Unable connect to FTP: Failed to retrieve directory listing

Symptoms

• FTP is not accessible with the error below:

  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:

  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.