your imagination run wild.
Also, I know of no inherent limit on top level domains (edu, com, uk, etc.). But so much software has probably been written that assumes a low limit a la the “year 2000” problem. In any case, new top level domains have to go thru a review process. You just can’t add your own long TLD. (Though some companies have tried.)
The real limit on the current Internet is IPv4 octet addressing. 4 bytes, with many reserved for special uses. So most machines on the Internet don’t have real Internet addresses but run thru a NAT router or some such. IPv6 will add a whole lot more: 128 bits total.
Note that the relation between a Internet machine name and its IP address is non-trivial. One machine can be a web host for a lot of sites. A network router can route traffic for the same address to different machines (each with different IP addresses) for load balancing.
Remember that the Web is only a fraction of the total Internet. There are dozens of protocols used on the Internet, such as NNTP (for Usenet) and POP (Post Office Protocol, for some email), and most of them don’t mess with any names of this form.
As has been said above, IPv4 is dying. The new thing is IPv6, which will use 128 bits, giving us 2[sup]128[/sup] addresses, which is more than 340 thousand decillion (340 with 36 zeroes behind it) (what is the correct power-of-1,000 past decillion?). That should be enough to give every machine in the world its own stable IP address, making routing easier.
Undecillion
I thought it was kajillion. 
There’s essentially an infinite number of hostnames, because you can subdomain (hotmail.com www.hotmail.com user2.hotmail.com) - plus hostnames really aren’t important in terms of technical limitations of growth, your real limitation is the number of IPs, which is the actual limit of the number of devices that can possibly be on the internet at once. There are 2^32 different 32 bit IPv4 addresses. But tons of those are in turn reserved (10.x.x.x, 192.168.1.x, 172.16.x.x, things with 255 or 0 in certain places, etc.) and then there’s the general problem of allocation… that is, there is overhead every time you divide up a block of IPs, IPs are wasted by delegation in a way not unlike that of phone numbers- someone can’t assign me a phone number in the 804 area code if I’m living in the 412 area, etc.
<P>
There are already problems in IP allocation in places like Japan, or so I’ve heard, and it’s likely that the rest of the world will join them soon. Or we’ll all wisen up to IPv6, where I think it’s safe to say we’ll never have to worry about there being IP shortages again…
Nitpick: It’s an ASSLOAD.
Since 98% will be dedicated to porn, this is only appropriate.
In regard to the extensions, there are about 270 or so, most are those 2-letter country ones like “us” for United States.
Derleth wrote
Well, sorta.
a) There are thousands of protocols out there, not dozens.
b) All of them involve talking between two hosts (over some TCP or UDP protocol). Therefore, all of them “mess with names of this form” as you put it. In the examples you gave, you’re familiar with the forms bill@example.com (for use by SMTP and POP) or nntp.example.com (for NNTP). Both of these are domain names.
c) IPv4 is not dying and will likely live at least another 10 years. It does have a limited address space, but NAT-ing, reclaiming large (class A) early give-aways and charging for addresses has extended it’s lifespan enormously. Replacing IPv4 would be a huge undertaking, requiring every router, server, client and every other device on the Internet to be modified. IPv6 is not an upgrade to IPv4; it’s a new Internet. It may be far more then 10 years before it’s replaced, and it’s not in any way ensured that IPv6 is the replacement. (although it is the leading contender today).
d) IPv6 has many benefits, including an extended address space, but that new address space will not “make routing easier”.
Everything else was accurate.
http://www.0-------------------------------------------------------------0.dk/
has 63 characters in between the dots.
(I’m not advertising or suggesting anyone go there. I don’t really know what it’s about, since it’s in what I presume is Danish. I’m only pointing it out for the remarkable URL.)
A fully qualified domain name (FQDN), which is the whole address, from host to root, can be 254 (I think… might be 255, or 256) characters long.
Protocols and other stuff aside, we’re now limited to the realm of “www.” Not to sound too wacky, but once they put a hold on that, they’ve got us in a head-lock.
Think what we could do if Concerned Citizens started patenting UNC Orders like “aaa” or “qqq” or “zzz” that would be inviolable under US Patent Law, and at least for now protected by appeals for one calendar year.
Just a thought.
Say again?
Sorry.
No, a kajillion is only 10[sup]12[/sup]. At least, that’s assuming that “jillion” is from one of the pronounciations of “gillion”, a back-formation from the prefix “giga”, and that “ka-” is from the prefix for 10[sup]3[/sup]. So a kajillion is equal to 10[sup]3[/sup] * 10[sup]9[/sup] (or, if you’re a programmer, 2[sup]10[/sup] * 2[sup]30[/sup], I suppose).
And Mr. B, what the heck are you talking about, being limited to “www.”? Look up your screen a bit: The web page you’re on at the very moment is boards.straightdope.com… , without a “www.” in sight. And I’ll bet you that for every string from “aaa” to “zzz”, there’s at least one website somewhere that starts with that string, and furthermore, that there’s such a website which has been up for more than a year, thus making such a prefix unpatentable (which it wouldn’t have been, anyway, of course).