Regional AS model

Owen DeLong owen at
Fri Mar 25 14:33:53 CDT 2011

On Mar 24, 2011, at 1:47 PM, Patrick W. Gilmore wrote:

> On Mar 24, 2011, at 3:40 PM, Owen DeLong wrote:
>> On Mar 24, 2011, at 12:42 PM, Zaid Ali <zaid at> wrote:
>>> I have seen age old discussions on single AS vs multiple AS for backbone and datacenter design. I am particularly interested in operational challenges for running AS per region e.g. one AS for US, one EU etc or I have heard folks do one AS per DC. I particularly don't see any advantage in doing one AS per region or datacenter since most of the reasons I hear is to reduce the iBGP mesh. I generally prefer one AS  and making use of confederation. 
>>> Zaid
>> If you have good backbone between the locations, then, it's mostly a matter of personal preference. If you have discreet autonomous sites that are not connected by internal circuits (not VPNs), then, AS per site is greatly preferable.
> We disagree.
> Single AS worldwide is fine with or without a backbone.
Only if you want to make use of ugly ugly BGP hacks on your routers, or, you don't care about Site A being
able to hear announcements from Site B.

> Which is "preferable" is up to you, your situation, and your personal tastes.  (I guess one could argue that wasting AS numbers, or polluting the table with lots of AS numbers is bad or un-ashetically pleasing, but I think you should do whatever fits your situation anyway.)
I don't see any significant downside to AS number consumption given a 32-bit AS Number space.
I do see significant downsides to disabling BGP loop detection.


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