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AS Number Change Could Affect Internet Routing from 1 January 2009

Amsterdam, 24 July 2008 - Regional Internet Registries (RIRs), including the RIPE Network Coordination Centre (NCC), have warned that routers and network management software should be upgraded ahead of the increased distribution of four-byte (also known as 32-bit) Autonomous System (AS) Numbers.

AS Numbers are a vital part of the Internet's core routing system, the Border Gateway Protocol (BGP). With existing two-byte AS Numbers predicted to run out in early 2011, RIRs will issue four-byte AS Numbers by default, unless otherwise specifically requested, beginning 1 January 2009, as the next phase of a transition from two-byte to four-byte numbers. Following a globally coordinated policy, the RIRs began allocating four-byte AS Numbers by request only in January 2007; January 2009 marks the transition to allocating four-byte AS Numbers by default.

Without timely support from vendors, network operators risk having routers and network administration systems that won't accept the expanded four-byte number format. As such, the RIRs urge operators to verify that their vendors' routers will support four-byte AS Numbers.

Geoff Huston, Chief Scientist at APNIC, the RIR for the Asia Pacific Region, expressed concerns over failure to prepare for four-byte AS Numbers: "AS Numbers are often used to identify external relationships, set routing attributes, and manage traffic. Learning from our current experiences with IPv6 preparation issues, Internet engineers designed four-byte AS Numbers to be backward compatible with much of the installed network infrastructure. But new entrants and networks that are expanding or merging will need new AS Numbers and, as of 1 January 2009, these will be, by default, four-byte AS Numbers. If router software and support systems in critical parts of the Internet's infrastructure aren't upgraded by January, we'll encounter some significant network routing problems. We're extremely concerned that a lot of routers and network management software out there cannot and will not be able to recognize four-byte AS Numbers".

An Autonomous System (AS) is a collection of networks, or routers, administered as a group sharing a common set of routing policies, each defined with a unique number, or AS Number. Massive Internet growth has depleted the existing pool of two-byte AS Numbers (65,536 numbers in total). As a result, engineers have expanded the AS Number space from two bytes to four bytes, to include over 4 billion AS Numbers. Some routers do not currently support the use of four-byte AS Numbers.

To help vendors understand what they need to do to provide four-byte AS Number support and to help network operators find products that support four-byte AS Numbers, APNIC has set up a special website at

Notes to Editors

About the Regional Internet Registries (RIRs)

Regional Internet Registries (RIRs) are independent, not-for-profit membership organisations that support the infrastructure of the Internet through technical coordination. There are five RIRs in the world today. Currently, the Internet Assigned Numbers Association (IANA) allocates blocks of IP addresses and ASNs, known collectively as Internet number resources, to the RIRs, who then distribute them to their members within their own specific service regions. RIR members include Internet Service Providers (ISPs), telecommunications organisations, large corporations, governments, academic institutions, and industry stakeholders, including end users.

The RIR model of open, transparent participation has proven successful at responding to the rapidly changing Internet environment. Each RIR holds one to two open meetings per year, as well as facilitating online discussion by the community, to allow the open exchange of ideas from the technical community, the business sector, civil society, and government regulators.

The five RIRs are:
AfriNIC - Africa region
APNIC - Asia and Pacific region
ARIN - Canada, many Caribbean and North Atlantic islands, and the United States
LACNIC - Latin America and parts of the Caribbean
RIPE NCC - Europe, Parts of Asia and the Middle East

Each RIR performs a range of critical functions including:

  • The reliable and stable allocation of Internet number resources (IPv4, IPv6 and AS Number resources)
  • The responsible storage and maintenance of this registration data
  • The provision of an open, publicly accessible database where this data can be accessed
  • RIRs also provide a range of technical and coordination services for the Internet community.

Media contacts:

For media enquiries please contact:
Blaise Hammond or Lucie Smith, Racepoint Group

tel: +44 20 8752 2274 / +44 20 8752 2271

lucie.smith _at_ racepointgroup _dot_ com / blaise.hammond _at_ racepointgroup _dot_ com