How Internet Explorer uses the cache for DNS host entries

Summary

In earlier versions of Internet Explorer (Internet Explorer 3.x), DNS host entries are cached for 24 hours by default. In many cases, this is too long. During this period, some host entries stop working because of change in the IP address of the remote server that was initially resolved.


Internet Explorer 4.x and later versions modify how DNS host entries are cached by decreasing the default time-out value to 30 minutes.

More Information

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.

In some cases, this new time-out setting is too short. If your environment has a number of clients that are connecting and are all performing DNS lookups every 30 minutes, you may experience an unwanted increase in network traffic. To modify this behavior, make the following registry change:

1. Start Registry Editor.

2. Locate and click the following key in the registry:

   HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings

3. On the Edit menu, click Add Value, and then add the following registry values:

   Value Name: DnsCacheTimeout
   Data Type: REG_DWORD
   Radix: Decimal
   Value: (time in seconds)
   
   
   Value Name: ServerInfoTimeOut
   Data Type: REG_DWORD
   Radix: Decimal
   Value: (time in milliseconds)

4. Quit Registry Editor.

For example, to set the time-out value to 10 minutes, use a value of 600 seconds.

Workaround

If you are making Synchronous calls in WinInet, the DNS timeouts do not work when set the way they are shown in the "More information" section. Asynchronous calls do pick up these values correctly.

            
hOpen=::InternetOpen(.....)
InternetCloseHandle(hOpen);
hOpen=::InternetOpen(.....);
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