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.
描述
The data connection is already open and the transfer is beginning. No need to open a new data connection.
何时出现
When the server reuses an existing data connection for a file transfer instead of opening a new one.
如何修复
No fix needed — the transfer is starting immediately. Your client should begin reading or writing data on the existing connection.
描述
Requested action aborted: page type unknown. The server does not recognize the requested page structure or format.
何时出现
When attempting a transfer with a page structure type the server does not support. This is extremely rare in modern FTP usage.
如何修复
Switch to stream transfer mode (MODE S) and file structure (STRU F), which are universally supported by all FTP servers.
主要区别
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.
何时使用哪个
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.