At the 2015 Campus Technology summit in Boston last week, the CEO of the American Registry for Internet Numbers (ARIN) indicated that the organization has about two weeks worth of IP addresses to distribute to organizations that request address blocks. In July 2015, the organization implemented a waiting list for unmet requests, as the demand for IP address blocks outpaces the remaining available inventory.

The global status of IPv4 exhaustion

At present, there are 223 assignable blocks available, or using the provided counter, 0.00374 of a /8 available for assigning — in total, less than 43,000 IP addresses, according to Hurricane Electric stats. Note: This is only for ARIN, the nonprofit organization that handles IP assignment for the US, Canada, and some Caribbean countries.

Corresponding regional internet registries (RIRs) around the world include APNIC, servicing Asia-Pacific countries, which began distributing IP addresses out of the last /8 provided to it by ARIN in April 2011. RIPE, which serves Europe and Central Asia, began distributing IP addresses out of the last /8 in September 2012. LACNIC, which serves Latin America and parts of the Caribbean, began assigning IP addresses out of the last /8 in June 2014.

The current situation for ARIN is somewhat more urgent, relative to the circumstances with other RIRs. ARIN implemented restrictive distribution policies after reaching the last /8 in April 2014, but for various reasons, including growth of IP-connected devices with the trend of the Internet of Things, currently holds far less available addresses than other RIRs — the current concern is complete exhaustion of available addresses for ARIN to distribute.

The problem with continuing with IPv4

Organizations that require additional IPv4 addresses would theoretically be left to the transfer market. ARIN requires that all organizations trying to acquire IP blocks demonstrate a need for the addresses (though, a demonstrable need was required prior to the current scarcity), and all block transfers must be approved by the organization.

The concept of selling IP address blocks adds unnecessary expense to communication, and it is possible this practice would discourage organizations with excess IP addresses from returning these unoccupied blocks to their RIR. Aside from these fiscally-minded consequences, the arbitrary reallocation of IP addresses threatens causing the BGP global routing table — which is used in routers to determine the correct or most optimal path to connect to other systems — to grow exponentially due to IP fragmentation, beyond the capabilities of certain routers.

Problems arising from the growth of the BGP table were felt particularly strongly in August and September of 2014, in which various social networking websites, as well as eBay, iTunes, and app stores on iOS and OS X faced outages following the growth of the BGP table above 512,000 entries. (This is as observed from an APNIC router in Tokyo, which has an average view of the network. Other factors and configurations may produce a different number.)

As various models and revisions of routers are used across the internet, this is not a situation where all systems failed at once — some routers experienced problems at 512,000 entries, whereas others had issues at 524,288 (2^19) entries. The source of this issue is related to the possible number of entries a router can handle.

By default, a great number of routers have an embedded limit of 512,000 entries for IPv4 — perhaps the most ubiquitous (or problematic) of which is the Cisco Catalyst 6500 series. These entries are stored on specialized memory called TCAM, which is faster than Flash-based memory, but more costly to produce. To fix the problem, space in TCAM reserved for the IPv6 BGP table must be reallocated for IPv4, an operation that requires a reboot, which introduces downtime.

Where IPv6 deployment is in the US

Most computers are already compatible with IPv6 — support was first added in Windows 2000 (though it is only installed by default starting with Vista), Mac OS X 10.3 (Panther), and in version 2.6 of the Linux kernel. For mobile operating systems, support is a little more haphazard — Apple added support in iOS 4.1, and support was added for it in BlackBerry 10. As of version 5.1.1, Android still lacks DHCPv6 support, despite a protracted fight about the issue dating back to June 2012 in the Android issue tracker.

According to this chart from the Internet Society, Verizon Wireless has achieved 70.27% deployment on its network, T-Mobile (USA) is at 57.55%, AT&T is at 52.10%, and Sprint is at 3.15%. Additionally, Google Fiber is at 71.77%, Comcast is at 39.24%, and Time Warner Cable is at 20.10%.

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