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+Network Working Group                                            E. Lear
+Request for Comments: 3617                                 Cisco Systems
+Category: Informational                                     October 2003
+
+
+              Uniform Resource Identifier (URI) Scheme and
+                    Applicability Statement for the
+                 Trivial File Transfer Protocol (TFTP)
+
+Status of this Memo
+
+   This memo provides information for the Internet community.  It does
+   not specify an Internet standard of any kind.  Distribution of this
+   memo is unlimited.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (2003).  All Rights Reserved.
+
+Abstract
+
+   The Trivial File Transfer Protocol (TFTP) is a very simple TRIVIAL
+   protocol that has been in use on the Internet for quite a long time.
+   While this document discourages its continued use, largely due to
+   security concerns, we do define a Uniform Resource Identifier (URI)
+   scheme, as well as discuss the protocol's applicability.
+
+1.  Introduction
+
+   The Trivial File Transfer Protocol (TFTP) has been around for quite
+   some time.  Its common uses are to initially configure devices or to
+   load new versions of operating system code [1].  As devices begin to
+   adopt use of Uniform Resource Identifiers (URIs) and Uniform Resource
+   Locators (URLs), for completeness we specify a way to reference files
+   that is still quite common.  Use of a URI is a convenient way to
+   indicate underlying mechanism, server name or address, and file name.
+
+   WHILE WE DEFINE THE TFTP URI TYPE, WE STRONGLY RECOMMEND AGAINST THE
+   CONTINUED USE OF TFTP, FOR REASONS LISTED IN SECTION 5 (amongst
+   others).  The definition of a URI merely allows tools that currently
+   use protocols such as TFTP to have a standard name space and
+   structure where one can understand the process used to resolve that
+   name.  Indeed it is hoped that the definition of this URI will ease
+   transition to modern file transfer mechanisms.
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+Lear                         Informational                      [Page 1]
+
+RFC 3617                  URI Scheme for TFTP               October 2003
+
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+2.  Syntax of a TFTP URI
+
+   A TFTP URI has the following ABNF syntax [2]:
+
+   tftpURI         = "tftp://" host "/" file [ mode ]
+   mode            = ";"  "mode=" ( "netascii" / "octet" )
+   file            = *( unreserved / escaped )
+   host            = <as specified by RFC 2732 [3]>
+   unreserved      = <as specified in RFC 2396 [4]>
+   escaped         = <as specified in RFC 2396>
+
+   A TFTP URI specifies a file that is to be found or placed on a TFTP
+   server.  The "mode" option is an option indicating how the file is to
+   be transferred.  If left unspecified, the mode is assumed to be
+   "octet".  A third "mail" mode was deprecated at the time RFC 1350 was
+   adopted, and is not specified.
+
+2.1.  Encoding Rules
+
+   Aside from syntax as described above, the TFTP protocol does not
+   specify length limits to either file names or file sizes.  In the
+   case of file names, they may contain any character so long as those
+   characters are properly escaped as described above.
+
+3.  Semantics and Operations
+
+   As previously stated the TFTP URI is a reference to a file.  The
+   allowed operations on a TFTP URI are read and write.  When a TFTP URI
+   is read the underlying mechanisms retrieve the named file via the
+   TFTP protocol from the specified host with the optionally specified
+   mode.  When a TFTP URI is written the underlying mechanisms transmit
+   a file via TFTP to a specified server to either the specified file
+   using the optionally specified mode.  No other operations are
+   supported.
+
+   Note that it is not possible to retrieve file size information prior
+   to retrieval, nor is it possible to determine file existence or
+   permissions prior to transfer.  Files transferred may or may not
+   arrive intact, as there is no guarantee of reliability or even
+   completeness.  See the TFTP standard for more details.  For more
+   robust file transfer, consider using either FTP or HTTP [5, 6].
+
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+Lear                         Informational                      [Page 2]
+
+RFC 3617                  URI Scheme for TFTP               October 2003
+
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+4. Examples
+
+      tftp://example.com/myconfigurationfile;mode=netascii
+
+   This example references file "myconfigurationfile" on server
+   "example.com" and requests that the transfer occur in netascii mode.
+
+      tftp://example.com/mystartupfile
+
+   This file references file "mystartupfile" on server "example.com".
+   The transfer should occur in octet mode, since no other mode was
+   specified.
+
+5.  Security Considerations and Concerns about TFTP's use
+
+   Use of TFTP has been historically limited to those devices where a
+   more full protocol stack is impractical due to either memory or CPU
+   constraints.  While this still may be the case with a toaster, it is
+   unlikely to be the case for even the simplest piece of network
+   support hardware, such as simple routers or switches.  There are a
+   myriad of reasons to use some protocol other than TFTP, only a few of
+   which are listed below.
+
+   TFTP has no mechanism for access control within the protocol, and
+   there is no protection from a man in the middle attack.
+   Implementations are left to their own devices in this area.  Because
+   TFTP has no way to determine file sizes in advance, implementations
+   should be prepared to properly check the bounds of transfers so that
+   neither memory nor disk limitations are exceeded.
+
+   TFTP is not well suited to large files for the following reasons.
+   TFTP has no inherent integrity check.  There is no way to determine
+   what one side sent is what the other received.  There is no way to
+   restart TFTP transfers from anywhere other than the beginning.  TFTP
+   is a lock step protocol.  Only one packet may be in flight at any one
+   time.  There is no slow start or smart backoff mechanism in TFTP, but
+   very simple timeouts.
+
+   TFTP is not well suited to file transfers across administrative
+   domains.  For one thing, TFTP utilizes UDP, and many NATs will not
+   either support or allow TFTP transfers.  More likely firewalls will
+   prohibit transfers.
+
+   There are no caching semantics within TFTP.  There is no safe way to
+   cache information using the TFTP protocol.
+
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+Lear                         Informational                      [Page 3]
+
+RFC 3617                  URI Scheme for TFTP               October 2003
+
+
+   In summary, use of TFTP is strongly discouraged except in the most
+   limited of circumstances where memory and CPU are at the highest
+   premium.
+
+6.  IANA Considerations
+
+   The IANA has registered the URL registration template found in
+   Appendix A in accordance with RFC 2717 [7].
+
+7.  Acknowledgments
+
+   The author thanks Larry Masinter, Randy Presuhn, Phil Schafer, and
+   Bill Fenner for their help in developing this document.
+
+8.  Intellectual Property Statement
+
+   The IETF takes no position regarding the validity or scope of any
+   intellectual property or other rights that might be claimed to
+   pertain to the implementation or use of the technology described in
+   this document or the extent to which any license under such rights
+   might or might not be available; neither does it represent that it
+   has made any effort to identify any such rights.  Information on the
+   IETF's procedures with respect to rights in standards-track and
+   standards-related documentation can be found in BCP-11.  Copies of
+   claims of rights made available for publication and any assurances of
+   licenses to be made available, or the result of an attempt made to
+   obtain a general license or permission for the use of such
+   proprietary rights by implementors or users of this specification can
+   be obtained from the IETF Secretariat.
+
+   The IETF invites any interested party to bring to its attention any
+   copyrights, patents or patent applications, or other proprietary
+   rights which may cover technology that may be required to practice
+   this standard.  Please address the information to the IETF Executive
+   Director.
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+Lear                         Informational                      [Page 4]
+
+RFC 3617                  URI Scheme for TFTP               October 2003
+
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+Appendix A. Registration Template
+
+   URL scheme name: tftp
+   URL scheme syntax: Section 2
+   Character encoding considerations: Section 2
+   Intended usage: Section 1
+   Applications and/or protocols which use this scheme: [1]
+   Interoperability considerations: None
+   Security considerations: Section 5
+   Relevant publications: [1]
+   Contact: The author, Section 8
+   Author/Change Controller: IESG
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+Lear                         Informational                      [Page 5]
+
+RFC 3617                  URI Scheme for TFTP               October 2003
+
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+References
+
+   [1]  Sollins, K., "The TFTP Protocol (Revision 2)", STD 33, RFC 1350,
+        July 1992.
+
+   [2]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
+        Specifications: ABNF", RFC 2234, November 1997.
+
+   [3]  Hinden, R., Carpenter, B. and L. Masinter, "Format for Literal
+        IPv6 Addresses in URL's", RFC 2732, December 1999.
+
+   [4]  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
+        Identifiers (URI): Generic Syntax", RFC 2396, August 1998.
+
+   [5]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
+        Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
+        HTTP/1.1", RFC 2616, June 1999.
+
+   [6]  Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9,
+        RFC 959, October 1985.
+
+   [7]  Petke, R. and I. King, "Registration Procedures for URL Scheme
+        Names", BCP 35, RFC 2717, November 1999.
+
+Author's Address
+
+   Eliot Lear
+   Cisco Systems, Inc.
+   170 W. Tasman Dr.
+   San Jose, CA 95134-1706
+
+   Phone: +1 (408) 527 4020
+   EMail: lear@cisco.com
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+Lear                         Informational                      [Page 6]
+
+RFC 3617                  URI Scheme for TFTP               October 2003
+
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+Full Copyright Statement
+
+   Copyright (C) The Internet Society (2003).  All Rights Reserved.
+
+   This document and translations of it may be copied and furnished to
+   others, and derivative works that comment on or otherwise explain it
+   or assist in its implementation may be prepared, copied, published
+   and distributed, in whole or in part, without restriction of any
+   kind, provided that the above copyright notice and this paragraph are
+   included on all such copies and derivative works.  However, this
+   document itself may not be modified in any way, such as by removing
+   the copyright notice or references to the Internet Society or other
+   Internet organizations, except as needed for the purpose of
+   developing Internet standards in which case the procedures for
+   copyrights defined in the Internet Standards process must be
+   followed, or as required to translate it into languages other than
+   English.
+
+   The limited permissions granted above are perpetual and will not be
+   revoked by the Internet Society or its successors or assignees.
+
+   This document and the information contained herein is provided on an
+   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
+   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
+   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
+   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
+Acknowledgement
+
+   Funding for the RFC Editor function is currently provided by the
+   Internet Society.
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+Lear                         Informational                      [Page 7]
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