On Thu, Oct 20, 2011 at 8:08 PM, <Valdis.Kletnieks@vt.edu> wrote:
Yes, it's possibly foolish to allocate x.y.z.0 or .255.
But saying that that x.y.z.0 is *not* *capable* of representing an interface is demonstrating a dangerous lack of knowledge. There's several totally legal .0 and .255 addresses in each /22 subnet, and yes people *do* use /22 subnets. Unfortunately, we're still stuck with "Don't use .0 or .255, because there are *still* people out there who don't understand CIDR and will hassle you about it"...
A decade ago, I recall allocating a /23 to a dialup pool and getting calls from customers who landed on .0 and .255 because they were unable to reach random sites. It should be legal, but doesn't always work. I assumed this was still the case. Several months ago, I fired up a permanent aws ec2 instance with a static IP. To my surprise, they allocated me a .0 address. I haven't noticed any issues with it at all. But I figure if Amazon is using .0 as a normal part of their deployments, their scale is so high that if it didn't work reliably you'd think they would have noticed by now. I don't know if they also use .255.