FTP Archives

How to fix “MLSD unable to build data connection” in ProFTP

I’ve come across an odd problem today on a server that’s been working fine for all kinds of FTP traffic for many years. Turns out that today, FileZilla started complaining about explicit TLS connections (when available) and gave the following error message: 425 MLSD unable to build data connection: operation not permitted Clients could still … Read more

How to allow resuming FTP uploads in Plesk and ProFTP

ProFTP has a handy feature that lets uploads resume if they were interrupted, much like Safari downloads. This feature has to be enabled both on the server and the client. By default however, resuming uploads are disabled for security reasons – a wise precaution if anonymous uploads are allowed to a server. Here’s how to … Read more

How to fix ProFTP Handshake Trouble in Plesk

I fixed a problem this morning which wouldn’t let the latest version of FileZilla v3.10.1.1 connect to one of my client’s servers anymore. This had not been a problem in the past. The connection itself worked, but FileZilla failed due to a problem with the TLS Certificate. Here’s the error: Status: Initializing TLS… Error: Received … Read more

How to allow passive FTP connections in Plesk on Amazon EC2

AWS LogoPassive FTP connections should work out of the box in Plesk. If no other firewall or NAT is interfering with it.

I’ve recently noticed that when I install Plesk on Amazon EC2 every passive FTP connection fails with an error such as “Server sent passive reply with unroutable address. Passive mode failed.”

The reason for this mishap is twofold:

EC2 instances are behind a NAT, and therefore have an internal (unroutable) IP, and an external (public) IP. When a passive connection request comes in, ProFTP – Plesk’s default FTP Server – tells the connecting client its internal private IP address, and in turn quite rightly fails to connect to it.

On top of that, we need to make sure to open a range of ports we want to use for passive FTP connections and tell ProFTP only to use those.

Let’s do all this this step by step!

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