Recently I noticed strange issue with macOS Big Sur 11.4 and 11.5 (Mac M1) where all FTP clients no matter which I use it will end up in same issue. (CyberDuck, FileZilla or just plain old MC). Issue was reported to my by other user on different network with same OS.
The issue is an FTP client will hang on MLSD command and will timeout. Sometimes you can list few directories and after a few seconds it will lock itself.
Same behaviour with TLS or just plain FTP. No network activity after MLSD. Checked with Wireshark.
12:06:29 Response: 257 "/public_html" is your current location
12:06:29 Trace: CFtpChangeDirOpData::ParseResponse() in state 5
12:06:29 Trace: CFtpControlSocket::ResetOperation(0)
12:06:29 Trace: CControlSocket::ResetOperation(0)
12:06:29 Trace: CFtpChangeDirOpData::Reset(0) in state 5
12:06:29 Trace: CFtpListOpData::SubcommandResult(0) in state 1
12:06:29 Trace: CControlSocket::SendNextCommand()
12:06:29 Trace: CFtpListOpData::Send() in state 2
12:06:29 Trace: CFtpRawTransferOpData::Send() in state 0
12:06:29 Trace: CFtpRawTransferOpData::Send() in state 2
12:06:29 Command: PASV
12:06:29 Trace: tls_layer_impl::on_read()
12:06:29 Trace: CFtpControlSocket::OnReceive()
12:06:29 Response: 227 Entering Passive Mode (*,*,*,*,133,42)
12:06:29 Trace: CFtpRawTransferOpData::ParseResponse() in state 2
12:06:29 Trace: CControlSocket::SendNextCommand()
12:06:29 Trace: CFtpRawTransferOpData::Send() in state 4
12:06:29 Trace: Binding data connection source IP to control connection source IP 192.168.1.145
12:06:29 Trace: tls_layer_impl::client_handshake()
12:06:29 Trace: Trying to resume existing TLS session.
12:06:29 Command: MLSD
I did test this with macOS Big Sur 11.2 with different MacBook (Intel) on same Wifi network with same version of FileZilla and it works without issue.
Also I noticed that on M1 Big Sur 11.4 and 11.5 sometimes Chrome will get "connection timeout" and im also unable to connect via SSH. My bet is there is something wrong on TCP.
Update: So I checked traffic with Wireshark and looks like for some reason there is one TCP SYN packet and on Big Sur 11.2 ill receive SYN ACK from FTP server. With Big Sur 11.4 and 11.5 there is TCP SYN but no ACK response from server. Server will receive SYN bud won't respond to that packet with ACK.
