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Most operating systems and DNS clients will automatically cache IP Addresses and other DNS results, this is done in order to speed up subsequent requests to the same hostname. Sometimes bad results will be cached and therefore need to be cleared from the cache in order for you to communicate with the host correctly. All major operating systems allow you to force this process, outlined below are the common steps you will need to follow in order to flush your DNS cache.

Windows 98/NT/2000/XP Flush DNS

Flushing the DNS on Windows is an easy process, outlined below is the steps that should be run if you wish to clear your DNS cache.

1. Open up a command prompt (Start > Run > "cmd.exe" > OK).
2. Type in the command "ipconfig /flushdns"

Windows Vista / Windows 7 Flush DNS

Flushing DNS on newer versions of Windows is almost as easy as the earlier versions but due to Microsofts security additions you must run the command prompt with administrator privileges.

1. Click the start button and navigate to the command prompt (Start > All Programs > Accessories > Command Prompt)
2. Make sure that you right click on the command prompt application and choose "Run as Administrator"
3. Type in the command "ipconfig /flushdns"

Note: It is also possible to type in "cmd" into the Windows Vista / Windows 7 start menu search field and then right click on the cmd.exe result instead of having to navigate through the various sub menus.

Mac OS X Flush DNS

Flushing the DNS in Mac OS X is an easy process, but the steps taken will depend on which version of OS X you are running.

If you are running Mac OS X Leopard, you need to do the following.

1. Open up a command terminal.
2. Run the command "dnscacheutil -flushcache"

If you are running Mac OS X 10.5.1 or below, you need to do the following.

1. Open a command terminal.
2. Run the command "lookupd -flushcache"

Linux Flush DNS

If you are running the nscd Name Service Cache Daemon then you will need to do the following.

1. Open up a command terminal (either as root or run step 2 with sudo)
2. Run the command "/etc/init.d/nscd restart"

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