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Introduction to Four-byte AS Numbers

In a situation similar to the exhaustion of IPv4 address space, the current pool of unassigned 2-byte Autonomous System (AS) numbers is predicted to run out.

While IPv6 is the industry's preferred solution to the IPv4 shortage, a new expanded system, which extends AS numbers to four bytes in length, is designed to address the AS number shortage.

Working cooperatively through the NRO (the Number Resource Organization) and in conjunction with ICANN (Internet Corporation for Assigned Names and Numbers) the world's five Regional Internet Registries (RIRs) are taking a coordinated approach to the transition from 2-byte to 4-byte AS numbers.

A major change in AS number management policy is for the RIRs to issue 4-byte AS numbers. Please refer to Section 6.3, "Timetable for moving from two-byte only AS numbers to four-byte AS numbers" in "Policies for Autonomous System number management in the Asia Pacific region".

Network builders may experience connectivity issues if their own equipment or the routing policies and hardware of their upstream providers is not compliant with this emerging standard.

To assist the Internet community to address these issues, share information about solutions and on-going issues, and to provide a forum for general discussion about the introduction of 4-byte Autonomous System numbers, ICONS is providing this information in the hope that other community members, including ISPs, users, and vendors can contribute up-to-date information for the benefit of all community members.

RIR Warns To Upgrade Routers

Regional Internet Registries (RIRs) have warned that routers and network
management software should be upgraded ahead of the increased
distribution of 4-byte AS numbers. Press Release

AS Number Resources

Why 4-byte AS Numbers
Autonomous System (AS) numbers are an integral part of the Border Gateway Protocol (BGP), why do we need to change them?


4-byte AS Number Specifications
The specification of how BGP has been altered to support 4-byte AS numbers is described in an IETF Internet Standard specification. Links to the Specifications

BGP and AS Number Backgrounder
If it is all a little confusing, you might find this beginner's guide to Autonomous System numbers a good place to start.

Operational Implications
Does everybody have to upgrade their routers? What about you? If you don't need to use 4-byte AS numbers do you need to upgrade?

AS Number News
blog-posts: 'AS' is not an existing label

Add News


AS Numbers Bookmarks

Regional Internet Registries (RIRs), including the RIPE NCC (Network Coordination Centre), 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.

Posted 2087 days ago | View Bookmark Page

APNIC is warning organisations they need to ensure their network infrastructure is compatible with the new 32-bit AS routing numbers, to be introduced next January

Posted 2087 days ago | View Bookmark Page

On 13 June 2008, the Chair of the Address Supporting Organization Address Council forwarded a Proposed Global Policy for Autonomous System Numbers, ASNs, for ratification by the ICANN Board. Essentially, the proposal defines timelines and allocation principles for a transition from 2-byte to 4-byte ASNs.

Posted 2115 days ago | View Bookmark Page

What are Autonomous System Numbers (ASNs), and what role do they play in the technology of the Internet? This article explores the role of ASNs exploring how the AS space is structured and how AS numbers are used in the interdomain routing. Also has analysis of the consumption rate and has a brief overview of Internet routing architecture.

Posted 2115 days ago | View Bookmark Page
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