Reducing IXP IPv4 assignment default size to a /26

Summary of Proposal

This proposal modifies the default size of IPv4 assignments for IXPs from a /24 to /26 and proposes an incentive to implement the exchange of IPv4 routing information over IPv6 for IXPs.

Policy Text:

a) Current policy text (if modification):

6.1. Assignments to Internet Exchange Points

A /15 will be held in reserve for exclusive use by Internet Exchange Points (IXPs). On application for IPv4 resources, an IXP will receive a single number resource block according to the following:

1. Organisations receiving space under this policy must be IXPs and must meet the definition as described in section two of the RIPE Document "IPv6 Address Space for Internet Exchange Points".
2. This space will be used to run an IXP peering LAN only; other uses are forbidden.
3. Assignments will only be made to IXPs that have applied for an IPv6 assignment for their peering LAN (or have already received one).
4. New IXPs will be assigned a /24 by default. Once they require a larger assignment, they must return their current one (or existing PI used as an IXP peering LAN) and receive a replacement up to maximum of a /22. After one year, utilisation of the new assignment must be at least 50%, unless special circumstances are defined. On request or once there are no more assignments of /24 (or larger) available, assignments can be made down to /27.
5. IXPs holding other PI IPv4 space for their peering LAN (i.e., they are seeking a larger assignment), and any IPv4 space assigned from this pool that is no longer in use, must be returned to the pool within 180 days of disuse or a new assignment.

b) New policy text:

6.1. Assignments to Internet Exchange Points

[...]

1. New IXPs will be initially assigned a /26 by default. Upon request, a /25 can be assigned initially. If the initial assignment has been utilised by at least 50%, IXPs can request the assignment of a /24. In this case, the IXP must return the existing assignment (or existing PI used as an IXP peering LAN).
2. Once an IXP utilises an assigned /24 or a larger assignment by more than 50%, they can request an assignment up to a maximum of a /22. In this case, the IXP must return the existing assignment (or existing PI used as an IXP peering LAN). After one year, utilisation of the new assignment must be at least 50%, unless special circumstances are defined.
3. Assignments strictly larger than a /24 will only be made to IXPs that offer the exchange of IPv4 routing information over IPv6 at their route servers (if they operate them). They must also provide public documentation on how to set up the BGP sessions (with route servers and/or for private peering sessions if no route server is operated).
4. On request or once there are no more available assignments of /26 (or larger), assignments can be made down to /27.
5. IXPs holding other PI IPv4 space for their peering LAN (i.e. seeking for a larger assignment), and any IPv4 space assigned from this pool that is no longer in use, must be returned to the pool within 180 days of disuse or a new assignment.

Rationale:

a. Motivation for the proposal

At RIPE85, RIPE NCC Registration Services manager Marco Schmidt presented a forecast of the IXP IPv4 pool lifetime dedicated to peering LANs [1]. He predicted the pool will be depleted around 2029. A depleted IXP pool will lead to high upfront costs for new IXP projects, since they will have to purchase IPv4 addresses from brokers. Currently, a /24 IPv4 block required to found an IXP costs more than 11,000 USD when bought on the free market [2].

b. Arguments supporting the proposal

An analysis of PeeringDB [3] data by one of the authors [4] shows that the current practice of handing out a default /24 to new IXPs is wasting a large amount of valuable IPv4 space from the IXP pool. A majority (~70%) of all IXPs would fit into a /26, including 100% overprovisioning in terms of IPv4 addresses. Lowering the default assignment size to /26 would stretch the lifetime of the IXP pool by a factor of four assuming a constant burn rate.

At the same time, it is obvious that IPv4 is a limited resource and IPv6 provides a technical solution to the IPv4 address shortage. This policy implements an incentive for IXPs to adopt the exchange of IPv4 routing information over IPv6, requiring its implementation and public documentation for requesting an assignment larger than a /24.

c. Arguments opposing the proposal

Lowering the default assignment size increases the probability for IXP operators to outgrow their assigned IPv4 prefix in terms of connected devices. Once this happens, the IXP operator is forced to apply for a new assignment and to renumber all routers connected to the IXP. During the mailing list discussions preceding this proposal, IXP operators showed some support for a /26. However, this is a delicate trade-off which must be reviewed within a reasonable timeframe after implementing this policy.

[1] https://ripe85.ripe.net/wp-content/uploads/presentations/66-RIPE85-Feeback-from-RS.pdf[2] https://auctions.ipv4.global/prior-sales[3] https://www.peeringdb.com/[4] https://github.com/mwichtlh/address-policy-wg