MacOS – What are the services Apple’s Firewall considers essential

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I'm trying to determine what Apple's Firewall considers essential services. Apple's Firewall has the following settings available:

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A search of Apple's site does not reveal a support document on the topic: http://www.google.com/search?q=firewall+"essential+services"+site:apple.com.

What are the services Apple's Firewall considers essential? And which of those services will be allowed to receive incoming connections, and make outbound connections?

Best Answer

Essential services are those in the Core Services layer. When that option is checked, only the incoming connections to the below services will be allowed:

From https://developer.apple.com/library/mac/documentation/MacOSX/Conceptual/OSX_Technology_Overview/CoreServicesLayer/CoreServicesLayer.html

The technologies in the Core Services layer are called core services because they provide essential services to apps but have no direct bearing on the app’s user interface.

Some of the notable core services are

  • accounts & Social media integration
  • identity service
  • time machine
  • keychain services
  • notifications
  • iCloud storage
  • cloudkit
  • file coordination
  • bundles and packages
  • internalization/localization
  • bonjour
  • security services
  • address book

And from http://www.macworld.com/article/1131116/firewall.html#configure

The second option, “Allow only essential services,” will block anything except a few default services that support networking, such as Bonjour. Only use this option if you want to block everything; this will prevent any file sharing, remote access, or other services activated elsewhere on your Mac.

You can switch your firewall settings and run nettop in Terminal to monitor the network activity of each process that is running.

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