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", RFC 1782,
   
       Xylogics, Inc., Hewlett Packard Co., March 1995.
   
   [2] Sollins, K., "The TFTP Protocol (Revision 2)", STD 33, RFC 1350,
       MIT, July 1992.

Related Documents

   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.

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