FTP 125 Data Connection Open vs 551 Page Type Unknown
FTP 125 (Data Connection Open) is a 1xx Positive Preliminary response, while 551 (Page Type Unknown) 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, 551 means that requested action aborted: page type unknown. The server does not recognize the requested page structure or format.
Description
The data connection is already open and the transfer is beginning. No need to open a new data connection.
Quand vous le voyez
When the server reuses an existing data connection for a file transfer instead of opening a new one.
Comment résoudre
No fix needed — the transfer is starting immediately. Your client should begin reading or writing data on the existing connection.
Description
Requested action aborted: page type unknown. The server does not recognize the requested page structure or format.
Quand vous le voyez
When attempting a transfer with a page structure type the server does not support. This is extremely rare in modern FTP usage.
Comment résoudre
Switch to stream transfer mode (MODE S) and file structure (STRU F), which are universally supported by all FTP servers.
Différences clés
125 is a 1xx Positive Preliminary response, while 551 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 551: Requested action aborted: page type unknown. The server does not recognize the requested page structure or format.
You encounter 125 when when the server reuses an existing data connection for a file transfer instead of opening a new one.
You encounter 551 when when attempting a transfer with a page structure type the server does not support. This is extremely rare in modern FTP usage.
Quand utiliser lequel
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 551 (Page Type Unknown): Switch to stream transfer mode (MODE S) and file structure (STRU F), which are universally supported by all FTP servers.