RFC 438 (rfc438) - Page 1 of 3

FTP server-server interaction

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Network Working Group                                          B. Thomas
Request for Comments: 438                                    B. Clements
NIC: 13770                                                     BBN-TENEX
References:  354,385,414,418                             15 January 1973


                     FTP Server-Server Interaction

   The current ARPANET File Transfer Protocol as specified by RFC 354
   and updated by RFC's 385, 414 and 418 allows for "third host"
   participation but does not specify a mechanism by which the process
   at the third site may be the FTP server at that site.  This RFC
   suggests a simple extension to FTP which would allow an FTP user
   process at one site to arrange for FTP server processes at other
   sites to act cooperatively on its behalf.

   Such server-server cooperation may appear to be of limited utility.
   Consider, however, the requirements placed on FTP by a Resource
   Sharing Executive (RSEXEC) program -  a command language interpreter
   which extends the range of a user's commands beyond the boundaries of
   the user's local system.  Among its services such as RSEXEC could
   provide its users with a network-wide file system, perhaps allowing,
   in certain contexts, the use of partially qualified pathnames which
   omit site specification.  Consider, for example the response of the
   RSEXEC to the user command:

      APPEND (FILE) PROG1.PL1 (TO FILE) PROG2.PL1

   for the case in which the two files are at different sites (PROG1.PL1
   at SITE1, PROG2.PL1 at SITE2) neither of which is the user's site.  A
   straightforward way for the RSEXEC to "perform" the APPEND would be
   to establish FTP control connections to the FTP servers at SITE1 and
   at SITE2, instruct the server at SITE1 to

      RETR PROG1.PL1

   using data connection C and instruct the server at SITE2 to

      APPE PROG2.PL1

   using the same data connection C.

   Unfortunately, at present there is no way within FTP to arrange for
   such server-server cooperation.  This is due primarily to the lack of
   symmetry in the way that FTP treats the ends of data connections
   during connection establishment.  It specifies one end to be the
   "server" end, the other to be the "user" end and specifies different
   means for establishing the connections from the two ends.



Thomas, et. al.
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