FTP (File Transfer Protocol) is an Internet protocol used to transfer data between a file server and a client. FTP transfers files by establishing a connection between the computer the user is working on and the computer hosting the file. FTP clients run on personal computers connected to the same LAN and are usually slow and unreliable.
An FTP file transfer usually consists of three phases:
- Connect: The FTP client connects to the FTP server to request access to the data on the server. The request is a single packet (called a connection request) sent in plain text (i.e. without encryption).
- Logging in: Once access is granted, the FTP client logs in and is authenticated to the server. This requires two more packets to be exchanged.
- Transfer: Once logged in, the user can begin transferring files. In a typical FTP transaction, the FTP client initiates a connection by sending a CONNECT request to the FTP server. The CONNECT request contains the user's login name and password. The server responds with a 220 response message when the connection is successfully established.
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