IPv4 address shortage is the exhaustion of the pool of unallocated Internet Protocol Version 4 (IPv4) addresses, which has been projected since the late 1980s.

IPv4 Description

Internet Protocol version 4 (IPv4) is the fourth version or fourth revision, in the development of the Internet Protocol (IP), it is widely used protocol as it routes most of the traffic on the Internet. It is a connectionless protocol that is used on the packet-switched network for example Ethernet. By providing identification for each device IPv4 provides the logical connection between network devices. There are numerous ways for configuring IPv4 with all kinds of devices – including automatic and configurations – which depends on the network type. IPv4 is based on the best-effort model which ensures neither delivery nor avoidance of duplicate delivery; all these aspects are handled by the upper layer transport.


It has been anticipated since late 1980, that IPv4 address will be exhausted. One of the factors for IPv4 depletion is development and deployment of its descendant protocol IPv6 and also IPv4 insufficient design capacity of the unique Internet infrastructure.

The Countdown Plan has four phases, and ARIN is currently in Phase Four:

  1. Phase One began in February 2011 when ARIN received its last /8 from IANA.
  2. Phase Two began in September 2012 when ARIN reached three remaining /8 equivalents.
  3. Phase Three began in August 2013 when ARIN reached two remaining /8 equivalents.
  4. Phase Four began in April 2014 when ARIN reached one remaining /8 equivalent.

Remaining IPv4 Inventory

Discrete Block Size (CIDR)
Number of Blocks Available
Per policy, a /10 was reserved out of the last /8 to facilitate IPv6 deployment and that space is not included in ARIN inventory count.

ARIN Description

The American Registry for Internet Numbers (ARIN) is the Regional Internet Registry (RIR) for the United States, Canada, and many other North Atlantic and Caribbean islands. ARIN controls the allocation of Internet number resources, which also includes IPv4 and IPv6 address space.

ARIN is one among the five Regional Internet Registries (RIRs) in the world, which provides following services

  1. Facilitates policy development by its members and stakeholders
  2. Provides services related to the technical coordination and management of Internet number resources
  3. Is a nonprofit, community-based organization
  4. Participates in the international Internet community
  5. Is governed by an executive board elected by its membership


The problem was not a bolt from blue. The Internet Engineering Task Force (IETF) has predicted the global growth of network-connected devices 20 years ago and in response drafted a new version of the Internet Protocol to address the looming shortage of IPv6.

IPv6 uses a 128-bit address space – that is, 2^128 – yielding far more potential addresses than IPv4’s 32-bit scheme, and in reality more addresses than there are grains of sand in the Earth’s crust.

So, why hasn’t everyone just switched over to IPv6?

Well, IPv6 is not backward companionable with IPv4, that means network operators need to run a dual stack IPv4/IPv6 network for many more years to come. And for IPv6 to be functional, it needs to be put into operation end to end, meaning IPv6 has to be enabled by transit providers, network hardware vendors, content providers, access providers, and endpoint hardware makers.

Since there was no economic motivation for being the first to invest in revamping the protocol support, many hardware and service providers stood on the sidelines and waited for a drive to build.

For enterprises, it made no logic to upgrade to IPv6 if their ISPs were still running IPv4. As John Brzozowski, fellow and chief architect for IPv6 at Comcast Cable puts it: We had a chicken-and-egg problem. “Service providers didn't want to implement IPv6 because the content providers weren't there, and content providers didn't want to implement it because the service providers weren't there.”