Flush DNS Cache in Lion and Mountain Lion Changed

To flush the DNS cache in Mac OS X 10.5 and 10.6, run this command in Terminal:

sudo dscacheutil -flushcache

This as been changed in 10.7 and 10.8, as per an article from Apple, to clear it out, run this command:

sudo killall -HUP mDNSResponder

Apple also says:

“You might want to do this, as OS X keeps a local cache of resolved DNS queries for a time defined by the DNS server, but sometimes it may be necessary to reset the cache immediately and re-query a DNS server. For example, you might do this after an entry on the server is changed or a new entry is added.”