Home > IPv4 address exhaustion

The IPv4 address space has 32 bits, limiting it to an absolute maximum of roughly 4.3×10⁹ (4.3 billion) possible addresses. For both administrative and technical reasons (the latter in large part being related to routing), IPv4 addresses are allocated in blocks which are restricted to sizes which are powers of 2; this leads to many addresses being unused at any given time. In addition to this, substantial parts of the IP address space are not easily usable because of early technical decisions reserving them for private network use, loopback addresses, multicast, and unspecified future uses, which has resulted in some of these limitations being programmed into devices; working around these limitations will require substantial amounts of re-engineering to increase the amount of available address space. Finally, some of the IPv4 address allocations made early in the development of the Internet (in the 1970s), when only blocks of 2²⁴ possible addresses (called a /8 in IPv4 address terminology) were supported, led to some institutions that were involved in the development of the Internet having disproportionally large allocations. MIT, for example, has an entire /8 block allocated to it.

In the late 1980s only three block sizes (/8, /16 and /24) were supported; since most institutions were too big for /24's, this led to rapid consumption of /16 blocks, and it was feared that the IPv4 address space would run out by the early 2000s. This has been addressed by a number of measures introduced to reduce the demand for new IPv4 addresses, including:

• CIDR, which allowed block sizes of any power of two, which led to more efficient allocation of addresses
• tighter control by Regional Internet Registries on the allocation of addresses to Local Internet Registries
• network renumbering , to reclaim large blocks of address space allocated in the early days of the Internet and now no longer needed
• DHCP, which allowed dynamic allocation of temporary-use addresses
• NAT, which allows a large number of hosts behind the NAT device to be globally represented by a single external IP address on the other side of the NAT device
• IPv6IPv6 is version 6 of the Internet Protocol; it was initially called IP Next Generation IPng when it was picked as the winner in the IETF's IPng selection process. IPv6 is intended to replace the previous standard, IPv4, which only supports up to about 4 b, the next version of the Internet Protocol, with vastly more addresses.

The top-level unit of allocation of IPv4 addresses is the /8 block, a unit of approximately 16 million addressses. As of April 20042004 is a leap year starting on Thursday (the link is to a full 2004 calendar), and has also been designated the: International Year of Rice International Year to Commemorate the Struggle against Slavery and its Abolition Elections are to be held in 73 co, 160 /8 blocks have been allocated out of a possible absolute maximum of 255.

As of 20042004 is a leap year starting on Thursday (the link is to a full 2004 calendar), and has also been designated the: International Year of Rice International Year to Commemorate the Struggle against Slavery and its Abolition Elections are to be held in 73 co, predictions for the exhaustion of the IP address space range from 20162016 is a Leap year starting on Friday. see link for calendar) Events 2016 Summer Olympics Host city to be chosen in 2009. November 8 United States Presidential and Congressional elections 2010s Years in the future. for unallocated pool exhaustion to 2023 for complete exhaustion of the address space. (It should be noted that historically these forward predictions for the date of address exhaustion have been unreliable; predictions from the late 1980s have not been borne out in practice.)

New needs for always-on devices, such as ADSL and cable modems, and the proliferation of mobile wireless devices such as laptop computers, PDAs and mobile phones, are putting pressure back on the consumption of IPv4 space. At the same time, the heavily populated countries of Asia such as India and China are rapidly rising in wealth, and it is clear that in time there are likely to be more than 4 billion always-on Internet-connected personal devices in the form of mobile phones alone.

This process may have already started, as the allocation rate of /8 blocks has risen sharply in the years 2002- 2004.

The planned long-term solution to the IPv4 address shortage is a transition to IPv6, with its 128-bit addresses. However, there are massive obstacles to be overcome for IPv6 deployment, including the need for roll-out of pervasive support for IPv6 throughout the Internet and its connected devices, and remaining architectural problems, such as the lack of proper support for IPv6 multihoming.

If IPv6 is not ready in time, a market in IPv4 addresses may need to be established prior to address exhaustion in an attempt to allocate these addresses as efficiently as possible.