DNS NS Question

Brad Knowles brad at stop.mail-abuse.org
Mon Nov 14 19:01:21 UTC 2005

At 2:07 PM +0000 2005-11-13, News wrote:

>  Does the DNS resolveer work like this.
>  Try ns1.example.net if there is no host found then it tries
>  ns2.example.net and so on. So it keeps working its way down until
>  one of the NS servers says it can Resolve the query?

	The resolver will retry the query and try alternative servers, 
but a lot depends on the order in which the records have been given 
to it, and what information it already has about which servers.

>  Or does it simply make a dns type query if it is not found then
>  say that is not there Return host not found.

	No, it will try more than once.

>                                                So the multiple NS
>  records just mean if it can make a tcp connection To the first
>  it tries the next one.

	The resolver won't fall back to TCP unless there is a truncation 
with the data returned via UDP.

>                          This is what I am trying to understand how
>  it works?

	The best explanation I know of can be found in the book _DNS and 
BIND_ by Paul Albitz and Cricket Liu.  If you want to understand how 
DNS works, buy a copy of this book, but make sure you get 4th edition.

Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.

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