Question about nameserver selection mechanism

Sebastian Castro Avila secastro at
Tue Feb 27 20:44:35 UTC 2007

Eric Jain wrote:
> According to DNS and BIND (5th edition) [] 
> "BIND chooses between a number of nameservers that are authoritative for 
> the same zone by selecting the nameserver with the lowest round-trip time."
> Can anyone point me towards more details about how BIND gathers and 
> maintains these statistics? Are all nameservers queried right away, or is 
> at most one nameserver queried for each lookup request (which would mean 
> that the results would have to be kept in some kind of database)?

As far as I know (and I write it here to get it clear for everyone),
when a BIND resolver receives an answer, keeps tracks of the RTT of the
servers queried and uses it to decide where the next query for that zone
will be directed to.

On the very beginning, without any information, I think the resolver
tries every NS available, and when the "recognition process" ends uses
the metric described above.

I remember i've seen a post on this mailing list giving a more detailed

Kind Regards

Sebastian Castro

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