[ppml] HD Ratio changes

Charles Scott cscott at gaslightmedia.com
Tue Feb 10 08:38:01 EST 2004

  When this last came up I questioned why HD Ratio should be applied to
ISP allocations/assignments and received no responses. In fact, I even
challenged the application of HD Ratio to end-user address space on the
premise that the argument for HD Radio is based on the need to implement a
strict hierarchical numbering scheme. With dynamic routing protocols it
is not necessary to have a network hierarchically arranged strictly by
numeric address--subnets can appear in networks to which they are not
numerically related. The arguments for HD Ratio have used telephone 
number distribution as an example, but that is not a comparative model 
today (although number portability may convolute that).
  Frankly I see this as being parallel to encouraging end-users to use NAT
in that the more they use it, the more they conserve address space. In
that respect, the more people rely on dynamic routing to permit more
flexible distribution of address space, the easier it is to manage address
space and the more they can conserve (and the more they avoid the concerns
driving HD Ratio).
  Regardless of the above, all of the references about the need for HD
Ratio relate to end-user address assignment issues and don't seem to be
relevant to allocating, or re-allocating (here we go with terminology
again) blocks of addresses by ISP's. Frankly, I can't see how it would be
relevant to that. I might be inclined to agree with the use of HD Ratio if
it only applies to end user implementation of address space and not to
address block assignment/allocation, and if I was convinced that the
mitigating issues addressed above do not relieve the concerns. Otherwise,
I'm, once again, concerned that this approach unnecessarily increases waste
and complexity and in doing so provides questionable relief.

Chuck Scott
cscott at gaslightmedia.com

On Tue, 10 Feb 2004 Michael.Dillon at radianz.com wrote:

> I've made some changes to the wording of the policy. First of all
> I've made the use of the HD Ratio optional. Secondly, I've decided
> to use the natural logarithm in the calculation because PERL has
> this and not the base 10 logarithm. The end result of the ratio
> calculation is identical, but now people will see that is clearly
> is easy to add the calculation to PERL IP address management
> systems. The Excel function LN(x) is the same as PERL's log(x).
> And lastly, I've pulled out the mention of reassignments since
> any definition of utilization belongs elsewhere and this was
> getting too close.
> 1. Anyone who has already been allocated 4096 IPv4 addresses or
>    more may choose to have additional requests for IPv4 addresses
>    evaluated using an HD (Host Density) Ratio calculation to determine 
>    sufficient utilization instead of a fixed percentage threshold.
> 2. All requests for additional IPv4 address space subject to the HD 
>    Ratio shall require the efficient utilization of the sum total of 
>    all existing allocations. The HD Ratio on the sum total of all 
>    existing allocations must be greater than or equal to .966.
> 3. In addition, the HD ratio of the most recent allocation must be 
>    greater than or equal to .930.
> 4. The HD ratio is calculated as log(utilized IPv4 addresses) divided
>    by log(total addresses in all previous allocations). In this formula, 
>    log refers to the natural logarithm.
> -------------------------------------------------------
> Michael Dillon
> Capacity Planning, Prescot St., London, UK
> Mobile: +44 7900 823 672    Internet: michael.dillon at radianz.com
> Phone: +44 20 7650 9493    Fax: +44 20 7650 9030

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