Re: Issues encountered with assigning .0 and .255 as usable addresses?

[Job Snijders <job () instituut net>]

Hi Paul,

On Oct 22, 2012, at 5:07 PM, Paul Zugnoni <paul.zugnoni () jivesoftware com> wrote:

> Curious whether it's commonplace to find systems that automatically regard .0 and .255 IP addresses (ipv4) as src/dst 
> in packets as traffic that should be considered invalid. When you have a pool of assignable addresses, you should 
> expect to see x.x.x.0 and x.x.x.255 in passing traffic (ie. VIP or NAT pool, or subnets larger than /24). Yet I've 
> run into a commercial IP mgmt product and getting reports of M$ ISA proxy that is specifically blocking traffic for 
> an IP ending in .0 or .255.
>
> Any experience or recommendations? Besides replace the ISA proxy…. Since it's not mine to replace. Also curious 
> whether there's an RFC recommending against the use of .0 or .255 addresses for this reason.

In the post-classfull routing world .0 and .255 should be normal IP addresses. CIDR was only recently defined 
(somewhere in 1993) so I understand it might take companies some time to adjust to this novel situation. Ok, enough 
snarkyness!

Quite recently a participant of the NLNOG RING had a problem related to an .255 IP address. You can read more about it 
here: https://ring.nlnog.net/news/2012/10/ring-success-the-ipv4-255-problem/ So yes, apparently problems like these 
still arise once in a while. My recommendation would be to fix the equipment and not blame it on .0 or .255. 

Kind regards,

Job Snijders