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| 2015-01-07 | 2015-01-07 | ||
| created (martin) | no summary (martin) | ||
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| [[ftp|FTP]] may operate in an active or a passive mode, which determines how a data connection is established. In both cases, a client creates a TCP control connection to an FTP server command port 21. This is a standard outgoing connection, as with any other file transfer protocol (SFTP, SCP, WebDAV) or any other %%TCP%% client application (e.g. web browser). So, usually there are no problems when opening the control connection. | [[ftp|FTP]] may operate in an active or a passive mode, which determines how a data connection is established. In both cases, a client creates a TCP control connection to an FTP server command port 21. This is a standard outgoing connection, as with any other file transfer protocol (SFTP, SCP, WebDAV) or any other %%TCP%% client application (e.g. web browser). So, usually there are no problems when opening the control connection. | ||
| - | Where %%FTP%% protocol is more complicated comparing to the other file transfer protocol are file transfers. While the other protocols use the same connection for both session control and file (data) transfers, the %%FTP%% protocol uses a separate connection for the file transfers. | + | Where %%FTP%% protocol is more complicated comparing to the other file transfer protocols are file transfers. While the other protocols use the same connection for both session control and file (data) transfers, the %%FTP%% protocol uses a separate connection for the file transfers. |
| In the //active// mode, the client starts listening on a random port for incoming data connections from the server (the client sends the %%FTP%% command ''PORT'' to inform the server on which port it is listening). Nowadays, it is typical that the client is behind a firewall (e.g. built-in Windows firewall) or NAT router (e.g. ADSL modem), unable to accept incoming %%TCP%% connections. | In the //active// mode, the client starts listening on a random port for incoming data connections from the server (the client sends the %%FTP%% command ''PORT'' to inform the server on which port it is listening). Nowadays, it is typical that the client is behind a firewall (e.g. built-in Windows firewall) or NAT router (e.g. ADSL modem), unable to accept incoming %%TCP%% connections. | ||