[arin-announce] 2-byte Autonomous System (AS) Number Pool Nearing Depletion

ARIN info at arin.net
Wed Jan 22 10:33:34 EST 2014

As reported today by the Number Resource Organization (NRO):

In September 2013, the IANA issued its last remaining full block (1024)
of 2-byte AS numbers, with 512 going to APNIC and 512 going to Ripe NCC.
Of the 65,536 total AS numbers in the 2-byte pool, there now remain just

Following a globally coordinated policy implemented in January 2007, the
five Regional Internet Registries (RIRs) began allocating 4-byte AS
numbers upon request. In January 2009, a new, replacement global policy
went into effect that directed IANA and the RIRs to make no distinction
between 2 and 4-byte AS numbers, and to issue them from a common pool.
To date, thousands of 4-byte AS numbers have been issued collectively by
the RIRs, but there are still reports of issues with the widespread
deployment of these 4-byte numbers.

The NRO has been working in conjunction with ICANN on the transition
from 2-byte to 4-byte AS numbers since 2007 and has publicly advised
network operators to upgrade their routers and network management
software in anticipation of the increased distribution of 4-byte AS numbers.

However, the RIRs are finding that there are still routers out there
that do not support the use of 4-byte AS numbers, resulting in some
customers coming back to the RIRs to exchange their 4-byte AS numbers
for 2-byte AS numbers.

As the pool of 2-byte AS numbers is depleted globally, networks will
need to rely on 4-byte AS numbers to identify the distinct autonomous
networks that make up the Internet’s core routing system. It has now
reached a critical point where all network operators must prepare their
networks to support 4-byte AS numbers or risk the successful growth of
the Internet.


Communications and Member Services
American Registry for Internet Numbers (ARIN)

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