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

[Barry Margolin]

In article <bor852$1asq$1 at sf1.isc.org>, Larry Liu  <larry.liu at cavcf.org> wrote:
>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?

It doesn't come from the server, it comes from the client.  The client puts
the ID into the query, and the server simply copies it into the reply.  The
client simply has to ensure that queries to the same server coming from a
particular client port have different IDs, so that it can tell which reply
is for which query.

If a particular application, like nslookup, makes several successive
queries, the simplest way to do this is to make the IDs sequential.  The
dig command, on the other hand, picks a random ID because it doesn't retain
any state from one invocation to the next.

-- 
Barry Margolin, barry.margolin at level3.com
Level(3), Woburn, MA
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