DNS Cache Resolver overrides NS TTLs

Barry Finkel b19141 at achilles.ctd.anl.gov
Thu Sep 7 13:36:55 UTC 2006

"Matthew Connor" <connah at gmail.com> wrote:

>Hi all!
>Would some please explain to me why Microsoft's DNS Cache Resolver has
>it's own built in TTL defaulting to 86400 (24 hours) instead of paying
>attention to the TTL that the domain's name server reports? This is
>very frustrating to me. We set our TTLs on our domains in BIND to be
>3600 (1 hour) so we can change our records and it get updated quickly.
>However, Windows caches names for a day without regard to that setting.
>It seems that since Windows being as ubiquitous as it is, the TTL
>setting on an SOA record is meaningless.
>I'm not just griping; I am truly hoping that I am wrong and someone
>will set me straight. I would ultimately like to have control over how
>long a client caches my domain's IP but it seems like Windows overrides
>me. Thanks for any input! 

I just ran a test.  I typed this command:

     dig mx.sth1.isc.org @ns-ext.sth1.isc.org.

and in the response I see

     sth1.isc.org.           1H IN NS        ns-ext.sth1.isc.org.
     sth1.isc.org.           1H IN NS        ns-ext.isc.org.
     sth1.isc.org.           1H IN NS        ns-ext.lga1.isc.org.
     sth1.isc.org.           1H IN NS        ns-ext.nrt1.isc.org.

Note the 1H TTL.  I then went to my Windows 2003 DNS Server and typed:

     server hippo308.anl.gov

and I received the answer

     Name:    mx.sth1.isc.org

I then opened the DNS management console and looked at the cached
entries.  I see

     ns-ext.nrt1.isc.org   TTL 0:0:58:28

This shows me that the nslookup query on the W2k+3 box produced a
cached entry with a correct TTL of 1H, which I then queried 1 1/2
minutes later.

What leads you to a different conclusion?  What build level of dns.exe
are you running?
Barry S. Finkel
Computing and Information Systems Division
Argonne National Laboratory          Phone:    +1 (630) 252-7277
9700 South Cass Avenue               Facsimile:+1 (630) 252-4601
Building 222, Room D209              Internet: BSFinkel at anl.gov
Argonne, IL   60439-4828             IBMMAIL:  I1004994

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