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rfc:rfc2982

Network Working Group R. Kavasseri Request for Comments: 2982 (Editor of this version) Category: Standards Track B. Stewart

                                          (Author of previous version)
                                                   Cisco Systems, Inc.
                                                          October 2000
               Distributed Management Expression MIB

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

 This memo defines a portion of the Management Information Base (MIB)
 for use with network management protocols in the Internet community.
 In particular, it describes managed objects used for managing
 expressions of MIB objects.  The results of these expressions become
 MIB objects usable like any other MIB object, such as for the test
 condition for declaring an event.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119.

Table of Contents

 1 The SNMP Management Framework ...............................    2
 2 Overview ....................................................    3
 2.1 Usage .....................................................    4
 2.2 Persistence ...............................................    4
 2.3 Operation .................................................    4
 2.3.1 Sampling ................................................    5
 2.3.2 Wildcards ...............................................    5
 2.3.3 Evaluation ..............................................    5
 2.3.4 Value Identification ....................................    6
 2.4 Subsets ...................................................    6
 2.4.1 No Wildcards ............................................    6

Kavasseri & Stewart Standards Track [Page 1] RFC 2982 Distributed Management Expression MIB October 2000

 2.4.2 No Deltas ...............................................    7
 2.5 Structure .................................................    7
 2.5.1 Resource ................................................    7
 2.5.2 Definition ..............................................    7
 2.5.3 Value ...................................................    8
 2.6 Examples ..................................................    8
 2.6.1 Wildcarding .............................................    8
 2.6.2 Calculation and Conditional .............................   10
 3 Definitions .................................................   12
 4 Intellectual Property .......................................   36
 5 Acknowledgements ............................................   37
 6 References ..................................................   37
 7 Security Considerations .....................................   38
 8 Author's Address ............................................   40
 9 Editor's Address ............................................   40
 10 Full Copyright Statement ...................................   41

1. The SNMP Management Framework

 The SNMP Management Framework presently consists of five major
 components:
  o   An overall architecture, described in RFC 2571 [RFC2571].
  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 [RFC1155], STD 16, RFC 1212 [RFC1212] and RFC
      1215 [RFC1215].  The second version, called SMIv2, is described
      in STD 58, RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and
      STD 58, RFC 2580 [RFC2580].
  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 [RFC1157].  A second version of
      the SNMP message protocol, which is not an Internet standards
      track protocol, is called SNMPv2c and described in RFC 1901
      [RFC1901] and RFC 1906 [RFC1906].  The third version of the
      message protocol is called SNMPv3 and described in RFC 1906
      [RFC1906], RFC 2572 [RFC2572] and RFC 2574 [RFC2574].
  o   Protocol operations for accessing management information.  The
      first set of protocol operations and associated PDU formats is
      described in STD 15, RFC 1157 [RFC1157].  A second set of
      protocol operations and associated PDU formats is described in
      RFC 1905 [RFC1905].

Kavasseri & Stewart Standards Track [Page 2] RFC 2982 Distributed Management Expression MIB October 2000

  o   A set of fundamental applications described in RFC 2573
      [RFC2573] and the view-based access control mechanism described
      in RFC 2575 [RFC2575].
 A more detailed introduction to the current SNMP Management Framework
 can be found in RFC 2570 [RFC2570].
 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.
 This memo specifies a MIB module that is compliant to the SMIv2.  A
 MIB conforming to the SMIv1 can be produced through the appropriate
 translations.  The resulting translated MIB must be semantically
 equivalent, except where objects or events are omitted because no
 translation is possible (use of Counter64).  Some machine readable
 information in SMIv2 will be converted into textual descriptions in
 SMIv1 during the translation process.  However, this loss of machine
 readable information is not considered to change the semantics of the
 MIB.

2. Overview

 Users of MIBs often desire MIB objects that MIB designers have not
 provided.  Furthermore, such needs vary from one management
 philosophy to another.  Rather than fill more and more MIBs with
 standardized objects, the Expression MIB supports externally defined
 expressions of existing MIB objects.
 In the Expression MIB the results of an evaluated expression are MIB
 objects that may be used like any other MIB objects.  These custom-
 defined objects are thus usable anywhere any other MIB object can be
 used.  For example, they can be used by a management application
 directly or referenced from another MIB, such as the Event MIB
 [MIBEventMIB].  They can even be used by the Expression MIB itself,
 forming expressions of expressions.
 The Expression MIB is instrumentation for a relatively powerful,
 complex, high-level application, considerably different from simple
 instrumentation for a communication driver or a protocol.  The MIB is
 appropriate in a relatively powerful, resource-rich managed system
 and not necessarily in a severely limited environment.
 Nevertheless, due to dependencies from the Event MIB [RFC2981] and
 the need to support as low-end a system as possible, the Expression
 MIB can be somewhat stripped down for lower-power, lower-resource
 implementations, as described in the Subsets section, below.

Kavasseri & Stewart Standards Track [Page 3] RFC 2982 Distributed Management Expression MIB October 2000

 Implementation of the Expression MIB in a managed system led to the
 addition of objects that may not have been necessary in an
 application environment with complete knowledge of compiled MIB
 definitions.  This is appropriate since implementation must be
 possible within typical managed systems with some constraints on
 system resources.

2.1. Usage

 On managed systems that can afford the overhead, the Expression MIB
 is a way to create new, customized MIB objects for monitoring.
 Although these can save some network traffic and overhead on
 management systems, that is often not a good tradeoff for objects
 that are simply to be recorded or displayed.
 An example of a use of the Expression MIB would be to provide custom
 objects for the Event MIB [RFC2981].  A complex expression can
 evaluate to a rate of flow or a boolean and thus be subject to
 testing as an event trigger, resulting in an SNMP notification.
 Without these capabilities such monitoring would be limited to the
 objects in predefined MIBs.  The Expression MIB thus supports
 powerful tools for the network manager faced with the monitoring of
 large, complex systems that can support a significant level of self
 management.

2.2. Persistence

 Although like most MIBs this one has no explicit controls for the
 persistence of the values set in configuring an expression, a robust,
 polite implementation would certainly not force its managing
 applications to reconfigure it whenever it resets.
 Again, as with most MIBs, it is implementation specific how a system
 provides and manages such persistence.  To speculate, one could
 imagine, for example, that persistence depended on the context in
 which the expression was configured, or perhaps system-specific
 characteristics of the expression's owner.  Or perhaps everything in
 a MIB such as this one, which is clearly aimed at persistent
 configuration, is automatically part of a system's other persistent
 configuration.

2.3. Operation

 Most of the operation of the MIB is described or implied in the
 object definitions but a few highlights bear mentioning here.

Kavasseri & Stewart Standards Track [Page 4] RFC 2982 Distributed Management Expression MIB October 2000

2.3.1. Sampling

 The MIB supports three types of object sampling for the MIB objects
 that make up the expression:  absolute, delta, and changed.
 Absolute samples are simply the value of the MIB object at the time
 it is sampled.
 Absolute samples are not sufficient for expressions of counters, as
 counters have meaning only as a delta (difference) from one sample to
 the next.  Thus objects may be sampled as deltas.  Delta sampling
 requires the application to maintain state for the value at the last
 sample, and to do continuous sampling whether or not anyone is
 looking at the results.  It thus creates constant overhead.
 Changed sampling is a simple fallout of delta sampling where rather
 than a difference the result is a boolean indicating whether or not
 the object changed value since the last sample.

2.3.2. Wildcards

 Wildcards allow the application of a single expression to multiple
 instances of the same MIB object.  The definer of the expression
 indicates this choice and provides a partial object identifier, with
 some or all of the instance portion left off.  The application then
 does the equivalent of GetNext to obtain the object values, thus
 discovering the instances.
 All wildcarded objects in an expression must have the same semantics
 for the missing portion of their object identifiers.  Otherwise, any
 successful evaluation of the wildcarded expression would be the
 result of the accidental matching of the wildcarded portion of the
 object identifiers in the expression.  Such an evaluation will likely
 produce results which are not meaningful.
 The expression can be evaluated only for those instances where all
 the objects in the expression are available with the same value for
 the wildcarded portion of the instance.

2.3.3. Evaluation

 There are two important aspects of evaluation that may not be
 obvious:  what objects and when.
 What objects get used in the evaluation depends on the type of
 request and whether or not the expression contains wildcarded
 objects.  If the request was a Get, that locks down the instances to

Kavasseri & Stewart Standards Track [Page 5] RFC 2982 Distributed Management Expression MIB October 2000

 be used.  If the request was a GetNext or GetBulk, the application
 must work its way up to the next full set of objects for the
 expression.
 Evaluation of expressions happens at two possible times, depending on
 the sampling method (delta or absolute) used to evaluate the
 expression.
 If there are no delta or change values in an expression, the
 evaluation occurs on demand, i.e. when a requester attempts to read
 the value of the expression.  In this case all requesters get a
 freshly calculated value.
 For expressions with delta or change values, evaluation goes on
 continuously, every sample period.  In this case requesters get the
 value as of the last sample period.  For any given sample period of a
 given expression, only those instances exist that provided a full set
 of object values.  It may be possible that a delta expression which
 was evaluated successfully for one sample period may not be
 successfully evaluated in the next sample period.  This may, for
 example, be due to missing instances for some or all of the objects
 in the expression.  In such cases, the value from the previous sample
 period (with the successful evaluation) must not be carried forward
 to the next sample period (with the failed evaluation).

2.3.4. Value Identification

 Values resulting from expression evaluation are identified with a
 combination of the object identifier (OID) for the data type from
 expValueTable (such as expValueCounter32Val), the expression owner,
 the expression name, and an OID fragment.
 The OID fragment is not an entire OID beginning with iso.dod.org
 (1.3.6).  Rather it begins with 0.0.  The remainder is either another
 0 when there is no wildcarding or the instance that satisfied the
 wildcard if there is wildcarding.

2.4. Subsets

 To pare down the Expression MIBs complexity and use of resources an
 implementor can leave out various parts.

2.4.1. No Wildcards

 Leaving out wildcarding significantly reduces the complexity of
 retrieving values to evaluate expressions and the processing required
 to do so.  Such an implementation would allow expressions made up of

Kavasseri & Stewart Standards Track [Page 6] RFC 2982 Distributed Management Expression MIB October 2000

 individual MIB objects but would not be suitable for expressions
 applied across large tables as each instance in the table would
 require a separate expression definition.
 Furthermore it would not be suitable for tables with arbitrary,
 dynamic instances, as expressions definitions could not predict what
 instance values to use.
 An implementation without wildcards might be useful for a self-
 managing system with small tables or few dynamic instances, or one
 that can do calculations only for a few key objects.

2.4.2. No Deltas

 Leaving out delta processing significantly reduces state that must be
 kept and the burden of ongoing processing even when no one is looking
 at the results.  Unfortunately it also makes expressions on counters
 unusable, as counters have meaning only as deltas.
 An implementation without deltas might be useful for a severely
 limited, self-managing system that has no need for expressions or
 events on counters.  Although conceivable, such systems would be
 rare.

2.5. Structure

 The MIB has the following sections:
     o   Resource -- management of the MIB's use of system resources.
     o   Definition -- definition of expressions.
     o   Value -- values of evaluated expressions.

2.5.1. Resource

 The resource section has objects to manage resource usage by
 wildcarded delta expressions, a potential major consumer of CPU and
 memory.

2.5.2. Definition

 The definition section contains the tables that define expressions.
 The expression table, indexed by expression owner and expression
 name, contains those parameters that apply to the entire expression,
 such as the expression itself, the data type of the result, and the
 sampling interval if it contains delta or change values.

Kavasseri & Stewart Standards Track [Page 7] RFC 2982 Distributed Management Expression MIB October 2000

 The object table, indexed by expression owner, expression name and
 object index within each expression, contains the parameters that
 apply to the individual objects that go into the expression,
 including the object identifier, sample type, discontinuity
 indicator, and such.

2.5.3. Value

 The value section contains the values of evaluated expressions.
 The value table, indexed by expression owner, expression name and
 instance fragment contains a "discriminated union" of evaluated
 expression results.  For a given expression only one of the columns
 is instantiated, depending on the result data type for the
 expression.  The instance fragment is a constant or the final section
 of the object identifier that filled in a wildcard.

2.6. Examples

 The examples refer to tables and objects defined below in the MIB
 itself.  They may well make more sense after reading those
 definitions.

2.6.1. Wildcarding

 An expression may use wildcarded MIB objects that result in multiple
 values for the expression.  To specify a wildcarded MIB object a
 management application leaves off part or all of the instance portion
 of the object identifier, and sets expObjectWildcard to true(1) for
 that object.  For our example we'll use a counter of total blessings
 from a table of people.  Another table, indexed by town and person
 has blessings just from that town.
 So the index clauses are:
     personEntry OBJECT-TYPE
     ...
     INDEX { personIndex }
 And:
     townPersonEntry OBJECT-TYPE
     ...
     INDEX { townIndex, personIndex }

Kavasseri & Stewart Standards Track [Page 8] RFC 2982 Distributed Management Expression MIB October 2000

 In our friendly application we may have entered our expression as:
     100 * townPersonBlessings.976.* / personBlessings.*
 What goes in expExpression is:
     100*$1/$2
 For example purposes we'll use some slightly far-fetched OIDs.  The
 People MIB is 1.3.6.1.99.7 and the Town MIB is 1.3.6.1.99.11, so for
 our two counters the OIDs are:
     personBlessings      1.3.6.1.99.7.1.3.1.4
     townPersonBlessings       1.3.6.1.99.11.1.2.1.9
 The rule for wildcards is that all the wildcarded parts have to match
 exactly.  In this case that means we have to hardwire the town and
 only the personIndex can be wildcarded.  So our values for
 expObjectID are:
     1.3.6.1.99.7.1.3.1.4
     1.3.6.1.99.11.1.2.1.9.976
 We're hardwired to townIndex 976 and personIndex is allowed to vary.
 The value of expExpressionPrefix can be either of those two counter
 OIDs (including the instance fragment in the second case), since
 either of them takes you to a MIB definition where you can look at
 the INDEX clause and figure out what's been left off.  What's been
 left off doesn't have to work out to be the same object, but it does
 have to work out to be the same values (semantics) for the result to
 make sense.  Note that the managed system can not typically check
 such semantics and if given nonsense will return nonsense.
 If we have people numbered 6, 19, and 42 in town number 976, the
 successive values of expValueInstance will be:
     0.0.6
     0.0.19
     0.0.42
 So there will be three values in expValueTable, with those OIDs as
 the expValueInstance part of their indexing.

Kavasseri & Stewart Standards Track [Page 9] RFC 2982 Distributed Management Expression MIB October 2000

2.6.2. Calculation and Conditional

 The following formula for line utilization of a half-duplex link is
 adapted from [PracPersp].
  utilization = (ifInOctets + ifOutOctets) * 800 / seconds / ifSpeed
 The expression results in the percentage line utilization per second.
 The total octets are multiplied by 8 to get bits and 100 to scale up
 the percentage as an integer.
 The following Expression MIB object values implement this as an
 expression for all ifIndexes that directly represent actual hardware.
 Since the octet counters are Counter32 values, they must be delta
 sampled to be meaningful.  The sample period is 6 seconds but for
 accuracy and independence is calculated as a delta of sysUpTime.
 The expObjectTable entry for ifInOctets has an expObjectConditional
 that checks for being a hardware interface.  Only one object in the
 expression needs that check associated, since it applies to the whole
 expression.  Since ifConnectorPresent is a TruthValue with values of
 1 or 2 rather than 0 and non-zero, it must also be in an expression
 rather than used directly for the conditional.
 The interface-specific discontinuity indicator is supplied only for
 ifInOctets since invalidating that sample will invalidate an attempt
 at evaluation, effectively invalidating ifOutOctets as well
 (correctly, because it has the same indicator).
 For notational clarity, in the rest of this document, a string in
 quotes as part of the object instance indicates the value that would
 actually be one subidentifier per byte.  The objects all belong to
 owner "me".
 Also for clarity OIDs are expressed as the object descriptor and
 instance.  In fact they must be supplied numerically, with all
 subidentifiers in place before the part for the particular object and
 instance.
 What the user would set in expExpressionTable:
 expExpression.2."me".4."hard"      = "$1==1"
 expExpressionValueType.2."me".4."hard"  = unsigned32
 expExpressionRowStatus.2."me"4."hard"   = 'active'

Kavasseri & Stewart Standards Track [Page 10] RFC 2982 Distributed Management Expression MIB October 2000

 expExpression.2."me".4."util"      = "($1+$2)*800/$4/$3"
 expExpressionValueType.2."me".4."util"  = integer32
 expExpressionDeltaInterval.2."me".4."util"   = 6
 expExpressionRowStatus.2."me"4."util"   = 'active'
 What the user would set in expObjectTable:
 expObjectID.2."me".4."hard".1      = ifConnectorPresent
 expObjectWildcard.2."me".4."hard".1     = 'true'
 expObjectSampleType.2."me".4."hard".1   = 'absoluteValue'
 expObjectRowStatus.2."me".4."hard".1    = 'active'
 expObjectID.2."me".4."util".1      = ifInOctets
 expObjectWildcard.2."me".4."util".1     = 'true'
 expObjectSampleType.2."me".4."util".1   = 'deltaValue'
 expObjectConditional.2."me".4."util".1  =
 expValueUnsigned32Val.4."hard".0.0
 expObjectConditionalWildcard.2."me".4."util".1    = 'true'
 expObjectDiscontinuityID.2."me".4."util".1   =
 ifCounterDiscontinuityTime
 expObjectDiscontinuityIDWildcard.2."me".4."util".1     = 'true'
 expObjectRowStatus.2."me".4."util".1    = 'active'
 expObjectID.2."me".4."util".2      = ifOutOctets
 expObjectWildcard.2."me".4."util".2     = 'true'
 expObjectSampleType.2."me".4."util".2   = 'deltaValue'
 expObjectRowStatus.2."me".4."util".2    = 'active'
 expObjectID.2."me".4."util".3      = ifSpeed
 expObjectWildcard.2."me".4."util".3     = 'true'
 expObjectSampleType.2."me".4."util".3   = 'absoluteValue'
 expObjectRowStatus.2."me".4."util".3    = 'active'
 expObjectID.2."me".4."util".4      = sysUpTime.0
 expObjectWildcard.2."me".4."util".4     = 'false'
 expObjectSampleType.2."me".4."util".4   = 'deltaValue'
 expObjectRowStatus.2."me".4."util".4    = 'active'
 These settings will result in populating one column of expValueTable:
 expValueInteger32Val.2."me".4."util".0.0.?
 The subidentifier represented by "?" above represents one
 subidentifier that takes on a value of ifIndex and identifies a row
 for each ifIndex value where ifConnectorPresent is 'true' and the
 interface was present for two samples to provide a delta.

Kavasseri & Stewart Standards Track [Page 11] RFC 2982 Distributed Management Expression MIB October 2000

 This value could in turn be used as an event threshold [RFC2981] to
 watch for overutilization of all hardware network connections.

3. Definitions

DISMAN-EXPRESSION-MIB DEFINITIONS ::= BEGIN

IMPORTS

  MODULE-IDENTITY, OBJECT-TYPE,
  Integer32, Gauge32, Unsigned32,
  Counter32, Counter64, IpAddress,
  TimeTicks, mib-2, zeroDotZero  FROM SNMPv2-SMI
  RowStatus, TruthValue, TimeStamp    FROM SNMPv2-TC
  sysUpTime                 FROM SNMPv2-MIB
  SnmpAdminString           FROM SNMP-FRAMEWORK-MIB
  MODULE-COMPLIANCE, OBJECT-GROUP     FROM SNMPv2-CONF;

dismanExpressionMIB MODULE-IDENTITY

  LAST-UPDATED "200010160000Z" -- 16 October 2000
  ORGANIZATION "IETF Distributed Management Working Group"
  CONTACT-INFO "Ramanathan Kavasseri
                Cisco Systems, Inc.
                170 West Tasman Drive,
                San Jose CA 95134-1706.
                Phone: +1 408 527 2446
                Email: ramk@cisco.com"
  DESCRIPTION
   "The MIB module for defining expressions of MIB objects for
   management purposes."

– Revision History

     REVISION     "200010160000Z" -- 16 October 2000
     DESCRIPTION  "This is the initial version of this MIB.
                  Published as RFC 2982"
  ::= { mib-2 90 }

dismanExpressionMIBObjects OBJECT IDENTIFIER ::=

                                          { dismanExpressionMIB 1 }

expResource OBJECT IDENTIFIER ::= { dismanExpressionMIBObjects 1 } expDefine OBJECT IDENTIFIER ::= { dismanExpressionMIBObjects 2 } expValue OBJECT IDENTIFIER ::= { dismanExpressionMIBObjects 3 }

– – Resource Control

Kavasseri & Stewart Standards Track [Page 12] RFC 2982 Distributed Management Expression MIB October 2000

expResourceDeltaMinimum OBJECT-TYPE

  SYNTAX      Integer32 (-1 | 1..600)
  UNITS       "seconds"
  MAX-ACCESS  read-write
  STATUS      current
  DESCRIPTION
   "The minimum expExpressionDeltaInterval this system will
   accept.  A system may use the larger values of this minimum to
   lessen the impact of constantly computing deltas.  For larger
   delta sampling intervals the system samples less often and
   suffers less overhead.  This object provides a way to enforce
   such lower overhead for all expressions created after it is
   set.
   The value -1 indicates that expResourceDeltaMinimum is
   irrelevant as the system will not accept 'deltaValue' as a
   value for expObjectSampleType.
   Unless explicitly resource limited, a system's value for
   this object should be 1, allowing as small as a 1 second
   interval for ongoing delta sampling.
   Changing this value will not invalidate an existing setting
   of expObjectSampleType."
  ::= { expResource 1 }

expResourceDeltaWildcardInstanceMaximum OBJECT-TYPE

  SYNTAX      Unsigned32
  UNITS       "instances"
  MAX-ACCESS  read-write
  STATUS      current
  DESCRIPTION
   "For every instance of a deltaValue object, one dynamic instance
   entry is needed for holding the instance value from the previous
   sample, i.e. to maintain state.
   This object limits maximum number of dynamic instance entries
   this system will support for wildcarded delta objects in
   expressions. For a given delta expression, the number of
   dynamic instances is the number of values that meet all criteria
   to exist times the number of delta values in the expression.
   A value of 0 indicates no preset limit, that is, the limit
   is dynamic based on system operation and resources.
   Unless explicitly resource limited, a system's value for
   this object should be 0.

Kavasseri & Stewart Standards Track [Page 13] RFC 2982 Distributed Management Expression MIB October 2000

   Changing this value will not eliminate or inhibit existing delta
   wildcard instance objects but will prevent the creation of more
   such objects.
   An attempt to allocate beyond the limit results in expErrorCode
   being tooManyWildcardValues for that evaluation attempt."
  ::= { expResource 2 }

expResourceDeltaWildcardInstances OBJECT-TYPE

  SYNTAX      Gauge32
  UNITS       "instances"
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The number of currently active instance entries as
   defined for expResourceDeltaWildcardInstanceMaximum."
  ::= { expResource 3 }

expResourceDeltaWildcardInstancesHigh OBJECT-TYPE

  SYNTAX      Gauge32
  UNITS       "instances"
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The highest value of expResourceDeltaWildcardInstances
   that has occurred since initialization of the managed
   system."
  ::= { expResource 4 }

expResourceDeltaWildcardInstanceResourceLacks OBJECT-TYPE

  SYNTAX      Counter32
  UNITS       "instances"
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The number of times this system could not evaluate an
   expression because that would have created a value instance in
   excess of expResourceDeltaWildcardInstanceMaximum."
  ::= { expResource 5 }

– Definition – – Expression Definition Table –

expExpressionTable OBJECT-TYPE

Kavasseri & Stewart Standards Track [Page 14] RFC 2982 Distributed Management Expression MIB October 2000

  SYNTAX      SEQUENCE OF ExpExpressionEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
   "A table of expression definitions."
  ::= { expDefine 1 }

expExpressionEntry OBJECT-TYPE

  SYNTAX      ExpExpressionEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
   "Information about a single expression.  New expressions
   can be created using expExpressionRowStatus.
   To create an expression first create the named entry in this
   table.  Then use expExpressionName to populate expObjectTable.
   For expression evaluation to succeed all related entries in
   expExpressionTable and expObjectTable must be 'active'.  If
   these conditions are not met the corresponding values in
   expValue simply are not instantiated.
   Deleting an entry deletes all related entries in expObjectTable
   and expErrorTable.
   Because of the relationships among the multiple tables for an
   expression (expExpressionTable, expObjectTable, and
   expValueTable) and the SNMP rules for independence in setting
   object values, it is necessary to do final error checking when
   an expression is evaluated, that is, when one of its instances
   in expValueTable is read or a delta interval expires.  Earlier
   checking need not be done and an implementation may not impose
   any ordering on the creation of objects related to an
   expression.
   To maintain security of MIB information, when creating a new row in
   this table, the managed system must record the security credentials
   of the requester.  These security credentials are the parameters
   necessary as inputs to isAccessAllowed from the Architecture for
   Describing SNMP Management Frameworks.  When obtaining the objects
   that make up the expression, the system must (conceptually) use
   isAccessAllowed to ensure that it does not violate security.
   The evaluation of the expression takes place under the
   security credentials of the creator of its expExpressionEntry.
   Values of read-write objects in this table may be changed

Kavasseri & Stewart Standards Track [Page 15] RFC 2982 Distributed Management Expression MIB October 2000

   at any time."
  INDEX       { expExpressionOwner, expExpressionName }
  ::= { expExpressionTable 1 }

ExpExpressionEntry ::= SEQUENCE {

  expExpressionOwner           SnmpAdminString,
  expExpressionName             SnmpAdminString,
  expExpression                OCTET STRING,
  expExpressionValueType       INTEGER,
  expExpressionComment         SnmpAdminString,
  expExpressionDeltaInterval   Integer32,
  expExpressionPrefix           OBJECT IDENTIFIER,
  expExpressionErrors          Counter32,
  expExpressionEntryStatus     RowStatus

}

expExpressionOwner OBJECT-TYPE

 SYNTAX      SnmpAdminString (SIZE(0..32))
 MAX-ACCESS  not-accessible
 STATUS      current
 DESCRIPTION
   "The owner of this entry. The exact semantics of this
   string are subject to the security policy defined by the
   security administrator."
  ::= { expExpressionEntry 1 }

expExpressionName OBJECT-TYPE

  SYNTAX      SnmpAdminString (SIZE (1..32))
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
   "The name of the expression.  This is locally unique, within
   the scope of an expExpressionOwner."
  ::= { expExpressionEntry 2 }

expExpression OBJECT-TYPE

  SYNTAX      OCTET STRING (SIZE (1..1024))
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
   "The expression to be evaluated.  This object is the same
   as a DisplayString (RFC 1903) except for its maximum length.
   Except for the variable names the expression is in ANSI C
   syntax.  Only the subset of ANSI C operators and functions
   listed here is allowed.
   Variables are expressed as a dollar sign ('$') and an

Kavasseri & Stewart Standards Track [Page 16] RFC 2982 Distributed Management Expression MIB October 2000

   integer that corresponds to an expObjectIndex.  An
   example of a valid expression is:
        ($1-$5)*100
   Expressions must not be recursive, that is although an expression
   may use the results of another expression, it must not contain
   any variable that is directly or indirectly a result of its own
   evaluation. The managed system must check for recursive
   expressions.
   The only allowed operators are:
        ( )
        - (unary)
        + - * / %
        & | ^ << >> ~
        ! && || == != > >= < <=
   Note the parentheses are included for parenthesizing the
   expression, not for casting data types.
   The only constant types defined are:
        int (32-bit signed)
        long (64-bit signed)
        unsigned int
        unsigned long
        hexadecimal
        character
        string
        oid
   The default type for a positive integer is int unless it is too
   large in which case it is long.
   All but oid are as defined for ANSI C.  Note that a
   hexadecimal constant may end up as a scalar or an array of
   8-bit integers.  A string constant is enclosed in double
   quotes and may contain back-slashed individual characters
   as in ANSI C.
   An oid constant comprises 32-bit, unsigned integers and at
   least one period, for example:
        0.
        .0
        1.3.6.1

Kavasseri & Stewart Standards Track [Page 17] RFC 2982 Distributed Management Expression MIB October 2000

   No additional leading or trailing subidentifiers are automatically
   added to an OID constant.  The constant is taken as expressed.
   Integer-typed objects are treated as 32- or 64-bit, signed
   or unsigned integers, as appropriate.  The results of
   mixing them are as for ANSI C, including the type of the
   result.  Note that a 32-bit value is thus promoted to 64 bits
   only in an operation with a 64-bit value.  There is no
   provision for larger values to handle overflow.
   Relative to SNMP data types, a resulting value becomes
   unsigned when calculating it uses any unsigned value,
   including a counter.  To force the final value to be of
   data type counter the expression must explicitly use the
   counter32() or counter64() function (defined below).
   OCTET STRINGS and OBJECT IDENTIFIERs are treated as
   one-dimensioned arrays of unsigned 8-bit integers and
   unsigned 32-bit integers, respectively.
   IpAddresses are treated as 32-bit, unsigned integers in
   network byte order, that is, the hex version of 255.0.0.0 is
   0xff000000.
   Conditional expressions result in a 32-bit, unsigned integer
   of value 0 for false or 1 for true. When an arbitrary value
   is used as a boolean 0 is false and non-zero is true.
   Rules for the resulting data type from an operation, based on
   the operator:
   For << and >> the result is the same as the left hand operand.
   For &&, ||, ==, !=, <, <=, >, and >= the result is always
   Unsigned32.
   For unary - the result is always Integer32.
   For +, -, *, /, %, &, |, and ^ the result is promoted according
   to the following rules, in order from most to least preferred:
        If left hand and right hand operands are the same type,
        use that.
        If either side is Counter64, use that.
        If either side is IpAddress, use that.

Kavasseri & Stewart Standards Track [Page 18] RFC 2982 Distributed Management Expression MIB October 2000

        If either side is TimeTicks, use that.
        If either side is Counter32, use that.
        Otherwise use Unsigned32.
   The following rules say what operators apply with what data
   types.  Any combination not explicitly defined does not work.
   For all operators any of the following can be the left hand or
   right hand operand: Integer32, Counter32, Unsigned32, Counter64.
   The operators +, -, *, /, %, <, <=, >, and >= work with
   TimeTicks.
   The operators &, |, and ^ work with IpAddress.
   The operators << and >> work with IpAddress but only as the
   left hand operand.
   The + operator performs a concatenation of two OCTET STRINGs or
   two OBJECT IDENTIFIERs.
   The operators &, | perform bitwise operations on OCTET STRINGs.
   If the OCTET STRING happens to be a DisplayString the results
   may be meaningless, but the agent system does not check this as
   some such systems do not have this information.
   The operators << and >> perform bitwise operations on OCTET
   STRINGs appearing as the left hand operand.
   The only functions defined are:
        counter32
        counter64
        arraySection
        stringBegins
        stringEnds
        stringContains
        oidBegins
        oidEnds
        oidContains
        average
        maximum
        minimum
        sum
        exists

Kavasseri & Stewart Standards Track [Page 19] RFC 2982 Distributed Management Expression MIB October 2000

   The following function definitions indicate their parameters by
   naming the data type of the parameter in the parameter's position
   in the parameter list.  The parameter must be of the type indicated
   and generally may be a constant, a MIB object, a function, or an
   expression.
   counter32(integer) - wrapped around an integer value counter32
   forces Counter32 as a data type.
   counter64(integer) - similar to counter32 except that the
   resulting data type is 'counter64'.
   arraySection(array, integer, integer) - selects a piece of an
   array (i.e. part of an OCTET STRING or OBJECT IDENTIFIER).  The
   integer arguments are in the range 0 to 4,294,967,295.  The
   first is an initial array index (one-dimensioned) and the second
   is an ending array index.  A value of 0 indicates first or last
   element, respectively.  If the first element is larger than the
   array length the result is 0 length.  If the second integer is
   less than or equal to the first, the result is 0 length.  If the
   second is larger than the array length it indicates last
   element.
   stringBegins/Ends/Contains(octetString, octetString) - looks for
   the second string (which can be a string constant) in the first
   and returns the one-dimensioned arrayindex where the match began.
   A return value of 0 indicates no match (i.e. boolean false).
   oidBegins/Ends/Contains(oid, oid) - looks for the second OID
   (which can be an OID constant) in the first and returns the
   the one-dimensioned index where the match began. A return value
   of 0 indicates no match (i.e. boolean false).
   average/maximum/minimum(integer) - calculates the average,
   minimum, or maximum value of the integer valued object over
   multiple sample times.  If the object disappears for any
   sample period, the accumulation and the resulting value object
   cease to exist until the object reappears at which point the
   calculation starts over.
   sum(integerObject*) - sums all available values of the
   wildcarded integer object, resulting in an integer scalar.  Must
   be used with caution as it wraps on overflow with no
   notification.
   exists(anyTypeObject) - verifies the object instance exists. A
   return value of 0 indicates NoSuchInstance (i.e. boolean
   false)."

Kavasseri & Stewart Standards Track [Page 20] RFC 2982 Distributed Management Expression MIB October 2000

  ::= { expExpressionEntry 3 }

expExpressionValueType OBJECT-TYPE

  SYNTAX      INTEGER { counter32(1), unsigned32(2), timeTicks(3),
               integer32(4), ipAddress(5), octetString(6),
               objectId(7), counter64(8) }
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
   "The type of the expression value.  One and only one of the
   value objects in expValueTable will be instantiated to match
   this type.
   If the result of the expression can not be made into this type,
   an invalidOperandType error will occur."
  DEFVAL      { counter32 }
  ::= { expExpressionEntry 4 }

expExpressionComment OBJECT-TYPE

  SYNTAX      SnmpAdminString
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
   "A comment to explain the use or meaning of the expression."
  DEFVAL      { ''H }
  ::= { expExpressionEntry 5 }

expExpressionDeltaInterval OBJECT-TYPE

  SYNTAX      Integer32 (0..86400)
  UNITS       "seconds"
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
   "Sampling interval for objects in this expression with
   expObjectSampleType 'deltaValue'.
   This object has no effect if the the expression has no
   deltaValue objects.
   A value of 0 indicates no automated sampling.  In this case
   the delta is the difference from the last time the expression
   was evaluated.  Note that this is subject to unpredictable
   delta times in the face of retries or multiple managers.
   A value greater than zero is the number of seconds between
   automated samples.
   Until the delta interval has expired once the delta for the

Kavasseri & Stewart Standards Track [Page 21] RFC 2982 Distributed Management Expression MIB October 2000

   object is effectively not instantiated and evaluating
   the expression has results as if the object itself were not
   instantiated.
   Note that delta values potentially consume large amounts of
   system CPU and memory.  Delta state and processing must
   continue constantly even if the expression is not being used.
   That is, the expression is being evaluated every delta interval,
   even if no application is reading those values.  For wildcarded
   objects this can be substantial overhead.
   Note that delta intervals, external expression value sampling
   intervals and delta intervals for expressions within other
   expressions can have unusual interactions as they are impossible
   to synchronize accurately.  In general one interval embedded
   below another must be enough shorter that the higher sample
   sees relatively smooth, predictable behavior.  So, for example,
   to avoid the higher level getting the same sample twice, the
   lower level should sample at least twice as fast as the higher
   level does."
  DEFVAL      { 0 }
  ::= { expExpressionEntry 6 }

expExpressionPrefix OBJECT-TYPE

  SYNTAX      OBJECT IDENTIFIER
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "An object prefix to assist an application in determining
   the instance indexing to use in expValueTable, relieving the
   application of the need to scan the expObjectTable to
   determine such a prefix.
   See expObjectTable for information on wildcarded objects.
   If the expValueInstance portion of the value OID may
   be treated as a scalar (that is, normally, 0) the value of
   expExpressionPrefix is zero length, that is, no OID at all.
   Note that zero length implies a null OID, not the OID 0.0.
   Otherwise, the value of expExpressionPrefix is the expObjectID
   value of any one of the wildcarded objects for the expression.
   This is sufficient, as the remainder, that is, the instance
   fragment relevant to instancing the values, must be the same for
   all wildcarded objects in the expression."
  ::= { expExpressionEntry 7 }

expExpressionErrors OBJECT-TYPE

Kavasseri & Stewart Standards Track [Page 22] RFC 2982 Distributed Management Expression MIB October 2000

  SYNTAX      Counter32
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The number of errors encountered while evaluating this
   expression.
   Note that an object in the expression not being accessible,
   is not considered an error. An example of an inaccessible
   object is when the object is excluded from the view of the
   user whose security credentials are used in the expression
   evaluation. In such cases, it is a legitimate condition
   that causes the corresponding expression value not to be
   instantiated."
  ::= { expExpressionEntry 8 }

expExpressionEntryStatus OBJECT-TYPE

  SYNTAX      RowStatus
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
   "The control that allows creation and deletion of entries."
  ::= { expExpressionEntry 9 }

– – Expression Error Table –

expErrorTable OBJECT-TYPE

  SYNTAX      SEQUENCE OF ExpErrorEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
   "A table of expression errors."
  ::= { expDefine 2 }

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 }

Kavasseri & Stewart Standards Track [Page 23] RFC 2982 Distributed Management Expression MIB October 2000

  ::= { expErrorTable 1 }

ExpErrorEntry ::= SEQUENCE {

  expErrorTime       TimeStamp,
  expErrorIndex      Integer32,
  expErrorCode       INTEGER,
  expErrorInstance   OBJECT IDENTIFIER

}

expErrorTime OBJECT-TYPE

  SYNTAX      TimeStamp
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The value of sysUpTime the last time an error caused a
   failure to evaluate this expression."
  ::= { expErrorEntry 1 }

expErrorIndex OBJECT-TYPE

  SYNTAX      Integer32
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The one-dimensioned character array index into
   expExpression for where the error occurred.  The value
   zero indicates irrelevance."
  ::= { expErrorEntry 2 }

expErrorCode OBJECT-TYPE

  SYNTAX      INTEGER {
        invalidSyntax(1),
        undefinedObjectIndex(2),
        unrecognizedOperator(3),
        unrecognizedFunction(4),
        invalidOperandType(5),
        unmatchedParenthesis(6),
        tooManyWildcardValues(7),
        recursion(8),
        deltaTooShort(9),
        resourceUnavailable(10),
        divideByZero(11)
        }
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The error that occurred.  In the following explanations the
   expected timing of the error is in parentheses.  'S' means
   the error occurs on a Set request.  'E' means the error

Kavasseri & Stewart Standards Track [Page 24] RFC 2982 Distributed Management Expression MIB October 2000

   occurs on the attempt to evaluate the expression either due to
   Get from expValueTable or in ongoing delta processing.
   invalidSyntax       the value sent for expExpression is not
                  valid Expression MIB expression syntax
                  (S)
   undefinedObjectIndex     an object reference ($n) in
                  expExpression does not have a matching
                  instance in expObjectTable (E)
   unrecognizedOperator     the value sent for expExpression held an
                  unrecognized operator (S)
   unrecognizedFunction     the value sent for expExpression held an
                  unrecognized function name (S)
   invalidOperandType  an operand in expExpression is not the
                  right type for the associated operator
                  or result (SE)
   unmatchedParenthesis     the value sent for expExpression is not
                  correctly parenthesized (S)
   tooManyWildcardValues    evaluating the expression exceeded the
                  limit set by
                  expResourceDeltaWildcardInstanceMaximum
                  (E)
   recursion      through some chain of embedded
                  expressions the expression invokes itself
                  (E)
   deltaTooShort       the delta for the next evaluation passed
                  before the system could evaluate the
                  present sample (E)
   resourceUnavailable some resource, typically dynamic memory,
                  was unavailable (SE)
   divideByZero        an attempt to divide by zero occurred
                  (E)
   For the errors that occur when the attempt is made to set
   expExpression Set request fails with the SNMP error code
   'wrongValue'.  Such failures refer to the most recent failure to
   Set expExpression, not to the present value of expExpression
   which must be either unset or syntactically correct.
   Errors that occur during evaluation for a Get* operation return
   the SNMP error code 'genErr' except for 'tooManyWildcardValues'
   and 'resourceUnavailable' which return the SNMP error code
   'resourceUnavailable'."
  ::= { expErrorEntry 3 }

expErrorInstance OBJECT-TYPE

  SYNTAX      OBJECT IDENTIFIER
  MAX-ACCESS  read-only

Kavasseri & Stewart Standards Track [Page 25] RFC 2982 Distributed Management Expression MIB October 2000

  STATUS      current
  DESCRIPTION
   "The expValueInstance being evaluated when the error
   occurred.  A zero-length indicates irrelevance."
  ::= { expErrorEntry 4 }

– – Object Table –

expObjectTable OBJECT-TYPE

  SYNTAX      SEQUENCE OF ExpObjectEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
   "A table of object definitions for each expExpression.
   Wildcarding instance IDs:
   It is legal to omit all or part of the instance portion for
   some or all of the objects in an expression. (See the
   DESCRIPTION of expObjectID for details.  However, note that
   if more than one object in the same expression is wildcarded
   in this way, they all must be objects where that portion of
   the instance is the same.  In other words, all objects may be
   in the same SEQUENCE or in different SEQUENCEs but with the
   same semantic index value (e.g., a value of ifIndex)
   for the wildcarded portion."
  ::= { expDefine 3 }

expObjectEntry OBJECT-TYPE

  SYNTAX      ExpObjectEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
   "Information about an object.  An application uses
   expObjectEntryStatus to create entries in this table while
   in the process of defining an expression.
   Values of read-create objects in this table may be
   changed at any time."
  INDEX       { expExpressionOwner, expExpressionName, expObjectIndex }
  ::= { expObjectTable 1 }

ExpObjectEntry ::= SEQUENCE {

  expObjectIndex                     Unsigned32,
  expObjectID                        OBJECT IDENTIFIER,
  expObjectIDWildcard                TruthValue,

Kavasseri & Stewart Standards Track [Page 26] RFC 2982 Distributed Management Expression MIB October 2000

  expObjectSampleType                INTEGER,
  expObjectDeltaDiscontinuityID      OBJECT IDENTIFIER,
  expObjectDiscontinuityIDWildcard   TruthValue,
  expObjectDiscontinuityIDType       INTEGER,
  expObjectConditional               OBJECT IDENTIFIER,
  expObjectConditionalWildcard       TruthValue,
  expObjectEntryStatus               RowStatus

}

expObjectIndex OBJECT-TYPE

  SYNTAX      Unsigned32 (1..4294967295)
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
   "Within an expression, a unique, numeric identification for an
   object.  Prefixed with a dollar sign ('$') this is used to
   reference the object in the corresponding expExpression."
  ::= { expObjectEntry 1 }

expObjectID OBJECT-TYPE

  SYNTAX      OBJECT IDENTIFIER
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
   "The OBJECT IDENTIFIER (OID) of this object.  The OID may be
   fully qualified, meaning it includes a complete instance
   identifier part (e.g., ifInOctets.1 or sysUpTime.0), or it
   may not be fully qualified, meaning it may lack all or part
   of the instance identifier.  If the expObjectID is not fully
   qualified, then expObjectWildcard must be set to true(1).
   The value of the expression will be multiple
   values, as if done for a GetNext sweep of the object.
   An object here may itself be the result of an expression but
   recursion is not allowed.
   NOTE:  The simplest implementations of this MIB may not allow
   wildcards."
  ::= { expObjectEntry 2 }

expObjectIDWildcard OBJECT-TYPE

  SYNTAX      TruthValue
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
      "A true value indicates the expObjecID of this row is a wildcard
      object. False indicates that expObjectID is fully instanced.
      If all expObjectWildcard values for a given expression are FALSE,

Kavasseri & Stewart Standards Track [Page 27] RFC 2982 Distributed Management Expression MIB October 2000

      expExpressionPrefix will reflect a scalar object (i.e. will
      be 0.0).
      NOTE:  The simplest implementations of this MIB may not allow
      wildcards."
  DEFVAL      { false }
  ::= { expObjectEntry 3 }

expObjectSampleType OBJECT-TYPE

  SYNTAX      INTEGER { absoluteValue(1), deltaValue(2),
                        changedValue(3) }
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
   "The method of sampling the selected variable.
   An 'absoluteValue' is simply the present value of the object.
   A 'deltaValue' is the present value minus the previous value,
   which was sampled expExpressionDeltaInterval seconds ago.
   This is intended primarily for use with SNMP counters, which are
   meaningless as an 'absoluteValue', but may be used with any
   integer-based value.
   A 'changedValue' is a boolean for whether the present value is
   different from the previous value.  It is applicable to any data
   type and results in an Unsigned32 with value 1 if the object's
   value is changed and 0 if not.  In all other respects it is as a
   'deltaValue' and all statements and operation regarding delta
   values apply to changed values.
   When an expression contains both delta and absolute values
   the absolute values are obtained at the end of the delta
   period."
  DEFVAL      { absoluteValue }
  ::= { expObjectEntry 4 }

sysUpTimeInstance OBJECT IDENTIFIER ::= { sysUpTime 0 }

expObjectDeltaDiscontinuityID OBJECT-TYPE

  SYNTAX      OBJECT IDENTIFIER
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
   "The OBJECT IDENTIFIER (OID) of a TimeTicks, TimeStamp, or
   DateAndTime object that indicates a discontinuity in the value
   at expObjectID.

Kavasseri & Stewart Standards Track [Page 28] RFC 2982 Distributed Management Expression MIB October 2000

   This object is instantiated only if expObjectSampleType is
   'deltaValue' or 'changedValue'.
   The OID may be for a leaf object (e.g. sysUpTime.0) or may
   be wildcarded to match expObjectID.
   This object supports normal checking for a discontinuity in a
   counter.  Note that if this object does not point to sysUpTime
   discontinuity checking must still check sysUpTime for an overall
   discontinuity.
   If the object identified is not accessible no discontinuity
   check will be made."
  DEFVAL      { sysUpTimeInstance }
  ::= { expObjectEntry 5 }

expObjectDiscontinuityIDWildcard OBJECT-TYPE

   SYNTAX      TruthValue
   MAX-ACCESS  read-create
   STATUS      current
   DESCRIPTION
   "A true value indicates the expObjectDeltaDiscontinuityID of
   this row is a wildcard object.  False indicates that
   expObjectDeltaDiscontinuityID is fully instanced.
   This object is instantiated only if expObjectSampleType is
   'deltaValue' or 'changedValue'.
   NOTE:  The simplest implementations of this MIB may not allow
   wildcards."
  DEFVAL      { false }
   ::= { expObjectEntry 6 }

expObjectDiscontinuityIDType OBJECT-TYPE

   SYNTAX      INTEGER { timeTicks(1), timeStamp(2), dateAndTime(3) }
   MAX-ACCESS  read-create
   STATUS      current
   DESCRIPTION
   "The value 'timeTicks' indicates the expObjectDeltaDiscontinuityID
   of this row is of syntax TimeTicks.  The value 'timeStamp' indicates
   syntax TimeStamp.  The value 'dateAndTime indicates syntax
   DateAndTime.
   This object is instantiated only if expObjectSampleType is
   'deltaValue' or 'changedValue'."
  DEFVAL      { timeTicks }
   ::= { expObjectEntry 7 }

Kavasseri & Stewart Standards Track [Page 29] RFC 2982 Distributed Management Expression MIB October 2000

expObjectConditional OBJECT-TYPE

  SYNTAX      OBJECT IDENTIFIER
  MAX-ACCESS  read-create
  STATUS      current
  DESCRIPTION
   "The OBJECT IDENTIFIER (OID) of an object that overrides
   whether the instance of expObjectID is to be considered
   usable.  If the value of the object at expObjectConditional
   is 0 or not instantiated, the object at expObjectID is
   treated as if it is not instantiated.  In other words,
   expObjectConditional is a filter that controls whether or
   not to use the value at expObjectID.
   The OID may be for a leaf object (e.g. sysObjectID.0) or may be
   wildcarded to match expObjectID.  If expObject is wildcarded and
   expObjectID in the same row is not, the wild portion of
   expObjectConditional must match the wildcarding of the rest of
   the expression.  If no object in the expression is wildcarded
   but expObjectConditional is, use the lexically first instance
   (if any) of expObjectConditional.
   If the value of expObjectConditional is 0.0 operation is
   as if the value pointed to by expObjectConditional is a
   non-zero (true) value.
   Note that expObjectConditional can not trivially use an object
   of syntax TruthValue, since the underlying value is not 0 or 1."
  DEFVAL      { zeroDotZero }
  ::= { expObjectEntry 8 }

expObjectConditionalWildcard OBJECT-TYPE

   SYNTAX      TruthValue
   MAX-ACCESS  read-create
   STATUS      current
   DESCRIPTION
   "A true value indicates the expObjectConditional of this row is
   a wildcard object. False indicates that expObjectConditional is
   fully instanced.
   NOTE: The simplest implementations of this MIB may not allow
   wildcards."
  DEFVAL      { false }
   ::= { expObjectEntry 9 }

expObjectEntryStatus OBJECT-TYPE

  SYNTAX      RowStatus
  MAX-ACCESS  read-create

Kavasseri & Stewart Standards Track [Page 30] RFC 2982 Distributed Management Expression MIB October 2000

  STATUS      current
  DESCRIPTION
   "The control that allows creation/deletion of entries.
   Objects in this table may be changed while
   expObjectEntryStatus is in any state."
  ::= { expObjectEntry 10 }

– – Expression Value Table –

expValueTable OBJECT-TYPE

  SYNTAX      SEQUENCE OF ExpValueEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
   "A table of values from evaluated expressions."
  ::= { expValue 1 }

expValueEntry OBJECT-TYPE

  SYNTAX      ExpValueEntry
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
   "A single value from an evaluated expression.  For a given
   instance, only one 'Val' object in the conceptual row will be
   instantiated, that is, the one with the appropriate type for
   the value.  For values that contain no objects of
   expObjectSampleType 'deltaValue' or 'changedValue', reading a
   value from the table causes the evaluation of the expression
   for that value.  For those that contain a 'deltaValue' or
   'changedValue' the value read is as of the last sampling
   interval.
   If in the attempt to evaluate the expression one or more
   of the necessary objects is not available, the corresponding
   entry in this table is effectively not instantiated.
   To maintain security of MIB information, when creating a new
   row in this table, the managed system must record the security
   credentials of the requester.  These security credentials are
   the parameters necessary as inputs to isAccessAllowed from
   [RFC2571]. When obtaining the objects that make up the
   expression, the system must (conceptually) use isAccessAllowed to
   ensure that it does not violate security.
   The evaluation of that expression takes place under the

Kavasseri & Stewart Standards Track [Page 31] RFC 2982 Distributed Management Expression MIB October 2000

   security credentials of the creator of its expExpressionEntry.
   To maintain security of MIB information, expression evaluation must
   take place using security credentials for the implied Gets of the
   objects in the expression as inputs (conceptually) to
   isAccessAllowed from the Architecture for Describing SNMP
   Management Frameworks.  These are the security credentials of the
   creator of the corresponding expExpressionEntry."
  INDEX       { expExpressionOwner, expExpressionName,
                IMPLIED expValueInstance }
  ::= { expValueTable 1 }

ExpValueEntry ::= SEQUENCE {

  expValueInstance          OBJECT IDENTIFIER,
  expValueCounter32Val      Counter32,
  expValueUnsigned32Val     Unsigned32,
  expValueTimeTicksVal      TimeTicks,
  expValueInteger32Val      Integer32,
  expValueIpAddressVal      IpAddress,
  expValueOctetStringVal    OCTET STRING,
  expValueOidVal            OBJECT IDENTIFIER,
  expValueCounter64Val      Counter64

}

expValueInstance OBJECT-TYPE

  SYNTAX      OBJECT IDENTIFIER
  MAX-ACCESS  not-accessible
  STATUS      current
  DESCRIPTION
   "The final instance portion of a value's OID according to
   the wildcarding in instances of expObjectID for the
   expression.  The prefix of this OID fragment is 0.0,
   leading to the following behavior.
   If there is no wildcarding, the value is 0.0.0.  In other
   words, there is one value which standing alone would have
   been a scalar with a 0 at the end of its OID.
   If there is wildcarding, the value is 0.0 followed by
   a value that the wildcard can take, thus defining one value
   instance for each real, possible value of the wildcard.
   So, for example, if the wildcard worked out to be an ifIndex,
   there is an expValueInstance for each applicable ifIndex."
  ::= { expValueEntry 1 }

expValueCounter32Val OBJECT-TYPE

  SYNTAX      Counter32
  MAX-ACCESS  read-only

Kavasseri & Stewart Standards Track [Page 32] RFC 2982 Distributed Management Expression MIB October 2000

  STATUS      current
  DESCRIPTION
   "The value when expExpressionValueType is 'counter32'."
  ::= { expValueEntry 2 }

expValueUnsigned32Val OBJECT-TYPE

  SYNTAX      Unsigned32
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The value when expExpressionValueType is 'unsigned32'."
  ::= { expValueEntry 3 }

expValueTimeTicksVal OBJECT-TYPE

  SYNTAX      TimeTicks
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The value when expExpressionValueType is 'timeTicks'."
  ::= { expValueEntry 4 }

expValueInteger32Val OBJECT-TYPE

  SYNTAX      Integer32
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The value when expExpressionValueType is 'integer32'."
  ::= { expValueEntry 5 }

expValueIpAddressVal OBJECT-TYPE

  SYNTAX      IpAddress
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The value when expExpressionValueType is 'ipAddress'."
  ::= { expValueEntry 6 }

expValueOctetStringVal OBJECT-TYPE

  SYNTAX      OCTET STRING (SIZE (0..65536))
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The value when expExpressionValueType is 'octetString'."
  ::= { expValueEntry 7 }

expValueOidVal OBJECT-TYPE

  SYNTAX      OBJECT IDENTIFIER
  MAX-ACCESS  read-only

Kavasseri & Stewart Standards Track [Page 33] RFC 2982 Distributed Management Expression MIB October 2000

  STATUS      current
  DESCRIPTION
   "The value when expExpressionValueType is 'objectId'."
  ::= { expValueEntry 8 }

expValueCounter64Val OBJECT-TYPE

  SYNTAX      Counter64
  MAX-ACCESS  read-only
  STATUS      current
  DESCRIPTION
   "The value when expExpressionValueType is 'counter64'."
  ::= { expValueEntry 9 }

– – Conformance –

dismanExpressionMIBConformance OBJECT IDENTIFIER ::=

  { dismanExpressionMIB 3 }

dismanExpressionMIBCompliances OBJECT IDENTIFIER ::=

  { dismanExpressionMIBConformance 1 }

dismanExpressionMIBGroups OBJECT IDENTIFIER ::=

  { dismanExpressionMIBConformance 2 }

– Compliance

dismanExpressionMIBCompliance MODULE-COMPLIANCE

   STATUS current
   DESCRIPTION
        "The compliance statement for entities which implement
        the Expression MIB."
   MODULE    -- this module
        MANDATORY-GROUPS {
             dismanExpressionResourceGroup,
             dismanExpressionDefinitionGroup,
             dismanExpressionValueGroup
        }
   OBJECT         expResourceDeltaMinimum
   SYNTAX         Integer32 (-1 | 60..600)
   DESCRIPTION
        "Implementation need not allow deltas or it may
        implement them and restrict them to higher values."
   OBJECT         expObjectSampleType
   WRITE-SYNTAX   INTEGER { absoluteValue(1) }
   DESCRIPTION
        "Implementation may disallow deltas calculation or

Kavasseri & Stewart Standards Track [Page 34] RFC 2982 Distributed Management Expression MIB October 2000

        change detection."
   OBJECT         expObjectIDWildcard
   WRITE-SYNTAX   INTEGER { false(2) }
   DESCRIPTION
        "Implementation may allow wildcards."
   OBJECT         expObjectDiscontinuityIDWildcard
   WRITE-SYNTAX   INTEGER { false(2) }
   DESCRIPTION
        "Implementation need not allow wildcards."
   OBJECT          expObjectConditionalWildcard
   WRITE-SYNTAX   INTEGER { false(2) }
   DESCRIPTION
        "Implementation need not allow deltas wildcards."
   ::= { dismanExpressionMIBCompliances 1 }

– Units of Conformance

dismanExpressionResourceGroup OBJECT-GROUP

   OBJECTS {
        expResourceDeltaMinimum,
        expResourceDeltaWildcardInstanceMaximum,
        expResourceDeltaWildcardInstances,
        expResourceDeltaWildcardInstancesHigh,
        expResourceDeltaWildcardInstanceResourceLacks
   }
   STATUS current
   DESCRIPTION
        "Expression definition resource management."
   ::= { dismanExpressionMIBGroups 1 }

dismanExpressionDefinitionGroup OBJECT-GROUP

   OBJECTS {
        expExpression,
        expExpressionValueType,
        expExpressionComment,
        expExpressionDeltaInterval,
        expExpressionPrefix,
        expExpressionErrors,
        expExpressionEntryStatus,
        expErrorTime,
        expErrorIndex,
        expErrorCode,
        expErrorInstance,

Kavasseri & Stewart Standards Track [Page 35] RFC 2982 Distributed Management Expression MIB October 2000

        expObjectID,
        expObjectIDWildcard,
        expObjectSampleType,
        expObjectDeltaDiscontinuityID,
        expObjectDiscontinuityIDWildcard,
        expObjectDiscontinuityIDType,
        expObjectConditional,
        expObjectConditionalWildcard,
        expObjectEntryStatus
   }
   STATUS current
   DESCRIPTION
        "Expression definition."
   ::= { dismanExpressionMIBGroups 2 }

dismanExpressionValueGroup OBJECT-GROUP

   OBJECTS {
        expValueCounter32Val,
        expValueUnsigned32Val,
        expValueTimeTicksVal,
        expValueInteger32Val,
        expValueIpAddressVal,
        expValueOctetStringVal,
        expValueOidVal,
        expValueCounter64Val
   }
   STATUS current
   DESCRIPTION
        "Expression value."
   ::= { dismanExpressionMIBGroups 3 }

END

4. Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 intellectual property or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; neither does it represent that it
 has made any effort to identify any such rights.  Information on the
 IETF's procedures with respect to rights in standards-track and
 standards- related documentation can be found in BCP-11.  Copies of
 claims of rights made available for publication and any assurances of
 licenses to be made available, or the result of an attempt made to
 obtain a general license or permission for the use of such
 proprietary rights by implementors or users of this specification can
 be obtained from the IETF Secretariat.

Kavasseri & Stewart Standards Track [Page 36] RFC 2982 Distributed Management Expression MIB October 2000

 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.

5. Acknowledgements

 This MIB contains considerable contributions from the Distributed
 Management Design Team (Andy Bierman, Maria Greene, Bob Stewart, and
 Steve Waldbusser), and colleagues at Cisco who did the first
 implementation.

6. References

 [RFC2571]   Harrington, D., Presuhn, R. and B. Wijnen, "An
             Architecture Describing SNMP Management Frameworks", RFC
             2571, April 1999.
 [RFC1155]   Rose, M. and K. McCloghrie, "Structure and Identification
             of Management Information for TCP/IP-based Internets",
             STD 16, RFC 1155, May 1990.
 [RFC1212]   Rose, M. and K. McCloghrie, "Concise MIB Definitions",
             STD 16, RFC 1212, March 1991.
 [RFC1215]   Rose, M., "A Convention for Defining Traps for use with
             the SNMP", RFC 1215, March 1991.
 [RFC2578]   McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
             Rose, M. and S. Waldbusser, "Structure of Management
             Information Version 2 (SMIv2)", STD 58, RFC 2578, April
             1999.
 [RFC2579]   McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
             Rose, M. and S. Waldbusser, "Textual Conventions for
             SMIv2", STD 58, RFC 2579, April 1999.
 [RFC2580]   McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
             Rose, M. and S. Waldbusser, "Conformance Statements for
             SMIv2", STD 58, RFC 2580, April 1999.
 [RFC1157]   Case, J., Fedor, M., Schoffstall, M. and J. Davin,
             "Simple Network Management Protocol", STD 15, RFC 1157,
             May 1990.

Kavasseri & Stewart Standards Track [Page 37] RFC 2982 Distributed Management Expression MIB October 2000

 [RFC1901]   Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
             "Introduction to Community-based SNMPv2", RFC 1901,
             January 1996.
 [RFC1906]   Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
             "Transport Mappings for Version 2 of the Simple Network
             Management Protocol (SNMPv2)", RFC 1906, January 1996.
 [RFC2572]   Case, J., Harrington D., Presuhn R. and B. Wijnen,
             "Message Processing and Dispatching for the Simple
             Network Management Protocol (SNMP)", RFC 2572, April
             1999.
 [RFC2574]   Blumenthal, U. and B. Wijnen, "User-based Security Model
             (USM) for version 3 of the Simple Network Management
             Protocol (SNMPv3)", RFC 2574, April 1999.
 [RFC1905]   Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
             "Protocol Operations for Version 2 of the Simple Network
             Management Protocol (SNMPv2)", RFC 1905, January 1996.
 [RFC2573]   Levi, D., Meyer, P. and B. Stewart, "SNMPv3
             Applications", RFC 2573, April 1999.
 [RFC2575]   Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based
             Access Control Model (VACM) for the Simple Network
             Management Protocol (SNMP)", RFC 2575, April 1999.
 [RFC2570]   Case, J., Mundy, R., Partain, D. and B. Stewart,
             "Introduction to Version 3 of the Internet-standard
             Network Management Framework", RFC 2570, April 1999.
 [RFC1903]   Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
             "Coexistence between Version 1 and version 2 of the
             Internet-standard Network Management Framework", RFC
             1903, January 1996.
 [RFC2981]   Stewart, B., "Event MIB", RFC 2981, October 2000.
 [PracPersp] Leinwand, A. and K. Fang, "Network Management: A
             Practical Perspective", Addison-Wesley Publishing
             Company, Inc., 1993.

7. Security Considerations

 Expression MIB security involves two perspectives:  protection of
 expressions from tampering or unauthorized use of resources, and
 protection of the objects used to calculate the expressions.

Kavasseri & Stewart Standards Track [Page 38] RFC 2982 Distributed Management Expression MIB October 2000

 Security of expression definitions and results depends on the
 expression owner (expExpressionOwner).  With view-based access
 control [RFC2575] a network manager can control who has what level of
 access to what expressions.
 Access control for the objects within the expression depends on the
 security credentials of the expression creator.  These are the
 security credentials used to get the objects necessary to evaluate
 the expression.  They are the security credentials that were used to
 set the expExpressionRowStatus object for that expression to
 'active', as recorded by the managed system.
 This means that the results of an expression could potentially be
 made available to someone who does not have access to the raw data
 that went into them.  This could be either legitimate or a security
 violation, depending on the specific situation and security policy.
 To facilitate the provisioning of access control by a security
 administrator for this MIB itself using the View-Based Access Control
 Model (VACM) defined in RFC 2575 [RFC2575] for tables in which
 multiple users may need to independently create or modify entries,
 the initial index is used as an "owner index".  Such an initial index
 has a syntax of SnmpAdminString, and can thus be trivially mapped to
 a securityName or groupName as defined in VACM, in accordance with a
 security policy.
 All entries in related tables belonging to a particular user will
 have the same value for this initial index.  For a given user's
 entries in a particular table, the object identifiers for the
 information in these entries will have the same subidentifiers
 (except for the "column" subidentifier) up to the end of the encoded
 owner index.  To configure VACM to permit access to this portion of
 the table, one would create vacmViewTreeFamilyTable entries with the
 value of vacmViewTreeFamilySubtree including the owner index portion,
 and vacmViewTreeFamilyMask "wildcarding" the column subidentifier.
 More elaborate configurations are possible.

Kavasseri & Stewart Standards Track [Page 39] RFC 2982 Distributed Management Expression MIB October 2000

8. Author's Address

 Bob Stewart
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA 95134-1706
 U.S.A.

9. Editor's Address

 Ramanathan Kavasseri
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, CA 95134-1706
 U.S.A.
 Phone: +1 408 527 2446
 EMail: ramk@cisco.com

Kavasseri & Stewart Standards Track [Page 40] RFC 2982 Distributed Management Expression MIB October 2000

10. Full Copyright Statement

 Copyright (C) The Internet Society (2000).  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.

Kavasseri & Stewart Standards Track [Page 41]

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