[ppml] [address-policy-wg] 2005-01 - Last Call for Comments (HD-ratio Proposal)

[Geoff Huston]

At 02:07 PM 23/02/2006, Randy Bush wrote:
> > HD Ratio Ratio Mean Std Dev
> > 0.98 1.04868 0.02285
> > 0.97 1.25899 0.03363
> > 0.96 1.45854 0.03371
> > 0.95 1.63073 0.02848
> > 0.94 1.78332 0.01859
>
>and what does .98 do to the flight ceiling of small folk?
>
>randy


I'll respond to this question, but in the interests of  not wishing to 
overwhelming a whole swag of mailing lists I'll make this my last posting 
on this topic today.

An HD Ratio of 0.98 imposes a higher  efficiency target than the existing 
80% rate for all prefix sizes smaller than a /16, and lower than 80% for 
allocations greater than a /16 (e.g. an HD Ratio of 0.98 implies an 
efficiency threshold of 72% for a /9 allocation.)

As an example, if you had an end use population of between 3,277 and 6,554 
numbered devices you would qualify for a /19 allocation under an 80% rule, 
while under an HD Ratio of 0.98 the end use population is between 3,468 and 
6,841, corresponding to a required address efficiency level of 84% on this 
address block in order  to qualify for a further address allocation.

The use of an HD Ratio of 0.96 corresponds to an 80% efficiency level for a 
/24, so that 0.96 is no worse than 80% for all allocations, whereas 
HD  Ratios greater than 0.96 impose an efficiency constraint greater than 
80% on  the smaller address blocks (/16 through to /24) - this can be 
easily modelled on any spreadsheet of course.

regards,

      Geoff