subnetviz is trivial tool to visualize hierarchical relationships in IP subnets. subnetviz takes a simple text-based input naming IP address blocks (base address and prefix length pairs), along with optional labels, and produces an HTML-based tree to show which networks belong under which other networks.
This tool is especially helpful if you try arranging your subnets hierarchically. It also makes it easy to spot areas of unallocated space.
Try it online, or download it below.
The most recent release is 0.4, released 2010-02-05. It depends on: Python 2.5 (Debian: python2.5), IPy (Debian: python-ipy)
I sign all my software with OpenPGP, key ID 0xE979FFBEA002D20F, fingerprint A87B 1C5A 28C4 03BD 54BA CE8E E979 FFBE A002 D20F. (Releases were previously signed with 0x80555CED7394F948, which has been revoked, but not compromised. See my OpenPGP transition statement.)
This software is licensed under permissive, BSD-like terms, copied from the ISC license:
Copyright (c) 2010, Jean-Paul Guy Larocque
Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
I'm reachable via e-mail for feedback, questions, help requests, and bug reports: jpl-software at thoughtcrime.us
— J.P. Larocque