IPv4 address exhaustion

IP address exhaustion is the decreasing supply of unallocated IPv4 addresses. This depletion has been a concern since the 1980s when the Internet started to experience dramatic growth. As a result, this has been the driving factor in creating and adopting several new technologies, including classful networks, Classless Inter-Domain Routing (CIDR) methods, network address translation (NAT) and a new version of the Internet Protocol, IPv6.

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 only just starting to consider widespread implementation and deployment of IPv6 technologies.

Synopsis

Main article: IP Address

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. These addresses are normally expressed in dotted decimal format (for example 66.230.200.110). Each octet, or part of the address, is a number from 0 to 255 and therefore there is a maximum of 4,294,967,296 addresses available for use. However, large blocks of 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 IPv4 device or service (which include desktop computers, mobile phones, embedded devices, and virtual hosts). This problem has been mitigated for some time using network address translation (NAT), whereby a single public Internet IP address can be shared by multiple internal local area network (LAN) hosts. Individual hosts behind NAT appear to be sending their data from the public IP address of the router used, and the router is able to keep track of which host originated the 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.

• As of April 21, 2009, Geoff Huston of APNIC predicts with detailed daily simulations an exhaustion of the unallocated IANA pool in August 2011. As of March 2009, Tony Hain of networking equipment manufacturer Cisco Systems predicts the exhaustion date to be around July 2011. These predictions are 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, during 14 months each individual regional Internet registry (RIR) will be able to supply with their last assigned addresses. These dates lie within a depreciation time of five to ten years of network equipment that is currently being acquired.
• 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.
• 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". 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".
• 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.

Less than three years until the first RIR exhaustion is a short time for the entire industry to transition to IPv6. This situation is aggravated by the fact that until exhaustion there will be no significant demand. 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 we should have started the transition to IPv6 much earlier, such that by the exhaustion date it would be completed, with all devices IPv6-capable, and IPv4 getting phased out.

It should be recognized that by the end of 2011, there will be new clients and servers on the Internet which have no choice but to only have an IPv6 address. For the rest of the Internet to be able to communicate with them they should then be able to: a) serve to IPv6 customers, and b) to access IPv6 servers. Within scalable solutions, the first requires Internet-facing servers to be on IPv6, and the second requires nearly all devices to be on IPv6.

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: unreasonable 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.

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 continually plummeted. As a result, formerly "dumb" mass-market devices such as mobile phones have become viable Internet hosts. With mobile phone market penetration continually increasing across the world, the result is a plausible scenario in which every person on the planet could be IP-addressable.

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. 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.

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 systems were too coarse for reasonable usage. For example, large companies or universities were given class A address blocks with over 16 million IPv4 addresses each, but 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.

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 things that can be done to mitigate the IPv4 address exhaustion are (not mutually exclusive):

• Network address translation (NAT)
• Use of private networks
• Dynamic Host Configuration Protocol (DHCP)
• Name-based virtual hosting
• 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 another method to get more use out of the IP address space generally. These addresses are subnetted by applying a subnet mask which denotes which portion of the address is the network portion and which is the host portion, cf. Classless Inter-Domain Routing.

Reclaiming unused IPv4 space

In the early days of the Internet, before classful network design and later Classless Inter-Domain Routing (CIDR), 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. 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 address 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 addresses that do not show up in the public BGP routing tables are actually in use on intranets. Again, it is likely that more time would be spent tracking down which IP address could be reclaimed than would extend the exhaustion date.

Finally, it may be possible to use IP addresses that are currently reserved by IANA. There are proposals to reclaim the class E network addresses; unfortunately, several operating systems and many types of routers would need to be modified or upgraded to make use of these addresses. Many operating systems' TCP/IP stacks, including Microsoft's widely deployed personal computer TCP/IP stack, disallow the use of class E IP addresses, resulting in configuration errors when attempting to assign the address to a host and refusing to communicate with hosts utilizing such an address. Similar TCP/IP implementations in many switches and routers also prohibit the use of the class E space. For this reason, the proposal seeks not to redesignate the class E space for public assignment, but instead looks to change the status of the class E range from "Reserved" to "Limited Use for Large Private Internets." This would allow the use of the class E space on large, private networks that require more address space than is currently available through RFC1918.

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 virtually all high-speed ISPs now have ISP-wide NAT in place, with an option of assigning a publicly routable IP address at an additional cost.

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 which country's legal system lawsuits would be resolved in.
• 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.
• IP addresses are numbers, so there is no intrinsic value of an IP address. Trading in goods with no intrinsic value (e.g. paper money) instead of goods with extrinsic value (e.g. food) can be risky and requires a stable market.
• Creation of a market requires a critical mass of buyers and sellers. Without that, there will not be price stability. And without an expectation of price stability, it is unlikely that companies will support formation of such a market.

IPv6 as a long-term solution

IPv6 is the standards-based solution to the IPv4 address shortage, endorsed 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).

External links

• Official current state of IPv4 /8 allocations, as maintained by IANA
• http://xkcd.com/195/ XKCD web-comic map of the internet, IPv4 address space, 2006.
• IPv6.com - Knowledge Center for Next Generation Internet IPv6
• ICANN recovers Large Block of Internet Addresses (14.0.0.0/8)