Most DNS clients cache the results of name resolution requests. This speeds up name resolution if multiple lookups are done to the same address, such as is common when browsing the web.
Sometimes a bad DNS entry will be cached and you will need to either flush the DNS cache to get rid of it, or wait up to 24 hours for it to be dropped from the cache automatically.
How to Flush DNS in Microsoft Windows
In Microsoft Windows, you can use the command ipconfig /flushdns to flush the DNS resolver cache.
You can also use the command ipconfig /displaydns to view the DNS resolver cache.
Windows IP Configuration
Successfully flushed the DNS Resolver Cache.
How to Flush DNS in Mac OSX
In Mac OSX, you can use the command lookupd -flushcache to flush the DNS resolver cache.
bash-2.05a$ lookupd -flushcache
How to Flush DNS in Linux
In Linux, the nscd daemon manages the DNS cache.
To flush the DNS cache, restart the nscd daemon.
To restart the nscd daemon, use the command `/etc/rc.d/init.d/nscd restart`.