Order of DNS selection

[Robert Gahl]

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?


===
Bob Gahl Bicycle (Ryan Vanguard) Mobile ||     @
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"Sahn joong moe low ful how jee yah ching wong" - "When the
mountain has no tigers, the monkey will also declare himself
king." Chinese Proverb