RFC 963 (rfc963) - Page 1 of 19

Some problems with the specification of the Military Standard Internet Protocol

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Network Working Group                                 Deepinder P. Sidhu
Request for Comments: 963                          Iowa State University
                                                           November 1985

              SOME PROBLEMS WITH THE SPECIFICATION OF THE
                  MILITARY STANDARD INTERNET PROTOCOL


STATUS OF THIS MEMO

   The purpose of this RFC is to provide helpful information on the
   Military Standard Internet Protocol (MIL-STD-1777) so that one can
   obtain a reliable implementation of this protocol standard.
   Distribution of this note is unlimited.

ABSTRACT

   This paper points out several significant problems in the
   specification of the Military Standard Internet Protocol
   (MIL-STD-1777, dated August 1983 [MILS83a]).  These results are based
   on an initial investigation of this protocol standard.  The problems
   are: (1) a failure to reassemble fragmented messages completely; (2)
   a missing state transition; (3) errors in testing for reassembly
   completion; (4) errors in computing fragment sizes; (5) minor errors
   in message reassembly; (6) incorrectly computed length for certain
   datagrams.  This note also proposes solutions to these problems.

1.  Introduction

   In recent years, much progress has been made in creating an
   integrated set of tools for developing reliable communication
   protocols.  These tools provide assistance in the specification,
   verification, implementation and testing of protocols.  Several
   protocols have been analyzed and developed using such tools.
   Examples of automated verification and implementation of several real
   world protocols are discussed in [BLUT82] [BLUT83] [SIDD83] [SIDD84].

   We are currently working on the automatic implementation of the
   Military Standard Internet Protocol (IP).  This analysis will be
   based on the published specification [MILS83a] of IP dated 12 August
   1983.

   While studying the MIL Standard IP specification, we have noticed
   numerous errors in the specification of this protocol.  One
   consequence of these errors is that the protocol will never deliver
   fragmented incoming datagrams; if this error is corrected, such
   datagrams will be missing some data and their lengths will be
   incorrectly reported.  In addition, outgoing datagrams that are
   divided into fragments will be missing some data.  The proof of these
   statements follows from the specification of IP [MILS83a] as
   discussed below.


Sidhu
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