藍色軒言

PORT : the ftp client TELLS the ftp server to connect to ftp client's IP address (with a port number)

PORT fail : if the ftp client doesn't even know its own real address (when this client is behind a NAT)

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PASV : the ftp server TELLS the ftp client to connect to ftp server's IP address (with a port number)

PASV fail : if the ftp server doesn't even know its own real address (when this server is behind a NAT)

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Prob 1: your ftp client can not LIST DIR because you see a "PORT command failed error" , because this command is sent by FTP client so if the client's IP+PORT listed in this command looks like an address behind the NAT

You know it's the ftp client's fault , you can try to tell this FTP user to setup his FTP client properly , ask him to user PASV mode , never use PORT mode , since his FTP client can't tell the difference

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Prob 2: your ftp client can connect to a FTP server , but can't LIST DIR and you see an error : PASV failed , no one connects to IP:PORT , now you need to look at the IP+PORT ... does it look like an IP address behind a NAT ?

if so , the server owner should configure it properly , he should not let the FTP server to use that internal IP address

1.Change to another FTP client software / upgrade version of your FTP client software , yes don't doubt that there are BADly designed ftp clients in the world and we will not say their name here . also note that when you do a FXP , the other FTP server becomes a FTP client also , and of course , there are badly designed FTP server in the world and we will not say their name here .

2.IF you are a FTP user , check if you are running any FIREWALL/Securitry application that blocks the 2nd connection , remove it

3.IF you are a site owner , check if you are running any FIREWALL/Securitry application that blocks the 2nd connection , remove it