Monitoring FTP servers
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When polling the status of an FTP server, the following steps are taken:

A TCP connection is established with the server IP address on port 21 (*).
Simple Failover waits for a "greeting".
If the greeting begins with 220…, (*), then the FTP server is considered functional.
With any other greeting, the server is considered non-functional.
The TCP connection is closed.

While performing above steps, Simple Failover may also encounter a communications error (winsock error), or that the TCP connection is unexpectedly closed by the remote server, or it may time out waiting for the TCP connection to be established or a response to be received.
In any of these cases, the server is considered non-functional.

For details on the FTP protocol, please see RFC959.
This and other RFCs can be obtained from http://www.rfc-editor.org/rfcsearch.html.

(*) Alternate port number can be specified in the Port field. Alternate status codes can be specified in the Advanced Server Set Properties dialog.