I'm working with a Sterling Commerce secure FTP client that seems to use
port 221 - you specify that port when connecting to the server.

I noticed looking through existing filters that port 21 is referenced in a
couple of packet types, and also port 20 for FTP data. Is it reasonable to
assume that I should copy all my existing FTP filters and packet types but
referring to port 221 and 220 where the current ones refer to 21 and 20,

Thanks in advance.