How can I change or specify DNS Cache Timings on Windows 2003 Server?

I'm trying to configure a monitor to check that a website is resolvable to its IP address.  We recent had a DNS failure with our ISP and our external web sites could not be reached.  I have the monitor in place and it seems to work but the concern is that DNS will cache the result and report positive even when the URL is no longer resolvable.  

What i need to be able to do is limit the length of time a DNS resolution is valid in the cache, effectively forcing a recheck.  I have had a look at DNS itself but there is little to configure.  I found the following for DNS clients, but it is unclear what impact this would have if applied to a 2003 server:-

"Tuning DNS Caching under Microsoft Windows
You can modify the behaviour of the Microsoft Windows DNS caching algorithm by setting two registry entries in the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters registry key.
The MaxCacheTtl represents the maximum time that the results of a DNS lookup will be cached. The default value is 86,400 seconds. If you set this value to 1, DNS entries will only be cashed for a single second.
MaxNegativeCacheTtl represents the maximum time that the results of a failed DNS lookup will be cached. The default value is 900 seconds. If you set this value to 0, failed DNS lookups will not be cached."

Thanks in advance,

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Toni UranjekConsultant/TrainerCommented:

If I understand your problem correctly, you need to change TTL value of your web server record. If you are using MS DNS, open DNS console, select Advanced in View menu and then double click web server's record to change TTL.


ccfcfcAuthor Commented:

I have looked at that but i could not find anywhere to adjust a single entry or even the whole server.  The TTL looks like its counting down from 24hrs, so i'm guessing thats what the default is.  


Toni UranjekConsultant/TrainerCommented:
Which DNS server do you use?
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ccfcfcAuthor Commented:
MS Windows 2003 Server DNS
Toni UranjekConsultant/TrainerCommented:
Go to Administrative tools, open DNS managment console, can you locate yor DNS zone and web server's record? Can you double click this record or right click it and select Properties? If you have enabled Advanced in View menu of DNS managment console, you should see TTL defined at the bottom of window.
ccfcfcAuthor Commented:
Hi, yes i can find the entry under the cache, but the option to change the TTL is grayed out.
Toni UranjekConsultant/TrainerCommented:
I don't think we understand each other correctly. I have a feeling that you are trying to manipulate cached records on internal DNS server. Where is external DNS server that hosts record for your web server? You should change TTL on external server.
ccfcfcAuthor Commented:
hi, yes thats exactly what I am trying to do.  I want the DNS server to have a shorter cache lifespan so that a URL is checked more frequently than 24 (which seems to be the default).  
Toni UranjekConsultant/TrainerCommented:
Because you can't change TTL of single cached record, I'm offering "dirty" workaround solution. If you don't have too many records you can create primary zone for your external DNS domain on internal DNS, add appropriate records and modify TTL of web server record. This is common practice for manipulation of external namespace on internal servers.
ccfcfcAuthor Commented:
I'm not looking to change the TTL for a single cached record - I'm looking for a parameter that I set in one place on the server that drops the TTL for the cache overall.
Is the setting at the start of this question the correct one to change, and if I change it what impact would I expect it to have and what potential consequences ?

Toni UranjekConsultant/TrainerCommented:
In this case, setting from your original post are correct. This will have immediate impact on your network and DNS server because amount of DNS traffic from and to your server will increase significantly. Whether or not you will face performance problems it depends on DNS server hardware, available bandwidth and number of clients and of course mainly on how do you configure registry settings.

You can use Performance monitor's DNS counters (for example: Total Query Received) to observe impact of the change.

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Windows Server 2003

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