Extended Passive Mode (EPSV) - KB Article #1979Related Articles --
The EPSV command tells the server to enter a passive FTP session rather than Active. (Its use is required for IPv6.) This allows users behind routers/firewalls to connect over FTP when they might not be able to connect over an Active (PORT/EPRT) FTP session. EPSV mode has the server tell the client where to connect for the data port on the server.
When issuing the EPSV command, the client will include information on the port that the server is to use in order to connect back to the client. Thus, the structure of the EPSV command is clearly defined to allow servers to parse this information from the command. The structure of the EPSV command is: EPSV (|||Port|). The EPSV command does not include IP address information since it is assumed that the IP address of the data channel is the same as the address of the control channel.