When applying content and security settings to a network, it is often useful to clear the DNS cache immediately afterward to facilitate the new settings taking effect. Since caches store results (pages) for recent queries, new settings may appear not to work until those cache results expire or are cleared.
Introduction to Clearing the DNS Cache
The DNS cache is a performance-enhancing feature used by Internet browsers, computers and DNS servers to store the results of recent DNS queries in order to increase the speed of future DNS queries. This is mostly good, except when you make changes to security and content filtering settings. The DNS cache may return results that fall into a category you specified to be filtered, which creates a temporary appearance that Umbrella is not working properly.
Therefore, it is recommended that you always clear the DNS cache of Internet browsers, computers and servers after setting or adjusting Umbrella filtering settings.
The following sections describe how to clear DNS cache on browsers, computers, and DNS servers.
Clearing the DNS Cache on Browsers
The following table provides instructions for clearing the DNS cache within common Internet browsers.
Internet Explorer 8 (Win)
- Go to the Tools menu, select Delete Browsing History, check all boxes (except passwords, if desired) and click Delete.
Internet Explorer 9 (Win)
- Select the Cog icon in the right-hand corner of the browser, select Delete underneath where it says Browsing History, check desired boxes, and then click Delete.
Mozilla Firefox (Win & Mac)
- Go to the Tools menu, select Clear Recent History and check all boxes. Under Time range to clear select Everything (except passwords, if desired) and click Clear Now.
Apple Safari (Win)
- Expand the Cog Icon in the upper right corner and select Reset Safari. Check all boxes and click Reset.
Apple Safari (Mac)
- Go to the Safari menu, select Reset Safari, check all boxes and click Reset.
Google Chrome (Win)
- Expand the Wrench Icon in the upper right corner and select History and check all boxes. Under Clear data for this time period, select Everything (except passwords, if desired) and click Clear Browsing Data.
Google Chrome (Mac)
- Under Go to the Chrome menu, select Clear Browsing Data and check all boxes (except passwords, if desired). Under Clear data for this time period, select Everything and click Clear Browsing Data.
Clearing the DNS Cache on Computers and Servers
The following table provides instructions for clearing the DNS cache on computers and servers. The commands need to be run at the command prompt with administrator privileges.
Computer and DNS Server by OS
Go to Command Prompt
Command to Use to
|Windows||Go to Start menu -> Run -> Type cmd -> press Enter/Return||ipconfig /flushdns|
|Mac OSX 10.4
|Click the Terminal icon in the dock or in Finder (in /Applications/Utilities/)||lookupd -flushcache|
|Mac OSX 10.5 & 10.6 (Leopards)||Click the Terminal icon in the dock or in Finder (in /Applications/Utilities/)||dscacheutil -flushcache|
|Mac OSX 10.7 & 10.8 (Lions)||Click the Terminal icon in the dock or in Finder (in /Applications/Utilities/)||sudo killall -HUP mDNSResponder|
|Open a terminal window (gnome-terminal, konsole, xterm, etc.)||sudo /etc/init.d/nscd restart
sudo /etc/init.d/networking restart