Any one knows what id's full meaning when doing nslookup?

[Larry Liu]

Thanks.  That's what the O'Reily book writes.
What I want to know is:

How is this id set?
Does it get reset to 0 or 1 in some period of time?
Is it in any way related to a DNS sever's internal operation?

O'Reily book mentions no thing deeper about the identifier. Maybe it is 
extremely trivial?

Barry Margolin wrote:

>In article <bor24n$1406$1 at sf1.isc.org>, Larry Liu  <Larry.Liu at cavcf.org> wrote:
>  
>
>>Below is a nslookup result with "set debug".  Does anyone have a full 
>>understanding  for id=15 in line 3 ?  Is the the 15th query from a 
>>particular client before the ttl, expiration day, or otherwise?  Thanks.
>>    
>>
>
>It's an identifier set by the client, used to match up the corresponding
>reply.
>
>  
>