Turn the firewall on or off on your Mac
Quick answer
Open System Settings, click Network, then Firewall, and use the Firewall switch. On means your Mac turns away unwanted incoming connections.
Why it happens
Every Mac has a built-in firewall, but it's off when the Mac is new. It doesn't slow your browsing or block websites. It only decides which apps may accept connections coming in from other devices on the network.
How to fix it
Click the Apple menu in the top-left corner and choose System Settings.
Click Network in the sidebar, then Firewall. Turn the Firewall switch on, or off if you need it off for a moment. Your Mac may ask for your password.
Network›Firewall
Click the back arrow to return to the main Network page. The Firewall row there shows whether it's on or off.
If you turned it off to test something, turn it back on when you're done. Keeping it on is the safer choice, especially on café, hotel or airport Wi-Fi.
Still not fixed?
When an app stops working with the firewall on, you don't need to turn the whole firewall off. Click Options… on the same page, find the app or click + to add it, and set it to allow incoming connections. Options… stays dimmed while the firewall is off.
Network›Firewall›Options…
If AirDrop, screen sharing or file sharing stopped working, look in Options… for Block all incoming connections. That setting blocks almost everything, so turn it off unless you really want that.
Network›Firewall›Options…
If the switch is dimmed or won't move, you may not be an administrator on this Mac, or a school or company may manage it. Ask an admin user, or whoever set the Mac up, to change it for you.
If the switch keeps turning itself back after a restart and no one manages your Mac, contact Apple Support. It's not a hardware problem, but they can look at it with you.
Questions people ask
Is my Mac firewall on by default?
No. A new Mac has the firewall off. You can check and turn it on in System Settings, under Network, then Firewall.
Should I turn on the firewall on my Mac?
Yes, it's a good idea, and it's most useful on public Wi-Fi. It only affects connections coming in, so normal browsing and email keep working.
Why does my Mac ask if an app can accept incoming network connections?
That message comes from the firewall when an app wants other devices to reach it. Click Allow for apps you trust. You can change your answer later in Network, Firewall, Options….
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