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FTPS PASV response contains internal IP address in Serv-U

This article explains what to do if the PASV command response contains an internal IP Address.

First published date

10/25/2018 3:59 PM

Last published date

3/30/2026 11:29 PM

Overview

Serv-U is capable of doing Active and Passive connections for FTPS in addition to doing plain FTP transfers. External client users connect to the Serv-U site using a public IP which resolves from the DNS/URL. The listeners set in Serv-U will normally use the internal IP of the MFT server and not the public IP or NAT IP. 

In some cases,it is required to have PASV response from the public IP which is allowed in the network firewall only and there is also some scenario where Serv-U was migrated from another server and retain this setting. In this case, either set the new public IP/URL of PASV response or leave it blank.

The usual logs that you would see in the Serv-U is just "Entering Passive mode" after that nothing happens and the FTP client will get directory listing failure.

Product section

Serv-U Managed File Transfer & Serv-U FTP Server

Cause

The issue is caused when the FTP listener is not set to use a public IP for PASV connections. By default, it does not have any public IPs listed.

 

Resolution

​​​​​Set the PASV IP in the FTP listener settings.
  1. Access the Serv-U Management Console.
  2. Go to Domains > Domain Details > Listeners tab.
  3. Edit the FTP port 21 listener.
  4. Remove or change the public IP in the PASV IP Address or Domain Name field
  5. Check the box "Use with LAN connection" (optional only).
  6. Save the changes.
If there is a Serv-U Gateway involved, edit the Gateway IP inside the MFT server.
  1. Access the Serv-U Management Console.
  2. Go to Global > Serv-U Gateway tab
  3. Click the Gateway entry and edit
  4. If the Gateway Address is using the DMZ internal IP, and the Public IP Address is using the public IP of the Gateway server, change the Public IP entry and use the DMZ IP.
  5. If the Gateway Address is using the DMZ internal IP, and the Public IP Address is the same, enter the public IP of the Gateway server in the Public IP Address field.
  6. Once these changes are done, make sure to update the FTP Domain Listener and use the new IP address.