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FTP: Active vs Passive

Article ID: 727

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Question: Should I configure my FTP client to use ACTIVE or PASSIVE mode FTP?

Answer: Prior to 12/2009, 3Essentials did not support PASSIVE mode FTP.  However, since eanbling FTPS, we have also enabled PASSIVE mode FTP for those servers with FTPS support.  The following should clarify:

  • ACTIVE mode support only: web14, web12, web10, web8, web6, web4, web5, web7, web9
  • ACTIVE and PASSIVE mode support: all other shared hosting servers.

If your shared hosting account is hosted on one of the servers listed above which supports ACTIVE mode only, be sure to configure the connection to use ACTIVE ftp mode.  Finding this option in your FTP client will depend on this FTP client software you choose to use.  This setting is not always called "ftp mode", and is not always present with the common ftp connection configuration options.  Instead it may be found under a tab or button called MORE, ADVANCED, OPTIONS, or something similar... it will depend on the FTP client software.  Please check with your FTP client software documentation for the specifics on where to set this option for your FTP connections.

Communications between your PC's FTP client software and the FTP server software are different than most TCP/IP based communications.  FTP uses 2 "channels" for the communications, a COMMAND channel, and a DATA channel.  Commands go back and forth between PC and FTP server over the command channel, on TCP 21... however data (including the results of a LIST command or upload/download of a file) traverse the data channel (TCP 20).  How the DATA channel is negotiated between the FTP client software and the FTP server software occurs depends on the "mode" you select in your FTP client software, being either "active mode" or "passive mode".  Our firewall configuration is designed to support active mode only.  Although sometimes passive mode may work, we do not support it.

If you are configured for PASSIVE mode connections to one of the servers listed above as supporting ACTIVE mode only, and are experiencing a problem as a result of it, the most common symptoms would be:

  • able to make a connection and login, but there is no response to the LIST, DIR, or LS command (because the response traverses the DATA channel, not properly set up by use of passive mode). 

Changing to ACITVE mode in your FTP client software typically will correct this issue.

If you're interested in further understanding the difference between active and passive modes, the best explanation on the difference can be found here:

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