Autonomous System (AS) Numbers

Like IP addresses, Autonomous System (AS) numbers are important Internet number resources. As the Internet has expanded over time, the original pool of available AS numbers has dwindled, and they are now running out.
As a result, engineers have adjusted the AS number specification from two bytes to four bytes. This means that the pool of AS numbers has grown from around 65,000 to over 4 billion.

Network managers and ICT vendors need to be aware of these changes and act now to ensure their networks and products are compatible with the new AS numbers.

What do you need to do?

If you have your own network:

  • Consult your router vendor
  • Consult your vendors of network management software/ Operating Support System
  • Consult your upstream connectivity provider

If you are a vendor to ISP and network managers:

  • Provide the necessary software upgrades for routers and network management software to support the use of 4-byte Autonomous System numbers

If you provide Internet connectivity:

  • Accommodate 4-byte AS numbers from your clients

What is an AS number?

An Autonomous System (AS) is a collection of networks administered as a group sharing a common set of routing policies, each defined with a unique number, or AS number. AS numbers were originally expressed as 16-bit (2 byte) numbers, but this was later expanded to 32-bit (4-byte) numbers, substantially increasing the pool of AS numbers.

Like IP addresses, the Regional Internet Registries (RIRs) distribute AS numbers according to the community based policies in their respective region.

The NRO promotes 4-byte ASN adoption

Working directly and through the RIRs, the NRO promotes the use of 4-byte ASNs in the following ways:

  • Development and implementation of a global policy that facilitates an ordered transition
  • Community outreach to the technical community
  • Research, education, and information distribution

Find out more

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