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When attempting to listen on certain TCP or UDP ports, I get weird error messages regarding permissions (or generic messages, depending on the program used to bind).

The message in German is "Der Zugriff auf einen Socket war aufgrund der Zugriffsrechte des Sockets unzulässig", I believe this equals "An attempt was made to access a socket in a way forbidden by its access permissions". (Some programs just return a more generic error, this is the one reported by ncat).

The affected ports seem to change across reboots. This time, ports 61974-63949 seem to be affected. Last session, 63014-64989 were affected. (Both ranges are exactly 1976 ports long.) Both TCP and UDP are affected on the same ports.

TCPView/netstat do not show anything regarding those ports. A nmap port scan did not see any difference between the affected and unaffected ports.

Any idea what may cause such behavior?

2

Through trial-and-error (shutting down services and testing if the port can be bound), I determined the cause to be the Internet Connection Sharing (ICS) service. I apparently had it enabled on an interface (to provide my hosted wifi used for testing with internet), and it was probably reserving those ports for NAT.

Note that in general, it is possible for programs to bind a port, but not listen to it. They will still block the port, but they will not appear on netstat. I have created a separate question regarding how to detect such ports/programs.

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