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Network Working Group                                      D. PiscitelloRequest for Comments: 1545                                      BellcoreCategory: Experimental                                     November 1993FTP Operation Over Big Address Records (FOOBAR)Status of this Memo   This memo defines an Experimental Protocol for the Internet   community.  This memo does not specify an Internet standard of any   kind.  Discussion and suggestions for improvement are requested.   Distribution of this memo is unlimited.Abstract   This paper describes a convention for specifying longer addresses in   the PORT command.Introduction   This RFC specifies a method for assigning long addresses in the   HOST-PORT specification for the data port to be used in establishing   a data connection for File Transfer Protocol, FTP (STD 9,RFC 959).   This is a general solution, applicable for all "next generation" IP   alternatives, and can also be extended to allow FTP operation over   transport interfaces other than TCP.Acknowledgments   Many thanks to all the folks in the IETF who casually mentioned how   to do this, but who left it to me to write this RFC.  Special thanks   to Rich Colella, Bob Ullmann, Shawn Ostermann, Steve Lunt, and Brian   Carpenter who had the time and decency to comment on the initial   draft.  :-)1.  Background   The PORT command of File Transfer Protocol allows users to specify an   address other than the default data port for the transport connection   over which data are transferred. The PORT command syntax is:      PORT <SP> <host-port> <CRLF>   The <host-port> argument is the concatenation of a 32-bit internet   <host-address> and a 16-bit TCP <port-address>.  This address   information is broken into 8-bit fields and the value of each field   is transmitted as a decimal number (in character stringPiscitello                                                      [Page 1]

RFC 1545                  FTP Over Big Address             November 1993   representation).  The fields are separated by commas.  A port command   is thus of the general form "PORT h1,h2,h3,h4,p1,p2", where h1 is the   high order 8 bits of the internet host address.   To accommodate larger network addresses anticipated for all IP "next   generation" alternatives, new commands and reply codes are needed for   FTP.  This memo addresses these needs.2.  The LPRT Command   The LPRT command allows users to specify a "long" address for the   transport connection over which data are transferred. The LPRT   command syntax is:      LPRT <SP> <long-host-port> <CRLF>   The <long-host-port> argument is the concatenation of the following   fields;   o  an 8-bit <address-family> argument (af)   o  an 8-bit <host-address-length> argument (hal)   o  a <host-address> of <host-address-length> (h1, h2, ...)   o  an 8-bit <port-address-length> (pal)   o  a <port-address> of <port-address-length> (p1, p2, ...)   The <address-family> argument takes the value of the version number   of IP (see Assigned Numbers, STD 2,RFC 1340), or generally speaking,   an Internet layer protocol.  Relevant assigned IPng version numbers   are:     Decimal         Keyword     ------          -------     0               reserved     1-3             unassigned     4               Internet Protocol (IP)     5               ST Datagram Mode     6               SIP     7               TP/IX     8               PIP     9               TUBA     10-14           unassigned     15              reservedPiscitello                                                      [Page 2]

RFC 1545                  FTP Over Big Address             November 1993   The value of each field is broken into 8-bit fields and the value of   each field is transmitted as an unsigned decimal number (in character   string representation, note that negative numbers are explicitly not   permitted).  The fields are separated by commas.   A LPRT command is thus of the general form      LPRT af,hal,h1,h2,h3,h4...,pal,p1,p2...   where h1 is the high order 8 bits of the internet host address, and   p1 is the high order 8 bits of the port number (transport address).3.  The LPSV Command   The L(ONG) PASSIVE command requests the server-DTP to listen on a   data port other than its default data port and to wait for a   connection rather than initiate one upon receipt of a transfer   command.  The response to this command includes the address family,   host address length indicator, host address, port address length, and   port address this server is listening on.  The reply code and text   for entering the passive mode using a long address is 228   (Interpretation according to FTP is: positive completion reply 2yz,   connections x2z, passive mode entered using long address xy8).  The   suggested textual message to accompany this reply code is:      228 Entering Long Passive Mode (af,hal,h1,h2,h3,h4...,pal,p1,p2...)4.  Permanent Negative Completion Reply Codes   The negative completion reply codes that are associated with syntax   errors in the PORT and PASV commands are appropriate for the LPRT and   LPSV commands (500, 501).  An additional negative completion reply   code is needed to distinguish the case where a host supports the LPRT   or LPSV command, but does not support the address family specified.   Of the FTP function groupings currently defined for reply codes   (syntax, information, connections, authentication and accounting, and   file system), "connections" seems the most logical choice; thus, an   additional negative command completion reply code, 521 is added, with   the following suggested textual message:      521 Supported address families are (af1, af2, ..., afn)   Where (af1, af2, ..., afn) are the values of the version numbers of   the "next generation" or other protocol families supported.  IP   address noted earlier.Piscitello                                                      [Page 3]

RFC 1545                  FTP Over Big Address             November 19935.  Rationale   An explicit address family argument in the LPRT command and LPSV   reply allows the Internet community to experiment with a variety of   "next generation IP" alternatives within a common FTP implementation   framework.  (It also allows the use of a different address family on   the command and data connections.)  An explicit length indicator for   the host address is necessary because some of the IPNG alternatives   make use of variable length addresses.  An explicit host address is   necessary because FTP says it's necessary.   The decision to provide a length indicator for the port number is not   as obvious, and certainly goes beyond the necessary condition of   having to support TCP port numbers. Currently, at least one IPng   alternative (TP/IX) supports longer port addresses.  And given the   increasingly "multi-protocol" nature of the Internet, it seems   reasonable that someone, somewhere, might wish to operate FTP operate   over Appletalk, IPX, and OSI networks as well as TCP/IP networks.   (In theory, FTP should operate over *any* transport protocol that   offers the same service as TCP.) Since some of these transport   protocols may offer transport selectors or port numbers that exceed   16 bits, a length indicator may be desirable.  If FTP must indeed be   changed to accommodate larger network addresses, it may be prudent to   determine at this time whether the same flexibility is useful or   necessary with respect to transport addresses.6.  Conclusions   The mechanism defined here is simple, extensible, and meets both IPNG   and possibly multi-protocol internet needs.7.  References   STD 9,RFC 959  Postel, J., and J. Reynolds, "File Transfer Protocol",                   STD 9,RFC 959, USC/Information Sciences Institute,                   October 1985.   STD 2,RFC 1340 Reynolds, J., and J. Postel, "Assigned Numbers",                   STD 2,RFC 1340, USC/Information Sciences Institute,                   July 1992.  (Does not include recently assigned IPv7                   numbers).   STD 3,RFC 1123 Braden, R., Editor, "Requirements for Internet                   Hosts - Application and Support", STD 3,RFC 1123,                   USC/Information Sciences Institute, October 1989.Piscitello                                                      [Page 4]

RFC 1545                  FTP Over Big Address             November 19938.  Security Considerations   Security issues are not discussed in this memo.9.  Author's Address   David M. Piscitello   Bell Communications Research   NVC 1C322   331 Newman Springs Road   Red Bank, NJ 07701   EMail: dave@mail.bellcore.comPiscitello                                                      [Page 5]