FTP 125 Data Connection Open vs 504 Parameter Not Implemented
FTP 125 (Data Connection Open) is a 1xx Positive Preliminary response, while 504 (Parameter Not Implemented) is a 5xx Permanent Negative response. 125 indicates that the data connection is already open and the transfer is beginning. No need to open a new data connection. In contrast, 504 means that command not implemented for that parameter. The command is supported but not with the specific parameter value provided.
Description
The data connection is already open and the transfer is beginning. No need to open a new data connection.
When You See It
When the server reuses an existing data connection for a file transfer instead of opening a new one.
How to Fix
No fix needed — the transfer is starting immediately. Your client should begin reading or writing data on the existing connection.
Description
Command not implemented for that parameter. The command is supported but not with the specific parameter value provided.
When You See It
When you use an unsupported transfer type or mode, such as TYPE E (EBCDIC) on a server that only supports ASCII and binary.
How to Fix
Use a supported parameter value. Check the server documentation or use FEAT to see which parameter options are available.
Key Differences
125 is a 1xx Positive Preliminary response, while 504 is a 5xx Permanent Negative response.
FTP 125: The data connection is already open and the transfer is beginning. No need to open a new data connection.
FTP 504: Command not implemented for that parameter. The command is supported but not with the specific parameter value provided.
You encounter 125 when when the server reuses an existing data connection for a file transfer instead of opening a new one.
You encounter 504 when when you use an unsupported transfer type or mode, such as TYPE E (EBCDIC) on a server that only supports ASCII and binary.
When to Use Which
For 125 (Data Connection Open): No fix needed — the transfer is starting immediately. Your client should begin reading or writing data on the existing connection. For 504 (Parameter Not Implemented): Use a supported parameter value. Check the server documentation or use FEAT to see which parameter options are available.