[arin-ppml] Draft Policy ARIN-2025-6: Fix formula in 6.5.2.1c

[Martin Hannigan]

I think it works mathematically? https://pastebin.com/r24VdGTy

Please spell out log_2 as "log base 2" or subscript 2 to avoid any
doubts. I don't see any reason why subscripts wouldn't work on the
ARIN website.

Why shift from linear to log?

Warm regards,

-M<




On Sat, Jul 12, 2025 at 7:09 AM William Herrin <bill at herrin.us> wrote:
>
> Hi folks,
>
> Just a reminder - the ARIN public policy process runs on positive
> consensus not silent assent. If you're okay with this policy draft as
> written, we need to hear you say it. If you agree there's a problem
> but want to see a different solution, we need to hear you say that
> too. If the advisory council hears nothing, we will eventually abandon
> the draft and the problematic section of the NRPM will persist until
> someone figures out how to abuse it.
>
> Regards,
> Bill Herrin
>
>
> On Wed, Jul 2, 2025 at 2:53 PM William Herrin <bill at herrin.us> wrote:
> > On Tue, Jul 1, 2025 at 11:34 AM ARIN <info at arin.net> wrote:
> > > Draft Policy ARIN-2025-6: Fix formula in 6.5.2.1c
> > >
> > > Problem Statement:
> > >
> > > Sections 6.5.2.1 explains the initial IPv6 ISP/LIR allocation in a way that is difficult to follow and the formula in section (c) does not match the remainder of the text.
> > >
> > > Policy Statement:
> > >
> > > In 6.5.2.1c, replace:
> > >
> > > "This calculation can be summarized as /N where N = P-(X+Y) and P is the organization’s Provider Allocation Unit X is a multiple of 4 greater than 4/3*serving sites and Y is a multiple of 4 greater than 4/3*end sites served by largest serving site."
> > >
> > > with:
> > >
> > > "This calculation can be summarized as /N where N = P-(X+Y) and P is the organization’s Provider Allocation Unit, X is a multiple of 4 greater than 4/3*log_2(serving sites) and Y is a multiple of 4 greater than 4/3*log_2(end sites served by largest serving site).
> >
> >
> > FYI, I'm the primary Advisory Council shepherd for this draft policy.
> > Here's some explanation:
> >
> > Section 6.5.2.1c holds the criteria for the _maximum_ initial IPv6
> > allocation for ISPs. They qualify for the number of IPv6 addresses
> > described here and may request that much or a smaller block. The
> > section is frankly hard to read. Here's what that part of the NRPM
> > currently says:
> >
> > "c. The maximum allowable allocation shall be the smallest
> > nibble-boundary aligned block that can provide an equally sized
> > nibble-boundary aligned block to each of the requesters serving sites
> > large enough to satisfy the needs of the requesters largest single
> > serving site using no more than 75% of the available addresses.
> > This calculation can be summarized as /N where N = P-(X+Y) and P is
> > the organization’s Provider Allocation Unit X is a multiple of 4
> > greater than 4/3*serving sites and Y is a multiple of 4 greater than
> > 4/3*end sites served by largest serving site.
> >
> > d. For purposes of the calculation in (c), an end site which can
> > justify more than a /48 under the end-user assignment criteria in
> > 6.5.8 shall count as the appropriate number of /48s that would be
> > assigned under that policy.
> >
> > e. For purposes of the calculation in (c), an LIR which has
> > subordinate LIRs shall make such reallocations according to the same
> > policies and criteria as ARIN. In such a case, the prefixes necessary
> > for such a reallocation should be treated as fully utilized in
> > determining the block sizing for the parent LIR. LIRs which do not
> > receive resources directly from ARIN will not be able to make such
> > reallocations to subordinate LIRs and subordinate LIRs which need more
> > than a /32 shall apply directly to ARIN."
> >
> >
> > Here's how ARIN staff explained the current implementation of NRPM 6.5.2.1c:
> >
> > "ARIN staff implements 6.5.2.1.c based on the text. The summarized
> > formula is overly complex and inaccurate for your typical IPv6
> > requestor. The text alone is more easily understood by customers and
> > implemented by ARIN staff.
> >
> > ARIN staff calculates Initial allocation sizes by verifying how many
> > serving sites the ISP has in the ARIN region, and how many customers
> > are served at the largest serving site. ARIN assumes each customer
> > will receive a /48 for simplicity and to promote IPv6 transition.
> >
> > Once the sites and customers are provided by the requestor, ARIN staff
> > confirms what size is justified at the largest serving site based on
> > the 75% rule. That size is applied to all sites, then checked against
> > the 75% rule for the overall allocation justified by the ISP. The ISP
> > can opt to request a smaller size. They are not required to request
> > the largest justified size, though it is recommended to avoid future
> > renumbering.
> >
> > For example:
> > An ISP has 7 sites and 30,000 customers at the largest site.
> >
> > ARIN assumes each of the 30,000 customers receives a /48. There are
> > only 4,096 /48s in a /36, so a /36 is too small. The next
> > nibble-boundary aligned subnet is a /32 which has 65,536 /48s. 30,000
> > is less than 75% of 65,536, so the ISP’s largest serving site
> > justifies a /32.
> >
> > Thus, each of the 7 sites receives a /32. The next nibble-boundary
> > after /32 is a /28. There are 16 /32s in a /28. 7 /32s of the total 16
> > /32s is less than 75%, so the organization justifies a total
> > allocation of a /28. 7 /32s for immediate allocation to each of their
> > 7 sites and 9 additional /32s for future growth.
> >
> > Example 2:
> >
> > Building off the previous example, if the largest serving site had
> > 60,000 customers, then a /32 would be too small. 60,000 is greater
> > than 75% of the available 65,536 /48s in a /32. The next
> > nibble-boundary aligned subnet is a /28, so the largest serving site
> > justifies a /28. Thus, each of the 7 sites receives a /28, so the
> > organization justifies a /24."
>
>
>
>
> --
> William Herrin
> bill at herrin.us
> https://bill.herrin.us/
> _______________________________________________
> ARIN-PPML
> You are receiving this message because you are subscribed to
> the ARIN Public Policy Mailing List (ARIN-PPML at arin.net).
> Unsubscribe or manage your mailing list subscription at:
> https://lists.arin.net/mailman/listinfo/arin-ppml
> Please contact info at arin.net if you experience any issues.