Re: Regional AS model

[Michael Hallgren <m.hallgren () free fr>]

Le vendredi 25 mars 2011 à 02:09 -0700, Zaid Ali a écrit :
> On Mar 24, 2011, at 3:17 PM, Michael Hallgren wrote:
>
> > Le jeudi 24 mars 2011 à 14:26 -0700, Bill Woodcock a écrit :
> > > 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 () zaidali com> 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. 
> > > > >
> > > > > 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.
> > > > Which is "preferable" is up to you, your situation, and your personal tastes. 
> > >
> > >
> > > We're with Patrick on this one.  We operate a single AS across seventy-some-odd locations in dozens of countries, 
> > > with very little of what an eyeball operator would call "backbone" between them, and we've never seen any 
> > > potential benefit from splitting them.  I think the management headache alone would be sufficient to make it 
> > > unattractive to us.
> > >
> > >                                -Bill
> >
> > Right. I think that a single AS is most often quite fine. I think our
> > problem space is rather about how you organise the routing in your AS.
> > Flat, route-reflection, confederations? How much policing between 
> > regions do you feel that you need? In some scenarios, I think 
> > confederations may be a pretty sound replacement of the multiple-AS
> > approach. Policing iBGP sessions in a route-reflector topology? Limits?
> > Thoughts?
>
> I always look at confederations as a longer term plan because you have some idea how your backbone is going to shape 
> out. Knowing where you are going makes confederation planning easier. Start with RR's and then see if confeds make 
> sense.

Yes, I agree. Confed's is a choice, in particular if you need elaborate
policies between regions of your network. Police sessions between
sub-ASes, keep iBGP simple...

Say, you start with RR... If or once your network is large, and having
customers connected to it, migrating to conferedrations may be a
challenge. Right? Thoughts? Experiences?

mh

> Zaid