Network Calculators

[David Bandel]

On 8/5/05, Kurt Wall <kwall at kurtwerks.com> wrote:
> On Wed, Aug 03, 2005 at 07:32:23PM -0700, Net Llama! took 7 lines to write:
> > wow, this looks damn handy:
> > http://www.subnetmask.info/
> 
> This is is pretty useful, too. I included it in my latest book:
> 
> http://jodies.de/ipcalc#
> 
> The "#" at the end of the URL is necessary or you wind up jumping to
> the bottom of the page (not that that isn't useful in this case, it's
> just unexpected behavior).
> 


OK, I have a nit to pick with _both_ of these calculators.  They BOTH
need to change their wording to say they are VLSM calculators.  They
are _NOT_ CIDR calculators.

VLSM:  variable length subnet mask
CIDR: classless interdomain routing

VLSM is a subset of CIDR.  VLSM, as a subset only allows you to use
descreet, defined subnet masks. i.e., those which cleanly divide host
and network portions of the netmask.  CIDR can make use of those
netmasks which don't cleanly divide the host and network portions of
the netmask.

Now, I hope no one here is silly enough to actually use a nonsensical
netmask, but your computer will happily play along.  Non-VLSM
netmasks, are, however, really only an academic exercise or a madman's
folly.  But a netmask of 255.255.255.200, while not a very bright
strategy, is certainly NOT illegal as the last IP calculator page
would have you believe.

Ciao,

David A. Bandel
-- 
Focus on the dream, not the competition.
            - Nemesis Air Racing Team motto