Policy Proposal 2001-4

Member Services memsvcs at arin.net
Wed Sep 26 11:24:08 EDT 2001

ARIN welcomes feedback and discussion about the following policy
proposal in the weeks leading to the ARIN Public Policy and Members
meetings in Miami, scheduled for October 28 - 31, 2001.  All feedback
received on the mailing lists about this policy proposal will be
included in the discussions that will take place in Miami.

  The three RIRs have compiled the proposal document provided below 
  using feedback received from the RIR communities since the publishing
  of the provisional IPv6 document in 1999.  In the interest of 
  maintaining global IPv6 policies, the IPv6 policy discussion in the 
  ARIN region will be held in conjunction with discussions taking place 
  in the APNIC and RIPE NCC regions.

  When formulating this framework document, the RIRs took the following 
  feedback into account:

  * The allocation criteria should be such that it is easy to obtain 
    IPv6 address space.

  * The size of the initial allocation should be large enough to allow 
    flexibility in addressing infrastructure and customer sites.

  This results in the following proposed IPv6 allocation criteria 

  1. recognize existing infrastructure (both IPv4 and IPv6) where it
     exists and calculate IPv6 address needs based on existing networks.

  2. apply the slow start mechanism only for 'IPv6 only' networks 
     without existing IPv4 infrastructure

  3. reduce the minimum allocation size for those IPv6 only networks
     (unless larger requirements are shown)

  4. measure the utilization rate with the HD ratio rather than

  5. make subsequent allocations when the HD ratio is reached

  The full text of the proposal document is provided below.

This policy proposal discussion will take place on the IPv6 working group
mailing list (v6wg at arin.net).  Subscription information is available at

Richard Jimmerson
Director of Operations
American Registry for Internet Numbers

*** Proposal Document ***

1. Abstract

This document provides a set of proposed policies for the management
of IPv6 address space, specifically concerning the allocation of
address space allocated by Regional Internet Registries (RIRs) to
organisations operating IPv6 networks.

2. Overview

Under the current system of management of global IP address space,
Regional Internet Registries (RIRs) are responsible for allocation of 
address space to organisations within their respective geographic 

In 1999, the RIRs APNIC, ARIN and RIPE NCC published a provisional policy 
document for IPv6, which has been in operation since then.  Since 2000, 
this document has been under review and discussion, and through this 
process many issues have been raised.

It is the aim of this document to propose a new policy framework for
IPv6 address space management which takes into account the operational
experience of the past 3 years, and addresses most if not all of the
major issues raised through the open review process.

This document does not attempt to provide details of policy
implementation, procedures or documentation; nor does it document requirements 
for management of address space which is allocated.  These policies can be 
established globally or regionally as appropriate, based on global 
consensus regarding the fundamental principles described here.

3. Address Space Requirement for Initial Allocation

It is proposed to recognise existing network infrastructure and
address utilisation (both IPv4 and IPv6). New IPv6 address needs are
then based on these existing networks.
In assessing a request for an initial allocation, there are 3 possible 
cases to consider: 

3.1. the requesting organisation has an existing IPv4 network which
     will be addressed by the new IPv6 allocation

3.2. the requesting organisation has an existing IPv6 network

3.3. the requesting organisation has no network at all

3.1. Case 1 - Existing IPv4 services

Where IPv6 address space is requested for addressing an existing IPv4
network, the address requirement is determined according to the
structure and customer base of the existing IPv4 network. This only
relates to the part of the network that will be migrated to IPv6.

Additional policies may require the return of IPv4 address space to
the RIR or upstream ISP, in the case the existing network is
renumbered to the new IPv6 space in future.

3.2. Case 2 - Existing IPv6 services

Where an IPv6 allocation is requested by an organisation to address
infrastructure which is already addressed by IPv6 addresses from an
upstream provider (or from the 6BONE), the address requirement is
determined from the number of site addresses assigned by the
organisation (as registered in the appropriate whois database).

Where existing address space is no longer used, it must be returned.

3.3. Case 3 - No existing IPv4 or IPv6 services

Where IPv6 address space is required by an organisation which has no
existing infrastructure, the address requirement will be assessed
according to network architecture plans and other documentation
provided to the RIR within the request process.  Such documentation be
thorough enough to satisfy the RIR that the network deployment is
genuine, however the specific details of documentation requirements
will be defined separately.

4. Size of Initial Allocation

The amount of addresses allocated to an existing network, will be
determined based on the existing infrastructure and address
utilisation of that network.

For new networks without existing infrastructure, it is proposed to
establish a minimum allocation for IPv6 address space. It is suggested
to keep the size of the initial allocation relatively small (a /35 or
smaller) and to determine the size of subsequent allocations based on
the utilisation rate of the initial allocation (this is called slow
start mechanism). This will allow easy access to IPv6 allocations for
newcomers. At the same time possible wastage of address space and 
routing table growth will be limited.

5. Qualification for Subsequent Allocation

An organisation which has already received address space from an RIR may 
receive a subsequent allocation providing that its existing address space 
is utilised in accordance with these policies.  As explained below, the 
HD-Ratio will be used to measure utilisation of the existing address

An organisation which is deploying substantial new network infrastructure 
may receive a subsequent allocation before it has reached the required 
utilisation threshold, providing that the address requirement would 
immediate cause the organisation to exceed the utilisation threshold.  In 
such cases, the new network infrastructure will be examined by the RIR as 
if it is a request for a new network, and the RIR may require the same 
level of documentation detail, in order to approve the allocation.

6. Address Space Requirement for Subsequent Allocation

For subsequent allocations, the RIR should assess the address requirement 
according to the organisation's history of IP address usage, as well as
stated requirements for future development.

In general, the RIR should provide address space for a fixed time
period of 2 years.

The above recommendation should be followed in cases where the
organisation concerned has complied with all relevant address management policies.  In 
other cases, the RIR may allocate for a shorter future timeframe, and 
require that identified problems be rectified before larger allocations
are made.

7. IPv6 Utilisation Metric: the HD-Ratio

In IPv4, currently, a "utilisation threshold" of 80% is applied
consistently in determining whether an IPv4 address pool is to be
considered utilised, regardless of the size of that block. 
Consequently, an organisation which holds IP address space may
not receive additional addresses until it has utilised at least 80% of
the address space held.

For IPv6 is it proposed to assess utilisation according to the "HD-Ratio" 
rather than by a simple percentage.  The HD-Ratio was proposed by Durand
"draft-durand-huitema-h-density-ratio-01.txt" (an adaptation of the 
original H-Ratio defined by Huitema in RFC-1715).

Using the HD-ratio we can establish a utilisation metric which allows 
percentage utilisation to decrease as the address space grows large.  This 
is appropriate for management of the much larger blocks of address space 
under IPv6, and the likelihood of complex routing and allocation 
hierarchies within those address blocks.

More details about the HD ratio can be found in Appendix A.

Appendix A:

In the general case, where individual objects are allocated out of an 
arbitrary address space, the HD-Ratio is calculated as follows:

               log(number of allocated objects)
    HD = --------------------------------------------
          log(maximum number of allocatable objects)

Where the objects being allocated are IPv6 site addresses (/48s) assigned 
from an IPv6 prefix of length P, we can restate this formula as follows 
(where A is the number of /48 prefixes actually assigned):

                log(A)             log(A)

In other words, the utilisation threshold T, expressed as a number of 
individual /48 prefixes to be allocated from IPv6 prefix P, can be 
calculated as:

    T =   2

In accordance with the recommendations of 
draft-durand-huitema-h-density-ratio-01.txt, it is proposed in this draft 
to adopt an HD-Ratio of 0.8 as the utilisation threshold for IPv6 address 
space allocations.

The following table provides equivalent absolute and percentage
address utilisation figures for IPv6 prefixes, corresponding to an
HD-Ratio of 0.8

    P    48-P          Total /48s        Threshold      Util%

   48       0                   1                1     100.0%
   47       1                   2                2      87.1%
   46       2                   4                3      75.8%
   45       3                   8                5      66.0%
   44       4                  16                9      57.4%
   43       5                  32               16      50.0%
   42       6                  64               28      43.5%
   41       7                 128               49      37.9%
   40       8                 256               84      33.0%
   39       9                 512              147      28.7%
   38      10                1024              256      25.0%
   37      11                2048              446      21.8%
   36      12                4096              776      18.9%
   35      13                8192             1351      16.5%
   34      14               16384             2353      14.4%
   33      15               32768             4096      12.5%
   32      16               65536             7132      10.9%
   31      17              131072            12417       9.5%
   30      18              262144            21619       8.2%
   29      19              524288            37641       7.2%
   28      20             1048576            65536       6.3%
   27      21             2097152           114105       5.4%
   26      22             4194304           198668       4.7%
   25      23             8388608           345901       4.1%
   24      24            16777216           602249       3.6%
   23      25            33554432          1048576       3.1%
   22      26            67108864          1825677       2.7%
   21      27           134217728          3178688       2.4%
   20      28           268435456          5534417       2.1%
   19      29           536870912          9635980       1.8%
   18      30          1073741824         16777216       1.6%
   17      31          2147483648         29210830       1.4%
   16      32          4294967296         50859008       1.2%
   15      33          8589934592         88550677       1.0%
   14      34         17179869184        154175683       0.9%
   13      35         34359738368        268435456       0.8%
   12      36         68719476736        467373275       0.7%
   11      37        137438953472        813744135       0.6%
   10      38        274877906944       1416810831       0.5%
   9       39        549755813888       2466810934       0.4%
   8       40       1099511627776       4294967296       0.4%
   7       41       2199023255552       7477972398       0.3%
   6       42       4398046511104      13019906166       0.3%
   5       43       8796093022208      22668973294       0.3%
   4       44      17592186044416      39468974941       0.2%
   3       45      35184372088832      68719476736       0.2%
   2       46      70368744177664     119647558364       0.2%
   1       47     140737488355328     208318498661       0.1%
   0       48     281474976710656     362703572709       0.1%

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