RFC1785 - TFTP Option Negotiation Analysis

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Network Working Group G. Malkin
Request for Comments: 1785 Xylogics, Inc.
Updates: 1350 A. Harkin
Category: Informational Hewlett Packard Co.
March 1995

TFTP Option Negotiation Analysis

Status of this Memo

This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.

Abstract

The TFTP option negotiation mechanism, proposed in [1], is a
backward-compatible extension to the TFTP protocol, defined in [2].
It allows file transfer options to be negotiated prior to the
transfer using a mechanism which is consistent with TFTP's Request
Packet format. The mechanism is kept simple by enforcing a request-
respond-acknowledge sequence, similar to the lock-step approach taken
by TFTP itself.

This document was written to allay concerns that the presence of
options in a TFTP Request packet might cause pathological behavior on
servers which do not support TFTP option negotiation.

Test Results

A TFTP client, modified to send TFTP options, was tested against five
unmodified servers:

DEC DEC 3000/400 alpha OSF1 V3.0
SGI IP17 mips IRIX 5.2
SUN sun4c sparc SunOS 5.1
IBM RS/6000 Model 320 AIX 3.4
SUN sun4m SunOS 4.1.3

In each case, the servers ignored the option information in the
Request packet and the transfer proceeded as though no option
negotiation had been attempted. In addition, the standard BSD4.3
source for TFTPD, the starting point for many implementations, was
examined. The code clearly ignores any extraneous information in
Request packets.

From these results and examinations, it is clear that the TFTP option

negotiation mechanism is fully backward-compatible with unmodified
TFTP servers.

Security Considerations

Security issues are not discussed in this memo.

References

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

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

Related Documents

Malkin, G., and A. Harkin, "TFTP Blocksize Option", RFC1783,
Xylogics, Inc., Hewlett Packard Co., March 1995.

Malkin, G., and A. Harkin, "TFTP Timeout Interval and Transfer Size
Options", RFC1784, 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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