Frequently Asked Question
1. Go to Applications -> Utilities -> Terminal.
2. Type the DNS command.
3. This command differs depending on which OS X version you use.
Mountain Lion or Lion: sudo killall -HUP mDNSResponder
Snow Leopard: dscacheutil -flushcache
Leopard and older: lookupd –flushcache
5. Type the administrator's password and press Enter on your keyboard.