February 3, 2011: The Day the Internet Ran Out of Addresses
Zusammenfassung
On February 3, 2011, the Internet Assigned Numbers Authority (IANA) allocated the last five blocks of IPv4 addresses to the five Regional Internet Registries. The 4.3 billion addresses in IPv4’s address space were exhausted. The internet has continued to function only because of Network Address Translation (NAT) — a technique that allows multiple devices to share a single public IP address — originally designed as a temporary workaround in 1994. IPv6, designed to provide 340 undecillion addresses, was standardized in 1998. As of 2024, approximately 45% of internet traffic uses IPv6; the migration has been ongoing for 26 years.
The Design Constraint
The IPv4 protocol (1981) allocates 32 bits for each IP address — a design choice that provides 2^32 = 4,294,967,296 unique addresses. In 1981, this seemed inexhaustible. The internet had approximately 300 connected computers; 4 billion addresses for 300 machines left a margin that felt permanent.
The internet grew faster than any plausible 1981 projection anticipated. By the early 1990s, network engineers were forecasting address exhaustion within decades. By the mid-1990s, the forecast had shortened to years. Two mechanisms bought time:
CIDR (Classless Inter-Domain Routing, 1993): Replaced the fixed address class system (Class A = 16M addresses, Class B = 65K addresses, Class C = 256 addresses) with variable-length prefix notation, allowing addresses to be allocated in sizes matched to actual need rather than in large fixed blocks. This reduced waste.
NAT (Network Address Translation, 1994): Allows a router to represent an entire private network (typically 192.168.x.x or 10.x.x.x addresses) behind a single public IP address. When a device inside the NAT sends a packet to the internet, the router replaces the private source address with the router’s public address and remembers the mapping. Responses are sent to the public address and the router forwards them to the correct private device. Multiple devices share one public IP.
The Exhaustion Event
IANA (the global address registry) managed the allocation of IPv4 addresses in /8 blocks (16.7 million addresses each). On February 3, 2011, IANA allocated its remaining five /8 blocks — one to each Regional Internet Registry — and declared the global pool exhausted. The five registries then continued allocating addresses to ISPs and companies from their regional pools; most regions exhausted their local allocations between 2011 and 2020.
New connections to the internet after exhaustion are almost entirely behind NAT. A smartphone on a mobile carrier may share its public IP with thousands of other devices on the same carrier. Servers that need to be directly reachable need either IPv6 addresses or payment for a scarce IPv4 address (which now trade on secondary markets for $40–$60 per address).
IPv6: The 26-Year Migration
IPv6 (1998) uses 128-bit addresses: 2^128 = 340 undecillion (3.4 × 10^38) unique addresses. This is enough for every atom on the Earth’s surface to have its own IP address. IPv6 was designed specifically to replace IPv4 and end the address scarcity problem permanently.
The migration has been slow for structural reasons: IPv4 and IPv6 are not backward-compatible. Every router, firewall, application, and network service needs to support both protocols during the transition, creating complexity and cost that organizations have consistently deferred. Google’s statistics show IPv6 usage rising from nearly zero in 2010 to approximately 45% of its traffic in 2024 — a successful but slow transition that required 26 years of sustained effort.