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