IPv4 Exhaustion Explained

What IPv4 Exhaustion Means

IPv4 exhaustion is the shortage of unassigned public IPv4 addresses. The 32-bit address format provides only about 4.3 billion addresses, far fewer than the number of devices that now connect to the internet. The central pool was handed out to regional registries, and several of those registries have since run out of free addresses for new allocations.

Exhaustion does not mean that IPv4 stops working. Existing addresses remain in use and networks keep operating. What changes is that new networks and organizations can no longer obtain a fresh block of public IPv4 addresses directly from a registry, so they must share, buy or work around the shortage. The format itself is explained in the comparison of IPv4 and IPv6.

How the Internet Has Coped With the Shortage

The main response has been network address translation (NAT). A router gives private addresses to the devices in a home or office and shares one public address among them, tracking each connection so that replies reach the right device. NAT lets large numbers of devices share a small number of public addresses, and it remains the most common reason IPv4 still serves new users.

Some internet providers go further with carrier-grade NAT, where many customers share one public address at the provider's network edge. This extends IPv4 but complicates inbound connections, because a customer no longer has a public address that others can reach directly. The private and public address ranges are described in the article on public and private IP addresses.

Another response is a market for IPv4 addresses. Organizations that no longer need their blocks can sell or transfer them to others. Prices have moved with demand, and this is one reason hosts often charge a separate fee for a dedicated IPv4 address.

IPv6 as the Long-Term Answer

IPv6 removes the shortage by providing an address space so large that exhaustion is not a practical concern. Its adoption has been gradual, because every device, router, server and piece of software must understand the new format. During the transition, most networks run dual stack, so IPv4 and IPv6 traffic coexist.

For a website owner, the practical effect is that IPv4 addresses cost money while IPv6 addresses are usually provided without the extra charge that dedicated IPv4 addresses often carry. Adding IPv6 reduces dependence on the scarce resource, although many sites still need an IPv4 address for visitors who lack IPv6.