classful routes redux

Thu Nov 3 01:14:03 UTC 2005

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