[arin-ppml] 2010-8: Rework of IPv6 assignment criteria

David Farmer farmer at umn.edu
Tue Sep 14 03:52:58 EDT 2010

Based on feedback and off-line discussion over the past few weeks I have 
made a number of updates to 2010-8;

These include:
- Changing from HD-Ratio to a 75% utilization threshold
- Major rewrites of the initial assignment size and subsequent 
assignment size sections
- Associated updates to the Rationale


1. Policy Proposal Name: Rework of IPv6 assignment criteria
2. Proposal Originator
name: David Farmer
email: farmer at umn.edu
telephone: 612-812-9952
organization: University of Minnesota
3. Proposal Version: 6.0
4. Date: 9/14/2010
5. Proposal type: modify
new, modify, or delete.
6. Policy term: Permanent
temporary, permanent, or renewable.
7. Policy statement:

Replace section 6.5.8 as follows;

6.5.8. Direct assignments from ARIN to end-user organizations Initial Assignment Criteria

Organizations may justify an initial assignment for addressing devices 
directly attached to their own network infrastructure, with an intent 
for the addresses to begin operational use within 12 months, by meeting 
one of the following criteria:

a. Having a previously justified IPv4 end-user assignment from ARIN or 
one of its predecessor registries, or;

b. Currently being IPv6 Multihomed or immediately becoming IPv6 
Multihomed and using an assigned valid global AS number, or;

c. By having a network consisting of a total of 1000 or more hosts, or;

d. By providing a reasonable technical justification indicating why IPv6 
addresses from an ISP or other LIR are unsuitable.

Examples of justifications for why addresses from an ISP or other LIR 
may be unsuitable include, but are not limited to:

• An organization that operates infrastructure critical to life safety 
or the functioning of society can justify the need for an assignment 
based on the fact that renumbering would have a broader than expected 
impact than simply the number of hosts directly involved. These would 
include: hospitals, fire fighting, police, emergency response, power or 
energy distribution, water or waste treatment, traffic management and 
control, etc…
• Regardless of the number of hosts directly involved, an organization 
can justify the need for an assignment if renumbering would affect 1000 
or more individuals either internal or external to the organization.
• An organization with a network not connected to the Internet can 
justify the need for an assignment by documenting a need for guaranteed 
uniqueness, beyond the statistical uniqueness provided by ULA (see RFC 
• An organization with a network not connected to the Internet, such as 
a VPN overlay network, can justify the need for an assignment if they 
require authoritative delegation of reverse DNS. Initial assignment size

Organizations that meet at least one of the initial assignment criteria 
above are eligible to receive an initial assignment of /48. Requests for 
larger initial assignments, reasonably justified with supporting 
documentation, will be evaluated based on the number of sites in an 
organization’s network and the number of subnets needed to support any 
extra-large sites defined below. /48 per site

An organization may request up to a /48 for each site in its network, 
including any sites that will be operational within 12 months.  Where a 
site is a discrete location that is part of an organization’s network. 
In the case of a multi-tenant building, each organization located at the 
site may separately justify a /48 for its network at the site.

A campus with multiple buildings may be considered as one or multiple 
sites, based on the implementation of its network infrastructure.  For a 
campus to be considered as multiple sites, reasonable technical 
documentation must be submitted describing how the network 
infrastructure is implemented in a manner equivalent to multiple sites. Extra-large site

In rare cases, an organization may request more than a /48 for an 
extra-large site which requires more than 16,384 /64 subnets.  In such a 
case, a detailed subnet plan must be submitted for each extra-large site 
in an organization’s network.  An extra-large site will receive the 
smallest prefix such that the total subnet utilization justified does 
not exceed 25%.  Each extra-large site will be counted as an equivalent 
number of /48 sites. Larger initial assignments

Larger initial assignments will be determined based on the number of 
sites justified above, aligned on a nibble boundary using the following 

More than 1 but less than or equal to 12 sites justified, receives a /44 
More than 12 but less than or equal to 192 /sites justified, receives a 
/40 assignment;
More than 192 but less than or equal to 3,072 sites justified, receives 
a /36 assignment;
More than 3,072 sites justified, receives a /32 assignment or larger.

In cases where more than 3,072 sites are justified, an assignment of the 
smallest prefix, aligned on a nibble boundary, will be made such that 
the total utilization based on the number of sites justified above does 
not exceed 75%. Subsequent assignments

Requests for subsequent assignments with supporting documentation will 
be evaluated based on the same criteria as an initial assignment under with the following modifications:

a. A subsequent assignment is justified when the total utilization based 
on the number of sites justified exceeds 75% across all of an 
organization’s assignments.  Except, if the organization received an 
assignment per section 6.11 IPv6 Multiple Discrete Networks, such 
assignments will be evaluated as if it were to a separate organization.

Organizations may have multiple separate assignments that should be 
considered in total, due to previous subsequent assignments made per 
clause below, or through Mergers and Acquisitions in section 8.2.

b. When possible subsequent assignments will result it the expansion of 
an existing assignment by one or more nibble boundaries as justified.

c. If it is not possible to expand an existing assignment, or to expand 
it adequately to meet the justified need, then a separate new assignment 
will be made of a size as justified. Consolidation and return of separate assignments

Organizations with multiple separate assignments should consolidate into 
a single aggregate, if feasible. If an organization stops using one or 
more of its separate assignments, any unused assignments must be 
returned to ARIN.


This proposal provides a complete rework of the IPv6 end-user assignment 
criteria, removing the dependency on IPv4 policy, providing clear 
guidance in requesting larger initial assignments, and eliminating 
HD-Ratio as criteria for evaluating end-user assignments.

The HD-Ratio is replaced with a simplified 75% utilization threshold 
based on nibble boundaries for end-user assignments.   This threshold is 
somewhat more restrictive for larger assignments, while slightly less 
restrictive for the smaller /44 assignments, than the HD-Ratio. 
However, in both cases it is much easier for an end-user to understand 
the policy criteria that applies to them.

The following general concepts are included:

• Previously justified IPv4 resources may be used to justify the need 
for IPv6 resources
• Internet multihoming is sufficient justification for an IPv6 end-user 
assignment in and of itself
• Networks with more than 1000 hosts have a justified need for IPv6 
resources; as is the case in current policy, it is just more clearly 
stated without relying on a reference to, and the consequences of, IPv4 
• Other end-users must justify why an ISP or LIR assignment is not 
sufficient for their needs
• Organizations with multiple sites may receive a /48 for each site in 
their network
• A campus with multiple buildings may be considered as one or multiple 
sites, based on the implementation of its network infrastructure
• Reservations are no longer necessary as ARIN has committed to sparse 
assignment for IPv6
• Providing sufficiently large initial assignments based on nibble 
boundaries along with sparse assignments will reduce route table growth 
caused solely by subsequent assignments

The 25% subnet utilization for an extra-large site is proposed as the 
threshold for a larger prefix in order to allow an extra-large site 
enough room to create an organized subnet plan.  Requiring denser usage 
would make it almost impossible for an extra-large site to maintain any 
kind of organized subnet plan.  Furthermore, even at 25% utilization, 
more than 16,384 subnets are required to justify more than a /48 for a 
site.  Few, if any, sites can actually meet or exceed this threshold.

The ARIN Board of Trusties should consider incentives that provide 
additional motivation for end-users to consolidate into a single 
aggregate per section of this policy.

Timetable for implementation: Immediate

David Farmer               Email:farmer at umn.edu
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota	
2218 University Ave SE	    Phone: 612-626-0815
Minneapolis, MN 55414-3029   Cell: 612-812-9952

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