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How can I view and clear my DNS cache content?. A. When a Windows XP or Windows 2000 machine queries a DNS server, the response is either positive (a match was found) or negative (no match was found). The OS stores these results in a local DNS cache so that local clients don't repeatedly query the DNS server for the same address. These DNS cache entries are known as DNS Resource Records (RR), and the DNS resolver always checks the local cache before it queries the DNS server. To view the current DNS resolver cache content and the entries preloaded from the Hosts file, go to the command prompt and type C:> ipconfig /displaydns Each entry shows the remaining Time to Live (TTL) in seconds. To clear the cache, go to the command prompt and type C:> ipconfig /flushdns Flushing the DNS cache clears all entries and reloads the entries from the Hosts file. [Windows XP and 2000 Tips & Tricks UPDATE 28 Oct 02] [Eric's incoming newsletters] |
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How can I configure the amount of time the DNS cache stores positive. and negative responses? A. By default, Windows stores positive responses in the DNS cache for 86,400 seconds (i.e., 24 hours) and stores negative responses for 300 seconds (i.e., 5 minutes). To modify these values, perform the following steps: 1. Start a registry editor (e.g., regedit.exe). 2. Navigate to the HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDnscacheParameters registry subkey. 3. From the Edit menu, select New, DWORD Value. 4. Enter the name MaxCacheEntryTtlLimit to change the positive cache period or the name NegativeCacheTime to change the negative cache period, then press Enter. 5. Double-click the new value, set it to the desired number of seconds (e.g., if you entered the name NegativeCacheTime, you could set the value to 0 to stop Windows from caching any negative responses), then click OK. 6. Repeat Step 5 for the other value, if required. 7. Close the registry editor. 8. Reboot the computer for the changes to take effect. [Windows XP and 2000 Tips & Tricks UPDATE 28 Oct 02] [Eric's incoming newsletters] |
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How can I ensure that the DNS resolver uses only results from. queried DNS servers? A. By default, if a client requests name resolution, the client will accept any response with the correct query ID, regardless of where the response is from. This behavior could lead to security problems if a rogue process that deliberately returns incorrect information exists on a system. To force the DNS resolver to match the source IP address of the response with the DNS servers that the DNS resolver queried, perform the following steps: 1. Start a registry editor (e.g., regedit.exe) on each client machine. 2. Navigate to the HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDnscacheParameters registry subkey. 3. From the Edit menu, select New, DWORD Value. 4. Enter the name QueryIpMatching, then press Enter. 5. Double-click the new value, set it to 1, then click OK. 6. Close the registry editor. 7. Reboot the machine for the change to take effect. [Windows XP and 2000 Tips & Tricks UPDATE 28 Oct 02] [Eric's incoming newsletters] |
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© Copyright
2002
Eric Hartwell.
Last update:
11/4/2002; 5:45:35 PM.
This theme is based on the SoundWaves
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"Data! data! data!" he cried impatiently. "I can't make bricks without clay."
— Sherlock Holmes to Dr. Watson in "The Adventure of the Copper Beeches" by
Arthur Conan Doyle.
"I
like deadlines," cartoonist Scott Adams once said. "I especially like the
whooshing sound they make as they fly by."
"There is nothing like that feeling of spending days and days banging your head
against a wall trying to solve a programming problem then suddenly finding that
one tiny obscure and seemingly unrelated piece of the puzzle that unlocks the
solution. Oh yeah!"
- Chris Maunder, CodeProject Newsletter 28 Jan 2002
"Management at eSnipe,
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- Tom Campbell, president of
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