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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 ('