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SFG FTP Put Fails with and FTP 500 Invalid Port response error

Technical Blog Post


SFG FTP Put Fails with and FTP 500 Invalid Port response error


There's nothing more frustrating than having your production environment running smoothly only to come in one day and discover failures. It might be a relief when you realize it's only happening to a certain Trading Partner (TP). This is your first clue.

A Little Background in the FTP Protocol

When an FTP client first establishes a connection to an FTP Server it does so over what is called a control channel. This is usually done over port 21. Once a connection has been established a new connection back to the client is created. Part of creating this new connection, called a data channel, is agreeing on which port will be used. In some implementations, your network team might expect this to occur over a range of ports they specify; more on this later on in this blog posting. The establishment of this data channel can occur either as Active or Passive.

In Active mode, the client issues a command back to the server telling them the port on which they'll be listening for the data channel. Most connections are done passively over port 20. The important point to grasp is that not all FTP Servers accept the client specifying the port on which to establish the data channel and indicate this by responding with an FTP "500 Invalid Port response error"

Active and Passive in Sterling File Gateway (SFG)

In SFG, Active and Passive is configured in the listening consumer's Trading Partner profile.


If modifying this setting does not resolve your problem, there could be a configuration setting in your network requiring you to engage your network team. Before opening a PMR with IBM it is highly beneficial that you provide a network packet trace.

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