Which setting in osx could block "ping localhost"?
The obvious choice would be if stealth mode were on. That blocks pings to localhost on all my Mac OS systems. Go to System Preferences, Security &amp; Privacy, Firewall, Firewall Options...  



Also, if you have "Block all incoming connections" that might also affect things. I would certainly turn off LittleSnitch since it also can and will block that sort of traffic if you haven't allowed it.