Sign up ×
Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Observation: If I use my local ISP DNS, or if choose a random Public DNS Server and ask it for, I get a different results in one country than I do in another country.

For example: I used to query from a shell on servers in distinct locations, and I get distinct results

I can understand the authorative servers for giving me different results based on my IP or GeoLocation or something like that, but how does a (possibly) caching DNS forwarder know how to differentiate? Even in the case that results were not cached and it has to ask to the Authorative server, my understanding was that the client IP is not forwarded by the DNS Server in such a request.

share|improve this question

2 Answers 2

up vote 3 down vote accepted

Google's resolvers are anycasted so the server you're querying also has a location somewhat close to your server's location. And the local Google resolver would get geo based answers from the authoritative DNS servers to cache for that region.

share|improve this answer
Thanks for that, but what I still don't understand is how ( gives different answers depending on where I query from. – Keith Jan 1 '13 at 19:42
I see that opendns also uses anycast, yet tracing to from both my clients goes to london, although one goes in via Level3 and the other by Tinet. – Keith Jan 1 '13 at 20:12
Ah, I think I have answered my own question with that last comment. I get my expected behaviour querying - same results regardless of where I query from. Thanks. – Keith Jan 1 '13 at 20:18

Anycast is generally what is used to accomplish what you're describing.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.