On 25Mar2011, at 09.17, 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 <z...@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.
Experience with a major backbone in the early 2000's that spanned 50 core sites and 4 continents - single AS is not really a problem. We chose IS-IS with wide metrics as the IGP, and one-layer of route-reflection for the bgp mesh control. The only reason I could possibly see doing multi-AS in a general case is if your route policies are different in different regions (i.e. in one region a peer AS is a 'peer' and in another region the same AS is a 'transit' or 'upstream'). You CAN do it with a single AS, but it's more painful... >> >> -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? > > Cheers, > > mh > >> >> >> >> > > > --- 李柯睿 Check my PGP key here: https://www.asgaard.org/~cdl/cdl.asc
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