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FTP Client Cannot See Directory Listings or Connect  -  KB Article #1146

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Sometimes Internet Service Providers (ISPs) prevent their customers from running FTP servers by preventing access on the FTP port, number 21. They "listen" to the traffic on this port and disable directory listings or file transfers, or they disable use of this port on incoming connections all together.

Some customers have found that by changing the port that Serv-U listens on from port 21 to a less commonly used port number, they can allow access to their FTP server. This can be done using the following steps:

  1. Open the Domain Details menu
  2. Go to the "Listeners" tab
  3. Click on the "FTP and Explicit SSL/TLS" listener, then click "Edit"
  4. Enter the port number to use

Rhinosoft recommends using ports between 1024 and 65535 because these ports are not specifically reserved for other network services. Other ports below 1024 besides 21 can also work, but there is a high risk of experiencing conflicts with other network services. The best way to test is to pick a port, attempt connecting using that port, and continue until a port is found that permits connections. IANA publishes a list of ports and their uses at their home page.

Another common problem is that PASV Mode might not be setup properly and a router / firewall is blocking the data connection. If there is a router / firewall in front of Serv-U make sure to read our article on configuring Serv-U to work with a router/firewall.

In addition, running an FTP server may violate your agreement with your ISP. Please ask your ISP for permission before making any of the suggested port changes.

NOTE: You must also change your port number in your FTP client. In FTP Voyager you can change the port number in the "Advanced" settings for your site profile, under the "Connection" category.