[ppml] Policy Proposal 2005-5: IPv6 HD ratio

Howard, W. Lee L.Howard at stanleyassociates.com
Thu May 26 12:58:40 EDT 2005

> -----Original Message-----
> From: owner-ppml at arin.net [mailto:owner-ppml at arin.net] On 
> Behalf Of Kevin Loch
> Sent: Wednesday, May 25, 2005 2:27 PM
> To: ppml at arin.net
> Subject: Re: [ppml] Policy Proposal 2005-5: IPv6 HD ratio
> Edward Lewis wrote:
>  > 1) Will the tightening of the HD-ratio mean that ARIN will 
> have to  > turn around addressing requests faster?  I am not 
> saying there is a  > problem now, but raising the HD-ration 
> means that I would have to  > delay asking for new space 
> until I passed the 0.8 threshold and until  > I hit the new 
> one.  Delaying here means losing lead time from request  > to 
> need to use.
> With HD=0.94 and an allocation of /32 the threshold would be 
> about 50%.  You would have about 32,000 customer assignments 
> left at that point.  Lead time should not be an issue.

Since the HD Ratio purportedly takes network hierarchy into
account, let's do the same while discussing it.  You might 
have 32,768 /48s remaining, but not necessarily contiguous or
in the part of the network where they're needed.  Carve your
/32 into 16 regional networks, (let's say British Columbia, 
Northwest US, and Central-West US are three regions) each of
which has 1/16 of the /32, or a /36.  Divvy the region into
metro areas of /39 each, and you only have 512 /48s in each
area.  It's easy to imagine running out of space in one area
while not meeting the HD Ratio.

Of course, cleverer folk among us will realize that you have
foolishly squandered your addresses by assigning the same size
block to every network.  What you should have done is to assign
a /39 to British Columbia (sorry, guys) and a /35 to San 
Francisco.  Even then, SF only have 8192 /48s, while BC has 
512; it still might not be enough.  Of course, since you can't 
delegate those ugly, off-byte allocation sizes to regional 
servers, you'll have to delegate multiple /40s.

Or you shouldn't have assigned so many /48s to end users who 
didn't need them, nevermind what the policies say.

>  > 2) Will the tightening of the HD-ratio mean a 
> significantly more dense  > use of the space resulting in 
> more incidents of end-user renumbering  > if their needs grow?
> The threshold appplies to total number of /48's.  The choice 
> of dense or sparse assignment policy does not affect the threshold.

If you require a higher host density, you have fewer reservations
of adjacent blocks when you go back for more.  You may have 
reserved the next /48 for your first customer, but if you have to
exceed 50% assignment, that reservation will have to be used before
you can request more space.  If Customer #1 outgrows their /48, they
will have to renumber to a different /47, or have two discontiguous

> - Kevin

If we must have an HD Ratio, I'd raise it.


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