There are 3 most used protocols supported in wodFtpDLX
(and additional subtype). Most known, FTP
protocol is old plaintext protocol. Typically, clients
connect to port 21 on the server and issue commands over so
called control connection. Once data needs to be
transferred, FTP protocol requires also additional data
connection to be opened, where large amount of data is
sent/received. Clients can optionally choose whether they
will use so called 'active' or 'passive'
transfers - determining who will initiate data connection
(and who will accept it, of course). You can set Passive property
to select one of these options. This protocol is NOT
encrypted, and is insecure.
FTPS is also known as
FTP/S or FTP-SSL
protocol, or even explicit FTPS protocol. Control
connection is always encrypted using SSL layer between
socket communication, and data actually transferred by the
application. Protocol is pretty straightforward like FTP,
only difference is in SSL encryption. wodFtpDLX supports
two types of this protocol - FTPSwithdata, and FTPSnodata.
As the name says - FTPSwithdata will also encrypt data
connection which is used to transfer files (and directory
listings), while FTPSnodata does not encrypt secondary
connection. You should use FTPSnodata if you don't care
about encrypting files (only want to protect your username
and password, for example) because it is much faster than
the other one.
There is also FTPSimplicit protocol
that is same as above, but will negotiate SSL before any
commands are sent to the server. It is widely used by 3rd
party wrapper software that actually translate between SSL
encrypted connections and older FTP servers that
wouldn't support SSL. Typical port is 990 for this
protocol.
SFTP is completelly different protocol
who has only one thing incommon to above protocols - file
transfer. Everything else is different. It is
packet-oriented, running on top of SSH2
(secure shell) and thus requires different server to be
installed (SSH2 with SFTP subsystem). It uses only one
connection (no separate data connection), and it
doesn't have text replies like FTP used to have.
Encryption and protection for this protocol is already
guaranteed by SSH layer.