A Primer on Ipv4 Scarcity

A Primer on IPv4 Scarcity Philipp Richter Mark Allman Randy Bush Vern Paxson TU Berlin / ICSI ICSI Internet Initiative Japan UC Berkeley / ICSI [email protected] [email protected] [email protected] [email protected] This article is an editorial note submitted to CCR. It has NOT been peer reviewed. The authors take full responsibility for this article’s technical content. Comments can be posted through CCR Online. ABSTRACT of policies and governance with the technology for one of the With the ongoing exhaustion of free address pools at the Internet’s key resources: IP addresses. registries serving the global demand for IPv4 address space, Transmission of data between hosts across the Internet re- scarcity has become reality. Networks in need of address quires network layer addresses to name the endpoints—i.e., space can no longer get more address allocations from their IP addresses. In IP version 4, an address is represented by respective registries. 32 bits in the IPv4 header; hence there is a finite pool of In this work we frame the fundamentals of the IPv4 ad- roughly 4B addresses available. The network routing sys- dress exhaustion phenomena and connected issues. We elab- tem cannot keep enough state to deal with each individ- orate on how the current ecosystem of IPv4 address space ual address and therefore aggregates addresses into blocks. has evolved since the standardization of IPv4, leading to Originally blocks were allocated quite informally, but as the the rather complex and opaque scenario we face today. We Internet grew the complexity of the process did as well. At outline the evolution in address space management as well this point the address space is nearly entirely allocated. as address space use patterns, identifying key factors of the The Internet engineering community has long recognized scarcity issues. We characterize the possible solution space the impending exhaustion of IPv4, and in response designed to overcome these issues and open the perspective of address a replacement network-layer protocol with much longer addresses, IPv6. However, given the network layer’s critical blocks as virtual resources, which involves issues such as dif- 1 ferentiation between address blocks, the need for resource functionality, deploying IPv6 has proven difficult. There- certification, and issues arising when transferring address fore, it is now widely acknowledged that IPv4 will continue space between networks. to play a significant role for a long time within the confines of the current resource limits. While there are technical ma- neuvers we can still make to cope—e.g., adding layers of net- Categories and Subject Descriptors work address translation (NATting)—IPv4 address blocks C.2.3 [Computer-Communication Networks]: Network have already become a good that people exchange on sec- Operations—Network Management; C.2.2 [Computer- ondary markets. This reality brings yet another challenge Communication Networks]: Network Protocols—Proto- to the Internet’s policy and governance ecosystem. col architecture (OSI model) In this paper we first survey the evolution of the community’s management of IP addresses, for which we include Keywords both a discussion of the relevant policy structures and organizations, as well as empirical illustrations of the allocation IPv4 address exhaustion; IPv6 transition. and use of IP addresses over time. This history then leads to a set of observations about protocol design and the ac- 1. INTRODUCTION companying stewardship of community resources. The Internet’s design philosophy has facilitated enormous, rapid, and de-centralized growth, from a specialized research facility to a massive network of global importance. In turn, 2. EVOLUTION OF ADDRESS MANAGE- the tremendous growth enabled by the original design also MENT outpaced engineers, researchers, and policy makers. This is From its standardization in 1981 [69] until now, the man- clear in the numerous technical challenges that have arisen— agement of IP addresses has undergone drastic change. The from the lack of support for traffic engineering and routing changes were mainly a result of the evolution of the Inter- security, to the scalability issues of the initial mapping of net from a research network to a global commercial net- hostnames to IP addresses, to the lack of congestion control, work and the corresponding need to establish international to the inability to accommodate mobility. frameworks to manage its critical resources. We elaborate The community has largely been able to address such is- on this evolution in three time phases: The Early Registra- sues, albeit not always in the most elegant way given that tion Phase starting with the arrival of IPv4, the Needs-based changing a running system presents a challenging target in Provision Phase leading to the modern registry framework, many cases. However, under the surface, policy and gover- and the recently entered Depletion and Exhaustion Phase. nance issues arose. While scientists and engineers often ig- nore these issues, they ultimately shape what we can deploy 1See [32] for an understanding of IPv6 deployment from mul- in production. In this paper we consider the entanglement tiple viewpoints. 1 ACM SIGCOMM Computer Communication Review 21 Volume 45, Number 2, April 2015 RIR ARIN APNIC IANA Framework exhausted exhaustion address space allocation Initiation Last RIR projection IPv4 RIPE First RIR (RIPE) (AFRINIC) Standard exhausted founded founded AFRINIC APNIC ARIN LACNIC RIPE 2011 1981 1992 2005 2012 2015 LIR LIR LIR LIR LIR Early Registration Needs-Based Provision Depletion & Exhaustion end-user end-user end-user end-user end-user address space assignment Figure 1: Evolution of address management. 2.1 First Phase: Early Registration. Figure 2: Regional Internet Registry system. Initially, address blocks were allocated quite informally, address space4 arose in 1993–4 to further conserve publicly with Jon Postel serving as the “czar” personally attending to routable address space. each allocation. Postel periodically re-published RFCs enu- The modern framework of Regional Internet Registries merating the current address assignments (“please contact (RIRs), established in the years between 1992 and 2005, Jon to receive a number assignment”) [68]. At that time, ad- was very specific that conservation of address space was a dresses block allocations came in one of three classes: class 24 16 8 primary goal [43]. Five RIRs emerged, run as non-profit A networks (2 addresses), class B (2 ), and class C (2 ). organizations: RIPE for Europe in 1992, APNIC for the Classful addressing required a network identifier of one of Asia-Pacific in 1993, ARIN for the North-Americans in 1997, these distinct types, meaning that an operator requesting LACNIC for Latin America in 2002, and AfriNIC for Africa significantly more addresses than provided by a particular in 2005. threshold would instead be allocated a larger class network. The RIRs manage the distribution of IP address resources, Given the coarse-grained nature of the differences between each according to their local policies. Policies within the these classes, this policy led to heavy internal fragmentation RIRs are created using a community process; for details of and thus waste of address space. the process for each RIR, see [5, 9, 13, 53, 77]. For the most Early (1981) in the Internet’s evolution, parties had al- part, anyone can submit an RIR policy proposal which then ready registered 43 class A networks, allocating in total more undergoes an open discussion and review process, usually than 700M addresses [68]—vastly larger than the number of 2 carried out on mailing lists as well as in working group and hosts actually connected at that time. While scarcity in policy meetings. Adopting a proposal requires the commu- address blocks was not mentioned as a looming issue, the no- nity to reach a degree of consensus as reflected in these dis- tion of different sizes of networks (A, B and C) suggests early cussions. recognition of the finite nature of network address blocks and We sketch the structure of the RIR framework in Fig- the need for some sort of stewardship when parceling them ure 2. The IANA serves as the parent organization, allocat- out to different parties. The responsibility for the manage- ing large free address blocks (/8, i.e. 224 addresses, granu- ment of address space led to formalizing the notion of the larity) to an RIR once their regional free pool reaches a low IANA (first mentioned in IETF documents in 1990 [72]), threshold level. The RIRs then further allocate subsets of and, in the same timeframe Solensky, drawing upon alloca- these address blocks to their members, the so-called LIRs tion statistics, predicted IPv4 address exhaustion in the late (Local Internet Registries), which are mainly ISPs. The ’90s [86]. LIRs then assign address blocks to either smaller ISPs or for their own infrastructure. Thus, the allocation of a block 2.2 Second Phase: Needs-based Provision. reserves it for (future) use, while the assignment of parts 5 The need for a more distributed and parsimonious frame- of an allocation puts that subset into use. ISPs decide for work to allocate IP addresses—shaping the modern registry themselves whether to become LIRs—meaning entering a structure—appeared at least as early as 1990 [31], with fur- direct contractual relationship with the respective RIR—or ther refinements in 1992 and 1993 [41]. The discussion at to rely upon their upstream provider to assign address space 6 that time included the need to distribute the administra- to them. tion of IP address blocks to regional registries, covering dis- 4 tinct geographic regions to better serve the respective local Reserved address blocks not globally routable, and thus community—consciously fragmenting the registry. In ad- usable concurrently within multiple networks as long as 3 the given hosts do not require globally reachable IP ad- dition, classless inter-domain routing (CIDR) and private dresses [71].

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