having to clear DNS cache frequently

Mark wrote:
> Hello
>
> My clients all point to my DNS server for resolution. Periodically
> one particular URL will fail to resolve on their PCs. If I clear the
> DNS server cache, resolution works for another 5 days or so. Any idea
> what's going on and whether or not I should setup some automated cache
> clearing task?

Have you changed the maximum cache TTL?
This is strange behavior in the fact that the default Maximum Cache TTL in
Windows 2000 is 1 day.
813964 - Description of DNS registry entries in Windows 2000 Server, part 2
of 3: http://support.microsoft.com/default.aspx?kbid=813964


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 >> Stay informed about: having to clear DNS cache frequently 

Thanks to all for the information.

What value do you recommend the maxcachettl be set to? I have not
played with it, although if the default is 1 day it seems like the
problem would have cleared after a day. Before I discovered clearing
the cache would restore the URL, the problem went on for at least 3
days with no change.

I also noticed a maxnegativecachettl entry. I set that to 0 to disable
negative cacheing. Maybe a bad record was being cached then sitting
there causing problems. That also defaults to 1 day though, so same
things as above: after 3 days it should have cleared up.

Mark
 >> Stay informed about: having to clear DNS cache frequently 

Mark wrote:
> Thanks to all for the information.
>
> What value do you recommend the maxcachettl be set to? I have not
> played with it, although if the default is 1 day it seems like the
> problem would have cleared after a day. Before I discovered clearing
> the cache would restore the URL, the problem went on for at least 3
> days with no change.
>
> I also noticed a maxnegativecachettl entry. I set that to 0 to
> disable negative cacheing. Maybe a bad record was being cached then
> sitting there causing problems. That also defaults to 1 day though,
> so same things as above: after 3 days it should have cleared up.

One particular URL?
What is the URL?
Are you using a forwarder?
What is the forwarder's IP address?


--
Best regards,
Kevin D. Goodknecht Sr. [MVP]
Hope This Helps
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 >> Stay informed about: having to clear DNS cache frequently 

Kevin - I don't use a forwarder, just root hints. I've never known why
I should specify a forwarder since the root hints work, but maybe
that's not a good practice.

The specific URL I see this problem with is: www.ncmb.uscourts.gov

My users haven't reported trouble with any other URLs.


Mark
 >> Stay informed about: having to clear DNS cache frequently 

Mark wrote:
> Kevin - I don't use a forwarder, just root hints. I've never known why
> I should specify a forwarder since the root hints work, but maybe
> that's not a good practice.
>
> The specific URL I see this problem with is: www.ncmb.uscourts.gov
>
> My users haven't reported trouble with any other URLs.
>
>
> Mark


Correction - it seems to be more than one uscourts.gov address causing
trouble.
Mark
 >> Stay informed about: having to clear DNS cache frequently 

Mark wrote:
> Kevin - I don't use a forwarder, just root hints. I've never known
> why I should specify a forwarder since the root hints work, but maybe
> that's not a good practice.

Actually, using root hints only or use a delegated root zone, which is my
preferred practice. You can download a delegated root zone from Internic.
294906 - How to Delegate All Internet Top-Level Domains on an Internal Root
DNS Server: http://support.microsoft.com/default.aspx?scid=kb;en-us;294906

> The specific URL I see this problem with is: www.ncmb.uscourts.gov

I don't see a problem that would cause an issue with this domain, all TTLs
and NS records and parent domains appear to be in line with RFCs. Verify
that secure cache against pollution is selected on the Advanced tab.
If the domain stops resolving again, you might use the DNS management
console to visually check that domain in the cache to make sure any cached
NS & SOA records are valid for the domain.
If you are using Root Hints, your Root Hints file may be corrupted or it may
have been hijacked. Check the Root Hints tab to see if only valid Root
Servers are listed and are resolved to correct IPs.

I prefer using a Delegated Root zone because if properly set up, they are
extremely difficult to hijack because only Authoritative DNS servers are
used for all resolution. Just make sure your firewall allows the Root Server
to make iterative queries, some firewalls will redirect all connections on
port 53 UDP and TCP to another DNS server, making iterative queries
impossible.

--
Best regards,
Kevin D. Goodknecht Sr. [MVP]
Hope This Helps
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===================================
 >> Stay informed about: having to clear DNS cache frequently