RFC1784 - TFTP Timeout Interval and Transfer Size Options

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　　Network Working Group G. Malkin
Request for Comments: 1784 Xylogics, Inc.
Updates: 1350 A. Harkin
Category: Standards Track Hewlett Packard Co.
March 1995

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.

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].

This document assumes that the reader is familiar with the
terminology and notation of both [1] and [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 insensitive).
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" octets,
inclusive. This is a NULL-terminated field.

For example:

+-------+--------+---+--------+---+--------+---+--------+---+
| 1 | foobar | 0 | binary | 0 | timeout| 0 | 1 | 0 |
+-------+--------+---+--------+---+--------+---+--------+---+

is a Read Request, for the file named "foobar", in 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 insensitive). This is
a NULL-terminated field.

size
The size of the file to be transfered, specified as a
NULL-terminated ASCII string.

For example:

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

is a Write Request, with the 673312-octet file named "foobar", in
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

Security issues are not discussed in this memo.

References

[1] Sollins, K., "The TFTP Protocol (Revision 2)", STD 33, RFC1350,
MIT, July 1992.

[2] Malkin, G., and A. Harkin, "TFTP Option Extension", RFC1782,
Xylogics, Inc., Hewlett Packard Co., March 1995.

Authors' Addresses

Gary Scott Malkin
Xylogics, Inc.
53 Third Avenue
Burlington, MA 01803

Phone: (617) 272-8140
EMail: gmalkin@xylogics.com

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

Phone: (408) 447-3755

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