Denis Walker

Making More 16-bit AS Numbers Available

Denis Walker
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Availability of 16-bit AS Numbers is getting low. We have many in reserve that have been returned but they need 'cleaning'. You can help with this.


The RIPE NCC currently has around 1,900 returned 16 and 32-bit Autonomous System (AS)  Numbers that are referenced in many objects. With the global supply of 16-bit AS Numbers becoming exhausted, there is a clear need for these resources from some operators. However, because they are referenced, they have not yet been reassigned.

Where are these references?

These AS Numbers are referenced in many objects. They are mostly in other AS Number objects in the policy statements of the "import:" and "export:" attributes and various set objects. We also found a handful of route objects which don't originate from these returned AS Numbers but reference them in other attributes. Detailed analysis shows a total of almost 4,000 objects referencing these 1,900 AS Numbers.

What can you do to help?

We need these references to be removed. This is best done by the maintainers of the referencing objects. One problem is the auto generation of many of these objects. So it won't help to just remove these references by a bulk update. The next time the object is generated the references will return. So the maintainers need to update any templates or scripts that generate the objects.

How will the RIPE NCC coordinate this activity?

At the Address Policy Working Group session at RIPE 66 , the RIPE NCC requested guidance from the RIPE community on what to do with these returned AS Numbers. Based on the feedback received there, and on the Address Policy Working Group Mailing List, the RIPE NCC will be taking the following actions:

  • We will send an email to the maintainer and contacts of the RIPE Database objects in which the returned AS Numbers are referenced, asking for the reference to be removed
  • We will send three additional reminders, at intervals of three weeks from each other, for a total of four emails
  • If, after four emails, the reference is still in place, we will update the RIPE Database object ourselves, removing the reference
  • If the reference is recreated within one month from deletion (possibly due to automatic updates), we will contact the organisation through means of communication other than email

Next Step

If one of your objects references a returned AS Number you will shortly receive an email from the RIPE NCC. In this email we will list which of your objects references which returned AS Number. When you receive such a mail, please remove the references and change any software you have that automatically generate your objects.

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About the author

From 2001 to 2015 I was a developer and then the business analyst for the RIPE Database with the RIPE NCC. During this time I have been involved in every aspect of it's design and development of the software, web services and infrastructure, it's philosophy, legal, political and policy aspects, documentation, testing and future planning and specifying of new features

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