FTP 110 Restart Marker Reply vs 425 Can't Open Data Connection
FTP 110 (Restart Marker Reply) is a 1xx Positive Preliminary response, while 425 (Can't Open Data Connection) is a 4xx Transient Negative response. 110 indicates that the server is sending a restart marker reply. The text is exact and not left to interpretation. This marker is used to indicate the point at which a file transfer should be restarted. In contrast, 425 means that can't open data connection. The server was unable to establish the data channel needed for the file transfer.
Description
The server is sending a restart marker reply. The text is exact and not left to interpretation. This marker is used to indicate the point at which a file transfer should be restarted.
When You See It
During a resumed file transfer when the server confirms the restart position in the data stream.
How to Fix
No fix needed — this is a normal response during transfer recovery. If restarts keep failing, verify the marker format matches what your client expects.
Description
Can't open data connection. The server was unable to establish the data channel needed for the file transfer.
When You See It
When a firewall or NAT is blocking the data connection, or the client failed to connect to the server's passive port.
How to Fix
Switch between active (PORT) and passive (PASV) modes. Check that your firewall allows the FTP data port range and that NAT is configured correctly.
Key Differences
110 is a 1xx Positive Preliminary response, while 425 is a 4xx Transient Negative response.
FTP 110: The server is sending a restart marker reply. The text is exact and not left to interpretation. This marker is used to indicate the point at which a file transfer should be restarted.
FTP 425: Can't open data connection. The server was unable to establish the data channel needed for the file transfer.
You encounter 110 when during a resumed file transfer when the server confirms the restart position in the data stream.
You encounter 425 when when a firewall or NAT is blocking the data connection, or the client failed to connect to the server's passive port.
When to Use Which
For 110 (Restart Marker Reply): No fix needed — this is a normal response during transfer recovery. If restarts keep failing, verify the marker format matches what your client expects. For 425 (Can't Open Data Connection): Switch between active (PORT) and passive (PASV) modes. Check that your firewall allows the FTP data port range and that NAT is configured correctly.