RFC 478 (rfc478) - Page 2 of 2

FTP server-server interaction - II

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RFC 478             FTP Server-Server Interaction-II       26 March 1973


                            +---------------+
                            |               |
                 +----------| USER PROCESS  |----------+
                 |          |       A       |          |
               telnet       +---------------+        telnet
                 |                                     |
                 |                                     |
          +-----------+                         +-------------+
          |           |-------->      --------->|             |
          |  SERVER   |data sockets  data socket|   SERVER    |
          |     B     |    Sb           Sc      |     C       |
          |           |<--------      <---------|             |
          +-----------+                         +-------------+


   USER A TO SERVER B                     USER A TO SERVER C
   __________________                     __________________

   A->B   SOCK  HOST-C  SKT- Sc           A->C   SOCK  HOST-B  SKT-  Sb

   B->A       ACK                         C->A      ACK

   A->B   PASV

   B->A       ACK

   A->B   STOR                            A->C   RTRV

      1. After the PASV command has been acknowledged, the two data
         transfer commands can be sent in either order, since the
         LISTENING action takes place with the PASV command

      2. The user knows the socket numbers Sc and Sb to be the data
         sockets as specified by the protocol.

      3. Note that it is not essential for a SOCK command to be sent to
         the same Host to whom a PASV will be sent.  Sending one to him
         provides security in that the incoming RFC can be checked.

   RB/nlg




          [This RFC was put into machine readable form for entry]
     [into the online RFC archives by Helene Morin, Via Genie 12/1999]





Bressler
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