GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc3512

Network Working Group M. MacFaden Request for Comments: 3512 Riverstone Networks, Inc. Category: Informational D. Partain

                                                              Ericsson
                                                            J. Saperia
                                                  JDS Consulting, Inc.
                                                          W. Tackabury
                                            Gold Wire Technology, Inc.
                                                            April 2003
               Configuring Networks and Devices with
             Simple Network Management Protocol (SNMP)

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 (2003).  All Rights Reserved.

Abstract

 This document is written for readers interested in the Internet
 Standard Management Framework and its protocol, the Simple Network
 Management Protocol (SNMP).  In particular, it offers guidance in the
 effective use of SNMP for configuration management.  This information
 is relevant to vendors that build network elements, management
 application developers, and those that acquire and deploy this
 technology in their networks.

Table of Contents

 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .   3
    1.1. The Internet Standard Management Framework. . . . . . . .   3
    1.2. Configuration and the Internet Standard Management
         Frame-work. . . . . . . . . . . . . . . . . . . . . . . .   4
 2. Using SNMP as a Configuration Mechanism. . . . . . . . . . . .   5
    2.1. Transactions and SNMP . . . . . . . . . . . . . . . . . .   6
    2.2. Practical Requirements for Transactional Control. . . . .   6
    2.3. Practices in Configuration--Verification. . . . . . . . .   7
 3. Designing a MIB Module . . . . . . . . . . . . . . . . . . . .   9
    3.1. MIB Module Design - General Issues. . . . . . . . . . . .  10
    3.2. Naming MIB modules and Managed Objects. . . . . . . . . .  11
    3.3. Transaction Control And State Tracking. . . . . . . . . .  12

MacFaden, et al. Informational [Page 1] RFC 3512 Configuring Networks and Devices with SNMP April 2003

         3.3.1. Conceptual Table Row Modification Practices. . . .  12
         3.3.2. Fate sharing with multiple tables. . . . . . . . .  13
         3.3.3. Transaction Control MIB Objects. . . . . . . . . .  14
         3.3.4. Creating And Activating New Table Rows . . . . . .  15
         3.3.5. Summary Objects and State Tracking . . . . . . . .  15
         3.3.6. Optimizing Configuration Data Transfer . . . . . .  18
    3.4. More Index Design Issues. . . . . . . . . . . . . . . . .  22
         3.4.1. Simple Integer Indexing. . . . . . . . . . . . . .  23
         3.4.2. Indexing with Network Addresses. . . . . . . . . .  23
    3.5. Conflicting Controls. . . . . . . . . . . . . . . . . . .  24
    3.6. Textual Convention Usage. . . . . . . . . . . . . . . . .  25
    3.7. Persistent Configuration. . . . . . . . . . . . . . . . .  26
    3.8. Configuration Sets and Activation . . . . . . . . . . . .  28
         3.8.1. Operational Activation Considerations. . . . . . .  28
         3.8.2. RowStatus and Deactivation . . . . . . . . . . . .  30
    3.9. SET Operation Latency . . . . . . . . . . . . . . . . . .  31
         3.9.1. Subsystem Latency, Persistence Latency,
                and Activation Latency . . . . . . . . . . . . . .  33
    3.10. Notifications and Error Reporting. . . . . . . . . . . .  33
         3.10.1. Identifying Source of Configuration Changes . . .  34
         3.10.2. Limiting Unnecessary Transmission of
                 Notifications . . . . . . . . . . . . . . . . . .  34
         3.10.3. Control of Notification Subsystem . . . . . . . .  36
    3.11 Application Error Reporting . . . . . . . . . . . . . . .  36
    3.12 Designing MIB Modules for Multiple Managers . . . . . . .  37
    3.13 Other MIB Module Design Issues. . . . . . . . . . . . . .  39
         3.13.1. Octet String Aggregations . . . . . . . . . . . .  39
         3.13.2 Supporting multiple instances of a MIB Module. . .  40
         3.13.3 Use of Special Optional Clauses. . . . . . . . . .  41
 4. Implementing SNMP Configuration Agents . . . . . . . . . . . .  41
    4.1. Operational Consistency . . . . . . . . . . . . . . . . .  41
    4.2. Handling Multiple Managers. . . . . . . . . . . . . . . .  43
    4.3. Specifying Row Modifiability. . . . . . . . . . . . . . .  44
    4.4. Implementing Write-only Access Objects. . . . . . . . . .  44
 5. Designing Configuration Management Software. . . . . . . . . .  44
    5.1. Configuration Application Interactions
         with Managed Systems. . . . . . . . . . . . . . . . . . .  45
         5.1.1. SET Operations . . . . . . . . . . . . . . . . . .  46
         5.1.2. Configuration Transactions . . . . . . . . . . . .  46
         5.1.3. Tracking Configuration Changes . . . . . . . . . .  47
         5.1.4. Scalability of Data Retrieval. . . . . . . . . . .  48
 6. Deployment and Security Issues . . . . . . . . . . . . . . . .  48
    6.1. Basic assumptions about Configuration . . . . . . . . . .  48
    6.2. Secure Agent Considerations . . . . . . . . . . . . . . .  49
    6.3. Authentication Notifications. . . . . . . . . . . . . . .  49
    6.4. Sensitive Information Handling. . . . . . . . . . . . . .  50
 7. Policy-based Management. . . . . . . . . . . . . . . . . . . .  51
    7.1. What Is the Meaning of 'Policy-based' . . . . . . . . . .  51

MacFaden, et al. Informational [Page 2] RFC 3512 Configuring Networks and Devices with SNMP April 2003

    7.2. Organization of Data in an SNMP-Based Policy System . . .  53
    7.3. Information Related to Policy-based Configuration . . . .  54
    7.4. Schedule and Time Issues. . . . . . . . . . . . . . . . .  56
    7.5. Conflict Detection, Resolution and Error Reporting. . . .  56
         7.5.1. Changes to Configuration Outside of the
                Policy System. . . . . . . . . . . . . . . . . . .  57
    7.6. More about Notifications in a Policy System . . . . . . .  57
    7.7. Using Policy to Move Less Configuration Data. . . . . . .  57
 8. Example MIB Module With Template-based Data. . . . . . . . . .  58
    8.1. MIB Module Definition. . . . . . . .  . . . . . . . . . .  61
    8.2. Notes on MIB Module with Template-based Data. . . . . . .  73
    8.3. Examples of Usage of the MIB . . . . . . .. . . . . . . .  74
 9. Security Considerations . . . . . . . . . . .. . . . . . . . .  77
 10. Acknowledgments. . . . . . . . . . . . . . .  . . . . . . . .  78
 11. Normative References. . . . . . . . . . . . . . . . . . . . .  78
 12. Informative References. . . . . . . . . . . . . . . . . . . .  79
 13. Intellectual Property . . . . . . . . . . . . . . . . . . . .  81
 14. Editors' Addresses. . . . . . . . . . . . . . . . . . . . . .  82
 15. Full Copyright Statement. . . . . . . . . . . . . . . . . . .  83

1. Introduction

1.1. The Internet Standard Management Framework

 The Internet Standard Management Framework has many components.  The
 purpose of this document is to describe effective ways of applying
 those components to the problems of configuration management.
 For reference purposes, the Internet Standard Management Framework
 presently consists of five major components:
 o  An overall architecture, described in RFC 3411 [1].
 o  Mechanisms for describing and naming objects and events for the
    purpose of management.  The first version of this Structure of
    Management Information (SMI) is called SMIv1 and described in STD
    16, RFC 1155 [15], STD 16, RFC 1212 [16] and RFC 1215 [17].  The
    second version, called SMIv2, is described in STD 58, RFC 2578
    [2], STD 58, RFC 2579 [3] and STD 58, RFC 2580 [4].
 o  Message protocols for transferring management information.  The
    first version of the SNMP message protocol is called SNMPv1 and
    described in STD 15, RFC 1157 [18].  A second version of the SNMP
    message protocol, which is not an Internet standards track
    protocol, is called SNMPv2c and described in RFC 1901 [19].  The
    third version of the message protocol is called SNMPv3 and
    described in RFC 3417 [5], RFC 3412 [6] and RFC 3414 [7].

MacFaden, et al. Informational [Page 3] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 o  Protocol operations for accessing management information.  The
    first set of protocol operations and associated PDU formats is
    described in STD 15, RFC 1157 [18].  A second set of protocol
    operations and associated PDU formats is described in RFC 3416
    [8].
 o  A set of fundamental applications described in RFC 3413 [9] and
    the view-based access control mechanism described in RFC 3415
    [10].
 A more detailed introduction to the current SNMP Management Framework
 can be found in RFC 3410 [12].
 Managed objects are accessed via a virtual information store, termed
 the Management Information Base or MIB.  Objects in the MIB are
 defined using the mechanisms defined in the SMI.

1.2. Configuration and the Internet Standard Management Framework

 Data networks have grown significantly over the past decade.  This
 growth can be seen in terms of:
 Scale - Networks have more network elements, and the network
    elements are larger and place more demands on the systems managing
    them.  For example, consider a typical number and speed of
    interfaces in a modern core network element.  A managed
    metropolitan area network switch can have a port density much
    greater than the port density built into the expectations of the
    management systems that predated it.  There are also many more
    interrelationships within and between devices and device
    functions.
 Functionality - network devices perform more functions.
    More protocols and network layers are required for the successful
    deployment of network services which depend on them.
 Rate of Change - the nature of modern network services
    causes updates, additions, and deletions of device configuration
    information more often than in the past.  No longer can it be
    assumed that a configuration will be specified once and then be
    updated rarely.  On the contrary, the trend has been towards much
    more frequent changes of configuration information.
 Correct configuration of network elements that make up data networks
 is a prerequisite to the successful deployment of the services on
 them.  The growth in size and complexity of modern networks increases
 the need for a standard configuration mechanism that is tightly
 integrated with performance and fault management systems.

MacFaden, et al. Informational [Page 4] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 The Internet Standard Management Framework has been used successfully
 to develop configuration management systems for a broad range of
 devices and networks.  A standard configuration mechanism that
 tightly integrates with performance and fault systems is needed not
 only to help reduce the complexity of management, but also to enable
 verification of configuration activities that create revenue-
 producing services.
 This document describes Current Practices that have been used when
 designing effective configuration management systems using the
 Internet Standard Management Framework (colloquially known as SNMP).
 It covers many basic practices as well as more complex agent and
 manager design issues that are raised by configuration management.
 We are not endeavoring to present a comprehensive how-to document for
 generalized SNMP agent, MIB module, or management application design
 and development.  We will, however, cover points of generalized SNMP
 software design and implementation practice, where the practice has
 been seen to benefit configuration management software.  So, for
 example, the requirement for management applications to be aware of
 agent limitations is discussed in the context of configuration
 operations, but many issues that a management application developer
 should consider with regard to manager-agent interactions are left
 for other documents and resources.
 Significant experience has been gained over the past ten years in
 configuring public and private data networks with SNMP.  During this
 time, networks have grown significantly as described above.  A
 response to this explosive growth has been the development of
 policy-based configuration management.  Policy-Based Configuration
 Management is a methodology wherein configuration information is
 derived from rules and network-wide objectives, and is distributed to
 potentially many network elements with the goal of achieving
 consistent network behavior throughout an administrative domain.
 This document presents lessons learned from these experiences and
 applies them to both conventional and policy-based configuration
 systems based on SNMP.

2. Using SNMP as a Configuration Mechanism

 Configuration activity causes one or more state changes in an
 element.  While it often takes an arbitrary number of commands and
 amount of data to make up configuration change, it is critical that
 the configuration system treat the overall change operation
 atomically so that the number of states into which an element
 transitions is minimized.  The goal is for a change request either to
 be completely executed or not at all.  This is called transactional
 integrity.  Transactional integrity makes it possible to develop

MacFaden, et al. Informational [Page 5] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 reliable configuration systems that can invoke transactions and keep
 track of an element's overall state and work in the presence of error
 states.

2.1. Transactions and SNMP

 Transactions can logically take place at very fine-grained levels
 such as an individual object instance or in very large aggregations
 that could include many object instances located in many tables on a
 managed device.  For this reason, reliance on transactional integrity
 only at the SNMP protocol level is insufficient.

2.2. Practical Requirements for Transactional Control

 A well-designed and deployed configuration system should have the
 following features with regard to transactions and transactional
 integrity.
 1) Provide for flexible transaction control at many different levels
    of granularity.  At one extreme, an entire configuration may be
    delivered and installed on an element, or alternately one small
    attribute may be changed.
 2) The transaction control component should work at and understand a
    notion of the kind of multi-level "defaulting" as described in
    Section 7.1.  The key point here is that it may make most sense to
    configure systems at an abstract level rather than on an
    individual instance by instance basis as has been commonly
    practiced.  In some cases it is more effective to send a
    configuration command to a system that contains a set of
    'defaults' to be applied to instances that meet certain criteria.
 3) An effective configuration management system must allow
    flexibility in the definition of a successful transaction.  This
    cannot be done at the protocol level alone, but rather must be
    provided for throughout the application and the information that
    is being managed.  In the case of SNMP, the information would be
    in properly defined MIB modules.
 4) A configuration management system should provide time-indexed
    transaction control.  For effective rollback control, the
    configuration transactions and their successful or unsuccessful
    completion status must be reported by the managed elements and
    stored in a repository that supports such time indexing and can
    record the user that made the change, even if the change was not
    carried out by the system recording the change.

MacFaden, et al. Informational [Page 6] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 5) The managed system must support transactional security.  This
    means that depending on who is making the configuration request
    and where it is being made, it may be accepted or denied based on
    security policy that is in effect in the managed element.
 Effective transactional control is a responsibility shared between
 design, implementation, and operational practice.  Transaction
 control techniques for MIB module design are discussed in Section
 3.3.  Transaction control considerations for the agent implementation
 are discussed in Section 5.2.2.

2.3. Practices in Configuration–Verification

 Verification of expected behavior subsequent to the commitment of
 change is an integral part of the configuration process.  To reduce
 the chance of making simple errors in configuration, many
 organizations employ the following change management procedure:
 pre-test - verify that the system is presently working properly
 change   - make configuration changes and wait for convergence
            (system or network stability)
 re-test  - verify once again that the system is working properly
 This procedure is commonly used to verify configuration changes to
 critical systems such as the domain name system (DNS).  DNS software
 kits provide diagnostic tools that allow automatic test
 procedures/scripts to be conducted.
 A planned configuration sequence can be aborted if the pre-
 configuration test result shows the state of the system as unstable.
 Debugging the unintended effects of two sets of changes in large
 systems is often more challenging than an analysis of the effects of
 a single set after test termination.
 Networks and devices under SNMP configuration readily support this
 change management procedure since the SNMP provides integrated
 monitoring, configuration and diagnostic capabilities.  The key is
 the sequencing of SNMP protocol operations to effect an integrated
 change procedure like the one described above.  This is usually a
 well-bounded affair for changes within a single network element or
 node.  However, there are times when configuration of a given element
 can impact other elements in a network.  Configuring network
 protocols such as IEEE 802.1D Spanning Tree or OSPF is especially
 challenging since the impact of a configuration change can directly
 affect stability (convergence) of the network the device is connected
 to.

MacFaden, et al. Informational [Page 7] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 An integrated view of configuration and monitoring provides an ideal
 platform from which to evaluate such changes.  For example, the MIB
 module governing IEEE 802.1D Spanning Tree (RFC 1493 [24]) provides
 the following object to monitor stability per logical bridge.
    dot1dStpTopChanges OBJECT-TYPE
        SYNTAX  Counter
        ACCESS  read-only
        STATUS  mandatory
        DESCRIPTION
           "The total number of topology changes detected by
           this bridge since the management entity was last
           reset or initialized."
        REFERENCE
           "IEEE 802.1D-1990: Section 6.8.1.1.3"
        ::= { dot1dStp 4 }
 Likewise, the OSPF MIB module provides a similar metric for stability
 per OSPF area.
    ospfSpfRuns OBJECT-TYPE
        SYNTAX   Counter32
        MAX-ACCESS   read-only
        STATUS   current
        DESCRIPTION
           "The number of times that the intra-area route
           table has been calculated using this area's
           link-state database.  This is typically done
           using Dijkstra's algorithm."
       ::= { ospfAreaEntry 4 }
 The above object types are good examples of a means of facilitating
 the principles described in Section 2.3.  That is, one needs to
 understand the behavior of a subsystem before configuration change,
 then be able to use the same means to retest and verify proper
 operation subsequent to configuration change.
 The operational effects of a given implementation often differ from
 one to another for any given standard configuration object.  The
 impact of a change to stability of systems such as OSPF should be
 documented in an agent-capabilities statement which is consistent
 with "Requirements for IP Version 4 Routers" [22], Section 1.3.4:
    A vendor needs to provide adequate documentation on all
    configuration parameters, their limits and effects.

MacFaden, et al. Informational [Page 8] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 Adherence to the above model is not fail-safe, especially when
 configuration errors are masked by long latencies or when
 configuration errors lead to oscillations in network stability.  For
 example, consider the situation of loading a new software version on
 a device, which leads to small, slow, cumulative memory leaks brought
 on by a certain traffic pattern that was not caught during vendor and
 customer test lab trials.
 In a network-based example, convergence in an autonomous system
 cannot be guaranteed when configuration changes are made since there
 are factors beyond the control of the operator, such as the state of
 other network elements.  Problems affecting this convergence may not
 be detected for a significant period of time after the configuration
 change.  Even for factors within the operator's control, there is
 often little verification done to prevent mis-configuration (as shown
 in the following example).
 Consider a change made to ospfIfHelloInterval and
 ospfIfRtrDeadInterval [24] timers in the OSPF routing protocol such
 that both are set to the same value.  Two routers may form an
 adjacency but then begin to cycle in and out of adjacency, and thus
 never reach a stable (converged) state.  Had the configuration
 process described at the beginning of this section been employed,
 this particular situation would have been discovered without
 impacting the production network.
 The important point to remember from this discussion is that
 configuration systems should be designed and implemented with
 verification tests in mind.

3. Designing a MIB Module

 Carefully considered MIB module designs are crucial to practical
 configuration with SNMP.  As we have just seen, MIB objects designed
 for configuration can be very effective since they can be associated
 with integrated diagnostic, monitoring, and fault objects.  MIB
 modules for configuration also scale when they expose their notion of
 template object types.  Template objects can represent information at
 a higher level of abstraction than instance-level ones.  This has the
 benefit of reducing the amount of instance-level data to move from
 management application to the agent on the managed element, when that
 instance-level data is brought about by applying a template object on
 the agent.  Taken together, all of these objects can provide a robust
 configuration subsystem.
 The remainder of this section provides specific practices used in MIB
 module design with SMIv2 and SNMPv3.

MacFaden, et al. Informational [Page 9] RFC 3512 Configuring Networks and Devices with SNMP April 2003

3.1. MIB Module Design - General Issues

 One of the first tasks in defining a MIB module is the creation of a
 model that reflects the scope and organization of the management
 information an agent will expose.
 MIB modules can be thought of as logical models providing one or more
 aspects/views of a subsystem.  The objective for all MIB modules
 should be to serve one or more operational requirements such as
 accounting information collection, configuration of one or more parts
 of a system, or fault identification.  However, it is important to
 include only those aspects of a subsystem that are proven to be
 operationally useful.
 In 1993, one of most widely deployed MIB modules supporting
 configuration was published, RFC 1493, which contained the BRIDGE-
 MIB.  It defined the criteria used to develop the MIB module as
 follows:
    To be consistent with IAB directives and good engineering
    practice, an explicit attempt was made to keep this MIB as simple
    as possible.  This was accomplished by applying the following
    criteria to objects proposed for inclusion:
 (1)  Start with a small set of essential objects and add only as
      further objects are needed.
 (2)  Require objects be essential for either fault or configuration
      management.
 (3)  Consider evidence of current use and/or utility.
 (4)  Limit the total (sic) of objects.
 (5)  Exclude objects which are simply derivable from others in this
      or other MIBs.
 (6)  Avoid causing critical sections to be heavily instrumented.  The
      guideline that was followed is one counter per critical section
      per layer.
 Over the past eight years additional experience has shown a need to
 expand these criteria as follows:
 (7)  Before designing a MIB module, identify goals and objectives for
      the MIB module.  How much of the underlying system will be
      exposed depends on these goals.

MacFaden, et al. Informational [Page 10] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 (8)  Minimizing the total number of objects is not an explicit goal,
      but usability is.  Be sure to consider deployment and usability
      requirements.
 (9)  During configuration, consider supporting explicit error state,
      capability and capacity objects.
 (10) When evaluating rule (5) above, consider the impact on a
      management application.  If an object can help reduce a
      management application's complexity, consider defining objects
      that can be derived.

3.2. Naming MIB modules and Managed Objects

 Naming of MIB modules and objects informally follows a set of best
 practices.  Originally, standards track MIB modules used RFC names.
 As the MIB modules evolved, the practice changed to using more
 descriptive names.  Presently, Standards Track MIB modules define a
 given area of technology such as ATM-MIB, and vendors then extend
 such MIB modules by prefixing the company name to a given MIB module
 as in ACME-ATM-MIB.
 Object descriptors (the "human readable names" assigned to object
 identifiers [2]) defined in standard MIB modules should be unique
 across all MIB modules.  Generally, a prefix is added to each managed
 object that can help reference the MIB module it was defined in.  For
 example, the IF-MIB uses "if" prefix for descriptors of object types
 such as ifTable, ifStackTable and so forth.
 MIB module object type descriptors can include an abbreviation for
 the function they perform.  For example the objects that control
 configuration in the example MIB module in Section 8 include "Cfg" as
 part of the object descriptor, as in bldgHVACCfgDesiredTemp.
 This is more fully realized when the object descriptors that include
 the fault, configuration, accounting, performance and security [33]
 abbreviations are combined with an organized OID assignment approach.
 For example, a vendor could create a configuration branch in their
 private enterprises area.  In some cases this might be best done on a
 per product basis.  Whatever the approach used, "Cfg" might be
 included in every object descriptor in the configuration branch.
 This has two operational benefits.  First, for those that do look at
 instances of MIB objects, descriptors as seen through MIB browsers or
 other command line tools assist in conveying the meaning of the
 object type.  Secondly, management applications can be pointed at
 specific subtrees for fault or configuration, causing a more
 efficient retrieval of data and a simpler management application with
 potentially better performance.

MacFaden, et al. Informational [Page 11] RFC 3512 Configuring Networks and Devices with SNMP April 2003

3.3. Transaction Control And State Tracking

 Transactions and keeping track of their state is an important
 consideration when performing any type of configuration activity
 regardless of the protocol.  Here are a few areas to consider when
 designing transaction support into an SNMP-based configuration
 system.

3.3.1. Conceptual Table Row Modification Practices

 Any discussion of transaction control as it pertains to MIB module
 design often begins with how the creation or modification of object
 instances in a conceptual row in the MIB module is controlled.
 RowStatus [3] is a standard textual convention for the management of
 conceptual rows in a table.  Specifically, the RowStatus textual
 convention that is used for the SYNTAX value of a single column in a
 table controls the creation, deletion, activation, and deactivation
 of conceptual rows of the table.  When a table has been defined with
 a RowStatus object as one of its columns, changing an instance of the
 object to 'active' causes the row in which that object instance
 appears to become 'committed'.
 In a multi-table scenario where the configuration data must be spread
 over many columnar objects, a RowStatus object in one table can be
 used to cause the entire set of data to be put in operation or stored
 based on the definition of the objects.
 In some cases, very large amounts of data may need to be 'committed'
 all at once.  In these cases, another approach is to configure all of
 the rows in all the tables required and have an "activate" object
 that has a set method that commits all the modified rows.
 The RowStatus textual convention specifies that, when used in a
 conceptual row, a description must define what can be modified.
 While the description of the conceptual row and its columnar object
 types is the correct place to derive this information on instance
 modifiability, it is often wrongly assumed in some implementations
 that:
 1) objects either must all be presently set or none need be set to
    make a conceptual RowStatus object transition to active(1)
 2) objects in a conceptual row cannot be modified once a RowStatus
    object is active(1).  Restricting instance modifiability like
    this, so that after a RowStatus object is set to active(1) is in
    fact a reasonable limitation, since such a set of RowStatus may
    have agent system side-effects which depend on committed columnar

MacFaden, et al. Informational [Page 12] RFC 3512 Configuring Networks and Devices with SNMP April 2003

    object instance values.  However, where this restriction exists on
    an object, it should be made clear in a DESCRIPTION clause such as
    the following:
    protocolDirDescr OBJECT-TYPE
      SYNTAX      DisplayString (SIZE (1..64))
      MAX-ACCESS  read-create
      STATUS      current
      DESCRIPTION
          "A textual description of the protocol encapsulation.
          A probe may choose to describe only a subset of the
          entire encapsulation (e.g., only the highest layer).
          This object is intended for human consumption only.
          This object may not be modified if the associated
          protocolDirStatus object is equal to active(1)."
      ::= { protocolDirEntry 4 }
 Any such restrictions on columnar object instance modification while
 a row's RowStatus object instance is set to active(1) should appear
 in the DESCRIPTION clause of the RowStatus columnar OBJECT-TYPE as
 well.

3.3.2. Fate sharing with multiple tables

 An important principle associated with transaction control is fate
 sharing of rows in different tables.  Consider the case where a
 relationship has been specified between two conceptual tables of a
 MIB module (or tables in two different MIB modules).  In this
 context, fate sharing means that when a row of a table is deleted,
 the corresponding row in the other table is also deleted.  Fate
 sharing in a transaction control context can also be used with the
 activation of very large configuration changes.  If we have two
 tables that hold a set of configuration information, a row in one
 table might have to be put in the 'ready' state before the second can
 be put in the 'ready' state.  When that second table can be placed in
 the 'ready' state, then the entire transaction can be considered to
 have been 'committed'.
 Fate sharing of SNMP table data should be explicitly defined where
 possible using the SMI index qualifier AUGMENTS.  If the relationship
 between tables cannot be defined using SMIv2 macros, then the
 DESCRIPTION clause of the object types which particularly effect the
 cross-table relationship should define what should happen when rows
 in related tables are added or deleted.

MacFaden, et al. Informational [Page 13] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 Consider the relationship between the dot1dBasePortTable and the
 ifTable.  These tables have a sparse relationship.  If a given
 ifEntry supports 802.1D bridging then there is a dot1dBasePortEntry
 that has a pointer to it via dot1dBasePortIfIndex.
 Now, what should happen if an ifEntry that can bridge is deleted?
 Should the object dot1dBasePortIfIndex simply be set to 0 or should
 the dot1dBasePortEntry be deleted as well?  A number of acceptable
 design and practice techniques can provide the answer to these
 questions, so it is important for the MIB module designer to provide
 the guidance to guarantee consistency and interoperability.
 To this end, when two tables are related in such a way, ambiguities
 such as this should be avoided by having the DESCRIPTION clauses of
 the pertinent row object types define the fate sharing of entries in
 the respective tables.

3.3.3. Transaction Control MIB Objects

 When a MIB module is defined that includes configuration object
 types, consider providing transaction control objects.  These objects
 can be used to cause a large transaction to be committed.  For
 example, we might have several tables that define the configuration
 of a portion of a system.  In order to avoid churn in the operational
 state of the system we might create a single scalar object that, when
 set to a particular value, will cause the activation of the rows in
 all the necessary tables.  Here are some examples of further usage
 for such object types:
 o  Control objects that are the 'write' or 'commit' objects.
    Such objects can cause all pending transactions (change MIB object
    values as a result of SET operations) to be committed to a
    permanent repository or operational memory, as defined by the
    semantics of the MIB objects.
 o  Control objects at different levels of configuration granularity.
    One of the decisions for a MIB module designer is what are the
    levels of granularity that make sense in practice.  For example,
    in the routing area, would changes be allowed on a per protocol
    basis such as BGP? If allowed at the BGP level, are sub-levels
    permitted such as per autonomous system? The design of these
    control objects will be impacted by the underlying software
    design.  RowStatus (see Section 3.3.1) also has important
    relevance as a general transaction control object.

MacFaden, et al. Informational [Page 14] RFC 3512 Configuring Networks and Devices with SNMP April 2003

3.3.4. Creating And Activating New Table Rows

 When designing read-create objects in a table, a MIB module designer
 should first consider the default state of each object in the table
 when a row is created.  Should an implementation of a standard MIB
 module vary in terms of the objects that need to be set in order to
 create an instance of a given row, an agent capabilities statement
 should be used to name the additional objects in that table using the
 CREATION-REQUIRES clause.
 It is useful when configuring new rows to use the notReady status to
 indicate row activation cannot proceed.
 When creating a row instance of a conceptual table, one should
 consider the state of instances of required columnar objects in the
 row.  The DESCRIPTION clause of such a required columnar object
 should specify it as such.
 During the period of time when a management application is attempting
 to create a row, there may be a period of time when not all of these
 required (and non-defaultable) columnar object instances have been
 set. Throughout this time, an agent should return a noSuchInstance
 error for a GET of any object instance of the row until such time
 that all of these required instance values are set.  The exception is
 the RowStatus object instance, for which a notReady(3) value should
 be returned during this period.
 One need only be concerned with the notReady value return for a
 RowStatus object when the row under creation does not yet have all of
 the required, non-defaultable instance values for the row.  One
 approach to simplifying in-row configuration transactions when
 designing MIB modules is to construct table rows that have no more
 instance data for columnar objects than will fit inside a single SET
 PDU.  In this case, the createAndWait() value for the RowStatus
 columnar object is not required.  It is possible to use createAndGo()
 in the same SET PDU, thus simplifying transactional management.

3.3.5. Summary Objects and State Tracking

 Before beginning a new set of configuration transactions, a
 management application might want to checkpoint the state of the
 managed devices whose configuration it is about to change.  There are
 a number of techniques that a MIB module designer can provide to
 assist in the (re-)synchronization of the managed systems.  These
 objects can also be used to verify that the management application's
 notion of the managed system state is the same as that of the managed
 device.

MacFaden, et al. Informational [Page 15] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 These techniques include:
 1. Provide an object that reports the number of rows in a table
 2. Provide an object that flags when data in the table was last
    modified.
 3. Send a notification message (InformRequests are preferable) to
    deliver configuration change.
 By providing an object containing the number of rows in a table,
 management applications can decide how best to retrieve a given
 table's data and may choose different retrieval strategies depending
 on table size.  Note that the availability of and application
 monitoring of such an object is not sufficient for determining the
 presence of table data change over a checkpointed duration since an
 equal number of row creates and deletes over that duration would
 reflect no change in the object instance value.  Additionally, table
 data change which does not change the number of rows in the table
 would not be reflected through simple monitoring of such an object
 instance.
 Instead, the change in the value of any table object instance data
 can be tracked through an object that monitors table change state as
 a function of time.  An example is found in RFC 2790, Host Resources
 MIB:
 hrSWInstalledLastUpdateTime OBJECT-TYPE
     SYNTAX     TimeTicks
     MAX-ACCESS read-only
     STATUS     current
     DESCRIPTION
         "The value of sysUpTime when the hrSWInstalledTable
         was last completely updated.  Because caching of this
         data will be a popular implementation strategy,
         retrieval of this object allows a management station
         to obtain a guarantee that no data in this table is
         older than the indicated time."
     ::= { hrSWInstalled 2 }
 A similar convention found in many standards track MIB modules is the
 "LastChange" type object.
 For example, the ENTITY-MIB, RFC 2737 [34], provides the following
 object:
 entLastChangeTime OBJECT-TYPE
   SYNTAX      TimeStamp

MacFaden, et al. Informational [Page 16] RFC 3512 Configuring Networks and Devices with SNMP April 2003

   MAX-ACCESS  read-only
   STATUS      current
   DESCRIPTION
           "The value of sysUpTime at the time a conceptual row is
           created, modified, or deleted in any of these tables:
                   - entPhysicalTable
                   - entLogicalTable
                   - entLPMappingTable
                   - entAliasMappingTable
                   - entPhysicalContainsTable"
   ::= { entityGeneral 1 }
 This convention is not formalized.  There tend to be small
 differences in what a table's LastChanged object reflects.  IF-MIB
 (RFC 2863 [20]) defines the following:
 ifTableLastChange  OBJECT-TYPE
     SYNTAX      TimeTicks
     MAX-ACCESS  read-only
     STATUS      current
     DESCRIPTION
             "The value of sysUpTime at the time of the last
             creation or deletion of an entry in the ifTable.  If
             the number of entries has been unchanged since the
             last re-initialization of the local network management
             subsystem, then this object contains a zero value."
     ::= { ifMIBObjects 5 }
 So, if an agent modifies a row with an SNMP SET on ifAdminStatus, the
 value of ifTableLastChange will not be updated.  It is important to
 be specific about what can cause an object to update so that
 management applications will be able to detect and more properly act
 on these changes.
 The final way to keep distributed configuration data consistent is to
 use an event-driven model, where configuration changes are
 communicated as they occur.  When the frequency of change to
 configuration is relatively low or polling a cache object is not
 desired, consider defining a notification that can be used to report
 all configuration change details.
 When doing so, the option is available to an SNMPv3 (or SNMPv2c)
 agent to deliver the notification using either a trap or an inform.
 The decision as to which PDU to deliver to the recipient is generally
 a matter of local configuration.  Vendors should recommend the use of
 informs over traps for NOTIFICATION-TYPE data since the agent can use
 the presence or absence of a response to help know whether it needs

MacFaden, et al. Informational [Page 17] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 to retransmit or not.  Overall, it is preferable to use an inform
 instead of a trap so that changes have a higher likelihood of
 confirmed end-to-end delivery.
 As a matter of MIB module design, when practical, the NOTIFICATION-
 TYPE should include in the PDU all of the modified columnar objects
 in a row of a table.  This makes it easier for the management
 application receiving the notification to keep track of what has
 changed in the row of a table and perform addition analysis on the
 state of the managed elements.
 However, the use of notifications to communicate the state of a
 rapidly changing object may not be ideal either.  This leads us back
 to the MIB module design question of what is the right level of
 granularity to expose.
 Finally, having to poll many "LastChange" objects does not scale
 well.  Consider providing a global LastChange type object to
 represent overall configuration in a given agent implementation.

3.3.6. Optimizing Configuration Data Transfer

 Configuration management software should keep track of the current
 configuration of all devices under its control.  It should ensure
 that the result is a consistent view of the configuration of the
 network, which can help reduce inadvertent configuration errors.
 In devices that have very large amounts of configuration data, it can
 be costly to both the agent and the manager to have the manager
 periodically poll the entire contents of these configuration tables
 for synchronization purposes.  A benefit of good synchronization
 between the manager and the agent is that the manager can determine
 the smallest and most effective set of data to send to managed
 devices when configuration changes are required.  Depending on the
 table organization in the managed device and the agent
 implementation, this practice can reduce the burden on the managed
 device for activation of these configuration changes.
 In the previous section, we discussed the "LastChange" style of
 object.  When viewed against the requirements just described, the
 LastChange object is insufficient for large amounts of data.
 There are three design options that can be used to assist with the
 synchronization of the configuration data found in the managed device
 with the manager:

MacFaden, et al. Informational [Page 18] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 1) Design multiple indices to partition the data in a table logically
    or break a table into a set of tables to partition the data based
    on what an application will use the table for
 2) Use a time-based indexing technique
 3) Define a control MIB module that manages a separate data delivery
    protocol

3.3.6.1. Index Design

 Index design has a major impact on the amount of data that must be
 transferred between SNMP entities and can help to mitigate scaling
 issues with large tables.
 Many tables in standard MIB modules follow one of two indexing
 models:
  1. Indexing based upon increasing Integer32 or Unsigned32 values of

the kind one might find in an array.

  1. Associative indexing, which refers to the technique of using

potentially sparse indices based upon a "key" of the sort one

    would use for a hash table.
 When tables grow to a very large number of rows, using an associative
 indexing scheme offers the useful ability to efficiently retrieve
 only the rows of interest.
 For example, if an SNMP entity exposes a copy of the default-free
 Internet routing table as defined in the ipCidrRouteTable, it will
 presently contain around 100,000 rows.
 Associative indexing is used in the ipCidrRouteTable and allows one
 to retrieve, for example, all routes for a given IPv4 destination
 192.0.2/24.
 Yet, if the goal is to extract a copy of the table, the associative
 indexing reduces the throughput and potentially the performance of
 retrieval.  This is because each of the index objects are appended to
 the object identifiers for every object instance returned.
 ipCidrRouteEntry OBJECT-TYPE
    SYNTAX   IpCidrRouteEntry
    MAX-ACCESS not-accessible
    STATUS   current
    DESCRIPTION
     "A particular route to a particular destination,

MacFaden, et al. Informational [Page 19] RFC 3512 Configuring Networks and Devices with SNMP April 2003

     under a particular policy."
    INDEX {
      ipCidrRouteDest,
      ipCidrRouteMask,
      ipCidrRouteTos,
      ipCidrRouteNextHop
      }
 A simple array-like index works efficiently since it minimizes the
 index size and complexity while increasing the number of rows that
 can be sent in a PDU.  If the indexing is not sparse, concurrency can
 be gained by sending multiple asynchronous non-overlapping collection
 requests as is explained in RFC 2819 [32], Page 41 (in the section
 pertaining to Host Group indexing).
    Should requirements dictate new methods of access, multiple
    indices can be defined such that both associative and simple
    indexing can coexist to access a single logical table.
 Two examples follow.
 First, consider the ifStackTable found in RFC 2863 [20] and the
 ifInvStackTable RFC 2864 [33].  They are logical equivalents with the
 order of the auxiliary (index) objects simply reversed.
 ifStackEntry  OBJECT-TYPE
      SYNTAX        IfStackEntry
      MAX-ACCESS    not-accessible
      STATUS        current
      DESCRIPTION
              "Information on a particular relationship between
              two sub-layers, specifying that one sub-layer runs
              on 'top' of the other sub-layer.  Each sub-layer
              corresponds to a conceptual row in the ifTable."
              INDEX { ifStackHigherLayer, ifStackLowerLayer }
      ::= { ifStackTable 1 }
 ifInvStackEntry  OBJECT-TYPE
    SYNTAX        IfInvStackEntry
    MAX-ACCESS    not-accessible
    STATUS        current
    DESCRIPTION
        "Information on a particular relationship between two
        sub-layers, specifying that one sub-layer runs underneath
        the other sub-layer.  Each sub-layer corresponds to a
        conceptual row in the ifTable."
        INDEX { ifStackLowerLayer, ifStackHigherLayer }
    ::= { ifInvStackTable 1 }

MacFaden, et al. Informational [Page 20] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 Second, table designs that can factor data into multiple tables with
 well-defined relationships can help reduce overall data transfer
 requirements.  The RMON-MIB, RFC 2819 [32], demonstrates a very
 useful technique of organizing tables into control and data
 components.  Control tables contain those objects that are configured
 and change infrequently, and the data tables contain information to
 be collected that can be large and may change quite frequently.
 As an example, the RMON hostControlTable provides a way to specify
 how to collect MAC addresses learned as a source or destination from
 a given port that provides transparent bridging of Ethernet packets.
 Configuration is accomplished using the hostControlTable.  It is
 indexed by a simple integer.  While this may seem to be array-like,
 it is common practice for command generators to encode the ifIndex
 into this simple integer to provide associative lookup capability.
 The RMON hostTable and hostTimeTable represent dependent tables that
 contain the results indexed by the hostControlTable entry.
 The hostTable is further indexed by the MAC address which provides
 the ability to reasonably search for a collection, such as the
 Organizationally Unique Identifier (OUI), the first three octets of
 the MAC address.
 The hostTimeTable is designed explicitly for fast transfer of bulk
 RMON data.  It demonstrates how to handle collecting large number of
 rows in the face of deletions and insertions by providing
 hostControlLastDeleteTime.
 hostControlLastDeleteTime OBJECT-TYPE
 SYNTAX     TimeTicks
 MAX-ACCESS read-only
 STATUS     current
 DESCRIPTION
     "The value of sysUpTime when the last entry
     was deleted from the portion of the hostTable
     associated with this hostControlEntry.  If no
     deletions have occurred, this value shall be zero."
 ::= { hostControlEntry 4 }

3.3.6.2. Time Based Indexing

 The TimeFilter as defined in RFC 2021 [44] and used in RMON2-MIB and
 Q-BRIDGE-MIB (RFC 2674 [26]) provides a way to obtain only those rows
 that have changed on or after some specified period of time has
 passed.

MacFaden, et al. Informational [Page 21] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 One drawback to TimeFilter index tables is that a given row can
 appear at many points in time, which artificially inflates the size
 of the table when performing standard getNext or getBulk data
 retrieval.

3.3.6.3. Alternate Data Delivery Mechanisms

 If the amount of data to transfer is larger than current SNMP design
 restrictions permit, as in the case of OCTET STRINGS (64k minus
 overhead of IP/UDP header plus SNMP header plus varbind list plus
 varbind encoding), consider delivery of the data via an alternate
 method, such as FTP and use a MIB module to control that data
 delivery process.  In many cases, this problem can be avoided via
 effective MIB design.  In other words, object types requiring this
 kind of transfer size should be used judiciously, if at all.
 There are many enterprise MIB modules that provide control of the
 TFTP or FTP protocol.  Often the SNMP part defines what to send where
 and setting an object initiates the operation (for an example, refer
 to the CISCO-FTP-CLIENT-MIB, discussed in [38]).
 Various approaches exist for allowing a local agent process running
 within the managed node to take a template for an object instance
 (for example for a set of interfaces), and adapt and apply it to all
 of the actual instances within the node.  This is an architecture for
 one form of policy-based configuration (see [36], for example).  Such
 an architecture, which must be designed into the agent and some
 portions of the MIB module, affords the efficiency of specifying many
 copies of instance data only once, along with the execution
 efficiency of distributing the application of the instance data to
 the agent.
 Other work is currently underway to improve efficiency for bulk SNMP
 transfer operations [37].  The objective of these efforts is simply
 the conveyance of more information with less overhead.

3.4. More Index Design Issues

 Section 3.3.5 described considerations for table row index design as
 it pertains to the synchronization of changes within sizable table
 rows. This section simply considers how to specify this syntactically
 and how to manage indices semantically.
 In many respects, the design issues associated with indices in a MIB
 module are similar to those in a database.  Care must be taken during
 the design phase to determine how often and what kind of information
 must be set or retrieved.  The next few points provide some guidance.

MacFaden, et al. Informational [Page 22] RFC 3512 Configuring Networks and Devices with SNMP April 2003

3.4.1. Simple Integer Indexing

 When indexing tables using simple Integer32 or Unsigned32, start with
 one (1) and specify the maximum range of the value.  Since object
 identifiers are unsigned long values, a question that arises is why
 not index from zero (0) instead of one(1)?
 RFC 2578 [2], Section 7.7, page 28 states the following: Instances
 identified by use of integer-valued objects should be numbered
 starting from one (i.e., not from zero).  The use of zero as a value
 for an integer-valued index object type should be avoided, except in
 special cases.  Consider the provisions afforded by the following
 textual convention from the Interfaces Group MIB module [33]:
 InterfaceIndexOrZero ::= TEXTUAL-CONVENTION
     DISPLAY-HINT "d"
     STATUS       current
     DESCRIPTION
         "This textual convention is an extension of the
         InterfaceIndex convention.  The latter defines a greater
         than zero value used to identify an interface or interface
         sub-layer in the managed system.  This extension permits the
         additional value of zero.  the value zero is object-specific
         and must therefore be defined as part of the description of
         any object which uses this syntax.  Examples of the usage of
         zero might include situations where interface was unknown,
         or when none or all interfaces need to be referenced."
     SYNTAX       Integer32 (0..2147483647)

3.4.2. Indexing with Network Addresses

 There are many objects that use IPv4 addresses (SYNTAX IpAddress) as
 indexes.  One such table is the ipAddrTable from RFC 2011 [14] IP-
 MIB.  This limits the usefulness of the MIB module to IPv4.  To avoid
 such limitations, use the addressing textual conventions INET-
 ADDRESS-MIB [13] (or updates to that MIB module), which provides a
 generic way to represent addresses for Internet Protocols.  In using
 the InetAddress textual convention in this MIB, however, pay heed to
 the following advisory found in its description clause:
    When this textual convention is used as the syntax of an index
    object, there may be issues with the limit of 128 sub-identifiers
    specified in SMIv2, STD 58.  In this case, the OBJECT-TYPE
    declaration MUST include a 'SIZE' clause to limit the number of
    potential instance sub-identifiers.

MacFaden, et al. Informational [Page 23] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 One should consider the SMI limitation on the 128 sub-identifier
 specification when using certain kinds of network address index
 types.  The most likely practical liability encountered in practice
 has been with DNS names, which can in fact be in excess of 128 bytes.
 The problem can be, of course, compounded when multiple indices of
 this type are specified for a table.

3.5. Conflicting Controls

 MIB module designers should avoid specifying read-write objects that
 overlap in function partly or completely.
 Consider the following situation where two read-write objects
 partially overlap when a dot1dBasePortEntry has a corresponding
 ifEntry.
 The BRIDGE-MIB defines the following managed object:
 dot1dStpPortEnable OBJECT-TYPE
     SYNTAX  INTEGER {
                 enabled(1),
                 disabled(2)            }
     ACCESS  read-write
     STATUS  mandatory
     DESCRIPTION
         "The enabled/disabled status of the port."
     REFERENCE
         "IEEE 802.1D-1990: Section 4.5.5.2"
     ::= { dot1dStpPortEntry 4 }
 The IF-MIB defines a similar managed object:
 ifAdminStatus OBJECT-TYPE
     SYNTAX  INTEGER {
                 up(1),       -- ready to pass packets
                 down(2),
                 testing(3)   -- in some test mode
             }
     MAX-ACCESS  read-write
     STATUS      current
     DESCRIPTION
         "The desired state of the interface.  The testing(3)
         state indicates that no operational packets can be
         passed.  When a managed system initializes, all
         interfaces start with ifAdminStatus in the down(2) state.
         As a result of either explicit management action or per
         configuration information retained by the managed system,
         ifAdminStatus is then changed to either the up(1) or

MacFaden, et al. Informational [Page 24] RFC 3512 Configuring Networks and Devices with SNMP April 2003

         testing(3) states (or remains in the down(2) state)."
     ::= { ifEntry 7 }
 If ifAdminStatus is set to testing(3), the value to be returned for
 dot1dStpPortEnable is not defined.  Without clarification on how
 these two objects interact, management implementations will have to
 monitor both objects if bridging is detected and correlate behavior.
 The dot1dStpPortEnable object type could have been written with more
 information about the behavior of this object when values of
 ifAdminStatus which impact it change.  For example, text could be
 added that described proper return values for the dot1dStpPortEnable
 object instance for each of the possible values of ifAdminStatus.
 In those cases where overlap between objects is unavoidable, then as
 we have just described, care should be taken in the description of
 each of the objects to describe their possible interactions.  In the
 case of an object type defined after an incumbent object type, it is
 necessary to include in the DESCRIPTION of this later object type the
 details of these interactions.

3.6. Textual Convention Usage

 Textual conventions should be used whenever possible to create a
 consistent semantic for an oft-recurring datatype.
 MIB modules often define a binary state object such as enable/disable
 or on/off.  Current practice is to use existing Textual Conventions
 and define the read-write object in terms of a TruthValue from
 SNMPv2-TC [3].  For example, the Q-BRIDGE-MIB [26] defines:
 dot1dTrafficClassesEnabled OBJECT-TYPE
     SYNTAX      TruthValue
     MAX-ACCESS  read-write
     STATUS      current
     DESCRIPTION
        "The value true(1) indicates that Traffic Classes are
        enabled on this bridge.  When false(2), the bridge
        operates with a single priority level for all traffic."
     DEFVAL      { true }
     ::= { dot1dExtBase 2 }
 Textual conventions that have a reasonable chance of being reused in
 other MIB modules ideally should also be defined in a separate MIB
 module to facilitate sharing of such object types.  For example, all
 ATM MIB modules draw on the ATM-TC-MIB [39] to reference and utilize
 common definitions for addressing, service class values, and the
 like.

MacFaden, et al. Informational [Page 25] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 To simplify management, it is recommended that existing SNMPv2-TC
 based definitions be used when possible.  For example, consider the
 following object definition:
 acmePatioLights OBJECT-TYPE
     SYNTAX  INTEGER {
                 on(1),
                 off(2),
     }
     MAX-ACCESS  read-write
     STATUS      current
     DESCRIPTION
         "Current status of outdoor lighting."
     ::= { acmeOutDoorElectricalEntry 3 }
 This could be defined as follows using existing SNMPv2-TC TruthValue.
 acmePatioLightsOn OBJECT-TYPE
     SYNTAX  TruthValue
     MAX-ACCESS  read-write
     STATUS      current
     DESCRI2096PTION
         "Current status of outdoor lighting.  When set to true (1),
         this means that the lights are enabled and turned on.
         When set to false (2), the lights are turned off."
      ::= { acmeOutDoorElectricalEntry 3 }

3.7. Persistent Configuration

 Many network devices have two levels of persistence with regard to
 configuration data.  In the first case, the configuration data sent
 to the device is persistent only until changed with a subsequent
 configuration operation, or the system is reinitialized.  The second
 level is where the data is made persistent as an inherent part of the
 acceptance of the configuration information.  Some configuration
 shares both these properties, that is, that on acceptance of new
 configuration data it is saved permanently and in memory.  Neither of
 these necessarily means that the data is used by the operational
 code.  Sometimes separate objects are required to activate this new
 configuration data for use by the operational code.
 However, many SNMP agents presently implement simple persistence
 models, which do not reflect all the relationships of the
 configuration data to the actual persistence model as described
 above.  Some SNMP set requests against MIB objects with MAX-ACCESS
 read-write are written automatically to a persistent store. In other
 cases, they are not.  In some of the latter cases, enterprise MIB

MacFaden, et al. Informational [Page 26] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 objects are required in order to get standard configuration stored,
 thus making it difficult for a generic application to have a
 consistent effect.
 There are standard conventions for saving configuration data.  The
 first method uses the Textual Convention known as StorageType [3]
 which explicitly defines a given row's persistence requirement.
 Examples include the RFC 3231 [25] definition for the schedTable row
 object schedStorageType of syntax StorageType, as well as similar row
 objects for virtually all of the tables of the SNMP View-based Access
 Control Model MIB [10].
 A second method for persistence simply uses the DESCRIPTION clause to
 define how instance data should persist.  RFC 2674 [26] explicitly
 defines Dot1qVlanStaticEntry data persistence as follows:
 dot1qVlanStaticTable OBJECT-TYPE
     SYNTAX      SEQUENCE OF Dot1qVlanStaticEntry
     MAX-ACCESS  not-accessible
     STATUS      current
     DESCRIPTION
      "A table containing static configuration information for
      each VLAN configured into the device by (local or
      network) management.  All entries are permanent and will
      be restored after the device is reset."
     ::= { dot1qVlan 3 }
 The current practice is a dual persistence model where one can make
 changes to run-time configuration as well as to a non-volatile
 configuration read at device initialization.  The DISMAN-SCHEDULE-MIB
 module [25] provides an example of this practice.  A row entry of its
 SchedTable specifies the parameters by which an agent MIB variable
 instance can be set to a specific value at some point in time and
 governed by other constraints and directives.  One of those is:
 schedStorageType OBJECT-TYPE
      SYNTAX      StorageType
      MAX-ACCESS  read-create
      STATUS      current
      DESCRIPTION
          "This object defines whether this scheduled action is kept
           in volatile storage and lost upon reboot or if this row is
           backed up by non-volatile or permanent storage.
           Conceptual rows having the value `permanent' must allow
           write access to the columnar objects schedDescr,
           schedInterval, schedContextName, schedVariable, schedValue,
           and schedAdminStatus.  If an implementation supports the

MacFaden, et al. Informational [Page 27] RFC 3512 Configuring Networks and Devices with SNMP April 2003

           schedCalendarGroup, write access must be also allowed to
           the columnar objects schedWeekDay, schedMonth, schedDay,
           schedHour, schedMinute."
      DEFVAL { volatile }
      ::= { schedEntry 19 }
 It is important, however, to reiterate that the persistence is
 ultimately controlled by the capabilities and features (with respect
 to the storage model of management data) of the underlying system on
 which the MIB Module agent is being implemented.  This falls into
 very much the same kind of issue set as, for example, the situation
 where the size of data storage in the system for a Counter object
 type is not the same as that in the corresponding MIB Object Type.
 To generalize, the final word on the "when" and "how" of storage of
 persistent data is dictated by the system and the implementor of the
 agent on the system.

3.8. Configuration Sets and Activation

 An essential notion for configuration of network elements with SNMP
 is awareness of the difference between the set of one or more
 configuration objects from the activation of those configuration
 changes in the actual subsystem.  That is, it often only makes sense
 to activate a group of objects as a single 'transaction'.

3.8.1. Operational Activation Considerations

 A MIB module design must consider the implications of the preceding
 in the context of changes that will occur throughout a subsystem when
 changes are activated.  This is particularly true for configuration
 changes that are complex.  This complexity can be in terms of
 configuration data or the operational ramifications of the activation
 of the changes in the managed subsystem.  A practical technique to
 accommodate this kind of activation is the partitioning of contained
 configuration sets, as it pertains to their being activated as
 changes.  Any complex configuration should have a master on/off
 switch (MIB object type) as well as strategically placed on/off
 switches that partition the activation of configuration data in the
 managed subsystem.  These controls play a pivotal role during the
 configuration process as well as during subsequent diagnostics.
 Generally, a series of set operations should not cause an agent to
 activate each object, causing operational instability to be
 introduced with every changed object instance.  To avoid this
 liability, ideally a series of Set PDUs can install the configuration
 and a final set series of PDUs can activate the changes.

MacFaden, et al. Informational [Page 28] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 During diagnostic situations, certain on/off switches can be set to
 localize the perceived error instead of having to remove the
 configuration.
 An example of such an object from the OSPF Version 2 MIB [29] is the
 global ospfAdminStat:
 ospfAdminStat OBJECT-TYPE
     SYNTAX   Status
     MAX-ACCESS   read-write
     STATUS   current
     DESCRIPTION
        "The administrative status of  OSPF  in the
        router.  The value 'enabled' denotes that the
        OSPF Process is active on at least one interface;
        'disabled' disables it on all interfaces."
    ::= { ospfGeneralGroup 2 }
 Elsewhere in the OSPF MIB, the semantics of setting ospfAdminStat to
 enabled(2) are clearly spelled out.
 The Scheduling MIB [25] exposes such an object on each entry in the
 scheduled actions table, along with the corresponding stats object
 type (with read-only ACCESS) on the scheduled actions row instance.
 This reflects a recurring basic design pattern which brings about
 semantic clarity in the object type usage.  A table can expose one
 columnar object type which is strictly for administrative control.
 When read, an instance of this object type will reflect its last set
 or defaulted value.  A companion operational columnar object type,
 with MAX-ACCESS of read-only, provides the current state of
 activation or deactivation resulting from the last set of the
 administrative columnar instance.  It is fully expected that these
 administrative and operational columnar instances may reflect
 different values over some period of time of activation latency,
 which is why they are separate.  Further sections display some of the
 problems which can result from attempting to combine the operational
 and administrative row columns into a single object type.
 Note that all of this is independent of the RowStatus columnar
 object, and the notion of 'activation' as it pertains to RowStatus.
 A defined RowStatus object type should be strictly concerned with the
 management of the table row itself (with 'activation' indicating "the
 conceptual row is available for use by the managed device" [3], and
 not to be confused with any operational activation semantics).

MacFaden, et al. Informational [Page 29] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 In the following example, schedAdminStatus controls activation of the
 scheduled action, and schedOperStatus reports on its operational
 status:
 schedAdminStatus OBJECT-TYPE
     SYNTAX      INTEGER {
                     enabled(1),
                     disabled(2)
                 }
     MAX-ACCESS  read-create
     STATUS      current
     DESCRIPTION
         "The desired state of the schedule."
     DEFVAL { disabled }
     ::= { schedEntry 14 }
 schedOperStatus OBJECT-TYPE
     SYNTAX      INTEGER {
                     enabled(1),
                     disabled(2),
                     finished(3)
                 }
     MAX-ACCESS  read-only
     STATUS      current
     DESCRIPTION
         "The current operational state of this schedule.  The state
          enabled(1) indicates this entry is active and that the
          scheduler will invoke actions at appropriate times.  The
          disabled(2) state indicates that this entry is currently
          inactive and ignored by the scheduler.  The finished(3)
          state indicates that the schedule has ended.  Schedules
          in the finished(3) state are ignored by the scheduler.
          A one-shot schedule enters the finished(3) state when it
          deactivates itself."
     ::= { schedEntry 15 }

3.8.2. RowStatus and Deactivation

 RowStatus objects should not be used to control
 activation/deactivation of a configuration.  While RowStatus looks
 ideally suited for such a purpose since a management application can
 set a row to active(1), then set it to notInService(2) to disable it
 then make it active(1) again, there is no guarantee that the agent
 won't discard the row while it is in the notInService(2) state.  RFC
 2579 [3], page 15 states:

MacFaden, et al. Informational [Page 30] RFC 3512 Configuring Networks and Devices with SNMP April 2003

    The agent must detect conceptual rows that have been in either
    state for an abnormally long period of time and remove them.  It
    is the responsibility of the DESCRIPTION clause of the status
    column to indicate what an abnormally long period of time would
    be.
 The DISMAN-SCHEDULE-MIB's managed object schedAdminStatus
 demonstrates how to separate row control from row activation.
 Setting the schedAdminStatus to disabled(2) does not cause the row to
 be aged out/removed from the table.
 Finally, a reasonable agent implementation must consider how many
 rows will be allowed to be created in the notReady/notInService state
 such that resources are not exhausted by an errant application.

3.9. SET Operation Latency

 Many standards track and enterprise MIB modules that contain read-
 write objects assume that an agent can complete a set operation as
 quickly as an agent can send back the status of the set operation to
 the application.
 Consider the subtle operational shortcomings in the following object.
 It both reports the current state and allows a SET operation to
 change to a possibly new state.

wheelRotationState OBJECT-TYPE

    SYNTAX        INTEGER { unknown(0),
                            idle(1),
                            spinClockwise(2),
                            spinCounterClockwise(3)
                           }
    MAX-ACCESS    read-write
    STATUS        current
    DESCRIPTION
    "The current state of a wheel."
::= { XXX 2 }

MacFaden, et al. Informational [Page 31] RFC 3512 Configuring Networks and Devices with SNMP April 2003

With the object defined, the following example represents one possible transaction.

Time Command Generator ——–> ←– Command Responder —– —————– —————–

A GetPDU(wheelRotationState.1.1)

B wheelRotationState.1.1 == spinClockwise(2)

C SetPDU(wheelRotationState.1.1 =

D wheelRotationState.1.1

                                         == spinCounterClockwise(3)

| E GetPDU(wheelRotationState.1.1)

F ResponsePDU(error-index 0,

V wheelRotationState.1.1 == spinClockwise(2)

 ....some time, perhaps seconds, later....

| G GetPDU(wheelRotationState.1.1)

H ResponsePDU(error-index 0,

V == spinCounterClockwise(3)

 The response to the GET request at time E will often confuse
 management applications that assume the state of the object should be
 spinCounterClockwise(3).  In reality, the wheel is slowing down in
 order to come to the idle state then begin spinning counter
 clockwise.
 This possibility of confusing and paradoxical interactions of
 administrative and operational state is inevitable when a single
 object type is used to control and report on both types of state.
 One common practice which we have already seen is to separate out the

MacFaden, et al. Informational [Page 32] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 desired (settable) state from current state.  The objects
 ifAdminStatus and ifOperStatus from RFC 2863 [20] provide such an
 example of the separation of objects into desired and current state.

3.9.1. Subsystem Latency, Persistence Latency, and Activation Latency

 A second way latency can be introduced in SET operations is caused by
 delay in agent implementations that must interact with loosely
 coupled subsystems.  The time it takes the instrumented system to
 accept the new configuration information from the SNMP agent, process
 it and 'install' the updated configuration in the system or otherwise
 process the directives can often be longer than the SNMP response
 timeout.
 In these cases, it is desirable to provide a "current state" object
 type which can be polled by the management application to determine
 the state of control of the loosely coupled subsystem which was
 affected by its configuration update.
 More generally, some MIB objects may have high latencies associated
 with changes to their values.  This could be either a function of
 saving the changed value to a persistent storage type, and/or
 activating a subsystem that inherently has high latency as discussed
 above.  When defining such MIB objects, it might be wise to have the
 agent process set operations in the managed subsystem as soon as the
 Set PDU has been processed, and then update appropriate status
 objects when the save-to- persistent storage and (if applicable)
 activation has succeeded or is otherwise complete.  Another approach
 would be to cause a notification to be sent that indicates that the
 operation has been completed.
 When you describe an activation object, the DESCRIPTION clauses for
 these objects should give a hint about the likely latency for the
 completion of the operation.  Keep in mind that from a management
 software perspective (as presented in the example of schedAdminStatus
 in Section 3.8.1), the combined latency of saving-to-persistence and
 activation are not distinguishable when they are part of a single
 operation.

3.10. Notifications and Error Reporting

 For the purpose of this section, a 'notification' is as described in
 the SMIv2, RFC 2578 [2], by the NOTIFICATION-TYPE macro.
 Notifications can be sent in either SNMPv2c [19] or SNMPv3 TRAP or
 InformRequest PDUs.  Given the sensitivity of configuration
 information, it is recommended that configuration operations always
 be performed using SNMPv3 due to its enhanced security capabilities.
 InformRequest PDUs should be used in preference to TRAP PDUs since

MacFaden, et al. Informational [Page 33] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 the recipient of the InformRequest PDUs responds with a Response PDU.
 This acknowledgment can be used to avoid unnecessary retransmission
 of NOTIFICATION-TYPE information when retransmissions are in fact
 required.  The use of InformRequest PDUs (as opposed to TRAPs) is not
 at the control of the MIB module designer or agent implementor.  The
 determination as to whether or not a TRAP or InformRequest PDU is
 sent from an SNMPv2c or SNMPv3 agent is generally a function of the
 agent's local configuration (but can be controlled with MIB objects
 in SNMPv3).  To the extent notification timeout and retry values are
 determined by local configuration parameters, care should be taken to
 avoid unnecessary retransmission of InformRequest PDUs.
 Configuration change and error information conveyed in InformRequest
 PDUs can be an important part of an effective SNMP-based management
 system.  They also have the potential to be overused.  This section
 offers some guidance for effective definition of NOTIFICATION-TYPE
 information about configuration changes that can be carried in
 InformRequest PDUs.  Notifications can also play a key role for all
 kinds of error reporting from hardware failures to configuration and
 general policy errors.  These types of notifications should be
 designed as described in Section 3.11 (Application Error Reporting).

3.10.1. Identifying Source of Configuration Changes

 A NOTIFICATION-TYPE designed to report configuration changes should
 report the identity of the management entity initiating the
 configuration change.  Specifically, if the entity is known to be a
 SNMP command generator, the transport address and SNMP parameters as
 found in table snmpTargetParamsTable from RFC 3413 SNMP-TARGET-MIB
 should be reported where  possible.  For reporting of configuration
 changes outside of the SNMP domain, the applicable change mechanism
 (for example, CLI vs. HTTP-based management client access) should be
 reported, along with whatever notion of "user ID" of the change
 initiator is applicable and available.

3.10.2. Limiting Unnecessary Transmission of Notifications

 The design of event-driven synchronization models, essential to
 configuration management, can use notifications as an important
 enabling technique.  Proper usage of notifications allows the
 manager's view of the managed element's configuration to be in close
 synchronization with the actual state of the configuration of the
 managed element.
 When designing new NOTIFICATION-TYPEs, consider how to limit the
 number of notifications PDUs that will be sent with the notification
 information defined in the NOTIFICATION-TYPE in response to a
 configuration change or error event.

MacFaden, et al. Informational [Page 34] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 InformRequest PDUs, when compared to TRAP PDUs, have an inherent
 advantage when the concern is the reduction of unnecessary messages
 from the system generating the NOTIFICATION-TYPE data, when in fact
 retransmission of this data is required.  That is, an InformRequest
 PDU is acknowledged by the receiving entity with a Response PDU.  The
 receipt of this response allows the entity which generated the
 InformRequest PDU to verify (and record an audit entry, where such
 facilities exist on the agent system) that the message was received.
 As a matter of notification protocol, this receipt guarantee is not
 available when using TRAP PDUs, and if it is required, must be
 accomplished by the agent using some mechanism out of band to SNMP,
 and usually requiring the penalty of polling.
 Regardless of the specific PDUs used to convey them, one way to limit
 the unnecessary generation of notifications is to include in the
 NOTIFICATION-TYPE definition situations where it need not be sent.  A
 good example is the frDLCIStatusChange defined in FRAME-RELAY-DTE-
 MIB, RFC 2115 [21].
 frDLCIStatusChange NOTIFICATION-TYPE
     OBJECTS  { frCircuitState }
     STATUS      current
     DESCRIPTION
        "This trap indicates that the indicated Virtual Circuit
        has changed state.  It has either been created or
        invalidated, or has toggled between the active and
        inactive states.  If, however, the reason for the state
        change is due to the DLCMI going down, per-DLCI traps
        should not be generated."
 ::= { frameRelayTraps 1 }
 There are a number of other techniques which can be used to reduce
 the unwanted generation of NOTIFICATION-TYPE information.  When
 defining notifications, the designer can specify a number of temporal
 limitations on the generation of specific instances of a
 NOTIFICATION-TYPE.  For example, a definition could specify that
 messages will not be sent more frequently than once every 60 seconds
 while the condition which led to the generation of the notification
 persists.  Alternately, a NOTIFICATION-TYPE DESCRIPTION clause could
 provide a fixed limit on the number of messages sent over the
 duration of the condition leading to sending the notification.
 If NOTIFICATION-TYPE transmission is "aggregated" in some way -
 bounded either temporally or by absolute system state change as
 described above - the optimal design technique is to have the data
 delivered with the notification reference the actual number of
 underlying managed element transitions which brought about the
 notification.  No matter which threshold is chosen to govern the

MacFaden, et al. Informational [Page 35] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 actual transmission of NOTIFICATION-TYPEs, the idea is to describe an
 aggregated event or related set of events in as few PDUs as possible.

3.10.3. Control of Notification Subsystem

 There are standards track MIB modules that define objects that either
 augment or overlap control of notifications.  For instance, FRAME-
 RELAY-DTE-MIB RFC 2115 defines frTrapMaxRate and DOCS-CABLE-DEVICE-
 MIB defines a set of objects in docsDevEvent that provide for rate
 limiting and filtering of notifications.
 In the past, agents did not have a standard means to configure a
 notification generator.  With the availability of the SNMP-
 NOTIFICATION-MIB module in RFC 3413 [9], it is strongly recommended
 that the filtering functions of this MIB module be used.  This MIB
 facilitates the mapping of given NOTIFICATION-TYPEs and their
 intended recipients.
 If the mechanisms of the SNMP-NOTIFICATION-MIB are not suitable for
 this application, a explanation of why they are not suitable should
 be included in the DESCRIPTION clause of any replacement control
 objects.

3.11. Application Error Reporting

 MIB module designers should not rely on the SNMP protocol error
 reporting mechanisms alone to report application layer error state
 for objects that accept SET operations.
 Most MIB modules that exist today provide very little detail as to
 why a configuration request has failed.  Often the only information
 provided is via SNMP protocol errors which generally does not provide
 enough information about why an agent rejected a set request.
 Typically, there is an incumbent and sizable burden on the
 configuration application to determine if the configuration request
 failure is the result of a resource issue, a security issue, or an
 application error.
 Ideally, when a "badValue" error occurs for a given set request, an
 application can query the agent for more details on the error.  A
 badValue does not necessarily mean the command generator sent bad
 data.  An agent could be at fault.  Additional detailed diagnostic
 information may aid in diagnosing conditions in the integrated
 system.

MacFaden, et al. Informational [Page 36] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 Consider the requirement of conveying error information about a MIB
 expression 'object' set within the DISMAN-EXPRESSION-MIB [40] that
 occurs when the expression is evaluated.  Clearly, none of the
 available protocol errors are relevant when reporting an error
 condition that occurs when an expression is evaluated.  Instead, the
 DISMAN-EXPRESSION-MIB provides objects to report such errors (the
 expErrorTable).  Instead, the expErrorTable maintains information
 about errors that occur at evaluation time:
  expErrorEntry OBJECT-TYPE
      SYNTAX      ExpErrorEntry
      MAX-ACCESS  not-accessible
      STATUS      current
      DESCRIPTION
      "Information about errors in processing an expression.
      Entries appear in this table only when there is a matching
      expExpressionEntry and then only when there has been an
      error for that expression as reflected by the error codes
      defined for expErrorCode."
 INDEX       { expExpressionOwner, expExpressionName }
 More specifically, a MIB module can provide configuration
 applications with information about errors on the managed device by
 creating columnar object types in log tables that contain error
 information particular to errors that occur on row activation.
 Notifications with detailed failure information objects can also be
 used to signal configuration failures.  If this approach is used, the
 configuration of destinations for NOTIFICATION-TYPE data generated
 from configuration failures should be considered independently of the
 those for other NOTIFICATION-TYPEs which are generated for other
 operational reasons.  In other words, in many management
 environments, the network operators interested in NOTIFICATION-TYPEs
 generated from configuration failures may not completely overlap with
 the community of network operators interested in NOTIFICATION-TYPEs
 generated from, for example, network interface failures.

3.12. Designing MIB Modules for Multiple Managers

 When designing a MIB module for configuration, there are several
 pertinent considerations to provide support for multiple managers.
 The first is to avoid any race conditions between two or more
 authorized management applications issuing SET protocol operations
 spanning over more than a single PDU.
 The standard textual convention document [3] defines TestAndIncr,
 often called a spinlock, which is used to avoid race conditions.

MacFaden, et al. Informational [Page 37] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 A MIB module designer may explicitly define a synchronization object
 of syntax TestAndIncr or may choose to rely on snmpSetSerialNo (a
 global spinlock object) as defined in SNMPv2-MIB.
 snmpSetSerialNo OBJECT-TYPE
 SYNTAX     TestAndIncr
 MAX-ACCESS read-write
 STATUS     current
 DESCRIPTION
         "An advisory lock used to allow several cooperating
         command generator applications to coordinate their
         use of the SNMP set operation.
         This object is used for coarse-grain coordination.
         To achieve fine-grain coordination, one or more similar
         objects might be defined within each MIB group, as
         appropriate."
 ::= { snmpSet 1 }
 Another prominent TestAndIncr example can be found in the SNMP-
 TARGET- MIB [9], snmpTargetSpinLock.
 Secondly, an agent should be able to report configuration as set by
 different entities as distinguishable from configuration defined
 external to the SNMP domain, such as application of a default or
 through an alternate management interface like a command line
 interface.  Section 3.10.1 describes considerations for this practice
 when designing NOTIFICATION-TYPEs.  The OwnerString textual
 convention from RMON-MIB RFC 2819 [32] has been used successfully for
 this purpose.  More recently, RFC 3411 [1] introduced the
 SnmpAdminString which has been designed as a UTF8 string.  This is
 more suitable for representing names in many languages.
 Experience has shown that usage of OwnerString to represent row
 ownership can be a useful diagnostic tool as well.  Specifically, the
 use of the string "monitor" to identify configuration set by an
 agent/local management has been prevalent and useful in applications.
 Thirdly, consider whether there is a need for multiple managers to
 configure the same set of tables.  If so, an "OwnerString" may be
 used as the first component of a table's index to allow VACM to be
 used to protect access to subsets of rows, at least at the level of
 securityName or groupName provided.  RFC 3231 [25], Section 6
 presents this technique in detail.  This technique does add
 complexity to the managed device and to the configuration management
 application since the manager will need to be aware of these
 additional columnar objects in configuration tables and act
 appropriately to set them.  Additionally, the agent must be

MacFaden, et al. Informational [Page 38] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 configured to provide the appropriate instance-level restrictions on
 the modifiability of the instances.

3.13. Other MIB Module Design Issues

3.13.1. Octet String Aggregations

 The OCTET STRING syntax can be used as an extremely flexible and
 useful datatype when defining managed objects that allow SET
 operation.  An octet string is capable of modeling many things and is
 limited in size to 65535 octets by SMIv2[2].
 Since OCTET STRINGS are very flexible, the need to make them useful
 to applications requires careful definition.  Otherwise, applications
 will at most simply be able to display and set them.
 Consider the following object from RFC 3418 SNMPv2-MIB [11].
 sysLocation OBJECT-TYPE
 SYNTAX      DisplayString (SIZE (0..255))
 MAX-ACCESS  read-write
 STATUS      current
 DESCRIPTION
         "The physical location of this node (e.g., `telephone
         closet, 3rd floor').  If the location is unknown, the value
         is the zero-length string."
 ::= { system 6 }
 Such informational object types have come to be colloquially known as
 "scratch pad objects".  While often useful, should an application be
 required to do more with this information than be able to read and
 set the value of this object, a more precise definition of the
 contents of the OCTET STRING is needed, since the actual format of an
 instance for such an object is unstructured.  Hence, alternatively,
 dividing the object type into several object type definitions can
 provide the required additional structural detail.
 When using OCTET STRINGS, avoid platform dependent data formats.
 Also avoid using OCTET STRINGS where a more precise SMI syntax such
 as SnmpAdminString or BITS would work.
 There are many MIB modules that attempt to optimize the amount of
 data sent/received in a SET/GET PDU by packing octet strings with
 aggregate data.  For example, the PortList syntax as defined in the
 Q-BRIDGE-MIB (RFC 2674 [26]) is defined as follows:

MacFaden, et al. Informational [Page 39] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 PortList ::= TEXTUAL-CONVENTION
  STATUS      current
  DESCRIPTION
      "Each octet within this value specifies a set of eight
      ports, with the first octet specifying ports 1 through
      8, the second octet specifying ports 9 through 16, etc.
      Within each octet, the most significant bit represents
      the lowest numbered port, and the least significant bit
      represents the highest numbered port.  Thus, each port
      of the bridge is represented by a single bit within the
      value of this object.  If that bit has a value of '1'
      then that port is included in the set of ports; the port
      is not included if its bit has a value of '0'."
  SYNTAX      OCTET STRING
 This compact representation saves on data transfer but has some
 limitations.  Such complex instance information is difficult to
 reference outside of the object or use as an index to a table.
 Additionally, with this approach, if a value within the aggregate
 requires change, the entire aggregated object instance must be
 written.
 Providing an SNMP table to represent aggregate data avoids the
 limitations of encoding data into OCTET STRINGs and is thus the
 better general practice.
 Finally, as previously mentioned in Section 3.3.6.3, one should
 consider the practical ramifications of instance transfer for object
 types of SYNTAX OCTET STRING where they have typical instance data
 requirements close to the upper boundary of SMIv2 OCTET STRING
 instance encoding.  Where such object types are truly necessary at
 all, SNMP/UDP may not be a very scalable means of transfer and
 alternatives should be explored.

3.13.2. Supporting multiple instances of a MIB Module

 When defining new MIB modules, one should consider if there could
 ever be multiple instances of this MIB module in a single SNMP
 entity.
 MIB modules exist that assume a one to many relationship, such as
 MIBs for routing protocols which can accommodate multiple "processes"
 of the underlying protocol and its administrative framework.
 However, the majority of MIB modules assume a one-to-one relationship
 between the objects found in the MIB module and how many instances
 will exist on a given SNMP agent.  The OSPF-MIB, IP-MIB, BRIDGE-MIB
 are all examples that are defined for a single instance of the
 technology.

MacFaden, et al. Informational [Page 40] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 It is clear that single instancing of these MIB modules limits
 implementations that might support multiple instances of OSPF, IP
 stacks or logical bridges.
 In such cases, the ENTITY-MIB [RFC2737] can provide a means for
 supporting the one-to-many relationship through naming scopes using
 the entLogicalTable.  Keep in mind, however, that there are some
 drawbacks to this approach.
 1) One cannot issue a PDU request that spans naming scopes.  For
    example, given two instances of BRIDGE-MIB active in a single
    agent, one PDU cannot contain a request for dot1dBaseNumPorts from
    both the first and second instances.
 2) Reliance on this technique creates a dependency on the Entity MIB
    for an application to be able to access multiple instances of
    information.
 Alternately, completely independently of the Entity MIB, multiple MIB
 module instances can be scoped by different SNMP contexts.  This
 does, however, require the coordination of this technique with the
 administrative establishment of contexts in the configured agent
 system.

3.13.3. Use of Special Optional Clauses

 When defining integer-based objects for read-create, read-write and
 read-only semantics, using the UNITS clause is recommended in
 addition to specification in the DESCRIPTION clause of any particular
 details of how UNITs are to be interpreted.
 The REFERENCE clause is also recommended as a way to help an
 implementer track down related information on a given object.  By
 adding a REFERENCE clause to the specific underlying technology
 document, multiple separate implementations will be more likely to
 interoperate.

4. Implementing SNMP Configuration Agents

4.1. Operational Consistency

 Successful deployment of SNMP configuration systems depends on
 understanding the roles of MIB module design and agent design.

MacFaden, et al. Informational [Page 41] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 Both module and agent design need to be undertaken with an
 understanding of how UDP/IP-based SNMP behaves.  A current practice
 in MIB design is to consider the idempotency of settable objects.
 Idempotency basically means being able to invoke the same set
 operation repeatedly but resulting in only a single activation.
 Here is an example of the idempotency in action:

Manager Agent ——– —— Set1 (Object A, Value B) —> receives set OK and responds

                        X<-------- Response PDU(OK) is dropped by
                                   network

Manager times out and sends again Set2 (Object A, Value B) —> receives set OK (does nothing),

                                  responds
                        <-------- with a Response PDU(OK)

Manager receives OK

 Had object A been defined in a stateful way, the set operation might
 have caused the Set2 operation to fail as a result of interaction
 with Set1.  If the agent implementation is not aware of such a
 possible situation on the second request, the agent may behave poorly
 by performing the set request again rather than doing nothing.
 The example above shows that all of the software that runs on a
 managed element and in managed applications should be designed in
 concert when possible.  Particular emphasis should be placed at the
 logical boundaries of the management system components in order to
 ensure correct operation.
 1. The first interface is between SNMP agents in managed devices and
    the management applications themselves.  The MIB document is a
    contract between these two entities that defines expected behavior
    - it is a type of API.
 2. The second interface is between the agent and the instrumented
    subsystem.  In some cases, the instrumented subsystem will require
    modification to allow for the dynamic nature of SNMP-based
    configuration, control and monitoring operations.  Agent
    implementors must also be sensitive to the operational code and
    device in order to minimize the impact of management on the
    primary subsystems.
 Additionally, while the SNMP protocol-level and MIB module-level
 modeling of configuration operations may be idempotent and stateless
 from one set operation to another, it may not be that way in the

MacFaden, et al. Informational [Page 42] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 underlying subsystem.  It is possible that an agent may need to
 manage this state in these subsystem architectures explicitly when it
 has placed the underlying subsystem into an "intermediate" state at a
 point in processing a series of SET PDUs.  Alternatively, depending
 on the underlying subsystem in question, the agent may be able to
 buffer all of the configuration set operations prior to activating
 them in the subsystem all at once (to accommodate the nature of the
 subsystem).
 As an example, it would be reasonable to define a MIB module to
 control Virtual Private Network (VPN) forwarding, in which a
 management station could set a set of ingress/egress IP addresses for
 the VPN gateway.  Perhaps the MIB module presumes that the level of
 transactionality is the establishment of a single row in a table
 defining the address of the ingress/egress gateway, along with some
 prefix information to assist in routing at the VPN layer to that
 gateway.  However, it would be conceivable that in an underlying
 Layer 2 VPN subsystem instrumentation, the requirement is that all
 existing gateways for a VPN be deleted before a new one can be
 defined--that, in other words, in order to add a new gateway, g(n),
 to a VPN, gateways g(1)..g(n-1) need to be removed, and then all n
 gateways reestablished with the VPN forwarding service.  In this
 case, one could imagine an agent which has some sort of timer to
 establish a bounded window for receipt of SETs for new VPN gateways,
 and to activate them in this removal-then-reestablishment of existing
 and new gateways at the end of this window.

4.2. Handling Multiple Managers

 Devices are often modified by multiple management entities and with
 different management techniques.  It is sometimes the case that an
 element is managed by different organizations such as when a device
 sits between administrative domains.
 There are a variety of approaches that management software can use to
 ensure synchronization of information between the manager(s) and the
 managed elements.
 An agent should report configuration changes performed by different
 entities.  It should also distinguish configuration defined locally
 such as a default or locally specified configuration made through an
 alternate management interface such as a command line interface.
 When a change has been made to the system via SNMP, CLI, or other
 method, a managed element should send an notification to the
 manager(s) configured as recipients of these applicable
 notifications.  These management applications should update their

MacFaden, et al. Informational [Page 43] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 local configuration repositories and then take whatever additional
 action is appropriate.  This approach can also be an early warning of
 undesired configuration changes.
 Managers should also develop mechanisms to ensure that they are
 synchronized with each other.

4.3. Specifying Row Modifiability

 Once a RowStatus value is active(1) for a given row, the management
 application should be able to determine what the semantics are for
 making additional changes to a row.  The RMON MIB control table
 objects spell out explicitly what managed objects in a row can and
 cannot be changed once a given RowStatus goes active.
 As described earlier, some operations take some time to complete.
 Some systems also require that they remain in a particular state for
 some period before moving to another.  In some cases, a change to one
 value may require re-initialization of the system.  In all of these
 cases, the DESCRIPTION clause should contain information about
 requirements of the managed system and special restrictions that
 managers should observe.

4.4. Implementing Write-only Access Objects

 The second version of the SNMP SMI dropped direct support for a
 write-only object. It is therefore necessary to return something when
 reading an object that you may have wished to have write-only
 semantics.  Such objects should have a DESCRIPTION clause that
 details what the return values should be.  However, regardless of the
 approach, the value returned when reading the object instance should
 be meaningful in the context of the object's semantics.

5. Designing Configuration Management Software

 In this section, we describe practices that should be used when
 creating and deploying management software that configures one or
 more systems using SNMP.  Functions all configuration management
 software should provide, regardless of the method used to convey
 configuration information to the managed systems are backup, fail-
 over, and restoration.  A management system should have the following
 features:
 1. A method for restoring a previous configuration to one or more
    devices.  Ideally this restoration should be time indexed so that
    a network can be restored to a configured state as of a specific
    time and date.

MacFaden, et al. Informational [Page 44] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 2. A method for saving back up versions of the configuration data in
    case of hardware or software failure.
 3. A method of providing fail-over to a secondary (management) system
    in case of a primary failure.  This capability should be deployed
    in such a way that it does not cause duplicate polling of
    configuration.
 These three capabilities are of course important for other types of
 management that are not the focus of this BCP.

5.1. Configuration Application Interactions with Managed Systems

 From the point of view of the design of the management application,
 there are three basic requirements to evaluate relevant to SNMP
 protocol operations and configuration:
    o Set and configuration activation operations
    o Notifications from the device
    o Data retrieval and collection
 Depending on the requirements of the specific services being
 configured, many other requirements may, and probably will, also be
 present.
 The design of the system should not assume that the objects in a
 device that represent configuration data will remain unchanged over
 time.
 As standard MIB modules evolve and vendors add private extensions,
 the specific configuration parameters for a given operation are
 likely to change over time.  Even in the case of a configuration
 application that is designed for a single vendor, the management
 application should allow for variability in the MIB objects that will
 be used to configure the device for a particular purpose.  The best
 method to accomplish this is by separating, as much as possible, the
 operational semantics of a configuration operation from the actual
 data. One way that some applications achieve this is by having the
 specific configuration objects that are associated with a particular
 device be table driven rather than hard coded.  Ideally, management
 software should verify the support in the devices it is expected to
 manage and report any unexpected deviations to the operator.  This
 approach is particularly valuable when developing applications that
 are intended to support equipment or software from multiple vendors.

MacFaden, et al. Informational [Page 45] RFC 3512 Configuring Networks and Devices with SNMP April 2003

5.1.1. SET Operations

 Management software should be mindful of the environment in which SET
 operations are being deployed.  The intent here is to move
 configuration information as efficiently as possible to the managed
 device.  There are many ways to achieve efficiency and some are
 specific to given devices.  One general case that all management
 software should employ is to reduce the number of SET PDU exchanges
 between the managed device and the management software to the
 smallest reasonable number.  One approach to this is to verify the
 largest number of variable bindings that can fit into a SET PDU for a
 managed device.  In some cases, the number of variable bindings to be
 sent in a particular PDU will be influenced by the device, the
 specific MIB objects and other factors.
 Maximizing the number of variable bindings in a SET PDU also has
 benefits in the area of management application transaction
 initiation, as we will discuss in the following section.
 There are, though, agents that may have implementation limitations on
 the number and order of varbinds they can handle in a single SET PDU.
 In this case, sending fewer varbinds will be necessary.
 As stated at the outset of this section, the management application
 software designer must be sensitive to the design of the SNMP
 software in the managed device.  For example, the software in the
 managed device may require that all that all related configuration
 information for an operation be conveyed in a single PDU because it
 has no concept of a transaction beyond a single SNMP PDU.  Another
 example has to do with the RowStatus textual convention.  Some SNMP
 agents implement a subset of the features available and as such the
 management application must avoid using features that may not be
 supported in a specific table implementation (such as createAndWait).

5.1.2. Configuration Transactions

 There are several types of configuration transactions that can be
 supported by SNMP-based configuration applications.  They include
 transactions on a scalar object, transactions in a single table
 (within and across row instances), transactions across several tables
 in a managed device and transactions across many devices.  The
 manager's ability to support these different transactions is partly
 dependent on the design of the MIB objects used in the configuration
 operation.
 To make use of any kind of transaction semantics effectively, SNMP
 management software must be aware of the information in the MIB
 modules that it is to configure so that it can effectively utilize

MacFaden, et al. Informational [Page 46] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 RowStatus objects for the control of transactions on one or more
 tables.  Such software must also be aware of control tables that the
 device supports that are used to control the status of one or more
 other tables.
 To the greatest extent possible, the management application should
 provide the facility to support transactions across multiple devices.
 This means that if a configuration operation is desired across
 multiple devices, the manager can coordinate these configuration
 operations such that they become active as close to simultaneously as
 possible.
 Several practical means are present in the SNMP model that support
 management application level transactions.  One was mentioned in the
 preceding section, that transactions can be optimized by including
 the maximum number of SET variable bindings possible in a single PDU
 sent to the agent.
 There is an important refinement to this.  The set of read-create row
 data objects for tables should be sent in a single PDU, and only
 placed across multiple PDUs if absolutely necessary.  The success of
 these set operations should be verified through the response(s) to
 the Set PDU or subsequent polling of the row data objects.  The
 applicable RowStatus object(s), may be set to active only after this
 verification.  This is the only tractable means of affording an
 opportunity for per-row rollback, particularly when the configuration
 change is across table row instances on multiple managed devices.
 Finally, where a MIB module exposes the kind of helpful transaction
 management object types that were discussed in Section 3.3.5, it is
 clearly beneficial to the integrity of the management application's
 capacity to handle transactions to make use of them.

5.1.3. Tracking Configuration Changes

 As previously described in Section 3.3.5 (Summary Objects and State
 Tracking), agents should provide the capability for notifications to
 be sent to their configured management systems whenever a
 configuration operation is completed or is detected to have failed.
 The management application must be prepared to accept these
 notifications so that it knows the current configured state of the
 devices under its control.  Upon receipt of the notification, the
 management application should use getBulk or getNext to retrieve the
 configuration from the agent and store the relevant contents in the
 management application database.  The GetBulkRequest-PDU is useful
 for this whenever supported by the managed device, since it is more
 efficient than the GetNextRequest-PDU when retrieving large amounts

MacFaden, et al. Informational [Page 47] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 of data.  For the purposes of backward compatibility, the management
 station should also support and make use of the GetNextRequest-PDU
 when the agent does not support the GetBulkRequest-PDU.
 Management systems should also provide configuration options with
 defaults for users that tend to retrieve the smallest amount of data
 to achieve the particular goal of the application, to avoid
 unnecessary load on managed devices for the most common retrieval
 operations.

5.1.4. Scalability of Data Retrieval

 The techniques for efficient data retrieval described in the
 preceding sections comprise only one aspect of what application
 developers should consider in this regard when developing
 configuration applications.  Management applications should provide
 for distributed processing of the configuration operations.  This
 also extends to management functions that are not the focus of this
 document.  Techniques of distributed processing can also be used to
 provide resilience in the case of network failures.  An SNMP-based
 configuration management system might be deployed in a distributed
 fashion where three systems in different locations keep each other
 synchronized.  This synchronization can be accomplished without
 additional polling of network devices through a variety of
 techniques.  In the case of a failure, a 'backup' system can take
 over the configuration responsibilities from the failed manager
 without having to re-synchronize with the managed elements since it
 will already be up to date.

6. Deployment and Security Issues

 Now that we have considered the design of SNMP MIB data for
 configuration, agent implementation of its access, and management
 application issues in configuration using SNMP, we turn to a variety
 of operational considerations which transcend all three areas.

6.1. Basic assumptions about Configuration

 The following basic assumptions are made about real world
 configuration models.
 1) Operations must understand and must be trained in the operation of
    a given technology.  No configuration system can prevent an
    untrained operator from causing outages due to misconfiguration.
 2) Systems undergoing configuration changes must be able to cope with
    unexpected loss of communication at any time.

MacFaden, et al. Informational [Page 48] RFC 3512 Configuring Networks and Devices with SNMP April 2003

    During configuration operations, network elements must take
    appropriate measures to leave the configuration in a
    consistent/recognizable state by either rolling back to a
    previously valid state or changing to a well-defined or default
    state.
 3) Configuration exists on a scale from relatively unchanging to a
    high volume, high rate of change.  The former is often referred to
    as "set and forget" to indicate that the configuration changes
    quite infrequently.  The latter, "near real-time change control"
    implies a high frequency of configuration change.  Design of
    configuration management must take into account the rate and
    volume of change expected in a given configuration subsystem.

6.2. Secure Agent Considerations

 Vendors should not ship a device with a community string 'public' or
 'private', and agents should not define default community strings
 except when needed to bootstrap devices that do not have secondary
 management interfaces.  Defaults lead to security issues that have
 been recognized and exploited.  When using SNMPv1, supporting read-
 only community strings is a common practice.
 Version 3 of the SNMP represents the current standard for the
 Internet Management Framework and is recommended for all network
 management applications.  In particular, SNMPv3 provides
 authorization, authentication, and confidentiality protection and is
 essential to meeting the security considerations for all management
 of devices that support SNMP-based configuration.

6.3. Authentication Notifications

 The default state of RFC 1215 [17] Authentication notifications
 should be off.  One does not want to risk accidentally sending out
 authentication failure information, which by itself could constitute
 a security liability.  Enabling authentication Notifications should
 be done in the context of a management security scheme which
 considers the proper recipients of this information.
 There are other liabilities where authentication notifications are
 generated without proper security infrastructure.  When notifications
 are sent in SNMPv1 trap PDUs, unsolicited packets to a device can
 causes one or more trap PDUs to be created and sent to management
 stations.  If these traps flow on shared access media and links, the
 community string from the trap may be gleaned and exploited to gain
 access to the device.  At the very least, this risk should be
 mitigated by having the authentication trap PDU be conveyed with a

MacFaden, et al. Informational [Page 49] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 community string which is only used for authentication traps from the
 agent, and would be useless for access inbound to the agent to get at
 other management data.
 A further liability of authentication traps can be seen when they are
 being generated in the face of a Denial Of Service (DOS) attack, in
 the form of a flood of PDUs with invalid community strings, on the
 agent system.  If it is bad enough that the system is having to
 respond to and recover from the invalid agent data accesses, but the
 problem will be compounded if a separate Authentication notification
 PDU is sent to each recipient on the management network.

6.4. Sensitive Information Handling

 Some MIB modules contain objects that may contain data for keys,
 passwords and other such sensitive information and hence must be
 protected from unauthorized access.  MIB documents that are created
 in the IETF must have a 'Security Considerations' section, which
 details how sensitive information should be protected.  Similarly,
 MIB module designers who create MIB documents for private MIB objects
 should include similar information so that users of the products
 containing these objects can take appropriate precautions.
 Even if a device does support DES, it should be noted that
 configuration of keys for other protocols via SNMP Sets protected by
 DES should not be allowed if the other keys are longer than the 56
 bit DES keys protecting the SNMP transmission.
 The DESCRIPTION clause for these object types and their Security
 Considerations sections in the documents which define them should
 make it clear how and why these specific objects are sensitive and
 that a user should only make them accessible for encrypted SNMP
 access.  Vendors should also document sensitive objects in a similar
 fashion.
 Confidentiality is not a mandatory portion of the SNMPv3 management
 framework [6].
 Prior to SNMPv3, providing customized views of MIB module data was
 difficult.  This led to objects being defined such as the following
 from [41].

MacFaden, et al. Informational [Page 50] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 docsDevNmAccessEntry OBJECT-TYPE
     SYNTAX      DocsDevNmAccessEntry
     MAX-ACCESS  not-accessible
     STATUS      current
     DESCRIPTION
         "An entry describing access to SNMP objects by a
          particular network management station.  An entry in
          this table is not readable unless the management station
          has read-write permission (either implicit if the table
          is empty, or explicit through an entry in this table.
          Entries are ordered by docsDevNmAccessIndex.  The first
          matching entry (e.g., matching IP address and community
          string) is used to derive access."
     INDEX { docsDevNmAccessIndex  }
     ::= {  docsDevNmAccessTable 1 }
 New MIB modules should capitalize on existing security capabilities
 of SNMPv3 Framework.  One way they can do this is by indicating the
 level of security appropriate to different object types.  For
 example, objects that change the configuration of the system might be
 protected by using the authentication mechanisms in SNMPv3.
 Specifically, it is useful to design MIB module object grouping with
 considerations for VACM views definition, such that users can define
 and properly scope what tables are visible to a given user and view.

7. Policy-based Management

 In some designs and implementations, a common practice used to move
 large amounts of data involves using SNMP as a control channel in
 combination with other protocols defined for transporting bulk data.
 This approach is sub-optimal since it raises a number of security and
 other concerns.  Transferring large amounts of configuration data via
 SNMP can be efficiently performed with several of the techniques
 described earlier in this document.  This policy section shows how
 even greater efficiency can be achieved using a set of relatively new
 design mechanisms.  This section gives background and defines terms
 that are relevant to this field and describes some deployment
 approaches.

7.1. What Is the Meaning of 'Policy-based'?

 In the past few years of output from standards organizations and
 networking vendor marketing departments, the term 'policy' has been
 heavily used, touted, and contorted in meaning.  The result is that
 the true meaning of 'policy' is unclear without greater qualification
 where it is used.
 [42] gives the term 'policy' two explicit definitions:

MacFaden, et al. Informational [Page 51] RFC 3512 Configuring Networks and Devices with SNMP April 2003

  1. A definite goal, course or method of action to guide and determine

present and future decisions. "Policies" are implemented or

    executed within a particular context (such as policies defined
    within a business unit).
  1. Policies as a set of rules to administer, manage, and control

access to network resources.

    Note that these two views are not contradictory since individual
    rules may be defined in support of business goals.
 As it pertains to our discussion of the term 'policy-based
 configuration', the meaning is significantly more specific.  In this
 context, we refer to a way of integrating data and the management
 actions which use it in such a way that:
  1. there is the ability to specify "default" configuration data for a

number of instances of managed elements, where those instances can

    be correlated in some data driven or algorithmic way.  The engine
    to do this correlation and activate instances from defaults may
    reside in the agent or externally.  Where the representation of
    these defaults are in the MIB design itself, the object types
    supporting this notion are referred to as "template objects".
  1. the activation of instance data derived from template object types

results from minimal activation directives from the management

    application, once the instances of the template object types have
    been established.
  1. somewhat independently, the architecture of the overall management

agent may accommodate the definition and evaluation of management

    and configuration policies.  The side-effects of the evaluation of
    these policies typically include the activation of certain
    configuration directives.  Where management data design exposes
    template object types, the policy-driven activation can (and
    ideally, should) include the application of template object
    instances to the analogous managed element instance-level values.
 As it pertains to template object data, the underlying notions
 implied here have been prevalent for some time in non-SNMP management
 regimes.  A common feature of many command line interfaces for
 configuring routers is the specification of one or more access
 control lists.  These typically provide a set of IP prefixes, BGP
 autonomous system numbers, or other such identifying constructs (see,
 for example, [42]).  Once these access control lists are assembled,
 their application to various interfaces, routing processes, and the
 like are specified typically in the configuration of what the access
 control list is applied to.  Consistent with the prior properties to

MacFaden, et al. Informational [Page 52] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 define our use of policy-based configuration, a) the access list is
 defined independent from its point of application, and b) its
 application is independent of the access list definition.  For
 example, changing the application of an access list from one
 interface to the other does not require a change in the access list
 itself.  The first point just mentioned suggests what is necessary
 for template-based data organization.  The second suggests its
 application in a policy-based manner.
 Let us now examine the motivation for such a system or subsystem
 (perhaps bounded at the level of a 'template-enabled' MIB module,
 given the above definition).  Let us explore the importance of
 policy-based techniques to configuration specifically.

7.2. Organization of Data in an SNMP-Based Policy System

 The number of configurable parameters and 'instances' such as
 interfaces has increased as equipment has become larger and more
 complex.
 At the same time, there is a need to configure many of these systems
 to operate in a coordinated fashion.  This enables the delivery of
 new specialized services that require this coordinated configuration.
 Examples include delivery of virtual private networks and connections
 that guarantee specific service levels.
 The growth in size and complexity of configuration information has
 significant implications for its organization as well as its
 efficient transfer to the management agent.  As an example, an agent
 that implements the Bridge MIB [24] could be used to represent a
 large VLAN with some 65,000 port entries.  Configuring such a VLAN
 would require the establishment of dot1dStpPortTable and
 dot1DStaticTable entries for each such virtual port.  Each table
 entry would contain several parameters.  A more efficient approach is
 to provide default values for the creation of new entries that are
 appropriate to the VLAN environment in our example.  The local
 management infrastructure should then iterate across the system
 setting the default values to the selected ports as groups.
 To date, this kind of large-scale configuration has been accomplished
 with file transfer, by setting individual MIB objects, or with many
 CLI commands.  In each of these approaches the details for each
 instance are contained in the file, CLI commands or MIB objects.
 That is, they contain not only the value, and type of object, but
 also the exact instance of the object to which to apply the value.
 It is this property that tends to make configuration operations
 explode as the number of instances (such as interfaces) grows.  This
 per-instance approach can work for a few machines configured by

MacFaden, et al. Informational [Page 53] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 experts, but there is a need for a more scalable solution.
 Template-based data organization and policy-based management
 abstracts the details above the instance level, which means that
 fewer SET requests are sent to a managed device.
 Realization of such a policy-driven system requires agents that can
 take defaults and apply them to instances based on a rule that
 defines under what conditions the defaults (policy) are to be
 applied.  A policy-driven configuration system which is to be
 scalable needs to expose a means of layering its application of
 defaults at discrete ranges of granularity.  The spectrum of that
 granularity might have a starting hierarchy point to apply defaults
 at the breadth of a network service.
 Ultimately, such a layering ends up with features to support
 instance-level object instance data within the running agent.
 An example of this kind of layering is implicit in the principle of
 operations of a SNMPCONF Policy-Based Management MIB [36] (PM-MIB)
 implementation.  However, other entity management systems have been
 employing these kinds of techniques end-to-end for some time, in some
 cases using SNMP, in some cases using other encodings and transfer
 technologies.  What the PM-MIB seeks to establish, in an environment
 ideal for its deployment, is an adaptation between MIB module data
 which was not designed using template object types, and the ability
 to allow the PM-MIB agent engine to apply instances of that data as
 though it were template-based.

7.3. Information Related to Policy-based Configuration

 In order for effective policy management to take place, a range of
 information about the network elements is needed to avoid making poor
 policy decisions.  Even in those cases where policy-based
 configuration is not in use, much of the information described in
 this section can be useful input to the decision-making process about
 what type of configuration operations to do.
 For this discussion it is important to make distinctions between
 distribution of policy to a system, activation of a policy in a
 system, and changes/failures that take place during the time the
 policy is expected to be active.  For example, if an interface is
 down that is included in a policy that is distributed, there may not
 be an error since the policy may not be scheduled for activation
 until a later time.
 On the other hand, if a policy is distributed and applied to an
 interface that should be operational and it is not, clearly this is a
 problem, although it is not an error in the configuration policy

MacFaden, et al. Informational [Page 54] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 itself.  With this as background, here are some areas to consider
 that are important to making good policy configuration decisions and
 establishing when a policy has 'failed'.
 o  The operational state of network elements that are to be
    configured.
    Care should be taken to determine if the sub-components to be
    configured are available for use.  In some cases the elements may
    not be available.  The policy configuration software should
    determine if this is a prerequisite to policy installation or if
    the condition is even acceptable.  This decision is separate from
    the one to be made about policy activation.  Installation is when
    the policy is sent from the policy manager to the managed device
    and activation is turning on the policy.  In those cases where
    policy is distributed when the sub-component such as an interface
    or disk is not available, the managed system should send a
    notification to the designated management station when the policy
    is to become active or if the resource is still not available.
 o  The capabilities of the devices in the network.
    A capability can be almost any unit of work a network element can
    perform.  These include routing protocols supported, Web server
    and OS versions, queuing mechanisms supported on each interface
    that can be used to support different qualities of service, and
    many others.  This information can be obtained from the
    capabilities table of the Policy MIB module [36].
    Historically, management applications have had to obtain this type
    of information by issuing get requests for objects they might want
    to use.  This approach is far less efficient since it requires
    many get requests and is more error prone since some instances
    will not exist until configured.  The new capabilities table is an
    improvement on the current technique.
 o  The capacity of the devices to perform the desired work.
    Capability is an ability to perform the desired work while a
    capacity is a measure of how much of that capability the system
    has.  The policy configuration application should, wherever
    possible, evaluate the capacity of the network element to perform
    the work identified by the policy.  In some systems it will not be
    possible to obtain the capacity of the managed elements to perform
    the desired work directly, even though it may be possible to
    monitor the amount of work the element performs.  In these cases,
    the management application may benefit from pre-configured

MacFaden, et al. Informational [Page 55] RFC 3512 Configuring Networks and Devices with SNMP April 2003

    information about the capacity of different network elements so
    that evaluations of the resources available can be done before
    distributing new policies.
    Utilization refers to how much capacity for a particular
    capability has been consumed.  For devices that have been under
    policy configuration control for any period of time, a certain
    percentage of the available capacity of the managed elements will
    be used.  Policies should not be distributed to systems that do
    not have the resources to carry out the policy in a reasonable
    period of time.

7.4. Schedule and Time Issues

 This section applies equally to systems that are not policy-based as
 well as policy-based systems, since configuration operations often
 need to be synchronized across time zones.  Wherever possible, the
 network elements should support time information using the standard
 DateAndTime TC that includes local time zone information.  Policy-
 based management often requires more complex time expressions than
 can be conveyed with the DateAndTime TC.  See the Policy-Based
 Management MIB document [36] for more information.  Some deployed
 systems do not store complex notions of local time and thus may not
 be able to process policy directives properly that contain time zone
 relevant data.  For this reason, policy management applications
 should have the ability to ascertain the time keeping abilities of
 the managed system and make adjustments to the policy for those
 systems that are time-zone challenged.

7.5. Conflict Detection, Resolution and Error Reporting

 Policies sent to a device may contain conflicting instructions.
 Detection of such commands can occur at the device or management
 level and may be resolved using any number of mechanisms (examples
 are, last configuration set wins, or abort change).  These unintended
 conflicts should be reported.  Conflicts can occur at different
 levels in a chain of commands.  Each 'layer' in policy management
 system should be able to check for some errors and report them.  This
 is conceptually identical to programs raising an exception and
 passing that information on to software that can do something
 meaningful with it.
 At the instance level, conflict detection has been performed in a
 limited way for some time in software that realizes MIB objects at
 this level of resolution.  This detection is independent of policy.
 The types of 'conflicts' usually checked for are resource
 availability and validity of the set operations.  In a policy enabled

MacFaden, et al. Informational [Page 56] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 system, there are no additional requirements for this software
 assuming that good error detection and reporting appropriate to this
 level have already been implemented.

7.5.1. Changes to Configuration Outside of the Policy System

 It is essential to consider changes to configuration that are
 initiated outside of the policy system.  A goal of SNMP-based policy
 management is to coexist with other kinds of management software that
 have historically been instance based management.  The best example
 is the command line interface.
 A notification should be sent whenever an out-of-policy control
 change is made to an element that is under the control of policy.
 This notification should include the policy that was affected, the
 instance of the element that was changed and the object and value
 that it was changed to.
 Even for those systems that have no concept of policy control, the
 ideas presented above make sense.  That is, if SNMP co-exists with
 other access methods such as a CLI, it is essential that the
 management station remain synchronized with changes that might have
 been made to the managed device using other methods.  As a result,
 the approach of sending a notification when another access method
 makes a change is a good one.  Of course this should be configurable
 by the user.

7.6. More about Notifications in a Policy System

 Notifications can be useful in determining a failure of a policy as a
 result of an error in the policy or element(s) under policy control.
 As with all notifications, they should be defined and controlled in
 such a way that they do not create a problem by sending more than are
 helpful over a specific period of time.  For example, if a policy is
 controlling 1,000 interfaces and fails, one notification rather than
 1,000 may be the better approach.  In addition, such notifications
 should be defined to include as much information as possible to aid
 in problem resolution.

7.7. Using Policy to Move Less Configuration Data

 One of the advantages of policy-based configuration with SNMP is that
 many configuration operations can be conveyed with a small amount of
 data.  Changing a single configuration parameter for each of 100
 interfaces on a system might require 100 CLI commands or 100 SNMP
 variable bindings using conventional techniques.

MacFaden, et al. Informational [Page 57] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 Using policy-based configuration with SNMP, a single SET PDU can be
 sent with the policy information necessary to apply a configuration
 change to 100 similar interfaces.  This efficiency gain is the result
 of eliminating the need to send the value for each instance to be
 configured.  The 'default' for each of the instances included in the
 policy is sent, and the rule for selection of the instances that the
 default is to be applied to can also be carried (see the Policy MIB
 module [36]).
 To extend the example above, assume that there are 10 parameters that
 need to change.  Using conventional techniques, there would now be
 1,000 variable bindings, one for each instance of each new value for
 each interface.  Using policy-based configuration with SNMP, it is
 still likely that all the information can be conveyed in one SET PDU.
 The only difference in this case is that there are ten parameters
 sent that will be the 'template' used to create instances on the
 managed interfaces.
 This efficiency gain not only applies to SET operations, but also to
 those management operations that require configuration information.
 Since the policy is also held in the storage for cross-instance
 defaults (for example, the pmPolicyTable in [36]), an entire data set
 that potentially controls hundreds of rows of information can be
 retrieved in a single GET request.
 A policy-friendly data organization such as this is consistent and
 integrates well with MIB module objects which support "summary"
 activation and activation reporting, of the kind discussed in Section
 3.3.5.

8. Example MIB Module With Template-based Data

 This section defines a MIB module that controls the heating and air
 conditioning system for a large building.  It contains both
 configuration and counter objects that allow operators to see how
 much cooling or heating a particular configuration has consumed.
 Objects that represent the configuration information at a "default"
 level (as referenced above) are also included.
 These tables, in combination with the application of the tables' row
 instance data as templated 'defaults', will allow operators to
 configure and monitor many rooms at once, change the configuration
 parameters based on time of day, and make a number of other
 sophisticated decisions based on the 'policy' implied by these
 defaults and their application.  For this reason, these configuration
 controls have their instances specified from template object types.

MacFaden, et al. Informational [Page 58] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 In our simplified Heating Ventilation and Air Conditioning (HVAC)
 model we will create three tables based on a simple analysis.  More
 complicated systems will need more tables, but the principles will be
 the same.

Step 1: As with any other MIB module design, the first step

      is to determine what objects are necessary for
      configuration and control operations.  The first table
      to be created is a fairly traditional monitoring
      table.  It includes indices so that we will know what
      rooms the counters and status objects are for.  It
      includes an object that is a RowPointer to a table
      that contains configuration information.  The objects
      for the bldgHVACTable, our first table in the HVAC
      MIB module are:

Index objects that identify what floor and office we are managing:

     bldgHVACFloor
     bldgHVACOffice

A single index reference to a table that 'glues' configuration information defaults with descriptive information:

     bldgHVACCfgTemplate

A set of objects that show status and units of work (bldgHVACCoolOrHeatMins) and standard per-row SnmpAdminString, StorageType, and RowStatus columnar objects:

      bldgHVACFanSpeed
      bldgHVACCurrentTemp
      bldgHVACCoolOrHeatMins
      bldgHVACDiscontinuityTime
      bldgHVACOwner
      bldgHVACStatus

Step 2: A configuration description table. The purpose of this

      table is to provide a unique string identifier for
      templates.  These may be driven by policies in a
      network.  If it were necessary to configure devices
      to deliver a particular quality of service, the
      index string of this table could be the name and the
      description part, it could be a brief description of the
      underlying motivation such as: "provides extra heat to
      corner offices to counteract excessive exterior wind

MacFaden, et al. Informational [Page 59] RFC 3512 Configuring Networks and Devices with SNMP April 2003

      chill".  Standard owner and status objects may also
      be helpful and are included here.  The row columnar
      objects are:
     bldgHVACCfgTemplateInfoIndex
     bldgHVACCfgTemplateInfoID
     bldgHVACCfgTemplateInfoDescr
     bldgHVACCfgTemplateInfoOwner
     bldgHVACCfgTemplateInfoStatus

Notice that to this point we have provided no configuration information. That will be in the next table. Some readers may wonder why this table is not combined with the configuration template table described in the next step. In fact, they can be. The reason for having a separate table is that as systems become more complex, there may be more than one configuration table that points to these descriptions. Another reason for two tables is that this in not reproduced for every template and instance, which can save some additional data movement. Every designer will have to evaluate the tradeoffs between number of objects and data movement efficiency just as with other MIB modules.

Step 3: The bldgHVACCfgTemplateTable contains the specific

      configuration parameters that are pointed to by the
      bldgHVACConfigPtr object.  Note that many rows in the
      bldgHVACTable can point to an entry in this table.  It
      is also possible for entries to be used by 1 or 0 rows
      of the bldgHVACTable.  It is the property of allowing
      multiple rows (instances) in the bldgHVACTable to
      point to a row in this table that can produce such
      efficiency gains from policy-based management with
      SNMP.  Also notice that the configuration data is tied
      directly to the counter data so that people can see
      how configurations impact behavior.

The objects in this table are all that are necessary for configuration and connection to the other tables as well as the usual SnmpAdminString, StorageType, and RowStatus objects:

A simple index to the table:

     bldgHVACCfgTemplateIndex

The configuration objects:

MacFaden, et al. Informational [Page 60] RFC 3512 Configuring Networks and Devices with SNMP April 2003

    bldgHVACCfgTemplateDesiredTemp
    bldgHVACCfgTemplateCoolOrHeat

Administrative objects for SnmpAdminString and RowStatus:

     bldgHVACCfgTemplateInfo
     bldgHVACCfgTemplateOwner
     bldgHVACCfgTemplateStorage
     bldgHVACCfgTemplateStatus

8.1. MIB Module Definition

BLDG-HVAC-MIB DEFINITIONS ::= BEGIN IMPORTS

  MODULE-IDENTITY, Counter32,
  Gauge32, OBJECT-TYPE, Unsigned32, experimental
      FROM SNMPv2-SMI
  MODULE-COMPLIANCE, OBJECT-GROUP
     FROM SNMPv2-CONF
  TEXTUAL-CONVENTION,
  TimeStamp, RowStatus, StorageType
      FROM SNMPv2-TC
  SnmpAdminString
      FROM SNMP-FRAMEWORK-MIB;

bldgHVACMIB MODULE-IDENTITY

  LAST-UPDATED "200303270000Z"
  ORGANIZATION "SNMPCONF working group
                E-mail: snmpconf@snmp.com"
  CONTACT-INFO
      "Jon Saperia
      Postal:     JDS Consulting
                  174 Chapman Street
                  Watertown, MA 02472
                  U.S.A.
      Phone:      +1 617 744 1079
      E-mail:     saperia@jdscons.com
      Wayne Tackabury
      Postal:     Gold Wire Technology
                  411 Waverley Oaks Rd.
                  Waltham, MA 02452
                  U.S.A.
      Phone:      +1 781 398 8800
      E-mail:     wayne@goldwiretech.com

MacFaden, et al. Informational [Page 61] RFC 3512 Configuring Networks and Devices with SNMP April 2003

      Michael MacFaden
      Postal:     Riverstone Networks
                  5200 Great America Pkwy.
                  Santa Clara, CA 95054
                  U.S.A.
      Phone:      +1 408 878 6500
      E-mail:     mrm@riverstonenet.com
      David Partain
      Postal:     Ericsson AB
                  P.O. Box 1248
                  SE-581 12  Linkoping
                  Sweden
      E-mail:     David.Partain@ericsson.com"
  DESCRIPTION
      "This example MIB module defines a set of management objects
      for heating ventilation and air conditioning systems.  It
      also includes objects that can be used to create policies
      that are applied to rooms.  This eliminates the need to send
      per-instance configuration commands to the system.
      Copyright (C) The Internet Society (2003).  This version of
      this MIB module is part of RFC 3512; see the RFC itself for
      full legal notices."
  REVISION "200303270000Z"
  DESCRIPTION
      "Initial version of BLDG-HVAC-MIB as published in RFC 3512."
  ::= { experimental 122 }

bldgHVACObjects OBJECT IDENTIFIER ::= { bldgHVACMIB 1 } bldgConformance OBJECT IDENTIFIER ::= { bldgHVACMIB 2 }

– – Textual Conventions –

BldgHvacOperation ::= TEXTUAL-CONVENTION

  STATUS             current
  DESCRIPTION
      "Operations supported by a heating and cooling system.
      A reference to underlying general systems would go here."
  SYNTAX      INTEGER {
                       heat(1),
                       cool(2)
              }

– – HVAC Objects Group

MacFaden, et al. Informational [Page 62] RFC 3512 Configuring Networks and Devices with SNMP April 2003

bldgHVACTable OBJECT-TYPE

  SYNTAX      SEQUENCE OF BldgHVACEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "This table is the representation and data control
      for building HVAC by each individual office.
      The table has rows for, and is indexed by a specific
      floor and office number.  Each such row includes
      HVAC statistical and current status information for
      the associated office.  The row also contains a
      bldgHVACCfgTemplate columnar object that relates the
      bldgHVACTable row to a row in the bldgHVACCfgTemplateTable.
      If this value is nonzero, then the instance in the row
      that has a value for how the HVAC has been configured
      in the associated template (bldgHVACCfgTeplateTable row).
      Hence, the bldgHVACCfgTeplateTable row contains the
      specific configuration values for the offices as described
      in this table."
  ::= { bldgHVACObjects 1 }

bldgHVACEntry OBJECT-TYPE

  SYNTAX       BldgHVACEntry
  MAX-ACCESS   not-accessible
  STATUS       current
  DESCRIPTION
      "A row in the bldgHVACTable.  Each row represents a particular
      office in the building, qualified by its floor and office
      number.  A given row instance can be created or deleted by
      set operations  upon its bldgHVACStatus columnar
      object instance."
  INDEX { bldgHVACFloor, bldgHVACOffice }
      ::= { bldgHVACTable 1 }

BldgHVACEntry ::= SEQUENCE {

      bldgHVACFloor             Unsigned32,
      bldgHVACOffice            Unsigned32,
      bldgHVACCfgTemplate       Unsigned32,
      bldgHVACFanSpeed          Gauge32,
      bldgHVACCurrentTemp       Gauge32,
      bldgHVACCoolOrHeatMins    Counter32,
      bldgHVACDiscontinuityTime TimeStamp,
      bldgHVACOwner             SnmpAdminString,
      bldgHVACStorageType       StorageType,
      bldgHVACStatus            RowStatus
      }

MacFaden, et al. Informational [Page 63] RFC 3512 Configuring Networks and Devices with SNMP April 2003

bldgHVACFloor OBJECT-TYPE

  SYNTAX      Unsigned32 (1..1000)
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "This portion of the index indicates the floor of the
       building.  The ground floor is considered the
       first floor.  For the purposes of this example,
       floors under the ground floor cannot be
       controlled using this MIB module."
  ::= { bldgHVACEntry 1 }

bldgHVACOffice OBJECT-TYPE

  SYNTAX      Unsigned32 (1..2147483647)
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "This second component of the index specifies the
      office number."
  ::= { bldgHVACEntry 2 }

bldgHVACCfgTemplate OBJECT-TYPE

  SYNTAX          Unsigned32
  MAX-ACCESS      read-create
  STATUS          current
  DESCRIPTION
      "The index (bldgHVACCfgTemplateIndex instance)
      of an entry in the 'bldgHVACCfgTemplateTable'.
      The bldgHVACCfgTable row instance referenced
      is a pre-made configuration 'template'
      that represents the configuration described
      by the bldgHVACCfgTemplateInfoDescr object.  Note
      that not all configurations will be under a
      defined template.  As a result, a row in this
      bldgHVACTable may point to an entry in the
      bldgHVACCfgTemplateTable that does not in turn
      have a reference (bldgHVACCfgTemplateInfo) to an
      entry in the bldgHVACCfgTemplateInfoTable.  The
      benefit of this approach is that all
      configuration information is available in one
      table whether all elements in the system are
      derived from configured templates or not.
      Where the instance value for this colunmar object
      is zero, this row represents data for an office
      whose HVAC status can be monitored using the
      read-only columnar object instances of this
      row, but is not under the configuration control

MacFaden, et al. Informational [Page 64] RFC 3512 Configuring Networks and Devices with SNMP April 2003

      of the agent."
  ::= { bldgHVACEntry 3 }

bldgHVACFanSpeed OBJECT-TYPE

  SYNTAX            Gauge32
  UNITS             "revolutions per minute"
  MAX-ACCESS        read-only
  STATUS            current
  DESCRIPTION
      "Shows the revolutions per minute of the fan.  Fan speed
      will vary based on the difference between
      bldgHVACCfgTemplateDesiredTemp and bldgHVACCurrentTemp.  The
      speed is measured in revolutions of the fan blade per minute."
  ::= { bldgHVACEntry 4 }

bldgHVACCurrentTemp OBJECT-TYPE

  SYNTAX            Gauge32
  UNITS             "degrees in celsius"
  MAX-ACCESS        read-only
  STATUS            current
  DESCRIPTION
      "The current measured temperature in the office.  Should
      the current temperature be measured at a value of less
      than zero degrees celsius, a read of the instance
      for this object will return a value of zero."
  ::= { bldgHVACEntry 5 }

bldgHVACCoolOrHeatMins OBJECT-TYPE

  SYNTAX            Counter32
  UNITS             "minutes"
  MAX-ACCESS        read-only
  STATUS            current
  DESCRIPTION
      "The total number of heating or cooling minutes that have
      been consumed since the row was activated.  Notice that
      whether the minutes represent heating or cooling is a
      function of the configuration of this row.  If the system
      is re-initialized from a cooling to heating function or
      vice versa, then the counter would start over again.  This
      effect is similar to a reconfiguration of some network
      interface cards.  When parameters that impact
      configuration are changed, the subsystem must be
      re-initialized.  Discontinuities in the value of this counter
      can occur at re-initialization of the management system,
      and at other times as indicated by the value of
      bldgHVACDiscontinuityTime."
  ::= { bldgHVACEntry 6 }

MacFaden, et al. Informational [Page 65] RFC 3512 Configuring Networks and Devices with SNMP April 2003

bldgHVACDiscontinuityTime OBJECT-TYPE

  SYNTAX      TimeStamp
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
      "The value of sysUpTime on the most recent occasion at which
      any heating or cooling operation for the office designated
      by this row instance experienced a discontinuity.  If
      no such discontinuities have occurred since the last re-
      initialization of the this row, then this object contains a
      zero value."
  ::= { bldgHVACEntry 7 }

bldgHVACOwner OBJECT-TYPE

  SYNTAX            SnmpAdminString
  MAX-ACCESS        read-create
  STATUS            current
  DESCRIPTION
      "The identity of the operator/system that
      last modified this entry.  When a new entry
      is created, a valid SnmpAdminString must
      be supplied.  If, on the other hand, this
      entry is populated by the agent 'discovering'
      unconfigured rooms, the empty string is a valid
      value for this object."
  ::= { bldgHVACEntry 8 }

bldgHVACStorageType OBJECT-TYPE

  SYNTAX            StorageType
  MAX-ACCESS        read-create
  STATUS            current
  DESCRIPTION
      "The persistence of this row of the table in system storage,
      as it pertains to permanence across system resets.  A columnar
      instance of this object with value 'permanent' need not allow
      write-access to any of the columnar object instances in the
      containing row."
  ::= { bldgHVACEntry 9  }

bldgHVACStatus OBJECT-TYPE

  SYNTAX            RowStatus
  MAX-ACCESS        read-create
  STATUS            current
  DESCRIPTION
      "Controls and reflects the creation and activation status of
      a row in this table.
      No attempt to modify a row columnar object instance value in

MacFaden, et al. Informational [Page 66] RFC 3512 Configuring Networks and Devices with SNMP April 2003

      the bldgHVACTable should be issued while the value of
      bldgHVACStatus is active(1).  Should an agent receive a SET
      PDU attempting such a modification in this state, an
      inconsistentValue error should be returned as a result of
      the SET attempt."
  ::= { bldgHVACEntry 10 }

– – HVAC Configuration Template Table –

bldgHVACCfgTemplateInfoTable OBJECT-TYPE

  SYNTAX      SEQUENCE OF BldgHVACCfgTemplateInfoEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "This table provides unique string identification for
      HVAC templates in a network.  If it were necessary to
      configure rooms to deliver a particular quality of climate
      control with regard to cooling or heating, the index string
      of a row in this table could be the template name.
      The bldgHVACCfgCfgTemplateInfoDescription
      contains a brief description of the template service objective
      such as: provides summer cooling settings for executive
      offices.  The bldgHVACCfgTemplateInfo in the
      bldgHVACCfgTemplateTable will contain the pointer to the
      relevant row in this table if it is intended that items
      that point to a row in the bldgHVACCfgTemplateInfoTable be
      identifiable as being under template control though this
      mechanism."
  ::= { bldgHVACObjects 2 }

bldgHVACCfgTemplateInfoEntry OBJECT-TYPE

  SYNTAX       BldgHVACCfgTemplateInfoEntry
  MAX-ACCESS   not-accessible
  STATUS       current
  DESCRIPTION
      "Each row represents a particular template and
      description.  A given row instance can be created or
      deleted by set operations upon its
      bldgHVACCfgTemplateInfoStatus columnar object
      instance."
  INDEX { bldgHVACCfgTemplateInfoIndex }
  ::= { bldgHVACCfgTemplateInfoTable 1 }

BldgHVACCfgTemplateInfoEntry ::= SEQUENCE {

      bldgHVACCfgTemplateInfoIndex          Unsigned32,
      bldgHVACCfgTemplateInfoID             SnmpAdminString,

MacFaden, et al. Informational [Page 67] RFC 3512 Configuring Networks and Devices with SNMP April 2003

      bldgHVACCfgTemplateInfoDescr          SnmpAdminString,
      bldgHVACCfgTemplateInfoOwner          SnmpAdminString,
      bldgHVACCfgTemplateInfoStatus         RowStatus,
      bldgHVACCfgTemplateInfoStorType       StorageType
      }

bldgHVACCfgTemplateInfoIndex OBJECT-TYPE

     SYNTAX       Unsigned32 (1..2147483647)
     MAX-ACCESS   not-accessible
     STATUS       current
     DESCRIPTION
         "The unique index to a row in this table."
      ::= { bldgHVACCfgTemplateInfoEntry 1 }

bldgHVACCfgTemplateInfoID OBJECT-TYPE

  SYNTAX       SnmpAdminString
  MAX-ACCESS   read-create
  STATUS       current
  DESCRIPTION
      "Textual identifier for this table row, and, consequently
      the template.  This should be a unique name within
      an administrative domain for a particular template so that
      all systems in a network that are under the same template
      can have the same 'handle' (e.g., 'Executive Offices',
      'Lobby Areas')."
  ::= { bldgHVACCfgTemplateInfoEntry 2 }

bldgHVACCfgTemplateInfoDescr OBJECT-TYPE

  SYNTAX       SnmpAdminString
  MAX-ACCESS   read-create
  STATUS       current
  DESCRIPTION
      "A general description of the template.  One example might
      be - Controls the cooling for offices on higher floors
      during the summer."
  ::= { bldgHVACCfgTemplateInfoEntry 3 }

bldgHVACCfgTemplateInfoOwner OBJECT-TYPE

  SYNTAX            SnmpAdminString
  MAX-ACCESS        read-create
  STATUS            current
  DESCRIPTION
      "The identity of the operator/system that last modified
      this entry."
  ::= { bldgHVACCfgTemplateInfoEntry 4 }

bldgHVACCfgTemplateInfoStatus OBJECT-TYPE

MacFaden, et al. Informational [Page 68] RFC 3512 Configuring Networks and Devices with SNMP April 2003

  SYNTAX            RowStatus
  MAX-ACCESS        read-create
  STATUS            current
  DESCRIPTION
      "The activation status of this row.
      No attempt to modify a row columnar object instance value in
      the bldgHVACCfgTemplateInfo Table should be issued while the
      value of bldgHVACCfgTemplateInfoStatus is active(1).
      Should an agent receive a SET PDU attempting such a modification
      in this state, an inconsistentValue error should be returned as
      a result of the SET attempt."
  ::= { bldgHVACCfgTemplateInfoEntry 5 }

bldgHVACCfgTemplateInfoStorType OBJECT-TYPE

  SYNTAX            StorageType
  MAX-ACCESS        read-create
  STATUS            current
  DESCRIPTION
      "The persistence of this row of the table in system storage,
       as it pertains to permanence across system resets.  A columnar
      instance of this object with value 'permanent' need not allow
      write-access to any of the columnar object instances in the
      containing row."
  ::= { bldgHVACCfgTemplateInfoEntry 6  }

– – HVAC Configuration Template Table – bldgHVACCfgTemplateTable OBJECT-TYPE

  SYNTAX      SEQUENCE OF BldgHVACCfgTemplateEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "This table contains the templates, which
      can be used to set defaults that will
      be applied to specific offices.  The application
      of those values is accomplished by having a row
      instance of the bldgHVACTable reference a row of
      this table (by the value of the former's
      bldgHVACCfgTemplate columnar instance).  Identifying
      information concerning a row instance of this table
      can be found in the columnar data of the row instance
      of the bldgHVACCfgTemplateInfoTable entry referenced
      by the bldgHVACCfgTemplateInfo columnar object of
      this table."
  ::= { bldgHVACObjects 3 }

MacFaden, et al. Informational [Page 69] RFC 3512 Configuring Networks and Devices with SNMP April 2003

bldgHVACCfgTemplateEntry OBJECT-TYPE

  SYNTAX       BldgHVACCfgTemplateEntry
  MAX-ACCESS   not-accessible
  STATUS       current
  DESCRIPTION
      "Each row represents a single set of template parameters
      that can be applied to selected instances - in this case
      offices.  These policies will be turned on and off by the
      policy module through its scheduling facilities.
      A given row instance can be created or
      deleted by set operations upon its
      bldgHVACCfgTemplateStatus columnar object instance."
  INDEX { bldgHVACCfgTemplateIndex }
  ::= { bldgHVACCfgTemplateTable 1 }

BldgHVACCfgTemplateEntry ::= SEQUENCE {

      bldgHVACCfgTemplateIndex           Unsigned32,
      bldgHVACCfgTemplateDesiredTemp     Gauge32,
      bldgHVACCfgTemplateCoolOrHeat      BldgHvacOperation,
      bldgHVACCfgTemplateInfo            Unsigned32,
      bldgHVACCfgTemplateOwner           SnmpAdminString,
      bldgHVACCfgTemplateStorage         StorageType,
      bldgHVACCfgTemplateStatus          RowStatus

}

bldgHVACCfgTemplateIndex OBJECT-TYPE

  SYNTAX      Unsigned32 (1..2147483647)
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
      "A unique value for each defined template in this
      table.  This value can be referenced as a row index
      by any MIB module that needs access to this information.
      The bldgHVACCfgTemplate will point to entries in this
      table."
  ::= { bldgHVACCfgTemplateEntry 1 }

bldgHVACCfgTemplateDesiredTemp OBJECT-TYPE

  SYNTAX            Gauge32
  UNITS             "degrees in celsius"
  MAX-ACCESS        read-create
  STATUS            current
  DESCRIPTION
      "This is the desired temperature setting.  It might be
      changed at different times of the day or based on
      seasonal conditions.  It is permitted to change this value
      by first moving the row to an inactive state, making the

MacFaden, et al. Informational [Page 70] RFC 3512 Configuring Networks and Devices with SNMP April 2003

      change and then reactivating the row."
  ::= { bldgHVACCfgTemplateEntry 2 }

bldgHVACCfgTemplateCoolOrHeat OBJECT-TYPE

  SYNTAX             BldgHvacOperation
  MAX-ACCESS         read-create
  STATUS             current
  DESCRIPTION
      "This controls the heating and cooling mechanism and is
      set-able by building maintenance.  It is permitted to
      change this value by first moving the row to an inactive
      state, making the change and then reactivating the row."
  ::= { bldgHVACCfgTemplateEntry 3 }

bldgHVACCfgTemplateInfo OBJECT-TYPE

  SYNTAX             Unsigned32
  MAX-ACCESS         read-create
  STATUS             current
  DESCRIPTION
      "This object points to a row in the
      bldgHVACCfgTemplateInfoTable.  This controls the
      heating and cooling mechanism and is set-able by
      building maintenance.  It is permissible to change
      this value by first moving the row to an inactive
      state, making the change and then reactivating
      the row.  A value of zero means that this entry
      is not associated with a named template found
      in the bldgHVACCfgTemplateInfoTable."
  ::= { bldgHVACCfgTemplateEntry 4 }

bldgHVACCfgTemplateOwner OBJECT-TYPE

  SYNTAX            SnmpAdminString
  MAX-ACCESS        read-create
  STATUS            current
  DESCRIPTION
      "The identity of the administrative entity
      that created this row of the table."
  ::= { bldgHVACCfgTemplateEntry 5 }

bldgHVACCfgTemplateStorage OBJECT-TYPE

  SYNTAX            StorageType
  MAX-ACCESS        read-create
  STATUS            current
  DESCRIPTION
      "The persistence of this row of the table across
       system resets.  A columnar instance of this object with
       value 'permanent' need not allow write-access to any
       of the columnar object instances in the containing row."

MacFaden, et al. Informational [Page 71] RFC 3512 Configuring Networks and Devices with SNMP April 2003

  ::= { bldgHVACCfgTemplateEntry 6 }

bldgHVACCfgTemplateStatus OBJECT-TYPE

  SYNTAX            RowStatus
  MAX-ACCESS        read-create
  STATUS            current
  DESCRIPTION
      "The activation status of this row of the table.
      No attempt to modify a row columnar object instance value in
      the bldgHVACCfgTemplateTable should be issued while the
      value of bldgHVACCfgTemplateStatus is active(1).
      Should an agent receive a SET PDU attempting such a modification
      in this state, an inconsistentValue error should be returned as
      a result of the SET attempt."
  ::= { bldgHVACCfgTemplateEntry 7 }

– – Conformance Information –

bldgCompliances OBJECT IDENTIFIER ::= { bldgConformance 1 } bldgGroups OBJECT IDENTIFIER ::= { bldgConformance 2 }

– Compliance Statements

bldgCompliance MODULE-COMPLIANCE

  STATUS current
  DESCRIPTION
      "The requirements for conformance to the BLDG-HVAC-MIB.  The
       bldgHVACObjects group must be implemented to conform to the
       BLDG-HVAC-MIB."
  MODULE -- this module
  GROUP bldgHVACObjectsGroup
  DESCRIPTION
      "The bldgHVACObjects is mandatory for all systems that
      support HVAC systems."
  ::= { bldgCompliances 1 }

bldgHVACObjectsGroup OBJECT-GROUP

  OBJECTS {
      bldgHVACCfgTemplate,
      bldgHVACFanSpeed, bldgHVACCurrentTemp,
      bldgHVACCoolOrHeatMins, bldgHVACDiscontinuityTime,
      bldgHVACOwner, bldgHVACStatus,
      bldgHVACStorageType, bldgHVACCfgTemplateInfoID,
      bldgHVACCfgTemplateInfoDescr, bldgHVACCfgTemplateInfoOwner,

MacFaden, et al. Informational [Page 72] RFC 3512 Configuring Networks and Devices with SNMP April 2003

      bldgHVACCfgTemplateInfoStatus,
      bldgHVACCfgTemplateInfoStorType,
      bldgHVACCfgTemplateDesiredTemp,
      bldgHVACCfgTemplateCoolOrHeat,
      bldgHVACCfgTemplateInfo,
      bldgHVACCfgTemplateOwner,bldgHVACCfgTemplateStorage,
      bldgHVACCfgTemplateStatus
  }
  STATUS current
  DESCRIPTION
      "The bldgHVACObjects Group."
  ::= { bldgGroups 1 }

END

8.2. Notes on MIB Module with Template-based Data

 The primary purpose of the example "HVAC" MIB module is to show how
 to construct a single module that includes configuration, template,
 counter and state information in a single module.  If this were a
 'real' module we would also have included definitions for
 notifications for the configuration change operations as previously
 described.  We also would have included notifications for faults and
 other counter threshold events.
 Implementation and Instance Extensions:
 Just as with networking technologies, vendors may wish to add
 extensions that can distinguish their products from the competition.
 If an HVAC vendor also wanted to support humidity control, they could
 add that facility to their equipment and use AUGMENTS for the
 bldgHVACTemplateTable with two objects, one that indicates the
 desired humidity and the other, the actual.  The
 bldgHVACTemplateTable could also be extended using this same approach
 so that HVAC policies could easily be extended to support this
 vendor.

MacFaden, et al. Informational [Page 73] RFC 3512 Configuring Networks and Devices with SNMP April 2003

8.3. Examples of Usage of the MIB

 The following two examples use two templates to configure the
 temperature in executive offices and in conference rooms.  The
 "conference rooms" template is applied to all conference rooms (which
 happen to be office 104 on each floor), and the "executive offices"
 template is applied to executive offices.
 If offices 24, 25, and 26 on the third floor are executive offices,
 the values in the bldgHVACTable might be:
 bldgHVACCfgTemplate.3.24 = 2
 bldgHVACFanSpeed.3.24 = 2989
 bldgHVACCurrentTemp.3.24 = 24
 bldgHVACCoolOrHeatMins.3.24 = 123
 bldgHVACDiscontinuityTime.3.24 = sysUpTime + 12h + 21m
 bldgHVACOwner.3.24 = "policy engine"
 bldgHVACStorageType.3.24 = nonVolatile(3)
 bldgHVACStatus.3.24 = active(1)
 bldgHVACCfgTemplate.3.25 = 2
 bldgHVACFanSpeed.3.25 = 0
 bldgHVACCurrentTemp.3.25 = 22
 bldgHVACCoolOrHeatMins.3.25 = 298
 bldgHVACDiscontinuityTime.3.25 = sysUpTime + 4h + 2m
 bldgHVACOwner.3.25 = "policy engine"
 bldgHVACStorageType.3.25 = nonVolatile(3)
 bldgHVACStatus.3.25 = active(1)
 bldgHVACCfgTemplate.3.26 = 2
 bldgHVACFanSpeed.3.26 = 0
 bldgHVACCurrentTemp.3.26 = 22
 bldgHVACCoolOrHeatMins.3.26 = 982
 bldgHVACOwner.3.26 = "policy engine"
 bldgHVACStorageType.3.26 = nonVolatile(3)
 bldgHVACStatus.3.26 = active(1)
 The second entry in the bldgHVACCfgTemplateTable, to which all of the
 above point, might have the following configuration:
 bldgHVACCfgTemplateDesiredTemp.2 = 22
 bldgHVACCfgTemplateCoolOrHeat.2 = cool(2)
 bldgHVACCfgTemplateInfo.2 = 2
 bldgHVACCfgTemplateOwner.2 = "Senior Executive assistant"
 bldgHVACCfgTemplateStorage.2 = nonVolatile(3)
 bldgHVACCfgTemplateStatus.2 = active(1)

MacFaden, et al. Informational [Page 74] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 and the associated template information ("executive offices") might
 be:
 bldgHVACCfgTemplateInfoID.2 = "executive offices"
 bldgHVACCfgTemplateInfoDescr.2 = "Controls temperature for executive
                                   offices"
 bldgHVACCfgTemplateInfoOwner.2 = "Senior Executive assistant"
 bldgHVACCfgTemplateInfoStorType.2 = nonVolatile(3)
 bldgHVACCfgTemplateInfoStatus.2 = active(1)
 The policy engine can now associate instances of executive offices
 with the template called "executive offices" and apply the values in
 the second entry of the bldgHVACCfgTemplateTable to each of the
 instances of the executive offices.  This will then attempt to set
 the temperature in executive offices to 22 degrees celsius.
 It is also possible that there may be an office configured for a
 particular temperature, but without using a template.  For example,
 office 28 on the third floor might look like this:
 bldgHVACCfgTemplate.3.28 = 3
 bldgHVACFanSpeed.3.28 = 50
 bldgHVACCurrentTemp.3.28 = 26
 bldgHVACCoolOrHeatMins.3.28 = 0
 bldgHVACDiscontinuityTime.3.28 = 0
 bldgHVACOwner.3.28 = "Executive with poor circulation"
 bldgHVACStorageType.3.28 = nonVolatile(3)
 bldgHVACStatus.3.28 = active(1)
 The entry in the bldgHVACCfgTemplateTable (to which
 bldgHVACCfgTemplate.3.28 points) might instead look like:
 bldgHVACCfgTemplateDesiredTemp.3 = 28
 bldgHVACCfgTemplateCoolOrHeat.3 = cool(2)
 bldgHVACCfgTemplateInfo.3 = 0.0
 bldgHVACCfgTemplateOwner.3 = "Executive with poor circulation"
 bldgHVACCfgTemplateStorage.3 = nonVolatile(3)
 bldgHVACCfgTemplateStatus.3 = active(1)
 Note that this entry does not point to a template.
 If the executive's circulation improves so that the temperature
 should be aligned with other executive offices, this is accomplished
 by changing the value of bldgHVACCfgTemplate.3.28 from
 bldgHVACCfgTemplateInfoID.3 to bldgHVACCfgTemplateInfoID.2 (shown
 above).

MacFaden, et al. Informational [Page 75] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 Finally, there might be offices for which there is no configured
 temperature but management applications can read the current
 temperature, fan speed, and cooling or heating minutes from the
 bldgHVACTable.  In that case, the value of bldgHVACCfgTemplate will
 be a zero index ("null"), as will the value of bldgHVACOwner.
 bldgHVACCfgTemplate.4.2 = 0
 bldgHVACFanSpeed.3.28 = 50
 bldgHVACCurrentTemp.3.28 = 26
 bldgHVACCoolOrHeatMins.3.28 = 0
 bldgHVACDiscontinuityTime.3.28 = 0
 bldgHVACOwner.3.28 = ""
 bldgHVACStorageType.3.28 = nonVolatile(3)
 bldgHVACStatus.3.28 = active(1)
 As a second example, the conference rooms on several floors are
 configured using the "conference rooms" template.  When the values in
 the bldgHVACTable pertaining to conference rooms are read, it might
 look like:
 bldgHVACCfgTemplate.12.104 = bldgHVACCfgTemplateDesiredTemp.1
 bldgHVACFanSpeed.12.104 = 1423
 bldgHVACCurrentTemp.12.104 = 21
 bldgHVACCoolOrHeatMins.12.104 = 2193
 bldgHVACDiscontinuityTime.12.104 = sysUpTime + 36h + 15m
 bldgHVACOwner.12.104 =  = "Bob the Conference Guy"
 bldgHVACStorageType.12.104 = nonVolatile(3)
 bldgHVACStatus.12.104 = active(1)
 bldgHVACCfgTemplate.14.104 = bldgHVACCfgTemplateDesiredTemp.1
 bldgHVACFanSpeed.14.104 = 1203
 bldgHVACCurrentTemp.14.104 = 20
 bldgHVACCoolOrHeatMins.14.104 = 293
 bldgHVACDiscontinuityTime.14.104 = sysUpTime + 5h + 54m
 bldgHVACOwner.14.104 =  = "Bob the Conference Guy"
 bldgHVACStorageType.14.104 = nonVolatile(3)
 bldgHVACStatus.14.104 = active(1)
 bldgHVACCfgTemplate.15.104 = bldgHVACCfgTemplateDesiredTemp.1
 bldgHVACFanSpeed.15.104 = 12
 bldgHVACCurrentTemp.15.104 = 19
 bldgHVACCoolOrHeatMins.15.104 = 1123
 bldgHVACDiscontinuityTime.15.103 = sysUpTime + 2d + 2h + 7m
 bldgHVACOwner.15.104 =  = "Bob the Conference Guy"
 bldgHVACStorageType.15.104 = nonVolatile(3)
 bldgHVACStatus.15.104 = active(1)

MacFaden, et al. Informational [Page 76] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 The desired temperature and whether to heat or cool is configured in
 the first entry of the bldgHVACCfgTemplateTable, which tries to set
 the temperature to 19 degrees celsius in conference rooms:
 bldgHVACCfgTemplateDesiredTemp.1 = 19
 bldgHVACCfgTemplateCoolOrHeat.1 = cool(2)
 bldgHVACCfgTemplateInfo.1 = bldgHVACCfgTemplateInfoID.1
 bldgHVACCfgTemplateOwner.1 = "Bob the Conference Guy"
 bldgHVACCfgTemplateStorage.1 = nonVolatile(3)
 bldgHVACCfgTemplateStatus.1 = active(1)
 The associated template information would then have:
 bldgHVACCfgTemplateInfoID.1 = "conference rooms"
 bldgHVACCfgTemplateInfoDescr.1 = "Controls temperature in conference
 rooms" bldgHVACCfgTemplateInfoOwner.1 = "Bob the Conference Guy"
 bldgHVACCfgTemplateInfoStorType.1 = nonVolatile(3)
 bldgHVACCfgTemplateInfoStatus.1 = active(1)
 The policy system can then apply this template (cool to 19 degrees
 Celsius) to its notion of all of the conference rooms in the
 building.

9. Security Considerations

 This document discusses practices and methods for using the SNMP for
 management and distribution of configuration information for network
 elements.  Any effective use of the SNMP in this application must
 concern itself with issues of authentication of the management
 entities initiating configuration change and management, in addition
 to the integrity of the configuration data itself.  Other more subtle
 considerations also exist.
 To that end, the section of this document entitled "Deployment and
 Security Issues" covers these security considerations to the extent
 they affect the current practices described throughout this document.
 In particular, in the subsection entitled "Secure Agent
 Considerations", there is a recommendation for the usage of Version 3
 of the SNMP, and its essential presumption as a foundation for other
 practices described throughout.  With the exception of a small number
 of cases where a mention is made to the contrary to illustrate
 techniques for coexistence with application entities dependent upon
 earlier versions of the SNMP, that recommendation of usage of Version
 3 of the SNMP is reiterated here.

MacFaden, et al. Informational [Page 77] RFC 3512 Configuring Networks and Devices with SNMP April 2003

10. Acknowledgments

 This document was produced by the SNMPCONF Working Group. In
 particular, the editors wish to thank:
    Christopher Anderson
    Andy Bierman
    Greg Bruell
    Dr Jeffrey Case
    Chris Elliott
    Joel Halpern
    Pablo Halpern
    Wes Hardaker
    David Harrington
    Harrie Hazewinkel
    Thippanna Hongal
    Bob Moore
    David T. Perkins
    Randy Presuhn
    Dan Romascanu
    Shawn Routhier
    Steve Waldbusser
    Bert Wijnen

11. Normative References

 [1]  Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for
      Describing Simple Network Management Protocol (SNMP) Management
      Frameworks", STD 62, RFC 3411, December 2002.
 [2]  McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Structure of
      Management Information Version 2 (SMIv2)", STD 58, RFC 2578,
      April 1999.
 [3]  McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Textual
      Conventions for SMIv2", STD 58, RFC 2579, April 1999.
 [4]  McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Conformance
      Statements for SMIv2", STD 58, RFC 2580, April 1999.
 [5]  Presuhn, R. (Ed.), "Transport Mappings for the Simple Network
      Management Protocol (SNMPv2)", STD 62, RFC 3417, December 2002.
 [6]  Case, J., Harrington D., Presuhn R. and B. Wijnen, "Message
      Processing and Dispatching for the Simple Network Management
      Protocol (SNMP)", STD 62, RFC 3412, December 2002.

MacFaden, et al. Informational [Page 78] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 [7]  Blumenthal, U. and B. Wijnen, "User-based Security Model (USM)
      for version 3 of the Simple Network Management Protocol
      (SNMPv3)", STD 62, RFC 3414, December 2002.
 [8]  Presuhn, R. (Ed.), "Version 2 of the Protocol Operations for the
      Simple Network Management Protocol (SNMP)", STD 62, RFC 3416,
      December 2002.
 [9]  Levi, D., Meyer, P., and B. Stewart, "Simple Network Management
      Protocol Applications", STD 62, RFC 3413, December 2002.
 [10] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access
      Control Model (VACM) for the Simple Network Management Protocol
      (SNMP)", STD 62, RFC 3415, December 2002.
 [11] Presuhn, R. (Ed.), "Management Information Base for the Simple
      Network Management Protocol (SNMPv2)", STD 62, RFC 3418,
      December 2002.
 [12] Case, J., Mundy, R., Partain, D. and B. Stewart, "Introduction
      and Applicability Statements for Internet-Standard Management
      Framework", RFC 3410, December 2002.
 [13] Daniele, M., Haberman, B., Routhier, S. and J. Schoenwaelder,
      "Textual Conventions for Internet Network Addresses", RFC 3291,
      May 2002.
 [14] McCloghrie, K. (Ed.), "SNMPv2 Management Information Base for
      the Internet Protocol using SMIv2", RFC 2011, November 1996.

12. Informative References

 [15] Rose, M. and K. McCloghrie, "Structure and Identification of
      Management Information for TCP/IP-based Internets", STD 16, RFC
      1155, May 1990.
 [16] Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16,
      RFC 1212, March 1991.
 [17] Rose, M., "A Convention for Defining Traps for use with the
      SNMP", RFC 1215, March 1991.
 [18] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple
      Network Management Protocol", STD 15, RFC 1157, May 1990.
 [19] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
      "Introduction to Community-based SNMPv2", RFC 1901, January
      1996.

MacFaden, et al. Informational [Page 79] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 [20] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB",
      RFC 2863, June 2000.
 [21] Brown, C. and F. Baker, "Management Information Base for Frame
      Relay DTEs Using SMIv2", RFC 2115, September 1997.
 [22] Baker, F. (Ed.), "Requirements for IP Version 4 Routers", RFC
      1812, June 1995.
 [23] Hawkinson, J. and T. Bates, "Guidelines for Creation, Selection,
      and Registration of an Autonomous System (AS)", BCP 6, RFC 1930,
      March 1996.
 [24] Decker, E., Langille, P., Rijsinghani, A. and K. McCloghrie,
      "Definitions of Managed Objects for Bridges", RFC 1493, July
      1993.
 [25] Levi, D. and J. Schoenwaelder "Definitions of Managed Objects
      for Scheduling Management Operations", RFC 3231, January 2002.
 [26] Bell, E., Smith, A., Langille, P., Rijsinghani, A. and K.
      McCloghrie, "Definitions of Managed Objects for Bridges with
      Traffic Classes, Multicast Filtering and Virtual LAN
      Extensions", RFC 2674, August 1999.
 [27] Baker, F., "IP Forwarding Table MIB", RFC 2096, January 1997.
 [28] St. Johns, M. (Ed.), "Radio Frequency (RF) Interface Management
      Information Base for MCNS/DOCSIS compliant RF interfaces", RFC
      2670, August 1999.
 [29] Baker, F. and R. Coltun, "OSPF Version 2 Management Information
      Base", RFC 1850, November 1995.
 [30] Blake, S., Black, D., Carlson M., Davies, E., Wang, Z. and W.
      Weiss, "An Architecture for Differentiated Services ", RFC 2475,
      December 1998.
 [31] Willis, S., Burruss, J. and J. Chu (Ed.), "Definitions of
      Managed Objects for the Fourth Version of the Border Gateway
      Protocol (BGP-4) using SMIv2", RFC 1657, July 1994.
 [32] Waldbusser, S., "Remote Network Monitoring Management
      Information Base", RFC 2819, May 2000.
 [33] McCloghrie, K. and G. Hanson, "The Inverted Stack Table
      Extension to the Interfaces Group MIB", RFC 2864, June 2000.

MacFaden, et al. Informational [Page 80] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 [34] McCloghrie, K. and A. Bierman, "Entity MIB (Version 2)", RFC
      2737, December 1999.
 [35] ITU-T,, Recommendation M.3010., PRINCIPLES FOR A
      TELECOMMUNICATIONS MANAGEMENT NETWORK.  February, 2000.
 [36] Waldbusser, S., Saperia, J., and Hongal, T., "Policy Based
      Management MIB", Work-in-progress.
 [37] Heintz, L., "SNMP Row Operations Extensions", Work-in-progress.
 [38] Zeltserman, D., "A Practical Guide to Snmpv3 and Network
      Management", Prentice Hall, 1999.
 [39] Noto, M., Spiegel, E. and K. Tesink, "Definitions of Textual
      Conventions and OBJECT-IDENTITIES for ATM Management", RFC 2514,
      February 1999.
 [40] Kassaveri, R., Editor, "Distributed Management Expression MIB",
      RFC 2982, October 2000.
 [41] St. Johns, M., "DOCSIS Cable Device MIB Cable Device Management
      Information Base for DOCSIS compliant Cable Modems and Cable
      Modem Termination Systems", RFC 2669, August 1999.
 [42] Westerinen, A., Schnizlein, J., Strassner, J., Scherling, M.,
      Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry, J. and S.
      Waldbusser, "Terminology for Policy-Based Management", RFC 3198,
      November 2001.
 [43] http://wwww.cisco.com/univercd/cc/td/product/software/ios113ed/
      11ed_cr/secur_c/scprt/scacls.pdf.
 [44] Waldbusser, S., "Remote Network Monitoring Management
      Information Base Version 2 using SMIv2", RFC 2021, January 1997.

13. 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

MacFaden, et al. Informational [Page 81] RFC 3512 Configuring Networks and Devices with SNMP April 2003

 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.

14. Editors' Addresses

 Michael R. MacFaden
 Riverstone Networks, Inc
 5200 Great America Parkway
 Santa Clara, CA 95054
 EMail: mrm@riverstonenet.com
 David Partain
 Ericsson AB
 P.O. Box 1248
 SE-581 12  Linkoping
 Sweden
 EMail: David.Partain@ericsson.com
 Jon Saperia
 JDS Consulting
 174 Chapman Street
 Watertown, MA 02472
 EMail: saperia@jdscons.com
 Wayne F. Tackabury
 Gold Wire Technology
 411 Waverley Oaks Rd.
 Waltham, MA  02452
 EMail: wayne@goldwiretech.com

MacFaden, et al. Informational [Page 82] RFC 3512 Configuring Networks and Devices with SNMP April 2003

15. Full Copyright Statement

 Copyright (C) The Internet Society (2003).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

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

MacFaden, et al. Informational [Page 83]

/data/webs/external/dokuwiki/data/pages/rfc/rfc3512.txt · Last modified: 2003/04/02 23:14 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki