TFTP Timeout/Tsize: TFTP Timeout Interval and Transfer Size Options
Two TFTP options for agreeing on retransmission timing and file size.
Malkin, G. and A. Harkin, "TFTP Timeout Interval and Transfer Size Options", RFC 1784, DOI 10.17487/RFC1784, March 1995, <https://www.rfc-editor.org/info/rfc1784>.
@misc{rfc1784,
series = {Request for Comments},
number = 1784,
howpublished = {RFC 1784},
publisher = {RFC Editor},
doi = {10.17487/RFC1784},
url = {https://www.rfc-editor.org/info/rfc1784},
author = {G. Malkin and A. Harkin},
title = {{TFTP Timeout Interval and Transfer Size Options}},
pagetotal = 4,
year = 1995,
month = mar,
} RFC text
Contents
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, RFC 1350,
MIT, July 1992.
[2] Malkin, G., and A. Harkin, "TFTP Option Extension", RFC 1782,
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
EMail: ash@cup.hp.com
ISO Plain Language
On this page
§1Negotiable TFTP Options
TFTP is a lock-step protocol for getting or putting a file on a remote host. This memo defines a timeout option and a transfer-size option using the TFTP Option Extension mechanism. Both options appear in the initial Read Request or Write Request and can be acknowledged by the server.
The options let the two TFTP endpoints agree on timing and learn the transfer size before they exchange file data.
§1The Timeout Option
The case-insensitive option name timeout carries a number of seconds to wait before retransmitting. The value is an ASCII string from 1 through 255, inclusive, terminated by a null character. If the server accepts the option, its Option Acknowledgment must echo the same value that the client proposed.
The client proposes how many seconds to wait before trying again. The server accepts the option by returning that same timeout value.
§2The Transfer-Size Option
The case-insensitive tsize option carries a file size as a null-terminated ASCII string. In a Read Request, the client sends a size of 0, and the server returns the file size in octets in its Option Acknowledgment. If the file is too large for the client, the client may abort with ERROR code 3.
In a Write Request, the client sends the file size in octets and the server echoes it in the acknowledgment. If the file is too large for the server, the server may abort with ERROR code 3. The memo does not discuss security issues.
For a download, the client asks for the size and the server reports it. For an upload, the client reports the size and the server repeats it before the transfer starts.