[arin-ppml] Board adopts 2008-5: Dedicated IPv4 block to facilitate IPv6 Deployment

Member Services info at arin.net
Thu Jan 8 16:01:38 EST 2009

On 5 January 2009 the ARIN Board of Trustees adopted the following
policy proposal:

     2008-5: Dedicated IPv4 block to facilitate IPv6 Deployment

2008-5 will be implemented no later than 31 May 2009.

The policy proposal text is provided below and is also available at:


Member Services Department
American Registry for Internet Numbers (ARIN)

## * ##

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

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

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

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.

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