Summary

  • Thomas Narten and Lea Roberts's 2005 proposal replaced a presumed uniform IPv6 /48 with provider judgment: normally /64 for one subnet, /56 for a small site and /48 for a larger one.
  • ARIN's adopted Policy 2005-8 left the actual end-site block to the ISP or LIR but counted a /56 as the unit for the provider's IPv6 utilization calculation. The policy record lists implementation on 30 August 2006.

The number that a customer receives and the number by which a registry measures the provider are easy to mistake for the same thing. Thomas Narten and Lea Roberts built a policy around separating them. One line hands the address-plan choice to the ISP. Another keeps ARIN's ruler on the desk.

Their first proposal, posted in August 2005, was blunt about the old default. A /48 gives a site 65,536 /64 subnets; a /56 gives it 256. The authors wanted /56 to be the ordinary case for homes, small offices and other modest sites, with /48 for a site needing more than 255 subnets. Those figures describe address capacity in the proposal. They are no survey of what homes actually used.

The later Policy 2005-8 text moved the decision further toward the operator. It says the exact end-site assignment is a local LIR or ISP decision. It gives /64, /56 and /48 as guidelines and allows a larger block when justified. That puts the argument over a customer's future subnets where it can be tested against a customer's network plan, rather than turning every household into a fixed registry row.

The registry did not put away its calculator. The same text says ARIN's IPv6 utilization criteria will use a /56 as the unit quantity for calculating an ISP or LIR's end-site allocation efficiency. A provider may choose a different customer assignment while ARIN uses the standard unit to decide how efficiently the provider's larger allocation is being consumed. The local choice and the institutional measurement coexist; that is the policy's hinge.

At ARIN XVII in April 2006, Roberts presented the proposal and asked whether policy should reward reasonable assignments or discourage very large ones. The room disputed what “reasonable” meant. Some speakers wanted a clear nudge against handing out /48s simply because it was easy. Others worried that tighter direction would cost IPv6 its simple network design, or that Japan would resist a global version. Another view left the choice with provider and customer under broad guidance. The meeting recorded consensus to move the proposal forward.

ARIN's tracking record marks Policy 2005-8 adopted and implemented on 30 August 2006. The ARIN XVIII members report separately records Board ratification. Neither record says every provider switched its households to /56, or measures how many addresses the policy saved. The result on paper is narrower and sharper: the provider owns the assignment decision; ARIN owns the denominator used to judge that provider's utilization.

That arrangement is an institutional compromise with teeth. A registry can stop prescribing every customer block and still influence the provider through the accounting rule for its next allocation. Narten's proposal did not abolish the ruler. It moved the hand that chooses the customer's block.

Sources: ARIN initial proposal, 29 August 2005; ARIN Policy 2005-8 and history; ARIN XVII meeting notes; ARIN XVIII members report.