Network Working Group R. Presuhn
Internet Draft BMC Software, Inc.
Expires: April 27 October 2002
Referential Integrity Considerations
in Management Information Base (MIB) Design
<draft-presuhn-referent-00.txt>
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This memo identifies some of referential integrity considerations of
which management information base (MIB) designers should be aware.
It is intended to promote discussion and the identification of
additional related issues.
Comments are welcomed, from the Operations and Management Area in
general, from MIB writers, and from participants in the sming and eos
working groups and the xmlconf BOF in particular. Please send
comments to the mibs@ops.ietf.org mailing list.
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Table of Contents
1. Introduction ................................................ 3
2. Notice on Intellectual Property ............................. 4
3. Security Considerations ..................................... 5
4. References .................................................. 5
4.1. Informative References .................................... 5
4.2. Normative References ...................................... 6
5. Author's Address ............................................ 6
6. Full Copyright Statement .................................... 6
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1. Introduction
This memo identifies some of referential integrity considerations of
which management information base (MIB) deisgners should be aware.
It is intended to promote discussion and the identification of
additional related issues.
This initial draft is just a strawman, so we'll have something to
discuss.
Referential integrity, a concept from the world of relational
databases, is useful in the design and use of MIBs as well. In
[RFC2571] how instances of management information are named is
spelled out in detail. When we look at how MIBs and management
applications handle references, we see several potential sources of
problems:
- In some MIBs, only the human-readable decription reveals that
two tables share a common index;
- When two tables share one or more common indexes, the nature of
the relationship between them, if it is spelled out at all, is
not machine-readable;
- When RowPointers and related textual conventions are used, they
are frequently used without an associated ContextName object,
limiting the scope of the relationship;
- In a few notorious cases, such as ifIndex, instance names are
not guaranteed to be stable across reboots.
The lack of specification (or, in some cases, the over-specification)
of inter-table relationships causes much consternation during the
processes of row creation and deletion.
However, instance name instability causes the most grief when it
interacts with other objects which have a requirement for persistance
of some kind, whether within the managed deviced or across the larger
systems which is the network. It impacts not only MIBs with shared
indexes or row pointers, but also things like disman script /
expression MIBs, configuration file formats, and system configuration
version management.
A family of problems that has surfaced in several MIBs arises from
the need to ensure that the references (e.g., RowPointers and
indexes) to persistent data remain consistent across reboots. An
example of where things become problematic is the use of ifIndex,
which is not guaranteed to keep its value across reboots. In
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addition to keeping direct references consistent, there are also
cases where keeping references stable across reboots is a
requirement. For example, a VACM access control policy could be
subverted if the indexes don't remain the same.
A similar problem results in MIBs that use "profiles" to reduce the
amount of configuration data. The ADSL extension MIB encountered
this problem. The solution adopted there, to require implementations
to adjust their indexes to match whatever happened to ifIndex, is not
terribly satisfying. First, it interacts badly with VACM. Secondly,
it requires configuration management applications to somehow be able
to figure out whether two or more configurations, in which the
indexes may have all been renumbered, are equivalent. (This can be
done, but it's not cheap.)
The problem only gets worse with things like scripts, the [RFC2573]
notification filtering mechanism, thresholds, alarms, and common log
management use cases,
Consequently, this memo recommends that objects like ifIndex be
implemented so that their values do not change across reboots, and
that in future MIB design the needs of configuration management
systems, scripts, and so on be taken into account.
2. Notice on Intellectual Property
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
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3. Security Considerations
Needless to say, there are lots of security considerations here. The
index structure of the view-based access control model [VACM]
reflects the naming of the resources to which access is being
controlled. Consequently, if resource names change across reboots,
the semantics of a stored access control configuration would not be
preserved.
4. References
4.1. Informative References
[RFC1155] Rose, M. and K. McCloghrie, "Structure and Identification
of Management Information for TCP/IP-based Internets", STD
16, RFC 1155, May 1990.
[RFC1157] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple
Network Management Protocol", STD 15, RFC 1157, May 1990.
[RFC1212] Rose, M., and K. McCloghrie, "Concise MIB Definitions", STD
16, RFC 1212, March 1991.
[RFC2578] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M., and S. Waldbusser, "Structure of Management
Information Version 2 (SMIv2)", STD 58, RFC 2578, April
1999.
[RFC2579] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M., and S. Waldbusser, "Textual Conventions for
SMIv2", STD 58, RFC 2579, April 1999.
[RFC2580] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M., and S. Waldbusser, "Conformance Statements for
SMIv2", STD 58, RFC 2580, April 1999.
[OpsReq] Woodcock, B., "Operator Requirements of Infrastructure
Management Methods", draft-ops-operator-req-mgmt-02.txt,
February 2002.
[ConfBcp] MacFaden, M., Saperia, J. and W. Tackabury, "Configuring
Networks and Devices With SNMP", draft-ietf-snmpconf-
bcp-07.txt, November 2001.
[RFC2575] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based
Access Control Model (VACM) for the Simple Network
Management Protocol (SNMP)", RFC 2575, April 1999.
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[RFC2574] Blumenthal, U. and B. Wijnen, "User-based Security Model
(USM) for version 3 of the Simple Network Management
Protocol (SNMPv3)", RFC 2574, April 1999.
[RFC3231] Levi, D. and J. Schoenwaelder, "Definitions of Managed
Objects for Scheduling Management Operations", RFC 3231,
January 2002.
[RFC3231] Levi, D. and J. Schoenwaelder, "Definitions of Managed
Objects for Scheduling Management Operations", RFC 3231,
January 2002.
[RFC3014] Kavasseri, R., "Notification Log MIB", RFC 3014, November
2000.
4.2. Normative References
5. Author's Address
Randy Presuhn
BMC Software, Inc.
2141 North First Street
San Jose, CA 95131
USA
Phone: +1 408 546 1006
EMail: randy_presuhn@bmc.com
6. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
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English.
The limited permissions granted above are perpetual and will not be
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revoked by the Internet Society or its successors or assigns.
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