[arin-ppml] ARIN-2012-3: ASN Transfers - Last Call

Owen DeLong owen at delong.com
Wed May 9 21:01:07 EDT 2012

On May 9, 2012, at 5:30 PM, William Herrin wrote:

> On 5/9/12, John Curran <jcurran at arin.net> wrote:
>>> ARIN-2012-3: ASN Transfers
>> I was asked recently about the number of issued and not presently
>> advertised ASN's in the ARIN region, and thought it best to reply
>> publicly so everyone has the same information.
>> ARIN does not directly monitor ASN usage, but the esteemed
>> Geoff Huston does at <http://www.potaroo.net/tools/asn32/>
>>> From that report as of this morning -
>>   There are 24406 16-bit ASN's assigned to the ARIN region, with
>>   1099 presently in the regional free pool, 8259 unadvertised in
>>   BGP, and 15048 advertised in BGP.
> Interesting!
> For folks looking for a reason for AS number transfers, here's a thought:
> Implementing BGP communities is a nuisance with a 32-bit AS number.
> The convention is: 16 bits AS number, 16 bits tag. Virtually every
> shipping router is configured to display them in this manner. AS
> numbers larger than 65535 require a service provider who wants to
> offer communities to implement it in an unconventional manner. This
> can be expected to cause collisions and other confusion in this
> tagging mechanism for downstreams with more than one BGP link. Where
> an organization wishes to implement communities, a 16-bit AS number is
> *highly* desirable on a technical basis.
> Geoff's numbers suggest that there are upwards of 8,000 16-bit as
> numbers recoverable in the ARIN region, some third of the total. Given
> some incentive for the current holders to release them of course. When
> we run out of fresh 16-bit AS numbers, the availability of those 8,000
> would simplify operations for new ISPs and new ISP efforts which use a
> distinct AS number.

Actually, Geoff's numbers only suggest that there are ≤8259 recoverable
numbers. They provide no lower bound whatsoever on the number.

The mere fact that a number does not appear in a routing table visible
to Geoff Huston's research in no way indicates that it is not fully utilized
in a context which is not visible to Geoff and which still requires global

> Tom, is that a good enough reason to allow an AS number transfer? As a
> technical necessity to follow the conventions for BGP communities?

I don't know about Tom, but, for me, no, it really isn't. We're going to have
to face 32 bit ASNs with BGP communities sooner or later anyway. As
such, some form of convention needs to be adopted and we might as well
get on with it.


More information about the ARIN-PPML mailing list