Enable Mac OS X StealthMode

Today I found I can't ping the localhost

ping 127.0.0.1
PING 127.0.0.1 (127.0.0.1): 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1
Request timeout for icmp_seq 2
^C
--- 127.0.0.1 ping statistics ---
4 packets transmitted, 0 packets received, 100.0% packet loss

And After some Google, it's related with the StealthMode, so you can turn it off

sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setstealthmode off

Refer

http://osxdaily.com/2015/11/18/enable-stealth-mode-mac-os-x-firewall/