On Sat, Jan 1, 2011 at 9:22 PM, Jeffrey 'jf' Lim <[email protected]>wrote:
> On Fri, Dec 31, 2010 at 4:21 PM, . <[email protected]> wrote: > >> I wrote about my experience back in Sep, and some other times before that >> - http://www.lugs.org.sg/pipermail/slugnet/2010-September/021026.html >> >> and you're quoting my reply to you > > I don't think it's fully accurate though. Ie, I think most CDNs use >> anycast rather than geolocation. >> >> > you think? Which CDNs are those? could you list them out? > I was either very confused, or the CDNs have changed their operations. The former sounds more plausible, but I recalled having observations that led to this concept of how they work: 1. service hostnames are cname'd to something else 2. nearest network with authoritative dns servers are reached via anycast 3. the returned ip is in the same network as the name server. - effectively, the same path selected for anycast dns traffic would be used for subsequent application traffic, with the benefit that these interactions would be with a stable physical server that wouldn't flap to another data centre unexpectedly due to variations in the network. 2 is still used by some CDNs. Eg, ns1-4.google.com is reached via anycast. 3 doesn't seem to be used anymore (if it ever was), replaced with some sort of lookup, and falling back to geolocation++.
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