Unable to login to ECMWF FTP server - Connection closed after AUTH TLS command

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1

Dear ECMWF Support Team,

I hope this message finds you well. I’m encountering an issue when trying to connect to the ECMWF User FTP service (ftp.ecmwf.int). Despite multiple attempts, I cannot complete the login process, and the connection is consistently closed by the server after sending the “AUTH TLS” command.

Below is a summary of the connection logs:

  • Status: Successfully resolved the address of ftp.ecmwf.int and established a connection to 136.156.208.195:21.

  • Server response: Received the welcome message (“220- European Centre for Medium-range Weather Forecasts… All connections and transfers are logged”).

  • Command sent: After the welcome message, the client sends “AUTH TLS” to initiate a secure connection.

  • Error: Immediately after sending “AUTH TLS”, the connection is closed by the server, with the error message: “Connection closed by server” and “Failed to connect to server”.

This issue persists across multiple retries, and I’ve verified that my network connection is stable. I’m using a standard FTP client (FileZilla-like) with default settings for TLS encryption.

Could you please assist in diagnosing the cause? Possible areas to check:

  1. Does the ECMWF FTP server currently support TLS encryption via the “AUTH TLS” command?

  2. Are there any temporary server-side issues affecting secure connections?

  3. Might there be specific configurations required on the client side to connect successfully?

Thank you for your time and support. I look forward to your guidance on resolving this issue.

Best regards,

2

Good morning @Wang_longtsing ,

I have forwarded your message to ECMWF’s service desk. I’ll let you know once I understand the best solution to your issue.

Kind regards,

Josh

3

Dear @Wang_longtsing ,

  1. Yes, AUTH TLS is supported.

  2. We haven’t got any other reports about issues with the FTP server. I have tried today to connect using FTP client from Linux machine and Transmit app from Mac and both worked without problems.

  3. We do not ask for any specific configuration on the client side.

Maybe we can run some further test to reproduce your issue if you can tell us which OS system and which FTP client you use to connect?
Thank you!

Bojan

4

Hello @Wang_longtsing

One tip which might help you is to make sure that your app / client is using what’s called 'passive ftp’ rather than ‘active ftp’. The difference is that active ftp will open up a new port number to do the transfer but this will be blocked by firewall. Passive ftp does the transfer of data on the same channel.