Different TTL Behavior from Microsoft DNS

[Martin McCormick]

	When one queries a BIND  DNS, the TTL in the response is
whatever TTL that particular zone has in it for that particular
record.  Yesterday, I was trouble-shooting some weirdness related to a
Microsoft DNS which is part of an Active Directory setup.  The record
was an MX record which the MS DNS had received from our master bind
DNS with a TTL of 600 seconds.

	When I used dig to query the MS box, I got a correct answer
but the TTL was less than 600 seconds.  I queried again and the number
was even less than before.  I then got it through my skull that
every query to the MS DNS returned a TTL based upon the number of
seconds left in the MS box's cache of the record.

	I wouldn't exactly call this wrong, but it is sure different
than what bind does.  It would appear that if 100 clients requested
that record from the MS system, all their TTL timers should time out
at the same second as the TTL timer on the Microsoft DNS.

	Is this behavior significant other than the fact it is different
than what I expected to see?

Martin McCormick WB5AGZ  Stillwater, OK 
OSU Information Technology Division Network Operations Group