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So, this is what I do with my time.

You know how the default IPv4 address setting on a router is usually 192.168.0.1? Have you ever wondered why those abstract digits were chosen? Instead of, say, 1.1.1.1? Well, I have. And it got stuck in my head, and now I can't let it rest until I find a satisfactory answer.

What I've found so far is still very, very, very incomplete. More technical users, I welcome additional comments and insight. But, what is here is perhaps enough to satisfy or scare off laypeople like me. So, readers who are just along for the ride, welcome to you, too. :)

The story dates back to February, 1996, in the infancyearly childhood of the Internet: RFC 1918, a memorandum (properly titled "Request for Comments") issued by the Internet Engineering Task Force. Unfortunately, RFC 1918 is a dreadfully dry piece of text, so here's the Cliff's Notes on what it says:

Quote

The Internet is growing far beyond anyone's expectations (lol), and TCP/IP has become the definitive communications protocol not only on the Internet, but in private and Internet-isolated networks as well. Some networks need to be accessible externally from the Internet, and others don't. For networks that don't need to be externally accessible, we're proposing to set aside some ranges of IP addresses for these networks to use. Because these addresses will be set aside, anyone who wants to form a private network can use them and stay in line with Internet standards without needing to get any permission from an Internet registry. Also, this means hundreds of thousands of companies and individuals can build private networks without intruding on the limited total IP address space, which is really only necessary for systems that need globally unique and accessible addresses. By the way, the blocks we chose for this are:

10.0.0.0        -   10.255.255.255
172.16.0.0      -   172.31.255.255
192.168.0.0     -   192.168.255.255

OK, great. This explains why home routers default to 192.168.0.1:
192.168.0.0 is used as a generic reference to private networks, so the next address step, 192.168.0.1 is used as a router default. (And some use 192.168.1.1.) They use 192.168.x.x because most home networks don't need the range of addresses available in the B-class 172.16.x.x to 172.31.x.x range, and they certainly don't need the massive range of addresses available in the A-class 10.x.x.x. But for enterprises and other users that want/need to use the bigger spaces, they're there.

I get that, and it doesn't really bother me.

What does bother me, is why one-hundred-and-ninety-two? And why one-hundred-and-sixty-eight? This has been the harder portion to justify.

The best answer I've seen so far is: These were areas of addresses that were available to use when IETF decided a standard ought to be issued. The A-class 10.x.x.x was used by DARPA until its retirement, and IETF suggested that reusing those addresses publicly could pose problems. So, that made 10.x.x.x an ideal candidate to restrict to private use when the need arose.

But 192.168.x.x? 172.16.x.x? The only answer appears to be that they were all-but-randomly selected from ranges of addresses that had not already been reserved for other purposes.

Technically-inclined users, please add to this! What have I missed? What else is going on with these magical number selections? Has anyone else actually wondered why these numbers were chosen? At least I have the support of some venturing posters on Yahoo! Answers, bastion of knowledge that site surely is.

By the way, if this kind of thing interests you, you can check out a list of all specially reserved address blocks (as they were in 2002) in RFC 3330.

This post has been edited by Phoenix on 6th December 2010 11:50

I just now came back around to this thread, and this is actually pretty interesting information. That page for RFC 3330, while maybe not illuminating, is pretty interesting to gloss over, at least.

I'm glad I work in technology but not in networking.

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"To create something great, you need the means to make a lot of really bad crap." - Kevin Kelly

Why aren't you shopping AmaCoN?

Friend of mine who is in networking don't know either. I'm guessing they did some equations to figure it all out and those were the numbers they came up with.

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