Order of DNS selection

Joseph S D Yao jsdy at cospo.osis.gov
Mon Dec 11 21:59:36 UTC 2000


On Mon, Dec 11, 2000 at 10:03:55AM -0800, Robert Gahl wrote:
> When one registers a domain at, say, Network Solutions, they are typically 
> given a primary and secondary DNS server. My question is "How does bind 
> resolve which one to use when an external site is attempting a lookup?"
> 
> That is, does the third party machine (ISP?) always go to the primary and 
> if the primary is non-responsive, it goes to the secondary to achieve 
> resolution, or does it do some sort of heuristics against the "list" of 
> posted DNS servers and select one based on some resultant test of 
> closeness? Or, is it simply "round robin or which one responds first?"
> 
> I had thought it was primary, then secondary, and now I'm not so sure 
> anymore. Can anyone illumine me?

Primary and secondary are totally meaningless in name resolution.  To
the resolver, they are only peer servers.

At first, querying is at random.  I know that for root servers, the
resolving server eventually finds one "closest" and tries to use it.  I
don't remember how this has changed over the years, but I believe that
currently 'named' tries to do something similar with other domains.
Certainly, it will always skip over non-responsive servers and stop at
the first authoritative responsive server.

-- 
Joe Yao				jsdy at cospo.osis.gov - Joseph S. D. Yao
COSPO/OSIS Computer Support					EMT-B
-----------------------------------------------------------------------
This message is not an official statement of COSPO policies.



More information about the bind-users mailing list