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
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.
- 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", RFC1611, May 1994.
[DNS-RESOLVER-MIB] Austein, R. and J. Saperia, "DNS Resolver MIB
Extensions", RFC1612, May 1994.
[DNS-DYNAMIC-UPDATE] Vixie, P., Thomson, S., Rekhter, Y. and J.
Bound, "Dynamic Updates in the Domain Name
System (DNS UPDATE)", RFC2136, April 1997.
[AGENTX] Daniele, M., Wijnen, B., Ellison, M., and D.
Francisco, "Agent Extensibility (AgentX)
Protocol Version 1", RFC2741, January 2000.
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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