Shostack + Friends Blog Archive

The Hazards of Not Using RFC 1918

RFC 1918 is a best-current-practicies RFC that describes network address ranges that we all agree we won’t use globally. They get used for private networks, NAT ranges and so on. There are three ranges:

10.0.0.0 to 10.255.255.255
172.16.0.0 to 172.31.255.255
192.168.0.0 to 192.168.255.255

They are thus the Internet equivalent of the American phone system not using the exchange 555, only more useful. If you need to give an example IP address, you can use one of those without causing anyone consternation or irritation.

An example of why you want to use one of these addresses can be found (at least for the next few minutes) at Microsoft’s site for the IE 8 beta [link to http://www.microsoft.com/windows/internet-explorer/beta/ no longer works]. One of the IE 8 features is the “SmartScreen Filter” [link to http://www.microsoft.com/windows/internet-explorer/beta/features/stay-safer-online.aspx no longer works] which can tell you IP addresses you’re best not going to. An example is the picture accompanying my post.

If you check out that address, 207.68.196.170, at ARIN Whois [link to http://ws.arin.net/whois no longer works], you find out that it’s owned by Microsoft themselves.

I suppose that using one of your own addresses as a hazardous address is better than using someone else’s, but immature people like Your Friendly Author will titter over it and point it out to other people as well.

There’s a reason RFC 1918 exists, and this is one of them. Oh, by the way, be sure to look at RFC 2606, which reserves the domains example.com, example.net, and example.org. It also reserves the top-level domains .test, .example, .invalid, and .localhost. Remember them.

Originally published by mordaxus on 28 Aug 2008
Last modified on 6 Jul 2017
Categories:   Amusements   microsoft   SysAdmin