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If I have 1 DNS server in the US, and 1 in the EU... if I'm in the EU and type in "" and it resolves, which server would handle the query? EU or US?

Consider that my US DNS Server is "ns1" and the other "ns2" and it's been setup, in that order, on my registrar for that domain...

(I'm trying to determine the viability of having cross-continent DNS servers/slaves)

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Both. NS records are returned in a round robin fashion.

As for the viability of having DNS servers in multiple places, this is typically done using anycast, which allows the same name/IP to be reached via the shortest network route regardless of the source of the traffic (DNS query in this case).

You're better off just paying someone to host your DNS, there's very little to be gained by doing it yourself.

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Thanks, but paying for my DNS hosting is going to be insane going from paying $15 every 3 months for unlimited zones and an API, to $150 per 100 domains PER MONTH. I have 2379 domains on that system and I have clients currently waiting in queue to be added ASAP. I hate that sold to Dyn. I'd rather push up 2 of my own DNS servers and never have to worry about (did I mention this?) manually editing 2379 domains' DNS settings at the registrar level... but thanks again for the answer. Was just wondering if it's worth it. I'll just push 2 servers in the US for now – AcidRaZor Jun 20 '11 at 16:17
The answer is "both". But you mis-stated the reason. It's not solely, or even necessarily mostly, round robin shuffling that causes this. Proxy DNS servers can do their own re-ordering as well (ironically, one of the the reasons that round-robin is so useless), which varies from software to software. The real answer is that there simply is no notion of either server being "first" in the DNS protocol. – JdeBP Jun 21 '11 at 12:22

Your resolver will contact the first recursive nameserver listed in resolv.conf or equivalent. This recursive nameserver will then contact the root nameservers for the tld for your domain. The root nameservers will direct your first recursive nameserver to each authoritative nameserver configured in your domain. If running BIND, the recursive nameserver will measure the round trip time to each of the authoritative nameservers listed and divide them into groups according to response time. The recursive nameserver will then select from the nameservers listed in the group with the shortest response time.

The most likely scenario is that queries originating from a european recursive nameserver will prefer a european authoritative nameserver for your domain.

To understand this more fully, please consult DNS and Bind published by O'Reilly.

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Only BIND and Microsoft's DNS server measure round trip times. Other resolving proxy DNS server softwares do not. – JdeBP Jun 21 '11 at 12:13
Edited to reflect the BIND-centric answer. Still, BIND is the dominant nameserver out there, 60% or greater of all nameservers at one count. – dmourati Jun 21 '11 at 16:34
@JdeBP I deleted my post ... thanks for correcting me, obviously my understanding is flawed ... may pick up that O'Reilly book. – Daniel B. Jun 21 '11 at 16:40
Beware of such poor statistics, dmourati. Many surveys don't make it clear that they are only counting content DNS servers. I haven't seen a survey of proxy DNS servers, and know of no-one who has even come up with a methodology for conducting such a survey. It's proxy DNS servers that we're talking about, and the percentages simply haven't been measured. (I suspect that ISC's BIND would turn out to have a small share and Microsoft's DNS server a quite large one if this were ever measured.) The figure that you are quoting is completely irrelevant. – JdeBP Jun 22 '11 at 8:49
Proxy nameservers are not common configurations in any environment I've ever seen. All information points to BIND as the leader over all nameservers regardless of type. See also DJBs stats for his djbdns which correlate closely with the numbers above. – dmourati Jun 22 '11 at 15:00

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