IPv4 Address Depletion

IPv4 address are 32 bits long, for a theoretical total of 232 (roughly 4.3 billion) unique addresses. In practice, much of that address space was reserved for various purposes, such as multicast or experimental use. Today, public unicast IPv4 addresses are no longer available from Regional Internet Registries in Asia/Pacific (APNIC) or Europe / Middle East (RIPE NCC). By mid 2014, they will no longer be available in North America (ARIN).

IPv4 addresses are represented externally in "dotted decimal". The 32 bits are broken up into 4 groups of 8 bits each. Each group is represented by a decimal value from 0 (all 8 bits off) to 255 (all 8 bits on). For example, a valid IPv4 address might represented as Internally, and on the wire, IP addresses are just a sequence of bits.

We can divide the IPv4 address space into 256 "/8" (pronounced "slash 8") blocks, each of which has 224 (about 16.7 million) addresses. All of the addresses in a given "/8" block all have the same bit pattern in the most significant 8 bits. The first "/8" block ("0/8") contains addresses from to The last "/8" block ("255/8") contains addresses from to

Blocks "224/8" to "239/8" (roughly 268 million addresses, or 6.25% of the total) were reserved as multicast addresses by RFC 5771, and addresses in these blocks may not be allocated to nodes for normal purposes.

Blocks "240/8" to "255/8" (roughly 268 million addresses, or 6.25% of the total) were reserved for future use by RFC 1112, and addresses in these blocks may not be allocated to nodes for normal purposes.

Some 21 "/8" blocks (roughly 352 million addresses, or 8.2% of the total) were allocated to non-government groups by Jon Postel before IANA took over allocation. These blocks are still owned by these groups (Stanford University returned their /8 block to IANA). Two of those companies actually own two "/8" blocks due to mergers (HP and AT&T).

Some 14 "/8" blocks (roughly 234 million or 5.4% of the total) were also allocated by Jon Postel to various parts of the U.S. government (mostly groups in the Department of Defense). They still own these.

This left 189 "/8" blocks, (roughly 3.17 billion, or 73.8 percent of the total) for allocating IPv4 public addresses to entire rest of the world (including most of the users in the United States).

ipv4 ripThe final five of the allocatable "/8" blocks were given to the five Regional Internet Registries on 3 February, 2011. Since then, no more IPv4 public addresses have been available to RIRs.

On 15 April, 2011, the first RIR (APNIC, who manage IP addresses for the Asia/Pacific region) ended normal IPv4 allocation when they reached their final 16.7 million addresses.

On 14 September, 2012, the second RIR (RIPE NCC, who manage IP address for EU and the Middle East) ended normal IPv4 allocation when they reached their final 16.7 million addresses.

Those remaining public addresses at APNIC and RIPE are available only in small lots of 1022 or fewer addresses, only once to any organization, and they must be used for transition to IPv6. That final pool of address must last each RIR for as much as 10 years, during the transition to a mostly IPv6 Internet.

It is currently predicted that the third RIR to reach the end of normal allocation of IPv4 will be ARIN (North America), around 25 December, 2014.

The United States, with under 5% of the world's population wound up with over 40% of the allocatable IPv4 public addresses, while the other 95% of the people must make do with the remaining 60%. Many countries were just getting started with large scale Internet deployment when IPv4 ran out for them. There is no shortage of IPv6 - every country can have as many as it could ever conceivably use. IPv6 makes the economic and cultural advantages of the Internet available to everyone.

In the mid 1990's the IETF estimated that at the rate addresses were being allocated, they would all be gone by the early 2000's. They encouraged users and ISPs to deploy Network Address Translation (NAT) and Private Addresses (RFC 1918) to stretch the lifetime of the IPv4 address space for a few more years. These measures have caused numerous problems by breaking the formerly worldwide single address space into millions of disjoint mini-Internets using private addresses, behind precious public IPv4 addresses. These measures have caused numerous problems with end-to-end connectivity (for example, with VoIP, multi-player games, and IPsec). Software that can traverse NAT (such as Skype) is very complicated to design and implement, and has many stability and security issues. NAT has had a chilling effect on network product innovation.

Some ISPs in the APNIC and RIPE regions still have some IPv4 public addresses in stock, but most are now running very low or are already out. They are now trying desperate measures, such as Carrier Grade NAT (CGN) to keep the IPv4 Internet going just a little while longer. These measures are causing significant problems with connectivity that used to work, and the total number of entries in the central routing tables. The IETF standards for these stopgap measures clearly state that they are not sustainable by themselves, but must be done only in conjunction with rollout of IPv6, which is the only long term solution.

There is no way to continue using only IPv4 much longer, especially with the explosive growth of devices such as smartphones and tablets each needing addresses, not to mention billions of other electronic devices coming to market that will need connections to the Internet.

When IPv6 was designed, it was assumed that it would be widely deployed before IPv4 was depleted. Most Internet users have put it off so long that now we have grave problems, and some transition mechanisms that might have been viable are no longer feasible.

Sixscape Communications is dedicated to the task of identifying barriers to the widespread deployment of IPv6, and creating products and services that can help adopters get around those barriers and accelerate adoption of IPv6.