[AusNOG] AS 4byte support in .au

[Geoff Huston]

On 02/07/2009, at 6:05 PM, James Spenceley wrote:

>>
>>
>> from the installed base of BGP all these 4 byte ASNs appear as AS
>> 23456. which is a perfectly fine AS number in the 2 byte AS BGP  
>> world.
>
>
> It's just not so great when you have more than one customer with  
> 23456.
>

yes, but thats not a _router_ issue - yes, your _operating support  
system_ needs to be aware of 4 byte AS numbers and needs to understand  
that eBGP customer is different from another eBGP customer even though  
the configs downloaded to the router will both use AS23456


>>
>>
>>> http://www.apricot.net/apricot2009/images/lecture_files/apricot-2008-32-bit-
>>> asn.pdf
>>> (Page 15) has a list of vendors and their versions required for
>>> support.
>>
>>
>> 4 byte AS numbers have been used in the Internet now for the last 2
>> 1/2 years - there are 31 visible today in BGP from where I sit in the
>> routing syste, and as far as I can see the Internet has been just  
>> fine
>> and noone has noticed, nor cared.
>
>
> I expect that all those 31 are configured to different parts of the
> Internet, so the Internet might be fine but our part of it would
> certainly have freaked out when the second customer turns up with
> 23456 :-)
>

Like I said, the router (or "BGP speaker" if you prefer) will be just  
fine - you can have as many distinct eBGP sessions with AS23456 as  
your heart (and the router's CPU and memory) desires without problem -  
forwarding works on next hop, not peer AS. The problem only arises  
when your internal IT systems start making assumptions about the  
relationship between AS numbers and customers that things may get a  
little twisted within your customer database.

Geoff