Re: .255 addresses still not usable after all these years?

[bmanning () vacation karoshi com]

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