DNS requests are cached to speed look up times for the host, but sometimes the information gets corrupt or is no longer correct. In that case you will need to flush your DNS cache. We will need to open the “Terminal” which is located in applications/utilities

Mavericks OSX 10.9

The command below will flush your DNS cache:

dscacheutil -flushcache

On Mavericks you will also need to reload DNS with the command below:

sudo killall -HUP mDNSResponder

And that should do it. I have also included commands for earlier versions of OSX below.

Mac OSX Lion 10.7 and Mac OSX Mountain Lion 10.8

sudo killall -HUP mDNSResponder

Mac OSX 10.5 and Mac OSX 10.6

dscacheutil -flushcache

Mac OSX 10.4 and below

lookupd -flushcache