    Network Working Group                                         R. Austein
    Request for Comments: 3197                                 InterNetShare
    Category: Informational                                    November 2001

                 Applicability Statement for DNS MIB Extensions

    Status of this Memo

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

    Copyright Notice

       Copyright (C) The Internet Society (2001).  All Rights Reserved.

    Abstract

       This document explains why, after more than six years as proposed
       standards, the DNS Server and Resolver MIB extensions were never
       deployed, and recommends retiring these MIB extensions by moving them
       to Historical status.

    1. History

       The road to the DNS MIB extensions was paved with good intentions.

       In retrospect, it's obvious that the working group never had much
       agreement on what belonged in the MIB extensions, just that we should
       have some.  This happened during the height of the craze for MIB
       extensions in virtually every protocol that the IETF was working on
       at the time, so the question of why we were doing this in the first
       place never got a lot of scrutiny.  Very late in the development
       cycle we discovered that much of the support for writing the MIB
       extensions in the first place had come from people who wanted to use
       SNMP SET operations to update DNS zones on the fly.  Examination of
       the security model involved, however, led us to conclude that this
       was not a good way to do dynamic update and that a separate DNS
       Dynamic Update protocol would be necessary.

       The MIB extensions started out being fairly specific to one
       particular DNS implementation (BIND-4.8.3); as work progressed, the
       BIND-specific portions were rewritten to be as implementation-neutral
       as we knew how to make them, but somehow every revision of the MIB
       extensions managed to create new counters that just happened to
       closely match statistics kept by some version of BIND.  As a result,
       the MIB extensions ended up being much too big, which raised a number

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    RFC 3197      Applicability Statement - DNS MIB Extensions November 2001

       of concerns with the network management directorate, but the WG
       resisted every attempt to remove any of these variables.  In the end,
       large portions of the MIB extensions were moved into optional groups
       in an attempt to get the required subset down to a manageable size.

       The DNS Server and Resolver MIB extensions were one of the first
       attempts to write MIB extensions for a protocol usually considered to
       be at the application layer.  Fairly early on it became clear that,
       while it was certainly possible to write MIB extensions for DNS, the
       SMI was not really designed with this sort of thing in mind.  A case
       in point was the attempt to provide direct indexing into the caches
       in the resolver MIB extensions: while arguably the only sane way to
       do this for a large cache, this required much more complex indexing
       clauses than is usual, and ended up running into known length limits
       for object identifiers in some SNMP implementations.

       Furthermore, the lack of either real proxy MIB support in SNMP
       managers or a standard subagent protocol meant that there was no
       reasonable way to implement the MIB extensions in the dominant
       implementation (BIND).  When the AgentX subagent protocol was
       developed a few years later, we initially hoped that this would
       finally clear the way for an implementation of the DNS MIB
       extensions, but by the time AgentX was a viable protocol it had
       become clear that nobody really wanted to implement these MIB
       extensions.

       Finally, the MIB extensions took much too long to produce.  In
       retrospect, this should have been a clear warning sign, particularly
       when the WG had clearly become so tired of the project that the
       authors found it impossible to elicit any comments whatsoever on the
       documents.

    2. Lessons

       Observations based on the preceding list of mistakes, for the benefit
       of anyone else who ever attempts to write DNS MIB extensions again:

       -  Define a clear set of goals before writing any MIB extensions.
          Know who the constituency is and make sure that what you write
          solves their problem.

       -  Keep the MIB extensions short, and don't add variables just
          because somebody in the WG thinks they'd be a cool thing to
          measure.

       -  If some portion of the task seems to be very hard to do within the
          SMI, that's a strong hint that SNMP is not the right tool for
          whatever it is that you're trying to do.

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    RFC 3197      Applicability Statement - DNS MIB Extensions November 2001

       -  If the entire project is taking too long, perhaps that's a hint
          too.

    3. Recommendation

       In view of the community's apparent total lack of interest in
       deploying these MIB extensions, we recommend that RFCs 1611 and 1612
       be reclassified as Historical documents.

    4. Security Considerations

       Re-classifying an existing MIB document from Proposed Standard to
       Historic should not have any negative impact on security for the
       Internet.

    5. IANA Considerations

       Getting rid of the DNS MIB extensions should not impose any new work
       on IANA.

    6. Acknowledgments

       The author would like to thank all the people who were involved in
       this project over the years for their optimism and patience,
       misguided though it may have been.

    7. References

       [DNS-SERVER-MIB]     Austein, R. and J. Saperia, "DNS Server MIB
                            Extensions", RFC 1611, May 1994.

       [DNS-RESOLVER-MIB]   Austein, R. and J. Saperia, "DNS Resolver MIB
                            Extensions", RFC 1612, May 1994.

       [DNS-DYNAMIC-UPDATE] Vixie, P., Thomson, S., Rekhter, Y. and J.
                            Bound, "Dynamic Updates in the Domain Name
                            System (DNS UPDATE)", RFC 2136, April 1997.

       [AGENTX]             Daniele, M., Wijnen, B., Ellison, M., and D.
                            Francisco, "Agent Extensibility (AgentX)
                            Protocol Version 1", RFC 2741, January 2000.

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    RFC 3197      Applicability Statement - DNS MIB Extensions November 2001

    8. Author's Address

       Rob Austein
       InterNetShare, Incorporated
       325M Sharon Park Drive, Suite 308
       Menlo Park, CA  94025
       USA

       EMail: sra@hactrn.net

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    RFC 3197      Applicability Statement - DNS MIB Extensions November 2001

    9. Full Copyright Statement

       Copyright (C) The Internet Society (2001).  All Rights Reserved.

       This document and translations of it may be copied and furnished to
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       The limited permissions granted above are perpetual and will not be
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    Acknowledgement

       Funding for the RFC Editor function is currently provided by the
       Internet Society.

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