Bill Woodcock wrote:
On Wed, 2 Nov 2005, Fred Baker wrote: > While I think /32, /48, /56, and /64 are reasonable prefix lengths > for what they are proposed for, I have this feeling of early > fossilization when it doesn't necessarily make sense.
Yeah, that's what seems important to me here... I mean, I've lived through the whole classful thing once... I'm still not clear why there are people who want to do it again.
It's not quite the same as classful addressing in IPv4. There is no definition of prefix length by address range. At the RIR->ISP level It is actually CIDR with a minimum allocation size that intentionally covers 95+% of applicants. Shorter allocations of various sizes are made based on justification. An extra 1-3 bits is even reserved around each allocation for future growth. The same thing applies to End sites. You can get a /47 or shorter with justification. It's might be rare but it is possible. I think the goal was to avoid making multiple non-aggregatable allocations as is done with IPv4. An alternative would be to allocate based on initial need but still reserve a much larger prefix for future growth. This would avoid the illusion of fixed sizes and carry less risk of unused space. Is that worth the extra RIR effort? Maybe, maybe not. - Kevin