I am also experiencing a similar issue. Basically: On macOS, macOS Playground, and iOS, allowLocalEndpointReuse always behaves as if it were false, even when set to true On iOS Simulator and iOS Playground, allowLocalEndpointReuse always behaves as if it were true, even when set to false I have submitted a radar against Network Framework (FB8658821) which also has a test project. I have also posted the content of the radar to OpenRadar for others to see (search for FB8658821). But basically, here is the output I get: > On macOS & iOS: > Running test with allowLocalEndpointReuse false > [OK] Listener #2 not started. Did not allow endpoint reuse, as expected: POSIXErrorCode: Address already in use > Running test with allowLocalEndpointReuse true > [FAIL] Failed to allow endpoint reuse despite being requested: POSIXErrorCode: Address already in use > > On iOS Simulator & iOS Playground: > Running test with allowLocalEndpointReuse false > [FAIL] Allowed endpoint reuse, despite asking to deny it > Running test with allowLocalEndpointReuse true > [OK] Listener #2 started. Did allow endpoint reuse, as expected