Policy 2005-8: Proposal to amend ARIN IPv6 assignment and utilisation requirement

Status: Adopted - NRPM Sections 6.1.1, 6.2.7, 6.5.1-5, 6.7, and 6.8.3

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Formal introduction on PPML on 1 September 2005

To be revised - 31 October 2005
Revised -13 March 2006
Last call from 14 April through 28 April 2006

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16 February 2006
23 March 2006
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4 May 2006
25 May 2006
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9 May 2006
27 July 2006


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30 August 2006


Thomas Narten and Lea Roberts

Policy Proposal 2005-8, version 2:

Proposal to amend ARIN IPv6 assignment and utilisation requirement

This proposal would amend the IPv6 address allocation policies (ARIN's NRPM, section 6) regarding the definition of the default size of End Site assignments and the threshold value for End Site allocation efficiency, no longer assuming the fixed values for End Site assignments established by RFC3177. Many references to "/48" will need to be replaced by "End Site assignment".

for example, section should be replaced as follows: Assignment address space size

End Users are assigned an End Site assignment from their LIR or ISP. The exact size of the assignment is a local decision for the LIR or ISP to make, using a minimum value of a /64 (when only one subnet is anticipated for the End Site) up to the normal maximum of /48, except in cases of extra large end sites where a larger assignment can be justified.

The following guidelines may be useful (but they are only guidelines):

- /64 when it is known that one and only one subnet is needed

- /56 for small sites, those expected to need only a few subnets over the next 5 years.

- /48 for larger sites

For end sites to whom reverse DNS will be delegated, the LIR/ISP should consider making an assignment on a nibble (4-bit) boundary to simplify reverse lookup delegation.

RIRs/NIRs are not concerned about which address size an LIR/ISP actually assigns. Accordingly, RIRs/NIRs will not request the detailed information on IPv6 user networks as they did in IPv4, except for the cases described in Section 6.4.4 and for the purposes of measuring utilization as defined in this document.

also, section 6.9 will need to be replaced:

6.9. IPv6 Reassignments policy

The size of IPv6 address assignments to End Sites is to be determined by the ISP/LIR.

ISPs and LIRs may choose whether to make changes to their procedures for assigning address blocks to End Sites. The threshold End Site allocation efficiency level is between 20% to 50% for most ISPs and LIRs when based on a 0.94 HD Ratio. ISPs and LIRs will need to operate address plans according to this target level of End Site allocation efficiency.

there's a need to change ARIN NRPM IPv6 Utilization:

The ARIN NRPM Section 6.7 will be amended so its IPv6 allocation utilization criteria will reflect the use of a /56 as the unit quantity in the calculation of the ISP or LIR's end site allocation efficiency.


The current IPv6 Address Allocation and Assignment Policy (section 6 of ARIN's NRPM) indicates that end sites should be allocated a /48 as a uniform allocation unit if using more than one host or one subnet.

This proposal alters the existing policy regarding LIR and ISP assignments to End Sites to allow the unit of assignment to be an LIR or ISP decision.

In assessing the address utilization efficiency for ISPs or LIRs, the definition of an End Site for the purposes of the calculation of ISP or LIR End Site allocation efficiency, is to be made according to a /56 size.

This measure, if undertaken generally by all RIRs, in conjunction with the further measures undertaken by the addressing community regarding increasing the HD ratio to 0.94, would increase the anticipated useful lifetime of IPv6 to encompass a period in excess of 100 years, in which case no further allocation policy changes would be anticipated.

A more detailed rationale is available in Geoff Huston's presentation on the subject, at RIPE 50, which can be found at:



Appendix A. References
This material is not formally part of the Policy Proposal. It is included here for informational purposes.

1. The IPv6 Address Plan - Geoff Huston

2. Internet Draft: Issues Related to the Management of IPv6 Address Space - Thomas Narten http://tools.ietf.org/wg/ipv6/draft-narten-iana-rir-ipv6-considerations-00.txt

[unfortunately, the ID expired, so use the URL:


3. Internet Draft: IPv6 Address Allocation to End Sites - Thomas Narten, Geoff Huston & Lea Roberts http://www.ietf.org/internet-drafts/draft-narten-ipv6-3177bis-48boundary-01.txt