Microsoft KB Archive/245437

= How to Disable Client-Side DNS Caching in Windows =

Article ID: 245437

Article Last Modified on 3/1/2007

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APPLIES TO


 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows 2000 Professional Edition
 * Microsoft Windows 2000 Datacenter Server

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This article was previously published under Q245437



IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry



SUMMARY
Windows contains a client-side Domain Name System (DNS) cache. The client-side DNS caching may generate a false impression that DNS "round robin" is not taking place from the DNS server to the Windows client. Pinging the same A-record domain name may result in the client using the same IP address. This behavior is different from previous Microsoft operating systems.

NOTE: This article refers to the client portion of DNS. Do not use this information for making changes to DNS servers.



MORE INFORMATION
The actual DNS request is being sent to the local DNS cache. If the entry is listed there, Windows uses the entry and does not make the request to the DNS server. After the entry has timed out (based on its Time to Live, or TTL value), it is cleared from the local DNS cache. The next attempt sends the request to the DNS server.

To view the DNS cache, type ipconfig /displaydns at a command prompt.

To delete the entries in the DNS cache, type ipconfig /flushdns at a command prompt.

To Disable Client-Side DNS Caching
WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

 Start Registry Editor (Regedit.exe). Locate the MaxCacheEntryTtlLimit value under the following registry key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters

 On the Edit menu, click Modify. Type 1, and then click OK. Quit Registry Editor.

Note that this setting does not really disable the client-side DNS cache. Instead, it lowers the Maximum TTL value within the client's DNS cache to one second. This gives the appearance that the client-side DNS cache has been disabled. Each sequential ping results in a DNS query to the DNS server.

Keywords: kbenv kbhowto KB245437

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