- FTP server listens for command connections on port 21
- FTP client creates a command connection from port (N > 1024) to the FTP Server port 21
- FTP client listens for a data connections on port (N+1)
- FTP server creates a data connection from port 20 to the port (N+1)
- FTP server listens for command connections on port 21
- FTP client creates a command connection from port (N > 1024) to the FTP server port 21
- FTP server starts listening for a data connection on a random port (P)
- FTP server sends a PORT P command back to the client with the data connection port
- FTP client creates a data connection from port (N > 1024) to the FTP server port P
To enable passive FTP open Control Panel -> Internet Options -> Advanced -> "Use Passive FTP for compatibility with some firewalls and DSL modems"
Note there is another Advanced option "Enable Folder View for FTP sites" (Sometimes seen as "Use Web Based FTP"). If this option is enabled, then it will ignore the Passive FTP setting and always use Active FTP, but enables one to upload files to the FTP if having the right permissions.[HKEY_CURRENT_USER \Software \Microsoft \Ftp]
Use PASV = "yes"
Note some FTP Servers (Like ftp.microsoft.com) doesn't respond back when a client connects passively. Instead one gets the error "425 Can't open data connection".[HKEY_CURRENT_USER \Software \Microsoft \Ftp]
Use Web Based FTP = "yes"
Related Use IE as a FTP client
More info MS KB217888
More info MS KB309816
More info MS KB323446
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