Network Working Group                                          G. Malkin
Request for Commments: 2349                                 Bay Networks
Updates: 1350                                                  A. Harkin
Obsoletes: 1784                                      Hewlett Packard Co.
Category: Standards Track                                       May 1998


            TFTP Timeout Interval and Transfer Size Options

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   The Trivial File Transfer Protocol [1] is a simple, lock-step, file
   transfer protocol which allows a client to get or put a file onto a
   remote host.

   This document describes two TFTP options. The first allows the client
   and server to negotiate the Timeout Interval.  The second allows the
   side receiving the file to determine the ultimate size of the
   transfer before it begins.  The TFTP Option Extension mechanism is
   described in [2].

Timeout Interval Option Specification

   The TFTP Read Request or Write Request packet is modified to include
   the timeout option as follows:

      +-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+
      |  opc  |filename| 0 |  mode  | 0 | timeout| 0 |  #secs | 0 |
      +-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+

      opc
         The opcode field contains either a 1, for Read Requests, or 2,
         for Write Requests, as defined in [1].

      filename
         The name of the file to be read or written, as defined in [1].
         This is a NULL-terminated field.

      mode
         The mode of the file transfer: "netascii", "octet", or "mail",
         as defined in [1].  This is a NULL-terminated field.

      timeout
         The Timeout Interval option, "timeout" (case in-sensitive).
         This is a NULL-terminated field.

      #secs
         The number of seconds to wait before retransmitting, specified
         in ASCII.  Valid values range between "1" and "255" seconds,
         inclusive.  This is a NULL-terminated field.

   For example:

      +-------+--------+---+--------+---+--------+---+-------+---+
      |   1   | foobar | 0 | octet  | 0 | timeout| 0 |   1   | 0 |
      +-------+--------+---+--------+---+--------+---+-------+---+

   is a Read Request, for the file named "foobar", in octet (binary)
   transfer mode, with a timeout interval of 1 second.

   If the server is willing to accept the timeout option, it sends an
   Option Acknowledgment (OACK) to the client.  The specified timeout
   value must match the value specified by the client.

Transfer Size Option Specification

   The TFTP Read Request or Write Request packet is modified to include
   the tsize option as follows:

      +-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+
      |  opc  |filename| 0 |  mode  | 0 | tsize  | 0 |  size  | 0 |
      +-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+

      opc
         The opcode field contains either a 1, for Read Requests, or 2,
         for Write Requests, as defined in [1].

      filename
         The name of the file to be read or written, as defined in [1].
         This is a NULL-terminated field.

      mode
         The mode of the file transfer: "netascii", "octet", or "mail",
         as defined in [1].  This is a NULL-terminated field.

      tsize
         The Transfer Size option, "tsize" (case in-sensitive).  This is
         a NULL-terminated field.

      size
         The size of the file to be transfered.  This is a NULL-
         terminated field.

   For example:

      +-------+--------+---+--------+---+--------+---+--------+---+
      |   2   | foobar | 0 | octet  | 0 | tsize  | 0 | 673312 | 0 |
      +-------+--------+---+--------+---+--------+---+--------+---+

   is a Write Request, with the 673312-octet file named "foobar", in
   octet (binary) transfer mode.

   In Read Request packets, a size of "0" is specified in the request
   and the size of the file, in octets, is returned in the OACK.  If the
   file is too large for the client to handle, it may abort the transfer
   with an Error packet (error code 3).  In Write Request packets, the
   size of the file, in octets, is specified in the request and echoed
   back in the OACK.  If the file is too large for the server to handle,
   it may abort the transfer with an Error packet (error code 3).

Security Considerations

   The basic TFTP protocol has no security mechanism.  This is why it
   has no rename, delete, or file overwrite capabilities.  This document
   does not add any security to TFTP; however, the specified extensions
   do not add any additional security risks.

References

   [1] Sollins, K., "The TFTP Protocol (Revision 2)", STD 33, RFC 1350,
       October 92.

   [2] Malkin, G., and A. Harkin, "TFTP Option Extension", RFC 2347,
       May 1998.

Authors' Addresses

   Gary Scott Malkin
   Bay Networks
   8 Federal Street
   Billerica, MA  01821

   Phone:  (978) 916-4237
   EMail:  gmalkin@baynetworks.com


   Art Harkin
   Internet Services Project
   Information Networks Division
   19420 Homestead Road MS 43LN
   Cupertino, CA  95014

   Phone: (408) 447-3755
   EMail: ash@cup.hp.com

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   Copyright (C) The Internet Society (1998).  All Rights Reserved.

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