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I moved to a new MacBook (High Sierra initially and BigSur now) and all incoming network connections are blocked on the new MacBook (restored from the backup couple of weeks ago). On an old one everything works as expected.

I don't have neither Little Snitch nor other 3d party software that can block connections (at least I hope that). List of the software on both MacBooks are very similar but not identical (new versions, some software could be reinstalled manually).

Any ideas how to debug that situation? I rechecked many times that the firewall is off and even from router I can't ping the MacBook (the same is for port 80, 8888, 5432 or any other port I choose).

If I start an app on port let's say 8888, I can open it locally by ip address, but not remotely.

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    Have you try boot in Safe Mode (push shift key at boot) to verify if you have the same problem?
    – user415185
    Sep 27, 2021 at 16:54
  • Not yet. I'll try and put the result here.
    – FoxyBOA
    Sep 27, 2021 at 16:54
  • To clarify, are you unable to connect to port 8888 from another computer within your network (on your private intranet), or only from outside your network (on the public internet)?
    – pion
    Sep 28, 2021 at 0:37
  • @pion Exactly. I can't connect to any port on that computer from LAN (my private network) and from router as well. I tested the following ports (tcp) 80, 8888, 5432 and icmp (ping). Locally (via LAN ip address) everything works as expected. Firewall is turned off. No idea what blocks connections (OSX, LAN equipment etc.)
    – FoxyBOA
    Sep 28, 2021 at 1:22
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    @pion I mean that if a server started let's say on port 8888, I can connect to the server from MackBox as localhost:8888 and as lan-ip-address:8888. But from any other host I can't connect to an-ip-address:8888
    – FoxyBOA
    Sep 30, 2021 at 6:37

2 Answers 2

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I just had the exact same problem. I turned off the firewall but the connection attempts were still blocked. I could see all the incoming SYN requests in Wireshark but there was no SYN ACK and nothing else either.

The magic solution was to reboot the machine (with the firewall turned off). Now it's working.

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  • Unfortunately, no luck for me yet.
    – FoxyBOA
    May 25, 2023 at 10:05
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After a prolonged effort, I've pinpointed the issue to the "Checkpoint Endpoint Security" VPN client.

In certain versions like E80 and E82, it unexpectedly blocks all incoming connections despite disabling the firewall. Updating to the latest version (E87) resolves the problem.

See also https://superuser.com/questions/703587/all-incoming-connections-are-blocked-on-os-x#

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