Hewlett Packard Co.
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.
The TFTP option negotiation mechanism, proposed in , is a backward-compatible extension to the TFTP protocol, defined in . 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.
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 issues are not discussed in this memo.
 Malkin, G., and A. Harkin, "TFTP Option Extension", RFC 1782, Xylogics, Inc., Hewlett Packard Co., March 1995.  Sollins, K., "The TFTP Protocol (Revision 2)", STD 33, RFC 1350, MIT, July 1992.
Malkin, G., and A. Harkin, "TFTP Blocksize Option", RFC 1783, Xylogics, Inc., Hewlett Packard Co., March 1995. Malkin, G., and A. Harkin, "TFTP Timeout Interval and Transfer Size Options", RFC 1784, Xylogics, Inc., Hewlett Packard Co., March 1995.
Gary Scott Malkin Xylogics, Inc. 53 Third Avenue Burlington, MA 01803 Phone: (617) 272-8140 EMail: firstname.lastname@example.org Art Harkin Internet Services Project Information Networks Division 19420 Homestead Road MS 43LN Cupertino, CA 95014 Phone: (408) 447-3755 EMail: email@example.com