[105192] in North American Network Operators' Group
Re: .255 addresses still not usable after all these years?
daemon@ATHENA.MIT.EDU (bmanning@vacation.karoshi.com)
Sat Jun 14 01:07:48 2008
Date: Sat, 14 Jun 2008 05:07:15 +0000
From: bmanning@vacation.karoshi.com
To: David Hubbard <dhubbard@dino.hostasaurus.com>
In-Reply-To: <FCD26398C5EDE746BFC47F43EA52A17303252D09@dino.ad.hostasaurus.com>
Cc: nanog@merit.edu
Errors-To: nanog-bounces@nanog.org
On Fri, Jun 13, 2008 at 03:08:47PM -0400, David Hubbard wrote:
> I remember back in the day of old hardware and operating
> systems we'd intentionally avoid using .255 IP addresses
> for anything even when the netmask on our side would have
> made it fine, so I just thought I'd try it out for kicks
> today. From two of four ISP's it worked fine, from Verizon
> FIOS and Road Runner commercial, it didn't. So I guess
> that old problem still lingers?
>
> David
>
well... .0 and .255 are still special in -some- contexts.
they still form the all-zeros and all-ones broadcast addresses
for the defined block... so:
192.168.16.0/23
192.168.16.0/32 is unusable
192.168.16.255/32 is useable
192.168.17.0/32 is useable
192.168.17.255/32 is unuseable.
crapy CPE, vendor instruction, poor software all contribute
to VLSM being poorly understood and these "gotchas" still
around - years - later.
my recommendation... place your caching nameservers and webservers on
these addresses... if you want to force the issue. :)
--bill
