File eXchange Protocol (FXP) is a method of data transfer which uses the FTP protocol to transfer data from one remote server to another without routing this data through the client s connection. Conventional FTP involves a single server and a single client; all data transmission is done between these two. In an FXP session, a client maintains a standard FTP connection to two servers, and can direct either server to connect to the other to initiate a data transfer. The advantage of using FXP over FTP is evident when a high-bandwidth server demands resources from another high-bandwidth server, but only a low-bandwidth client, such as a network administrator working away from location, has the authority to access the resources on both servers.

Enabling FXP support, however, can make a server vulnerable to a denial-of-service attack, known as FTP bounce attack. FXP is also frequently used for Warez trafficking. FTP server software often disables FXP by default.

Although FXP may be classed as it s own protocol , it is in fact merely an extension of FTP and is specified in RFC 959.

User-PI - Server A User-PI - Server B ------------------ ------------------ C->A : Connect C->B : Connect C->A : PASV A->C : 227 Entering Passive Mode. A1,A2,A3,A4,a1,a2 C->B : PORT A1,A2,A3,A4,a1,a2 B->C : 200 Okay C->A : STOR C->B : RETR B->A : Connect to HOST-A, PORT-a

Some advanced FTP Server such as GlFTPd and RaidenFTPd support negotiation of a secure data channel between two servers using either the FTP protocol extension commands CPSV or SSPN.

=References=

This protocol is Standardization as a subset of Request for Comments 0959 by the IETF as:

=See also=