Let's see how this works automatically:
- Make sure that the only box that's checked is the one that says, "Automatically allow signed software to receive incoming connections"
- Take note of the applications listed in the list of allowed applications
- Click OK
- Open the Sharing preference in System Preferences
- Put a check in the box that says File Sharing or, if that's already selected, put a check in one of the other sharing boxes
- Re-open the Security and Privacy preference
- Click the Firewall Options button
- Look at the list of allowed applications
If you selected File Sharing in the Sharing preference you should now see File Sharing (AFP, SMB) in the list of allowed applications.
The beauty of Apple's built-in Application Level Firewall is that you don't need to do anything other than turn it on. Your Mac will take care of determining whether or not an application should be allowed to send and receive network traffic.
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