IP Address Allocation: From IANA to Your ISP

Every IP address you use — whether at home, at work, or on a mobile network — arrived at your device through a carefully organized global hierarchy. Understanding this system reveals not just how the internet is administered, but why IPv4 addresses are scarce, why IPv6 was necessary, and how the market for address space actually works.

The Allocation Hierarchy

IP address distribution follows a strict four-level hierarchy. At each level, a larger organization delegates smaller blocks to more specific operators.

IANA
  └── Regional Internet Registries (RIRs) — 5 regions
        └── Local Internet Registries (LIRs) / National Internet Registries (NIRs)
              └── End Users (ISPs, enterprises, hosting providers)
                    └── Your device (via DHCP or static assignment)

Level 1: IANA (Internet Assigned Numbers Authority)

The Internet Assigned Numbers Authority sits at the top of the hierarchy. IANA is a function of ICANN (the Internet Corporation for Assigned Names and Numbers) and holds the master list of all IP address blocks.

IANA does not assign addresses directly to ISPs or enterprises. Its role is to allocate large address blocks — called slash-8 blocks (/8, containing 16.7 million IPv4 addresses each) — to the five Regional Internet Registries. IANA also maintains the registries for special-use addresses, protocol numbers, and port assignments.

Level 2: Regional Internet Registries (RIRs)

There are five Regional Internet Registries, each responsible for a geographic region:

RIR	Region	Website
ARIN	North America	arin.net
RIPE NCC	Europe, Middle East, Central Asia	ripe.net
APNIC	Asia-Pacific	apnic.net
LACNIC	Latin America and Caribbean	lacnic.net
AFRINIC	Africa	afrinic.net

Each RIR receives large blocks from IANA, then distributes smaller blocks to organizations within their region. RIRs also maintain WHOIS databases — public records of who holds which address blocks. When you look up an IP address and see its registrant, you are querying an RIR's WHOIS database.

Level 3: Local Internet Registries (LIRs)

Local Internet Registries are organizations that have received IP address space from an RIR and can allocate it further. Most LIRs are ISPs, hosting companies, or large enterprises. To become an LIR, an organization pays a membership fee to their regional RIR and agrees to follow allocation policies.

In some regions, an intermediate layer called a National Internet Registry (NIR) exists — for example, JPNIC in Japan operates under APNIC and distributes addresses to Japanese ISPs.

Level 4: End Users

End users — including individuals, businesses, and universities — receive address space from LIRs. A small business might receive a /29 block (6 usable addresses) from their ISP. A large enterprise might receive a /24 (256 addresses) or larger. Universities and research institutions often hold historically large allocations from the early internet era.

IPv4 Exhaustion: A Slow-Motion Crisis

The internet was designed with a 32-bit address space, providing approximately 4.29 billion unique IPv4 addresses. In the early 1980s, this seemed limitless. By the 2000s, it was clear the internet was running out.

The Timeline

• 1992: IANA allocates its 100th /8 block. Jon Postel warns the address space is shrinking.
• 1993: CIDR (Classless Inter-Domain Routing) is introduced, replacing rigid Class A/B/C allocations and slowing consumption.
• 1994: RFC 1918 defines private address ranges (10.x, 172.16.x, 192.168.x), enabling NAT and dramatically extending IPv4's lifespan.
• 2011-02-03: IANA exhausts its free pool, distributing the last five /8 blocks (one each) to the five RIRs.
• 2011: APNIC (Asia-Pacific) announces it has reached its last /8, entering its final exhaustion policy.
• 2012: RIPE NCC enters final exhaustion phase in Europe.
• 2015: ARIN exhausts its free pool for North America.
• 2017: LACNIC enters final exhaustion for Latin America.
• 2020: AFRINIC begins strict conservation policies.

What Happened After Exhaustion

Exhaustion did not mean the internet stopped growing. Several mechanisms extended IPv4's functional life:

NAT (Network Address Translation) allows many devices to share a single public IP. A household of 10 devices with one public IP appears as one address to the internet. Carrier-grade NAT (CGNAT) lets ISPs share a single public IP among hundreds or thousands of customers.

IPv6 deployment accelerated. While IPv6 has been available since the 1990s, its adoption rate roughly doubled after IPv4 exhaustion events. Major content providers (Google, Facebook, Netflix) and ISPs enabled dual-stack operation.

The IPv4 Transfer Market emerged, allowing organizations with surplus addresses to sell them to those who need them.

The IPv4 Transfer Market

Since RIRs can no longer issue new IPv4 addresses from a free pool, organizations that need addresses must either receive them via legacy allocation, obtain them through CGNAT workarounds, or buy them on the open market.

How Transfers Work

Each RIR maintains a Transfer Log — a public record of address block transfers between organizations. To transfer an IPv4 block:

1. The seller notifies their RIR that they wish to transfer a block.
2. The buyer submits a needs assessment (under most RIR policies) demonstrating they will use the addresses.
3. The RIR approves the transfer and updates the WHOIS registry.
4. Both parties coordinate the actual routing changes with their upstream providers.

Transfer Prices

IPv4 address prices have risen dramatically. In 2011, a single IPv4 address traded for roughly $10. By 2020, prices reached $25-30 per address. By 2024, prices for /24 blocks (256 addresses) routinely exceeded $50 per address, making a single /24 worth more than $12,000.

Prices vary by: - Block size — Larger blocks often command a premium because they are easier to route - Region — Transfers within a single RIR's region avoid inter-RIR complexity - History — Clean blocks with no spam or abuse history fetch more

Brokers like Hilco Streambank, IPv4.Global, and IPXO operate marketplaces for address trading.

Legacy Holders

Some of the largest IPv4 holders received address space in the 1980s before the hierarchical system existed. These legacy allocations include:

• MIT received 18.0.0.0/8 (16.7 million addresses) — more than the entire continent of Africa was allocated
• Apple holds 17.0.0.0/8
• The US Department of Defense holds several /8 blocks
• Ford Motor Company holds 19.0.0.0/8

Some legacy holders have sold portions of their space. In 2017, MIT sold half its /8 block to Amazon for a reported $8 per address. In 2021, the US Department of Defense temporarily announced routing for large legacy blocks, a move that drew significant scrutiny.

IPv6 Allocation Policies

IPv6 uses 128-bit addresses, providing approximately 340 undecillion (3.4 × 10^38) unique addresses. This is enough to assign millions of addresses to every atom on Earth's surface.

IPv6 allocation operates similarly to IPv4, but the scale is so vast that policies differ in important ways:

IPv6 Block Sizes

Level	Typical Allocation	Addresses
IANA to RIR	/12	1,048,576 /32s
RIR to LIR	/32	4 billion /64s
LIR to end-site	/48	65,536 /64 subnets
End-site to device	/64	18 quintillion addresses

A standard home or small business receives a /48, which contains more address space than the entire IPv4 internet.

No Need for NAT

Because IPv6 provides globally unique addresses for every device, NAT is not needed. Each device can have a direct, routable IPv6 address. This restores the original end-to-end connectivity model that NAT broke.

Privacy Extensions

Because IPv6 addresses are globally unique and long-lived, they could theoretically be used to track individual devices. RFC 4941 defines Privacy Extensions — devices generate temporary, randomized IPv6 addresses for outgoing connections, changing them periodically to prevent tracking.

How Your ISP Gets Your IP Address

When you connect to the internet, your ISP assigns you one or more IP addresses through a chain of delegation:

1. Your ISP received a block (e.g., a /20 or /18) from its RIR or purchased it on the transfer market.
2. The ISP's DHCP servers (or RADIUS servers for PPPoE connections) draw from this pool.
3. When you connect, your router receives a lease — a temporary assignment of a public IP from the ISP's pool.
4. Your router then runs its own DHCP server, assigning private RFC 1918 addresses (typically 192.168.x.x) to your devices.

CGNAT: The Shared IP Reality

Many ISPs, especially mobile carriers and smaller broadband providers, no longer give each customer a unique public IPv4 address. Instead, they use Carrier-Grade NAT (CGNAT), defined in RFC 6598, which uses the 100.64.0.0/10 address range.

Under CGNAT, hundreds of customers share a single public IP. The ISP's CGNAT device translates connections between shared customer addresses and the public IP. This means:

• Port forwarding becomes impossible without special ISP support
• Incoming connections (hosting a game server, remote desktop) are blocked by default
• IP-based rate limiting may affect multiple unrelated customers
• Abuse reports traced to a CGNAT address affect all customers sharing that IP

Checking Your Allocation

You can look up the allocation details for any IP address using WHOIS:

# Query ARIN (automatically redirects to correct RIR)
whois 8.8.8.8

# Query RIPE NCC directly
whois -h whois.ripe.net 1.2.3.4

# Query APNIC directly
whois -h whois.apnic.net 203.0.113.1

The WHOIS record shows: - NetRange / inetnum — The block containing this IP - Organization / netname — Who holds the block - OrgId / mnt-by — Registry identifier - RegDate — When the block was first allocated - Updated — Last modification - Ref / source — Which RIR database to query for more info

Understanding the allocation hierarchy demystifies why some IP ranges behave differently, why your ISP may use CGNAT, and why IPv6 adoption matters for the long-term health of the internet.