cidr-convert

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CIDR block calculator.

Takes a set of dotted-quad IP addresses, ranges, or CIDR blocks, on stdin; at EOF, prints a minimal set of CIDR ranges to stdout.

Input consists of a stream of dotted-quads, pairs of dotted-quads separated by a dash, or dotted-quads with /number widths after them. Dash-separated ranges refer to all addresses between the two, inclusive; an address with a /number after it refers to a CIDR-style block. It is not an error for an address to be specified in the input more than once. Whitespace may appear anywhere except within a dotted-quad or CIDR width. Characters other than digits, dots, dashes, and whitespace are errors. If a number in a dotted-quad is greater than 255, or a CIDR width is greater than 32, or other syntax errors occur (such as too many dots without whitespace, dash, or slash) a complaint is printed and the dotted-quad, range, or block in which it appears is skipped.

Output consists of zero or more lines, each a dotted-quad/width CIDR net-with-mask, including all and only the addresses in the input. It will be a minimal set, in that no two blocks in the output can be collapsed without resorting to noncontiguous netmasks.

Compile-time options:

 -DNO_PROGNAME
         Provide __progname, for systems that don't have it.  If
         it shows up undefined at link time, try compiling with
         this turned on.

This file is in the public domain.

Originally obtained from: http://www.spamshield.org/cidr-convert.c

Added to github on 02-01-2012 initially to fix a simple display bug for initial quads over 127. The goal is to allow for collaborative tweaking and development of this useful tool.

As of 05-27-2015, I have ported the tool to Go as well. Mostly as a learning exercise. Build with 'go build cidr-convert.go' to prevent the compiler from getting confused.