[sig-policy] prop-090-v002: Optimizing IPv6 allocation strategies
Dear SIG members,
Version 2 of the proposal, 'Optimizing IPv6 allocation strategies',
has been sent to the Policy SIG for review. It will be presented at
the Policy SIG at APNIC 31 in Hong Kong SAR, China, 21-25 February 2011.
Changes in version 2:
- In section 3, the status of the proposal in the ARIN region has
- The calculation for probable impact over 50 years in section 5,
"Disadvantages", has been changed from 99.62% to 99.54%.
We invite you to review and comment on the proposal on the mailing list
before the meeting.
The comment period on the mailing list before an APNIC meeting is an
important part of the policy development process. We encourage you to
express your views on the proposal:
- Do you support or oppose this proposal?
- Does this proposal solve a problem you are experiencing? If
so, tell the community about your situation.
- Do you see any disadvantages in this proposal?
- Is there anything in the proposal that is not clear?
- What changes could be made to this proposal to make it more
Information about this and other policy proposals is available from:
Gaurab, Ching-Heng, and Terence
prop-090-v002: Optimizing IPv6 Allocation Strategies
Author: Owen DeLong
Date: 18 February 2011
This is a proposal to change how the size of IPv6 allocations and end
site assignments are determined, allowing more room for LIRs to grow
within their allocation, while also preventing excessive address
consumption. The proposal also assists to prevent potential human errors
in configuration that can be caused by the current IPv6 policies, which
allow allocations and assignments to be made on non-nibble boundaries.
2. Summary of the current problem
2.1 Many ISPs expect to make all of their users fit within a /32 IPv6
This assumption has led to such problems as end user customers
receiving single /64s, minimal /60s, or even /56s. If the practice
of unnecessarily limited address spaces becomes widespread, vendors
will not produce the innovations that are possible in home
networking with larger address spaces. Just as NAT has delayed or
prevented many forms of innovation in IPv4, small customer
assignment sizes could seriously reduce innovation in IPv6.
If this proposed policy were to be implemented, in 50
years, the projected IPv6 free pool would be 99.54% of total
IPv6 space vs 99.9975% if the current policy were still in place
at that time. Given the small amount of extra IPv6 addresses that
would be consumed by implementation of this proposed policy, it
would be a shame for innovation to be stifled by continuing the
2.2 Mistakes are made when calculating end addresses for non-nibble
boundary allocations and assignments
In IPv6, non-nibble boundary prefixes can lead to human error in
calculating the end address of the prefix. For example, if a network
The LIR would need to calculate that the end address of that /30 was
However, even experienced engineers can make mistakes when making
such calculations. In fact, to clarify the problem, as I was
writing the above example, I initially made the mistake of
calculating the end of the range as
When mistakes like this are made in routers, it causes outages.
2.3 If /32s continue to be the default allocation size, it will also
eventually lead to unnecessary disaggregation and larger
2.4 The HD Ratio is confusing to many ISPs and misunderstood by many in
Therefore, this proposal replaces the HD ratio with simple ratios
for utilization thresholds and reduces the frequency with which
utilization thresholds would need to be calculated.
3. Situation in other RIRs
Draft Policy ARIN-2011-3, "Better IPv6 Allocations for ISPs",
is currently under discussion and will be presented at ARIN XXVII
The author intends to submit a similar proposal to LACNIC and AfriNIC.
As RIPE NCC seems to be currently issuing generous allocations, the
author currently has no intention of submitting this proposal to
RIPE. However, the author may eventually submit a proposal to RIPE
to address the problem of non-nibble boundary allocations.
This is a proposal to amend the IPv6 policy to:
4.1 Add the following definitions:
Serving site: A location where an ISP terminates or aggregates
customer connections, including, but not limited to
Points of Presence (POPs), Datacenters, Central or
Local switching offices or regional or local
Provider The prefix of the smallest IPv6 block a given ISP
assignment assigns to end sites.
Nibble A network mask which aligns on a 4-bit boundary.
boundary: This means that the prefix length must be divisible
by 4. For example, /24, /28, /32, and /48 are all
aligned on a nibble boundary while /22, /26, /29,
/30, and /47 are not.
4.2 Redefine the following terms:
End site: A single structure or service delivery address, or
a single tenant within a multi-tenant structure
- The aim of this more generous interpretation of end
site to provide a clear definition which is easily
understood and provides maximum flexibility for
service providers to meet the needs of their
Utilized: (i) A provider assignment unit shall be considered
fully utilized when it is assigned to an
(ii) The utilization percentage of a block at the LIR
level is calculated as the fraction of total
provider assignment units which have been assigned
to end sites.
4.3 Make all allocations and assignments on nibble boundaries
Removing the ability to make delegations on non-nibble boundaries
makes it easier for end addresses of IPv6 blocks to be calculated.
For example, if the next allocation one size larger than /32 is /28,
then, 2001:0db0::/28 has an end address of:
Allocating and assigning on nibble boundaries also makes DNS
4.4 Change the size of initial allocations to LIRs according to the
4.4.1 The minimum allocation size for an LIR shall be a /32, unless
the LIR specifically requests a /36.
4.4.2 The maximum allocation unit shall be the smallest block which:
- Is nibble-boundary aligned
- Permits the largest serving site to be assigned a large
enough block to allow <=0.75 (75%) utilization
- Can provide an equal-sized block to each serving site
- Permits each serving site's block to be nibble-boundary
This can be summarized as /N where:
N = 48-(X+Y) where:
X is a multiple of 4 such that 2^X is greater than
Y is a multiple of 4 such that 2^Y is greater than
4/3*(end sites served by the largest serving site)
(i) An end site which can justify more than a /48 under
the current end-user assignment policy  shall count
as the appropriate number of /48s that would be
assigned under that policy.
(ii) An LIR which has subordinate LIRs shall make such
allocations according to the same policies and
criteria as APNIC. In such a case, the prefixes
necessary for such an allocation shall be treated as
fully utilized in determining the block sizing
for the parent LIR.
(iii) An LIR is not required to design or deploy their
network according to this structure. It is strictly a
mechanism to determine the largest IP address block to
which the LIR is entitled.
4.5 Change the criteria for an allocation
To qualify for an allocation, an LIR must meet the criteria
described in one of the following sections: 4.5.1, 4.5.2, or 4.5.3:
4.5.1 The LIR:
- Has a previously justified IPv4 allocation from APNIC, OR
- Has a previously justified IPv4 allocation from one
of APNIc's predecessor registries, OR
- Can qualify for an IPv4 ISP allocation under current
4.5.2 The LIR:
- Will be making reassignments to other organizations AND
- Is currently multihomed for IPv6, OR
- Will immediately become multihomed for IPv6 using a valid
assigned global AS number
4.5.3 The LIR must provide APNIC a reasonable technical
justification of why an allocation is necessary including:
- The intended purposes for the allocation
- A description of the network infrastructure the allocation
will be used to support.
- A plan detailing assignments to other organizations or
customers for one, two, and five year periods, with a
minimum of 50 assignments within 5 years.
4.6 Change the way subsequent allocations to LIRs are made
To qualify for a subsequent allocation, an LIR must meet one of the
following two criteria:
- Utilization of 75% or more of their total address space, OR
- One the LIR/ISP's serving sites has a 90% utilization rate
Note: the process for calculating the utilization rate is detailed
in Appendix A.
When making subsequent allocations to LIRs, APNIC will follow the
allocation procedure below:
- Wherever possible, APNIC will make an allocation that expands one
or more existing allocations.
- Where APNIC cannot expand one or more existing allocations, APNIC
shall make a new allocation based on the initial allocation
criteria described in section 4.5 above.
When this occurs, the LIR is encouraged, but not required, to
renumber into the new allocation over time and return any
allocations no longer in use. In such a case, it is legitimate for
an end-site to have assignments from as many as two of these
blocks at a time to facilitate transition to the new range.
4.7 Change the recommendations for LIRs to make assignments to end users
The recommended provider assignment unit is /48. In no case will
policy consider a provider assignment unit larger than /48.
Instead, if an LIR/ISP chooses to assign more than a /48 to an
end site, that will be considered to be multiples of the provider
If the LIR/ISP chooses to have a provider assignment unit
smaller than a /48, then calculations of its address space
utilization will accordingly use the smaller prefix size.
An LIR may issue up to a /48 to an end site without requiring
4.8 Allow LIRs with existing IPv6 allocations to expand their allocation
size if they are eligible for a larger block under the allocation
criteria suggested in this proposal.
Any LIR which received an allocation under previous policies which
is smaller than what they are entitled to under this policy may
receive a new initial allocation under this policy provided that
they agree to renumber into that new allocation and return their
prior allocation(s) within 5 years.
If possible, APNIC will simply expand their existing allocation
rather than requiring renumber and return.
- Provides nibble-boundaries for direct allocations and for at least
one level of network hierarchy within the LIR, reducing the
potential for human factors errors.
- Increases the potential for network aggregation by issuing very
large blocks to ISPs.
- Reduces the potential for harmful under-sized assignments to end
users by removing any incentive to do so.
- Simplifies the IPv6 allocation policy by removing logarithmic
computations in favor of simple ratios.
- Reduces the number of times any given LIR will need to return to
APNIC for additional allocations.
- Allows for better network planning and growth.
- Increases IPv6 address allocation. Probable impact over 50 years,
free pool drops from 99.9995% to 99.54%.
6. Effect on APNIC
APNIC LIR members will be able to obtain significantly larger blocks of
IPv6 addresses and both receive and make their allocations and
assignments on nibble boundaries to simplify human factors and network
management while improving aggregation.
7. Effect on NIRs
This policy should not significantly impact NIRs.
 Section 5.5, 'Assignment', in 'APNIC IPv6 Allocation Policy'
In general, the following formula is used to calculate the utilization
rate in IPv6:
No. of provider assignment units assigned
Utilization % = ----------------------------------------- x 100
Total no. of provider assignment units
within allocation block(s)
However, there may be occasions when the calculation may need to be
amended if an LIR is in the process of renumbering out of an earlier
IPv6 block into a subsequent block from APNIC. If this is the case,
the following is permitted:
- An LIR can count provider assignment units made to end sites
in both the original and newer block into which the LIR is in
the process of renumbering into.
- The LIR can count assignments made to serving sites in both the
original and newer block into which the LIR is in the process of
This double-counting during renumbering means that APNIC would always
allocate enough space to an LIR to encompass both existing customers and
growth of the LIR within a single new aggregatable block.
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