Policy 2008-5: Dedicated IPv4 block to facilitate IPv6 Deployment [Archived]


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Status: Adopted - NRPM Section 4.10

Tracking Information

Discussion Tracking

Mailing List:

Formal introduction on PPML on 6 June 2008

Staff Assessment - 8 October 2008
Last Call - 22 October thru 7 November 2008
Revised/Reposted to Last Call - 25 November thru 15 December 2008Public Policy Mailing List

ARIN Public Policy Meeting:

Nassau, Bahamas

ARIN Advisory Council:

AC Shepherds:
Owen DeLong and Matt Pounsett

19 June 2008
17 July 2008
21 August 2008
18 September 2008
17 October 2008
20 November 2008
18 December 2008

ARIN Board of Trustees:

5 January 2009


Previous version(s)


1 April 2009


Alain Durand

Policy Proposal 2008-5
Dedicated IPv4 block to facilitate IPv6 deployment

Author: Alain Durand

Date: 25 November 2008

Proposal type: New

Policy term: Permanent

Policy statement:

When ARIN receives its last /8 IPv4 allocation from IANA, a contiguous /10 IPv4 block will be set aside and dedicated to facilitate IPv6 deployment. Allocations and assignments from this block must be justified by immediate IPv6 deployment requirements. Examples of such needs include: IPv4 addresses for key dual stack DNS servers, and NAT-PT or NAT464 translators. ARIN staff will use their discretion when evaluating justifications.

This block will be subject to a minimum size allocation of /28 and a maximum size allocation of /24. ARIN should use sparse allocation when possible within that /10 block.

In order to receive an allocation or assignment under this policy:

  1. the applicant may not have received resources under this policy in the preceding six months;
  2. previous allocations/assignments under this policy must continue to meet the justification requirements of this policy;
  3. previous allocations/assignments under this policy must meet the utilization requirements of end user assignments;
  4. the applicant must demonstrate that no other allocations or assignments will meet this need;
  5. on subsequent allocation under this policy, ARIN staff may require applicants to renumber out of previously allocated / assigned space under this policy in order to minimize non-contiguous allocations.

Rationale for reserving IPv4 space:

This policy provides predictability on how the end game of IPv4 is going to be played after IANA completion. It will facilitate IPv6 deployment by ensuring that some small chunks of IPv4 space will remain available for a long time to ease the co-existence of IPv4 & IPv6.

Rationale for reserving a contiguous /10

This is a balance between setting aside too much space and not having enough to facilitate IPv6 deployment for many years. Out of the last /8, that would leave the equivalent of 3 /10 to ARIN either for business as usual or for other policies in the spirit of this one.

A /10 represents 4,194,304 IP addresses, If all of them were to be used in NAT-PT or NAT464 type devices with a consolidation factor of 100 users behind each IP address, that would represent about 400 million users.

Most networks today filter IPv4 announcements more specific than /24.
This policy creates allocations & assignment prefixes as long as /28.
Allocating out of a contiguous block will mitigate the impact of this policy on filter lists.

Rationale for minimum size allocation of /28

This minimum size allocation will put a cap at 250k additional entries in the global IPv4 routing table.

Rationale for maximum size allocation of /24 and for the 6 month delay between allocations

This maximum allocation size coupled with the requirement of a 6 months delay between allocations will prevent hoarding and make sure this pool will last several years.

Rationale for forced renumbering for further allocation

The minimum allocation size of /28 may create a huge increase in the
IPv4 routing table size. Forcing renumbering for subsequent allocations under this policy will somehow limit the growth of the routing table size by enabling the announcement of aggregated space. It is expected that the savings in routing table entries will outweigh the pain of forced renumbering.

However, renumbering is never an easy task, so it should only be considered as last resort. it is expected that sparse allocation techniques will prevent the need of force renumbering for a fairly long time.

Note: This policy proposal hints that the /10 should come out of the last /8 received by ARIN from IANA. However, it does not say so explicitly, leaving the final decision up to the ARIN staff.

Timetable for implementation:

As soon as ARIN gets its last /8 allocation from IANA.


Here in the Vault, information is published in its final form and then not changed or updated. As a result, some content, specifically links to other pages and other references, may be out-of-date or no longer available.