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Paul Gregg's Blog:
PHP algorithms: Determining if an IP is within a specific range.
Apr 28, 2009 @ 09:25:39

Paul Gregg has shared a method he's come up with to determine if a given IP is within a selected range.

Unfortunately although people usually understand that an IP address is simply an unsigned 32 bit integer, and is easily determined, usually with $_SERVER['REMOTE_ADDR'], where the real challenge is - is in specifying the range within which they wish to check that IP address. IP ranges are usually specified in three common ways (in increasing complexity): wildcard, start-end range, classless inter-domain routing.

He looks at each method and includes descriptions and code examples as well as a link to the source code and a live demo of it in action.

tagged: algorithms ip address specific range three method wildcard cidr startend