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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 the 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.
Risk Enabling FXP support, however, can make a server vulnerable to an exploit known as FTP bounce. FXP is also frequently used for warez trafficking. As a result of this, FTP server software often has FXP disabled by default. FXP over SSL Some FTP clients such as FlashFXP and FTP Servers such as glFTPd and RaidenFTPd support negotiation of a secure data channel between two servers using either of the FTP protocol extension commands; CPSV or SSCN. This normally works by the client issuing one of these commands in lieu of the PASV command, which instructs the server to create either a SSL or TLS connection. Technical Although FXP may be classed as its own "protocol", it is in fact merely an extension of FTP and is specified in RFC 959: User-PI - Server A (Dest) User-PI - Server B (Source) ------------------ ------------------ C->A Connect C->BConnect 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->BRETR B->A Connect to HOST-A, PORT-a See also | ||||||||
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