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

Job Snijders job at instituut.net
Mon Oct 22 22:20:13 UTC 2012


Hi Paul,

On Oct 22, 2012, at 5:07 PM, Paul Zugnoni <paul.zugnoni at 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


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