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PASV response contains internal IP address

Updated April 20, 2017


This article provides steps to resolve the issue when the PASV command response contains an internal IP address.

There are two ways to transfer data in FTP communications, active (PORT) and PASV.

To learn more about the difference between these two modes of data transfer, see Active and Passive FTP Transfers defined.


All Serv-U versions



The issue is caused when the FTP server is not correctly configured for PASV mode data transfers.



For FTP Voyager and later, substitute the known external IP address for an FTP server when it receives an internal IP address in the PASV command response from the server.


This is especially useful for secure/SSL connections where the server's NAT router cannot translate the internal IP address into the proper external IP address since the communication is encrypted.





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