IPv4 Exhaustion and IPv6: Why the Internet Ran Out of Addresses
On 3 February 2011 the last blocks of IPv4 addresses were handed out. Learn why the internet ran short, what IPv6 changes, and what it means for you.
Every device connected to the internet needs an address, and for decades those addresses came from a limited supply. On 3 February 2011, the Internet Assigned Numbers Authority (IANA) allocated its last blocks of IPv4 addresses to the regional registries. It was a milestone that people in the network community had predicted for years, and it started a slow transition whose effects reach all the way to your hosting account.
How IPv4 addresses work
The version of the Internet Protocol that has been in use since the 1983 switch to TCP/IP is IPv4. Its addresses are 32 bits long, usually written as four numbers separated by dots, such as 192.0.2.1 (a reserved example). A 32-bit space has about 4.3 billion possible addresses. In the early days, this seemed enormous. Large organisations were handed blocks of millions of addresses, and the design did not assume that billions of phones, laptops and appliances would one day connect.
Early warnings and workarounds
By the early 1990s, engineers could see that the address space would not last. Several measures were taken to stretch it:
- CIDR (1993). Classless Inter-Domain Routing allocated addresses in blocks of flexible size, rather than fixed large classes, which reduced waste.
- NAT. Network Address Translation lets a whole home or company network share one public address. Your home router does this for all your devices.
- Private address ranges. Reserved ranges can be reused inside many separate networks.
- Tighter allocation policies by the regional registries.
These measures worked well enough to postpone the problem by many years, but they did not solve it.
Running out
Addresses are distributed from IANA to five regional internet registries, which pass them on to internet providers and organisations. IANA's final blocks were assigned in February 2011. After that, each registry ran out of its own free pool at a different time. The Asia-Pacific registry (APNIC) reached its final allocation stage in April 2011, the registry for Europe, the Middle East and parts of Central Asia (RIPE NCC) in September 2012, and the North American registry (ARIN) in 2015. Registries that had run out have continued to recycle returned addresses and run waiting lists.
Today IPv4 addresses are scarce, and they are traded on a market. That is why hosting providers may charge for extra IPv4 addresses, and why some services give customers an IPv6 address by default.
IPv6
The Internet Engineering Task Force had begun working on a replacement in the 1990s, and the IPv6 specification was published in 1998. It uses 128-bit addresses, written in hexadecimal groups separated by colons, for example 2001:db8::1 (an example range). That gives about 340 undecillion addresses, a number so large that exhaustion is not a practical concern.
| Feature | IPv4 | IPv6 |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Example | 192.0.2.1 | 2001:db8::1 |
| NAT needed to stretch supply | Very common | Not needed |
| DNS record type | A | AAAA |
IPv6 is not compatible with IPv4 on the wire, so a device that only speaks one cannot talk directly to one that only speaks the other. For this reason the two are run side by side, in what is called dual stack, and translation mechanisms exist for networks that are IPv6-only.
A slow transition
World IPv6 Day in June 2011 was a trial in which large websites enabled IPv6 for 24 hours, and World IPv6 Launch on 6 June 2012 made it permanent for many of them. Adoption has grown steadily since, with mobile networks and large content providers leading the way, while many smaller networks and sites still lag. Because most visitors can still reach IPv4-only sites, there has been little pressure to hurry.
What IPv6 means for a website
- A site can have both an A record (IPv4) and an AAAA record (IPv6) in DNS.
- Visitors on IPv6-only or IPv6-preferring networks reach you more directly when you have an AAAA record.
- Every address you reserve for a service, such as a dedicated IP for an SSL setup or a mail server, may be a limited and priced resource.
- A CDN in front of your site can serve IPv6 visitors even if your origin server only has IPv4.
Dedicated IP addresses and shared hosting
On shared hosting, many sites share a single IPv4 address, which is possible because the web server tells sites apart by the name the visitor asked for. For many years a dedicated IP address was needed for each SSL site, until the TLS extension called Server Name Indication, which sends the site name during the handshake, became widely supported. This removed one of the biggest demands on the IPv4 supply. Today you rarely need your own address for a website, though services such as mail servers sometimes benefit from one, because the reputation of an address affects how receiving mail servers treat the messages sent from it.
The lesson for site owners
You don't need to do anything urgent about IPv6, but it is useful to know that it exists, and to prefer a host and a CDN that support it. A CDN in front of your site handles IPv6 visitors for you, and you can read how this works on our CDN page. If you run a VPS, the VPS plans give you the control to configure both address types, and the knowledgebase explains how to manage your DNS records.
