File eXchange Protocol

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File eXchange Protocol ( FXP ; German file exchange protocol ) is the procedure defined in the File Transfer Protocol and unnamed there, how a client controls file transfers between two servers ( server-to-server ). The files do not go through the client, which saves time. Many current FTP clients support FXP.

FXP uses both the active mode and the passive mode of servers. In active mode , the client opens a random port and notifies the server of this and its own IP address using the PORTcommand. The server then connects to this destination, whereupon the data transfer can take place. In passive mode , this principle is reversed, the client sends a PASVcommand, the server opens a port and transmits it to the client together with the IP address.

With the FXP, the client sends a PASVcommand to an FTP server and receives its IP address and open port in response. Now it sends a PORTcommand to another FTP server , which does not contain its own IP address and port as arguments, but the response from the first FTP server. The second FTP server establishes a data connection to the first FTP server. The client can now transmit a RETRcommand to the second FTP server and a command to the first STORto start a file transfer.

If one of the two FTP servers has problems with this constellation, for example the target server does not support passive mode , the PASVcommand can also be executed on the source computer . One then speaks of alternative fashion .

Typically, FXP data connections between the FTP servers are unencrypted. To get around this, some FTP servers and clients support the command CPSV(instead of PASV) to establish an encrypted connection between the servers. In the meantime, another variant called SSCN( set secured client negotiation ) has established itself for encrypted transfers due to its good compatibility with outdated FTP clients. Both methods, CPSV and SSCN, can, however, be susceptible to man-in-the-middle attacks if the certificate of the remote station is not checked.

Web links

Individual evidence

  1. ^ File Exchange Protocol (FXP). Retrieved September 25, 2018 .
  2. ↑ a b Active and Passive FTP Transfers Defined. Retrieved September 25, 2018 .
  3. ↑ FXP: CPSV. Retrieved September 25, 2018 .
  4. ↑ FXP: SSCN. Retrieved September 25, 2018 .