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 © 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 © The Internet Society (1998). All Rights Reserved.

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