Regional AS model

Graham Wooden graham at
Thu Mar 24 16:51:06 CDT 2011

Quoting Zaid Ali <zaid at>:

> 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

Hi Zaid,

What timing - this is fresh on my mind too as I am in the middle of  
doing this myself with three locations, all with independent edges  
with different transit providers.  I actually do have a private Layer2  
circuit between, with one site being in the middle. I only have one  
public AS, but I have selected doing the confederation approach (which  
some may consider to be overkill with only three edges).

Each site has their own set of IPs and would originate out of their  
respective edge, and using EIGRP metric changes at each core to get from another edge if the local fails.  Each edge is then  
announcing each others' subnets with an extra pad or two to keep the  
asymmetrical routing down (the private L2 isn't as fast as my transits).

Good luck with your deployment!


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