The "425 Could not open data connection to port" error in FTP means your client established a control connection to the server but cannot open the secondary data connection needed to transfer files or list directories. This is almost always a passive/active mode issue.
Switch to passive FTP mode
In FileZilla: Edit > Settings > Connection > FTP > set Transfer Mode to Passive. Passive mode works behind NAT routers and firewalls, which is the network setup for the vast majority of users.
01. What Causes This Error
FTP uses two connections: a control connection (port 21) for commands, and a data connection for actual file transfers and directory listings. In active mode, the server tries to connect back to your computer on a random port. If your router, firewall, or NAT blocks this incoming connection, the data channel fails with a 425 error.
Passive mode reverses this: your computer initiates both connections (outbound), which works through almost all routers and firewalls.
02. Fix: Switch to Passive Mode
FileZilla
- Go to Edit > Settings (or FileZilla > Preferences on Mac)
- Click "FTP" under Connection
- Set Transfer Mode to "Passive"
- Check "Allow fall back to other transfer mode on failure"
- Click OK and reconnect
Other clients
Look for "Passive mode," "PASV," or "Transfer mode" in your FTP client's settings. In WinSCP, it is under Session > Advanced > Connection > Passive mode. For more FTP client setups, see our FTP guide.
03. Reduce Concurrent Connections
If you have too many simultaneous transfers open, extra connections may be refused. Set your maximum simultaneous transfers to 2-3. See Changing Concurrent Connections in FileZilla.
04. Check Firewall Blocks
If passive mode does not help:
- Check if your IP is blocked by our firewall using the Firewall Unblock tool
- Try a different network (phone hotspot) to rule out your local network blocking FTP
- Try FTPS (Explicit FTP over TLS) which may bypass ISP restrictions. In FileZilla Site Manager, set Encryption to "Require explicit FTP over TLS"
- Increase timeout to 60 seconds. See FileZilla Timeout Fix
Still Cannot Connect?
If switching to passive mode does not resolve the issue, open a ticket with your FTP client log output.
Open a Support TicketFrequently Asked Questions
What does FTP error 425 Could not open data connection mean?
A 425 means your FTP control connection worked and you logged in, but the separate data connection used to transfer files or list directories could not be opened. It is almost always an active-versus-passive mode problem or a firewall blocking the data ports, not a login or server fault.
How do I fix a 425 data connection error?
Switch your FTP client to passive mode, which in FileZilla means setting the Site Manager encryption and transfer mode so the client opens the data connection. Passive mode works behind routers and firewalls that block the incoming connections active mode needs. Reducing concurrent connections to 2 or 3 also helps.
Why does FTP log in but fail to list files or transfer?
Because login uses the control connection while listings and transfers use a second data connection. If only the data connection is blocked, you log in successfully but directory listings hang and transfers fail with a 425. Passive mode fixes the data connection in most cases.
Does FTPS help with a 425 error?
It can. Switching to explicit FTP over TLS sometimes bypasses ISP or network restrictions that interfere with plain FTP data connections. In FileZilla set Encryption to Require explicit FTP over TLS, keep passive mode on, and retry.
Quick Recap
- 425 error = data connection failed - Control connection works but file transfers cannot start
- Switch to passive mode - Works behind routers and firewalls
- Reduce concurrent connections to 2-3
- Check for firewall blocks on your IP
- Try FTPS to bypass ISP restrictions
Resolving FTP connection errors · Last updated November 2026 · Browse all FTP articles
