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IPv4 address exhaustion is the decreasing supply of unallocated IPv4 addresses available at the Internet Assigned Numbers Authority (IANA) and the regional Internet registries for assignment to end users and local Internet registries, such as Internet service providers.

The depletion of the IPv4 allocation pool has been a concern since the 1980s when the Internet started to experience dramatic growth. IPv4 only provided for approximately 4 billion addresses with a current primary allocation granularity of /8 blocks by IANA, a limit that is estimated to be reached before 2012. The anticipated shortage has been the driving factor in creating and adopting several new technologies, including classful networks in the 1980s, Classless Inter-Domain Routing (CIDR) methods in 1993, network address translation (NAT) and a new version of the Internet Protocol, IPv6, in 1998.

The transition of the Internet to IPv6 is the only practical and readily available long-term solution to IPv4 address exhaustion. Although the predicted IPv4 address exhaustion approaches its final stages, most ISPs, software vendors and service providers are just beginning IPv6 deployment. A 2008 study by Google indicated that IPv6 penetration was still less than one percent of Internet-enabled hosts in any country.^[1]

Address depletion

Every host on an IP network, such as a computer or networked printer, is assigned an IP address that is used to communicate with other hosts on the same network or globally. Internet Protocol version 4 provides approximately 4.3 billion (short scale) addresses. However, large blocks of IPv4 addresses are reserved for special uses and are unavailable for public allocation.

There are insufficient publicly routable IPv4 addresses to provide a distinct address to every Internet device or service. This problem has been mitigated for some time using network address translation (NAT), whereby a single public IP address can masquerade multiple internal local area network (LAN) hosts using private addresses. Individual hosts behind NAT appear to be sending their data from the public IP address of the translator device, and the translator maintains a mapping of each host's source address originating traffic inside the network and forwards replies from the Internet accordingly.

Exhaustion date

Exhaustion will occur on all continents approximately at the same time, as all registries follow similar allocation policies of about 12 to 18 months stock allocated at each request. Only specific organizations that requested addresses in the pre-CIDR or pre-RIR eras possibly have significant unused address space remaining.

• On May 21, 2007, the American Registry for Internet Numbers (ARIN), the North American RIR, advised the Internet community that due to the expected exhaustion in 2010 "migration to IPv6 numbering resources is necessary for any applications which require ongoing availability from ARIN of contiguous IP numbering resources".^[2] It should be noted that "applications" include general connectivity between devices on the Internet, as some devices only have an IPv6 address allocated.
• On June 20, 2007, the Latin American and Caribbean Internet Addresses Registry (LACNIC), the South American RIR, advised "preparing its regional networks for IPv6" by January 1, 2011 for the exhaustion of IPv4 addresses "in three years time".^[3]
• On June 26, 2007, the Asia-Pacific Network Information Centre (APNIC), the RIR for the Pacific and Asia, endorsed a statement by the Japan Network Information Center (JPNIC) that to continue the expansion and development of the Internet a move towards an IPv6-based Internet is advised. This with an eye on the expected exhaustion around 2010 which will create a great restriction on the Internet.^[4][5]
• In March 2009, Tony Hain of networking equipment manufacturer Cisco Systems predicted the exhaustion date of the unallocated IANA pool to be around July 2011.^[6]
• On April 15, 2009, the American Registry for Internet Numbers (ARIN), the North American RIR, sent a letter to all CEO/Executives of companies who have IPv4 addresses allocated informing them that ARIN expects the IPv4 space will be depleted within the next two years.^[7]
• On 25 August 2009 ARIN announced a joint series event in the Caribbean region to push for the implementation of IPv6. ARIN reported at this time that less than 10.9% of IPv4 address space is remaining.^[8]
• As of January 2010, Geoff Huston's daily IPv4 Address Report predicts the exhaustion date of the unallocated IANA pool to be in September 2011.^[9] These predictions were derived from current trends, and do not take into account any last chance rush to acquire the last available addresses. After the IANA pool exhaustion, each individual regional Internet registry (RIR) will be able to supply from their last assigned addresses. These are expected to be fully allocated within 14 months.

The time remaining until the first RIR exhaustion is a short time for the entire industry to transition to IPv6. This situation is aggravated by the likelihood that until exhaustion there will be no significant demand for IPv6. David Conrad, the general manager of IANA acknowledges, "I suspect we are actually beyond a reasonable time frame where there won't be some disruption. Now it's more a question of how much." Geoff Huston claims the transition to IPv6 should have started much earlier, such that by the exhaustion date it would be completed, with all devices IPv6-capable, and IPv4 being phased out.

By the end of 2012, there will be new devices and services on the Internet that have no choice but to use only IPv6 addresses. For the rest of the Internet to be able to communicate with them older hosts must implement IPv6 as well, or utilize special translator gateway services.

After exhaustion

Apart from enforcing long-standing assignment rules, there is no significant effort to conserve the remaining IPv4 addresses. Consequently, it is expected that IANA will first run out permanently in early 2011, and then the RIRs in early 2012, and subsequently LIRs.

Even when the RIR and IANA pools are officially exhausted, there will still be unused IPv4 addresses, however, for example: historical over-allocations and user-abandoned ranges. The existing mechanisms do not address such scenarios. Mechanisms that have been discussed for this stage have included the reclamation of unused address space, re-engineering hosts and routers to allow the use of areas of the IPv4 address space which are currently unusable for technical reasons, and the creation of a market in IPv4 addresses.

ARIN, RIPE and APNIC, and the Internet community are conducting discussions on the question whether organizations that require IPv4 addresses can acquire them from other organizations.^[10]

Exhaustion-aggravating developments

While the primary reason for IPv4 address exhaustion is insufficient design capacity of the original Internet infrastructure, several additional driving factors have aggravated the shortcomings. Each of them increased the demand on the limited supply of addresses, often in ways unanticipated by the original designers of the network.

Mobile devices

As IPv4 increasingly became the de facto standard for networked digital communication, the cost of embedding substantial computing power into handheld devices dropped. Mobile phones have become viable Internet hosts. New specifications of 4G devices require IPv6 addressing.

Always-on connections

Throughout the 1990s, the predominant mode of consumer Internet access was telephone modem dialup. The rapid growth of the dialup networks increased address consumption rates, although it was common that the modem pools, and as a result, the pool of assigned IP addresses, were shared to a large degree amongst a larger customer base. By 2007, however, broadband Internet access had begun to exceed 50% penetration in many markets.^[11] Broadband connections are usually always active as the gateway devices (routers, broadband modems) are rarely turned off and require only little power, so that the address uptake by Internet service providers continued at an accelerating pace.

Internet demographics

There are hundreds of millions of households in the developed world. In 1990, only a fraction of these had Internet connectivity. Just 15 years later, almost half of them had persistent broadband connections.^[12]

Inefficient address use

Organizations that obtained IP addresses in the 1980s were often allocated far more addresses than they actually required, because the initial allocation method was inadequate to reflect reasonable usage. For example, large companies or universities were assigned class A address blocks with over 16 million IPv4 addresses each, because the next smaller allocation unit (Class B network) was too small for their intended deployments.

Many organizations continue to utilize public IP addresses for devices not accessible outside their local network. From a global address allocation view point, this is inefficient in many cases, but scenarios exist where this is preferred in the organizational network implementation strategies.

Due to inefficiencies caused by subnetting, it is difficult to use all addresses in a block. The host-density ratio, as defined in RFC 3194, is an intuitive metric for utilization of IP address blocks.

Mitigation

Some methods of mitigation of IPv4 address exhaustion have been:

• Network address translation (NAT)
• Use of private networks
• Dynamic Host Configuration Protocol (DHCP)
• Name-based virtual hosting of web sites
• 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

Subnetting

Subnetting is a popular method of managing and subdividing address space, thereby reducing additional allocations for expanding networks.

Reclaiming unused IPv4 space

Before classful network design and later Classless Inter-Domain Routing (CIDR) were introduced, large blocks of IP addresses were allocated to individual companies and organizations. IANA could potentially reclaim these ranges and reissue the addresses in smaller blocks. However, it can be expensive in terms of cost and time to renumber a large network so these organizations will likely object and legal conflicts are foreseeable.^{[citation needed]} Moreover, at the current rate of IPv4 address consumption, even if all of these could be reclaimed, it would only result in postponing the address exhaustion date.

Similarly, many IP addresses have been allocated to companies that no longer exist or were never used. Unfortunately, the stricter accounting of IP address allocation currently in place was not always in place and it would take quite a bit of effort to track down which addresses really are unused. Many IP address blocks are not routed in the global BGP routing tables, but are actually in use on intranets.

Some address space that was previously reserved by IANA has been added to the available pool. There are proposals to reclaim the class E network addresses.^[13][14] However, many computer and router operating systems and firmware are incompatible with the use of these addresses.^{[15][16][17][18][19]} For this reason, the proposal seeks not to redesignate the class E space for public assignment, but instead proposes to change its status from "Reserved" to "Limited Use for Large Private Internets." This would allow the use of the space on large, private networks that require more address space than is currently available through RFC 1918.

ISP-wide NAT

Similar to how many companies use NAT for most employee computers, an ISP can use NAT for many customers instead of giving them publicly routable IP addresses.

This has been already successfully implemented in some countries like Russia, where many broadband ISPs now have ISP-wide NAT in place, with an option of assigning a publicly routable IP address at an additional cost.^[20]

Markets in IP addresses

The creation of markets to buy and sell IPv4 addresses has been proposed many times as an efficient means of allocation. The primary benefit of an address market would be that IPv4 addresses would continue to be available, although the market price of addresses would be expected to rise over time. These schemes have major drawbacks that have prevented their implementation, as outlined in RFC 2008:

• The creation of a market in IPv4 addresses would only delay the practical exhaustion of the IPv4 address space for a relatively short time, since the public Internet is still growing. This implies that absolute exhaustion of the IPv4 space would follow within at most a couple of years after the exhaustion of addresses for new allocations.
• The concept of legal "ownership" of IP addresses as property is explicitly denied by ARIN and RIPE policy documents and by the ARIN Registration Services Agreement. It is not even clear in which country's legal system the lawsuits would be resolved.
• The administration of such a scheme is outside the experience of the current regional address registries.
• Ad-hoc trading in addresses would lead to fragmented patterns of allocation that would vastly expand the global routing table, resulting in severe routing problems for many network operators which still use older routers with limited FIB memory or low-powered routing processors. This large cost placed on everyone who uses the Internet by those that buy/sell IP addresses is a negative economic externality that any market would need to correct for.
• Trading in IP blocks that are large enough to prevent fragmentation problems would reduce the number of potentially tradeable units to a few million at most.
• The cost of changing from one set of IP addresses to another is very high, reducing the market liquidity. Organizations that can potentially reorganize their IP addresses usage to free them up so that they can be sold will demand a high price and once bought, will not be resold without a large profit. The cost of renumbering an organization's IP address space each time is comparable to the cost of switching to IPv6 once.

Long-term solution

IPv6 is currently the only viable solution to the IPv4 address shortage, endorsed and implemented by all Internet technical standards bodies and network equipment vendors. In addition to other design improvements, it replaces the 32-bit IPv4 address (4.3 billion possible hosts) with a 128-bit address for a capacity of 3.4×10³⁸ hosts. IPv6 has been in active production deployment since June 2006 when organized worldwide efforts of testing and evaluation ceased (6bone).

References

External links

• Official current state of IPv4 /8 allocations, as maintained by IANA
• IPv6.com - Knowledge Center for Next Generation Internet IPv6
• ICANN recovers Large Block of Internet Addresses (14.0.0.0/8) 2008-02-10
• Global Policy Proposal for Remaining IPv4 Address Space – Background Report 2008-09-08