Draft Policy ARIN-2024-11

IPv4 Transition Efficiency Reallocation Policy (ITERP)

Status: Under Discussion
Shepherds: Brian Jones, Kaitlyn Pellak

Current Text (30 October 2024)

Problem Statement:

As the exhaustion of IPv4 addresses continues, ISPs and end-users face increasing challenges in managing their transition to IPv6. Many end-users require small amounts of IPv4 space to implement technologies like Carrier-Grade NAT (CG-NAT) or dual-stack environments, which are critical for their own IPv6 deployment efforts. Under the current NRPM 4.10 policy, ISPs are prohibited from reallocating portions of their IPv4 blocks to end-users, forcing these organizations to request larger, inefficiently used blocks (e.g., /24s) from ARIN.

This practice contributes to the unnecessary consumption of scarce IPv4 resources, as many end-users only need small blocks (e.g., /29s or /28s) for their CG-NAT and IPv6 transition processes. The inability to reallocate these smaller blocks results in wasteful allocations and hampers the overall efficiency of IPv4 address management.

Without a mechanism to allow ISPs to reallocate small portions of their NRPM 4.10 space to qualified end-users, the current policy inadvertently encourages inefficient IPv4 address utilization, which conflicts with ARIN’s goal of maximizing the use of remaining IPv4 resources while facilitating the widespread adoption of IPv6.

The problem is twofold:

1. End-users are forced to request larger, underutilized IPv4 blocks for their IPv6 transition needs.

2. ISPs are unable to efficiently manage and reallocate their IPv4 resources under NRPM 4.10 to meet end-user demands for small-scale CG-NAT and IPv6 transition deployments.

Policy Statement:

Add these bullets to section 4.10 of the NRPM to facilitate ARIN approved reallocation of 4.10 resources.

• ISPs may reassign a /29 or /28 for their direct downstream customers for IPv6 transition only. ARIN reserves the right to validate any downstream allocations from ISPs to direct customers.

• Anyone wishing to perform a reassignment of a 4.10 allocation must be approved through ARIN and meet all the justification requirements of this policy.

Timetable for Implementation: Immediate.

Comments: IPv4 Transition Efficiency Reallocation Policy (ITERP) and Its Impact on CG-NAT, IPv6, and Efficient Resource Use

Utilization of Reallocated IP Space by End-Users and Small ISPs for CG-NAT

Under the IPv4 Transition Efficiency Reallocation Policy (ITERP), end-users and even small ISPs can efficiently use reallocated IPv4 space for CG-NAT (Carrier-Grade NAT) while leveraging their IPv6 deployments. Many smaller ISPs, particularly those that only have NRPM 4.10 space and limited IPv4 allocations, could benefit from this policy by reallocating IPv4 subnets (e.g., /29 or /28) to their customers or other ISPs who require minimal IPv4 addresses for CG-NAT in dual-stack environments.

Through the use of BGP for IPv6, along with alternative IPv4 multi-homing technologies like source and policy based routing combined with CG-NAT, end-users or small ISPs could even connect to multiple providers utilizing IPv6 natively while performing CG-NAT towards multiple providers over IPv4. This approach helps balance traffic, increase redundancy, and achieve better failover capabilities. By employing IPv6 for outward-facing traffic and CG-NAT for IPv4 communication, smaller networks can provide their customers a seamless experience without consuming large amounts of IPv4 space.

Eligibility and Address Space Efficiency

This policy amendment is strictly intended for organizations that would otherwise be eligible for a /24 under NRPM 4.10. Instead of receiving an entire /24 (256 addresses) that may go largely underutilized, these end-users could now request smaller blocks (e.g., /29s or /28s) from multiple providers that only hold NRPM 4.10 space. This allows for much more efficient use of IPv4 resources, as the smaller allocations can directly serve CG-NAT needs without wasting a significant portion of the address space.

Such end-users are typically transitioning to IPv6 and need small amounts of IPv4 space only for backward compatibility and legacy systems. This policy ensures that they don’t have to unnecessarily consume large blocks of IPv4 addresses that are rapidly depleting, especially since most of their traffic will run over IPv6.

Incentivizing IPv6 Deployment by ISPs

This policy can also incentivize ISPs to evangelize IPv6 deployment to their customers. As the ISPs are held accountable for monitoring and reporting the usage of reallocated space, they are motivated to actively assist their customers in migrating to IPv6 to ensure compliance with ARIN’s policies. By reallocating IPv4 space under the NRPM 4.10 policy, ISPs will naturally push for greater IPv6 adoption and encourage their end-users to take advantage of the superior capabilities and scalability of IPv6.

In many cases, ISPs can act as trusted technology advocates, guiding their customers through the transition process, offering resources, and providing technical support for deploying dual-stack environments. This not only supports IPv6 growth but also fosters stronger partnerships between ISPs and their customers as they collectively work toward the next generation of networking technologies.

Supporting ISPs with Only NRPM 4.10 Space and IPv6

Many ISPs, particularly newer or smaller ones, may only have access to NRPM 4.10 IPv4 space and IPv6 allocations. These ISPs often lack sufficient general-purpose IPv4 space but are fully invested in deploying IPv6 to their customers. The IPv4 Transition Efficiency Reallocation Policy provides an efficient and pragmatic way for these ISPs to serve end-users with small-scale CG-NAT needs, helping them facilitate IPv6 adoption without having to apply for entire /24s of IPv4 space that they don’t require.

By allowing the reallocation of small IPv4 blocks to end-users for CG-NAT and IPv6 dual-stack environments, IPv4 exhaustion can be minimized, and numbering resources can be more efficiently utilized. These ISPs can push their customers toward IPv6 while offering minimal IPv4 resources needed for NAT and legacy services. This policy, therefore, promotes responsible IPv4 stewardship and accelerates the migration to IPv6.

Conclusion: Efficient Use of Resources and Push for IPv6 Adoption

The IPv4 Transition Efficiency Reallocation Policy (ITERP) ensures that IPv4 address space is used efficiently by allowing small allocations to end-users for specific transitional technologies like CG-NAT. By utilizing BGP for IPv6 and multi-homing technologies, end-users can effectively route traffic while minimizing their reliance on IPv4. This policy enables ISPs, particularly those that only have NRPM 4.10 space, to act as leaders in the push for IPv6, ensuring that numbering resources are preserved while advancing the deployment of the next generation of Internet technology.

Other technologies are also available, such as routing IPv4 space over IPv6, which is supported in many modern routing systems, meaning a /32 of IPv4 space could be routed to an end-user over a native IPv6 network with no other space involved. This policy would encourage ISPs to evangelize and accelerate the deployment of an IPv6 Internet by making deploying IPv6 even more beneficial to end users, while also preserving the precious remaining IPv4 address space.

By embracing this approach, ARIN can foster greater IPv6 adoption, prevent IPv4 depletion, and empower ISPs and end-users alike to move forward with innovative, future-proof network architectures.

This policy provides a more efficient and responsible approach to achieving the goals initially intended by ARIN-2008-5, which aimed to allow the use of longer prefixes than /24s without causing the complications associated with ARIN allocating such longer prefixes directly.

When ARIN-2008-5 was introduced, the idea was to allow networks to receive smaller allocations than /24, recognizing that many organizations, particularly those transitioning to IPv6, do not require a full /24 for their IPv4 needs. However, allocating smaller prefixes directly from ARIN would have created routing and administrative challenges, including concerns about route fragmentation and maintaining the integrity of the global routing table.

The IPv4 Transition Efficiency Reallocation Policy (ITERP) resolves these issues by enabling ISPs to handle the reallocation of small IPv4 blocks (such as /29 or /28) from their NRPM 4.10 space, instead of ARIN directly assigning longer prefixes. This allows for more granular and flexible use of address space without fragmenting ARIN’s allocations, ensuring that the allocations remain efficient and manageable.

Furthermore, by placing responsibility on the ISPs to ensure proper utilization, ITERP:

• Minimizes the risk of route table bloat, as ISPs manage these smaller blocks within their own infrastructure.
• Ensures IPv4 allocations are tied to specific, justified use cases (such as CG-NAT and IPv6 transition), aligning with the original intent of ARIN-2008-5 to avoid wasteful consumption of IPv4 addresses.

In doing so, this policy not only promotes efficient use of IPv4 space but also strengthens the transition to IPv6 by encouraging ISPs to work closely with their customers on deploying dual-stack environments, thus driving greater IPv6 adoption. This policy balances the need for flexibility in smaller allocations while preventing the complications that could arise from direct ARIN allocations of smaller prefixes.

Staff and Legal Review (19 May 2025)

Staff Understanding: Current staff implementation for NRPM section 4.10. Dedicated IPv4 Allocation to Facilitate IPv6 Deployment does not consider Reallocations/Reassignments made from parent reserved 4.10 IPv4 subnets to downstream customers/organizations to be within policy. Staff’s current practice is to issue allocations from the reserved 4.10 pool strictly for in-region use by the requesting organization and only for IPv6 translation services. The requesting organization must provide proof of having and using IPv6 translation services.

Staff understands this Draft Policy would:

• allow ISPs to reassign, from their allocated parent NRPM section 4.10 subnet, a /29 or /28 to their direct downstream customers for IPv6 transition only.
• explicitly reserve the right for ARIN staff to validate any downstream allocations from ISPs to direct customers.
• require that anyone wishing to perform a reassignment of a NRPM section 4.10 allocation must be approved through ARIN and meet all the justification requirements of this policy.

This policy text is implementable as written, however ARIN staff notes the following:

Staff has concerns that this proposed policy change could enable inappropriate use of the section 4.10 reserved address block. Staff currently expends a significant amount of time and resources auditing, tracking, and reclaiming NRPM section 4.10 space where it has been misused by direct allocation holders. Allowing direct allocation holders to reallocate or reassign this reserved space to downstream customers adds additional difficulties to policy enforcement. Policy enforcement is further complicated if the customer holds multiple 4.10 reallocations/reassignments from multiple different ISPs. Once reallocated or reassigned, the space could be used for any purpose, effectively undermining the intent of the reservation. This would require additional resources in order to verify, track and manage these allocations.

It is unclear how reallocating small blocks (such as /28 or /29) to downstream customers would support IPv6 transition needs like dual-stack DNS. These smaller blocks are not independently routable, and the upstream ISP would still be responsible for reverse DNS management—further complicating implementation and oversight.

This Draft Policy states, “ISPs may reassign…,” and later states, “Anyone wishing to perform a reassignment…”. Both ISPs and End-users receive direct allocations from ARIN, granting both types of organizations the ability to create reallocations and reassignments. If the intent is to permit anyone to reallocate/reassign (ISPs and End-users) or if the intent is to permit only ISPs to reallocate/reassign, then the Draft Policy text should be refined to reflect the intention clearly and consistently.

Usage of “reassign” and “allocation” are used interchangeably in the proposed text, however Reallocations and Reassignments have different permissions. Reallocations can be further reallocated or reassigned by the downstream customer to their own downstream customers. Reassignments cannot be further reallocated or reassigned. Staff recommends refining the text to avoid confusion and a possible means for abuse.

Implementable as Written?: Yes

Impact on ARIN Registry Operations and Services: Increased staff resources required to adequately review NRPM section 4.10 requests and holdings.

Legal Review: No material legal issue

Implementation Timeframe Estimate: 3 Months

Implementation Requirements:

• Staff Training
• Updates to public documentation
• Updates to internal procedures and guidelines

Proposal/Draft Policy Text Assessed: 30 October 2024

History and Earlier Versions

Related Meetings