Network Working Group                                          M. O'Dell
Request for Comments: 2438                            UUNET Technologies
BCP: 27                                                    H. Alvestrand
Category: Best Current Practice                                  Maxware
                                                               B. Wijnen
                                               IBM T. J. Watson Research
                                                              S. Bradner
                                                      Harvard University
                                                            October 1998

     Advancement of MIB specifications on the IETF Standards Track

Status of this Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

2. Abstract

   The Internet Standards Process [1] requires that all IETF Standards
   Track specifications must have "multiple, independent, and
   interoperable implementations" before they can be advanced beyond
   Proposed Standard status.  This document specifies the process which
   the IESG will use to determine if a MIB specification document meets
   these requirements.  It also discusses the rationale for this
   process.

3. The Nature of the Problem

   The Internet Standards Process [1] requires that for an IETF
   specification to advance beyond the Proposed Standard level, at least
   two genetically unrelated implementations must be shown to
   interoperate correctly with all features and options. There are two
   distinct reasons for this requirement.

   The first reason is to verify that the text of the specification is
   adequately clear and accurate.  This is demonstrated by showing that
   multiple implementation efforts have used the specification to
   achieved interoperable implementations.

   The second reason is to discourage excessive options and "feature
   creep". This is accomplished by requiring interoperable
   implementation of all features, including options.  If an option is
   not included in at least two different interoperable implementations,
   it is safe to assume that it has not been deemed useful and must be
   removed before the specification can advance.

   In the case of a protocol specification which specifies the "bits on
   the wire" exchanged by executing state machines, the notion of
   "interoperability" is reasonably intuitive - the implementations must
   successfully "talk to each other", exchanging "bits on the wire",
   while exercising all features and options.

   In the case of an SNMP Management Information Base (MIB)
   specification, exactly what constitutes "interoperation" is less
   obvious.  This document specifies how the IESG has decided to judge
   "MIB specification interoperability" in the context of the IETF
   Standards Process.

   There are a number of plausible interpretations of MIB specification
   interoperability, many of which have merit but which have very
   different costs and difficulties in realization.

   The aim is to ensure that the dual goals of specification clarity and
   feature evaluation have been met using an interpretation of the
   concept of MIB specification interoperability that strikes a balance
   between testing complexity and practicality.

4. On The Nature of MIB specifications

   Compared to "state machine" protocols which focus on procedural
   specifications, a MIB specification is much more data oriented.  To
   over-generalize, in a typical MIB specification the collection of
   data type and instance specifications outnumbers inter-object
   procedural or causal semantics by a significant amount.

   A central issue is that a MIB specification does not stand alone; it
   forms the access interface to the instrumentation underneath it.
   Without the instrumentation, a MIB has form but no values.  Coupled
   with the large number of objects even in a simple MIB specification,
   a MIB specification tends to have more of the look and feel of an API
   or a dictionary than a state machine protocol.

   It is important to distinguish between assessing the interoperability
   of applications which may use or interact with MIBs, and the MIBs
   themselves.  It is fairly obvious that "black-box testing" can be

   applied to such applications and that the approach enjoys a certain
   maturity in the software engineering arts.  A MIB specification, on
   the other hand is not readily amenable to black box test plans.

5. Discussion and Recommended Process

   In order to meet their obligations under the IETF Standards Process,
   the Operations and Management Area Directors and the IESG must be
   convinced that each MIB specification advanced to Draft Standard or
   Internet Standard status is clearly written, that there are the
   required multiple interoperable implementations, and that all options
   have been implemented.  There are multiple ways to achieve this goal.
   Appendix A lists some testing approaches that could be used when
   attempting to document multiple implementations.

   The Full Coverage or Stimulus-Response approaches are very through,
   and would increase confidence that the requirement has been met, if
   applied.  However, experience in real-world software engineering
   makes it clear that such confidence comes at an extremely high price;
   even with the most exhaustive testing, it is often not clear what
   precisely has been demonstrated by such testing.  We believe that
   both of those standards of evidence are materially beyond what can be
   reasonably accomplished in an operational sense, and achieving the
   requisite semantic specifications are even more unlikely.

   Therefore, the Operations and Management Area and the IESG have
   adopted a more pragmatic approach to determining the suitability of a
   MIB specification for advancement on the standards track beyond
   Proposed Standard status.  Each MIB specification suggested for
   advancement must have one or more advocates who can make a convincing
   argument that the MIB specification meets the multiple implementation
   and feature support requirements of the IETF Standards Process.  The
   specific way to make the argument is left to the advocate, but will
   normally include reports that basic object comparison testing has
   been done.

   Thus any recommendation for the advancement of a MIB specification
   must be accompanied by an implementation report, as is the case with
   all requests for the advancement of IETF specifications.  The
   implementation report must include the reasons why the IESG should
   believe that there are multiple implementations of the MIB
   specification in question and that the all of the MIB objects in the
   specification to be advanced are supported in more than one
   implementation.  But note that the prime concern of the IESG will be
   that the underlying reasons for the interoperable implementations are
   met, i.e., that the text of the specification is clear and
   unambiguous, and that features of the specification which have not
   garnered support have been removed.

   The implementation report will be placed on the IETF web page along
   with the other pre-advancement implementation reports and will be
   specifically referred to in the IETF Last-Call.  As with all such
   implementation reports, the determination of adequacy is made by the
   Area Director(s) of the relevant IETF Area.  This determination of
   adequacy can be challenged during the Last-Call period.

6. Security Considerations

   Some may view this policy as possibly leading to a reduction in the
   level of confidence people can have in MIB specifications but the O&M
   Area Directors and the IESG feel that it will adequately ensure a
   reasonable evaluation of the level of clarity of MIB specifications
   and to ensure that unused options can be identified and removed
   before the advancement of a specification.

   Good, clearly written MIB specifications can be of great assistance
   in the management of the Internet and other networks and thus assist
   in the reduction of some types of security threats.

8. References

   [RFC2026] Bradner, S., "The Internet Standards Process --
             Revision 3", BCP 9, RFC 2026, October 1996.

9. Authors' Addresses

   Michael D. O'Dell
   UUNET Technologies, Inc.
   3060 Williams Drive
   Fairfax, VA 22031

   Phone: +1-703-206-5890
   EMail: mo@uu.net

   Harald T. Alvestrand
   Maxware
   Pirsenteret
   N-7005 Trondheim, Norway

   Phone: +47-73-54-57-94
   EMail: Harald.Alvestrand@maxware.no

   Bert Wijnen
   IBM T. J. Watson Research
   Schagen 33
   3461 GL Linschoten
   Netherlands

   Phone: +31-348-432-794
   EMail: wijnen@vnet.ibm.com

   Scott Bradner
   Harvard University
   1350 Mass. Ave.
   Cambridge MA 02138

   Phone: +1-617-495-3864
   EMail: sob@harvard.edu

Appendix A

A. Some Testing Alternatives

   The IESG debated a number of interoperability and testing models in
   formulating this specification.  The following list is not an
   exhaustive enumeration of the alternatives, but it does capture the
   major plausible models which were examined in the course of the
   discussion.

A.1 Basic Object Comparison

   Assume the requisite two genetically unrelated implementations of the
   MIB in an SNMP agent and an SNMP management station which can do a
   "MIB Dump" (extract the complete set of MIB object types and values
   from the agent implementation).  Extract a MIB Dump from each
   implementation and compare the two dumps to verify that both provide
   the complete set of mandatory and optional objects and that the
   individual objects are of the correct types.

A.2 Stimulus/Response Testing

   Proceed as in A.1, but in addition, comprehensively exercise the two
   (network) elements containing the agent implementations to verify
   that all the MIB objects reflect plausible values in operational
   conditions.  An even stricter interpretation would require that the
   MIB objects in the two network elements track identically given the
   identical stimulus.  While this would test "read-only" or
   "monitoring" information obtained from the underlying
   instrumentation, it is important to observe that such instrumentation
   is actually an *application* which uses the MIB and is not part of
   the MIB itself.

A.3 Full Coverage Testing

   This model extends the notion of Stimulus/Response Testing to its
   logical extreme. The MIB is viewed as an API and the software
   engineering notion of full coverage testing is applied to a MIB.
   This involves exercising all paths through the causal semantics and
   verifying that all objects change state correctly in all cases.
   Again, note that much more than the MIB definition is being exercised
   and evaluated.

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