(Caution: Chris is a chemical engineer, not an anycast engineer) On Wed, 1 Sep 2004, Steve Francis wrote:
Bill Woodcock wrote:
...how good/bad using DNS anycast is as a kludgey traffic optimiser?
I'd hardly call it a kludge. It's been standard best-practice for over a decade.
If I read your original request correctly you were planning on: 1) having presence in multiple datacenters (assume multiple providers as well) 2) having a 'authoritative' DNS server in each facility (or 2/3/4 whatever per center) 3) return datacenter-1-host-1 from datacenter-1-authserver-1, datacenter-2-host-2 from datacenter-2-authserver-1, and so forth. This isn't really 'anycast' so much as 'different A records depending on server which was asked' So, you'd be dependent on: 1) order of DNS requests made to AUTH NS servers for your domain/host 2) speed of network(s) between requestor and responder 3) effects of using caching DNS servers along the route You are not, now, making your decision on 'network closeness' so much as 'application swiftness'. I suspect you'd really also introduce some major troubleshooting headaches with this setup, not just for you, but for your users as well. I think in the end you probably want to obtain PI space from ARIN and use that as the 'home' for your DNS and Application servers, or atleast the application servers. There was some mention, and research I believe(?), about the value of having a partial Anycast deployment, so 3/4ths of your capacity on Anycast servers and 1/4th on 'normal' hosts to guard against route flaps and dampening of prefixes... I'm sure that some of the existing anycast users could provide much mode relevant real-world experiences though. -chris