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IPv4 Address Exhaustion: Why We Ran Out and How the Internet Coped

The internet was built on a 32-bit address space that seemed limitless in the 1980s — here's how it actually ran out, and what has kept things working since.

How many IPv4 addresses actually exist

IPv4 represents addresses using 32 bits, which caps the total at roughly 4.3 billion (2 to the 32nd power) unique addresses. That felt more than sufficient in the internet's early days, but it's nowhere near enough once you account for the world's population and device count.

Why addresses ran short

An explosion in internet-connected devices — smartphones, IoT devices, PCs — was one major driver, along with the fact that some organizations were allocated far more generous address blocks than they needed back in the internet's early years, which accelerated the shortage.

When exhaustion actually happened

IANA, the body overseeing global address allocation, exhausted its central pool of free IPv4 addresses in 2011. Regional internet registries around the world subsequently ran through their own remaining stock at different points afterward. Getting a brand-new IPv4 address block today is, in practice, extremely difficult.

Fix #1: CIDR (classless addressing)

Instead of handing out addresses only in fixed-size blocks under the old Class A/B/C system, CIDR (Classless Inter-Domain Routing) allows blocks to be carved out flexibly in whatever size is actually needed, dramatically cutting down on wasted address space.

Fix #2: NAT (private address sharing)

Homes and offices use private IP addresses internally, and a router's NAT (Network Address Translation) function lets a single public IP address handle internet access for many devices at once — sharply reducing how many public addresses are actually needed.

Fix #3: CGNAT (carrier-level NAT)

When home-router NAT still wasn't enough, internet providers introduced CGNAT (Carrier-Grade NAT), which groups multiple subscribers behind a single shared public IP address at the carrier level. The trade-off is that it commonly breaks port forwarding for affected subscribers.

The real long-term fix: IPv6

IPv6, which uses a 128-bit address system, offers a functionally limitless supply of addresses, solving the exhaustion problem at its root. Because so much existing IPv4 hardware and infrastructure still needs to be supported, though, the transition period running both systems side by side has stretched on for years.

A market for buying and selling IPv4 addresses

With new allocations essentially unavailable, a real market has emerged where organizations sell off unused IPv4 address blocks to others for a price — individual addresses now carry an actual market value and change hands as a tradable asset.

A shortage nobody planned for this soon

When IPv4 was designed decades ago, 4.3 billion addresses looked effectively infinite. The explosive growth of the internet — and later, of smartphones and connected devices — turned that number into a real bottleneck far sooner than anyone originally expected, setting the stage for everything from CIDR to IPv6.

A patchwork of fixes rather than one clean solution

What kept the internet running wasn't a single fix but a layered stack of workarounds — CIDR reducing waste, NAT multiplying usable addresses within a household, and CGNAT stretching that even further at the carrier level — buying enough time for IPv6 to gradually take over as the actual long-term answer.

Frequently Asked Questions

If IPv4 ran out, how is the internet still working normally?

Techniques like NAT and CGNAT let many devices share a much smaller pool of public IPv4 addresses, and most networks now run IPv4 and IPv6 side by side, which is why the shortage stays mostly invisible to everyday users.

Why does CGNAT sometimes break things like remote camera access or online gaming?

CGNAT groups many subscribers behind one shared public IP, which means an individual subscriber typically can't set up port forwarding to receive incoming connections directly — a common requirement for hosting a game server or accessing a home camera remotely.