32 bits ASN on Cisco

Franck Martin franck at genius.com
Sun Apr 11 05:15:28 CDT 2010

Yes Gary, I understood how to run 16bit ASN with 32bit ASN, I'm just trying to confirm/understand how it is supported today on Cisco hardware.

I have seen for instance policy change in APNIC, as since this year they assign 32bits ASN (which could fall in the 16bit part if you are lucky) but if you want a 16bit, then you need to justify. I feel this policy is a bit premature as hardware does not support it. I guess this exhaustion is not as critical as for IPv4, but still... 

To come back, to your statement that says it is just supported on 7200, means you cannot use a 32bit ASN in production today on any hardware?

----- Original Message -----
From: "Gary T. Giesen" <giesen at snickers.org>
To: "Franck Martin" <franck at genius.com>
Cc: nanog at nanog.org
Sent: Sunday, 11 April, 2010 6:36:01 PM
Subject: Re: 32 bits ASN on Cisco

You can still request a 16 bit ASN from the registries, so if this is
a concern for a new deployment you're not out of luck (yet). There is
a compatibility mechanism, so you can still receive routes sourced
from (or passing through) 32 bit ASNs, they will simply appear as AS
23456. Even if you have 32-bit ASN-compatible gear, all your direct
peers need to support it as well (more or less), and many providers
still don't have support for this yet (for example, the 7600 platform
only just got support with 12.2(33) SRE0, and no one in their right
mind is running it in production yet).

A great resource for information on 32-bit ASN's is


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