Unable connect to FTP: Failed to retrieve directory listing

Symptoms

• FTP is not accessible with the error below:

  CONFIG_TEXT: Error: Connection timed out after 20 seconds of inactivity
  Error: Failed to retrieve directory listing

• There are several internal IP addresses with assigned to the external IP addresses.

• When connection is established from the server with the debug mode in Filezilla, the following records appear:

  CONFIG_TEXT: Response: 227 Entering Passive Mode (203,0,113,2,192,7).
  Trace: CFtpRawTransferOpData::ParseResponse() in state 2
  Trace: CControlSocket::SendNextCommand()
  Trace: CFtpRawTransferOpData::Send() in state 4
  Trace: Binding data connection source IP to control connection source IP 192.0.2.2
  Command: LIST
  Trace: CTlsSocketImpl::OnRead()
  Trace: CFtpControlSocket::OnReceive()
  Response: 150 Opening BINARY mode data connection.
  Trace: CFtpRawTransferOpData::ParseResponse() in state 4
  Trace: CControlSocket::SendNextCommand()
  Trace: CFtpRawTransferOpData::Send() in state 5
  Error: Connection timed out after 20 seconds of inactivity
  Trace: CRealControlSocket::DoClose(2050)
  Trace: CControlSocket::DoClose(2050)
  Trace: CFtpControlSocket::ResetOperation(2114)
  Trace: CControlSocket::ResetOperation(2114)
  Trace: CFtpRawTransferOpData::Reset(2114) in state 5
  Trace: CFtpControlSocket::ResetOperation(2114)
  Trace: CControlSocket::ResetOperation(2114)
  Trace: CFtpListOpData::Reset(2114) in state 3
  Error: Failed to retrieve directory listing

  Whereas, IP address 203.0.113.2 is bound with 192.0.2.3 internal IP in IIS > Sites > 192.0.2.3 > FTP Firewall Support > external IP address of Firewall.

• When the external IP address of Firewall is set to none, connection from the server over internal IP address is established fine.

Cause

Misconfigured routing/external Firewall settings.

Resolution

Contact your Hosting Provider in order to check NAT routing/filtering on the server.