Information
A firewall is a piece of software that blocks unwanted incoming connections to a system. Apple has posted general documentation about the application firewall.
[http://support.apple.com/en-us/HT201642](http://support.apple.com/en-us/HT201642)
Rationale:
A firewall minimizes the threat of unauthorized users from gaining access to your system while connected to a network or the Internet.
Solution
Perform the following to implement the prescribed state:
1. Open System Preferences
2. Select Security & Privacy
3. Select Firewall
4. Select Turn On Firewall
Alternatively:
1. Run the following command in Terminal:
defaults write /Library/Preferences/com.apple.alf globalstate - int <value>
2. Where <value> is:
- '1' = on for specific services
- '2' = on for essential services