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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)                 9  TCP/IP General File Transfer Protocols (FTP and TFTP)                      9  File Transfer Protocol (FTP)                           9  FTP Concepts and General Operation

FTP Concepts and General Operation 1 2 3 4 FTP Control Connection Establishment, User Authentication and Anonymous FTP Access

Third-Party File Transfer (Proxy FTP)

The FTP standard actually defines a separate model for an alternative way of using the protocol. In this technique, a user on one host performs a file transfer from one server to another. This is done by opening two control connections: one each from the User-PI on the user's machine to the two Server-PI's on the two servers. Then, a Server-DTP is invoked on each server to send data; the User-DTP is not used.

This method, sometimes called third-party file transfer or proxy FTP, is not widely used today. A major reason for this is that it raises security concerns, and has been exploited in the past. Thus, while I felt it was worth mentioning, I will not be discussing it further in my coverage of FTP.

FTP Concepts and General Operation 1 2 3 4 FTP Control Connection Establishment, User Authentication and Anonymous FTP Access