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Re: DNS Anycast as traffic optimizer?
On 2 Sep 2004, at 06:05, Bill Woodcock wrote:
If you want nearest server, anycast will give you that essentially 100% of the time.
Just to clarify this slightly, since I've known people to misinterpret this point: a clear, contextual understanding of the word "nearest" is important in understanding this sentence.
Here's an example: France Telecom was an early supporter of F-root's anycast deployment in Hong Kong. Due to the peering between OpenTransit and F at the HKIX, the nearest F-root server to OT customers in Paris was in Asia, despite the fact that there were other F-root nodes deployed in Europe. Those OT customers were indeed reaching the nearest F-root node, or maybe they weren't, depending on what you understand by the word "near".
Another one: where anycast nodes are deployed within the scope of an IGP, topological nearness does not necessarily indicate best performance (since not all circuits will have the same loading, in general, and maybe a short, congested hop is not as "near" as several uncongested hops).
For F, we don't worry too much about which flavour of "near" we achieve for every potential client: redundancy/diversity/reliability/availability is more important than minimising the time to do a lookup, and the fact that the "near" we achieve in many cases corresponds to what human users expect it to mean is really just a bonus.
However, in the general case it's important to understand what kind of "near" you need, and to deploy accordingly.