Active Directory Cookbook

13.11. Clearing the DNS Cache

Problem

You want to clear the DNS cache. The DNS cache contains resource records that are cached for a period of time in memory so that repeated requests for the same record can be returned immediately. There are two types of DNS cache. One pertains to the resolver on any Windows client (servers and workstations), and the other to the cache used by the Microsoft DNS server.

Solution

To flush the client resolver cache, use the following command:

> ipconfig /flushdns

To flush the DNS server cache, use any of the following solutions.

Using a graphical user interface

1. Open the DNS Management snap-in.

2. Right-click on DNS in the left pane and select Connect to DNS Server.

3. Enter the server you want to connect to and click Enter.

4. Right-click on the server and select Clear Cache.

Using a command-line interface

The following command will clear the cache on <DNSServerName>. You can leave out <DNSServerName> to run against the local server:

> dnscmd <DNSServerName> /clearcache

Using VBScript

' This code clears the DNS server cache on the specified server.
' ------ SCRIPT CONFIGURATION ------
strServer = "<DNSServerName>" ' e.g. dc1.rallencorp.com ' ------ END CONFIGURATION --------- set objDNS = GetObject("winmgmts:\\" & strServer & "\root\MicrosoftDNS") set objDNSServer = objDNS.Get("MicrosoftDNS_Server.Name="".""") set objDNSCache = objDNS.Get("MicrosoftDNS_Cache.ContainerName=""..Cache""" & _ ",DnsServerName=""" & objDNSServer.Name & _ """,Name=""..Cache""") objDNSCache.ClearCache ...