• Start with the relevant RIR’s transfer rules and the registration chain: a block that cannot be transferred, divided or accepted by the recipient has no executable market value at the quoted date.
  • There is no universal large-block premium. A RIPE NCC report based on 2024 interviews observed roughly €30 per address for /24 to /20 blocks while larger /16 prices were expected to weaken; it is dated evidence, not a current executable quote.
  • Compare after-tax net sale proceeds with the risk-adjusted present value of leasing or internal use. Broker, escrow, legal, registry, remediation, delay, abuse and routing costs belong in the model.

Eligibility comes before the price per address

IPv4 scarcity is real, but the familiar 2011 milestone is often misstated. ICANN announced on 3 February 2011 that the central IANA free pool had made its final allocations to the five Regional Internet Registries; it did not mean that every RIR inventory became unavailable on the same day. Today a seller is offering registered use and transfer rights under an RIR agreement and policy, not a freehold asset detached from the registry. The RIPE NCC's June 2025 report makes that distinction explicit for its service region.

Before asking for a price, establish the source holder, registration chain, applicable RIR, agreement status, encumbrances and disputes. Test whether the prefix can be split, whether a holding period or other restriction applies, and whether the intended recipient qualifies. ARIN's current Number Resource Policy Manual and pre-approval process require a recipient case based on projected need. RIPE NCC checks registration, documentation and policy conditions, while APNIC requires demonstrated need and applies a five-year restriction to addresses obtained from its 103/8 free pool. Rules differ by source, destination and date.

Build comparables and calculate net proceeds

A usable comparable set records transaction date, RIR pair, prefix size, whether the block was contiguous, legal and registry status, and whether the number is an asking price, a bid, a broker average or a completed trade. Do not infer that a /20 is always worth more per address than a /24, or that a /16 always commands a premium. The RIPE NCC report describes 2024 interview observations of about €30 per address for /24 to /20 space and softer expectations for /16 blocks. That finding rebuts a universal size rule but is neither an audited global index nor a live quote.

For a sale, calculate gross consideration as executable price multiplied by transferable addresses, then subtract broker and escrow fees, legal work, RIR and membership costs, taxes, financing, reputation remediation and the expected cost of delay or failure. Run low, base and high cases and show the valuation date. Preserve an operational reserve before marketing surplus space: replacing addresses later can force renumbering, customer migration, allow-list changes and service risk. “Maximum ROI” is not a defensible promise without these denominators.

Lease, sell or retain: compare risks as well as cash

Leasing is not simply a way to “retain ownership”. Model the present value of net rent after utilisation, vacancy, collection risk, support, abuse handling, route operations, legal exposure and termination costs. Discount those cash flows for counterparty concentration and regulatory uncertainty, then add a conservative residual value. Compare that result with net sale proceeds and with the value of keeping the block for growth, acquisitions, disaster recovery or customer commitments.

Technical diligence affects both price and closing risk. Check registry history and disputes; historic BGP announcements and hijacks; spam and malware reputation through tools such as the Spamhaus IP and Domain Reputation Checker; RPKI, IRR, reverse DNS and geolocation state; letters of authorisation; and the buyer's abuse controls. ARIN's transfer best-practices guidance notes that ROAs, IRR objects and reverse DNS need coordinated updates. Escrow should release funds against agreed registry and routing milestones, not merely a signed contract.