Internet Draft Expression MIB 4 November 1998 Expression MIB 4 November 1998 draft-ietf-disman-express-mib-07.txt Bob Stewart Cisco Systems, Inc. bstewart@cisco.com Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as ``work in progress.'' To view the entire list of current Internet-Drafts, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this document is unlimited. Please send comments to the Distributed Management Working Group, . Copyright Notice Copyright (C) The Internet Society (1998). All Rights Reserved. Expires 4 November 1998+6 months [Page 1] Internet Draft Expression MIB 4 November 1998 1. Abstract This memo defines an experimental 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 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. 2. The SNMP Management Framework The SNMP Management Framework presently consists of five major components: o An overall architecture, described in RFC 2271 [1]. o Mechanisms for describing and naming objects and events for the purpose of management. The first version of this Structure of Management Information (SMI) is called SMIv1 and described in RFC 1155 [2], RFC 1212 [3] and RFC 1215 [4]. The second version, called SMIv2, is described in RFC 1902 [5], RFC 1903 [6] and RFC 1904 [7]. o Message protocols for transferring management information. The first version of the SNMP message protocol is called SNMPv1 and described in RFC 1157 [8]. A second version of the SNMP message protocol, which is not an Internet standards track protocol, is called SNMPv2c and described in RFC 1901 [9] and RFC 1906 [10]. The third version of the message protocol is called SNMPv3 and described in RFC 1906 [10], RFC 2272 [11] and RFC 2274 [12]. o Protocol operations for accessing management information. The first set of protocol operations and associated PDU formats is described in RFC 1157 [8]. A second set of protocol operations and associated PDU formats is described in RFC 1905 [13]. o A set of fundamental applications described in RFC 2273 [14] and the view-based access control mechanism described in RFC 2275 [15]. Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. Objects in the MIB are defined Expires 4 November 1998+6 months [Page 2] Internet Draft Expression MIB 4 November 1998 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. Expires 4 November 1998+6 months [Page 3] Internet Draft Expression MIB 4 November 1998 3. Overview End users of MIBs often desire MIB objects that MIB designers have not provided. Furthermore, such needs vary from one management philosphy 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 appear no different from any other and are thus usable anywhere any other MIB object can be used, whether by a management application directly or via another MIB, including 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 more limited environment. Implementation of the Expression MIB in an agent environment 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 that is the expected environment and it is not reasonable that the MIB should assume a full-blown application-level environment. 3.1. 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. The primary purpose of the Expression MIB is to provide custom objects for the Event MIB [16]. 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 the Expression MIB such monitoring is 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. Expires 4 November 1998+6 months [Page 4] Internet Draft Expression MIB 4 November 1998 3.2. Operation Most of the operation of the MIB is described or implied in the object definitions but a few highlights bear mentioning here. 3.2.1. 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. 3.2.2. 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 or the results are unpredictable. The expression can be evaluated only for those instances where all the objects in the given potential of the expression are available. Expires 4 November 1998+6 months [Page 5] Internet Draft Expression MIB 4 November 1998 3.2.3. 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 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. For fully absolute expressions evaluation occurs on demand, when a requester attempts to read a value. 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. No obsolete values are kept from one sample period to the next. 3.3. 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. 3.3.1. Resource The resource section has objects to manage resource usage by wildcarded delta expressions, a potential major consumer of CPU and memory. Expires 4 November 1998+6 months [Page 6] Internet Draft Expression MIB 4 November 1998 3.3.2. Definition The definition section contains the tables that define expressions. The expression table, indexed by 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. The object table, indexed by 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. 3.3.3. Value The value section contains the values of evaluated expressions. The value table, indexed by 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 object identifier that filled in a wildcard. Expires 4 November 1998+6 months [Page 7] Internet Draft Expression MIB 4 November 1998 4. Definitions EXPRESSION-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, Integer32, Gauge32, Unsigned32, Counter32, Counter64, IpAddress, TimeTicks, experimental FROM SNMPv2-SMI TEXTUAL-CONVENTION, RowStatus, TruthValue, TimeStamp, DisplayString FROM SNMPv2-TC OwnerString FROM IF-MIB sysUpTime FROM SNMPv2-MIB SnmpAdminString FROM SNMP-FRAMEWORK-MIB MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF; expressionMIB MODULE-IDENTITY LAST-UPDATED "9811041700Z" ORGANIZATION "IETF Distributed Management Working Group" CONTACT-INFO "Bob Stewart Cisco Systems, Inc. 170 West Tasman Drive, San Jose CA 95134-1706. Phone: +1 408 526 4527 Email: bstewart@cisco.com" DESCRIPTION "The MIB module for defining expressions of MIB objects for network management purposes." ::= { experimental xx } expressionMIBObjects OBJECT IDENTIFIER ::= { expressionMIB 1 } expResource OBJECT IDENTIFIER ::= { expressionMIBObjects 1 } expDefine OBJECT IDENTIFIER ::= { expressionMIBObjects 2 } expValue OBJECT IDENTIFIER ::= { expressionMIBObjects 3 } -- -- Wildcarding Example -- -- This example refers to tables and objects defined below. It may well -- make more sense after reading those definitions. -- -- An expression may use wildcarded MIB objects that result in multiple Expires 4 November 1998+6 months [Page 8] Internet Draft Expression MIB 4 November 1998 -- 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 } -- -- 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, but -- the weirdity won't matter. 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 Expires 4 November 1998+6 months [Page 9] Internet Draft Expression MIB 4 November 1998 -- 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 agent 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. -- -- -- Resource Control -- 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. The value -1 indicates this system will not accept deltaValue as a value for expObjectSampleType. Unless explicitly resource limited, a system's value for this object should be 1. Changing this value will not invalidate an existing setting of expObjectSampleType." ::= { expResource 1 } expResourceDeltaWildcardInstanceMaximum OBJECT-TYPE Expires 4 November 1998+6 months [Page 10] Internet Draft Expression MIB 4 November 1998 SYNTAX Unsigned32 UNITS "instances" MAX-ACCESS read-write STATUS current DESCRIPTION "The maximum number of dynamic instance entries this system will support for wildcarded delta objects in expressions. These are the entries that maintain state, one for each instance of each deltaValue object for each value of an expression. That is, for a given delta expression, the number of such 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. Changing this value will not eliminate or inhibit existing delta wildcard instance objects but will prevent the creation of more such objects." ::= { 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 management system." ::= { expResource 4 } Expires 4 November 1998+6 months [Page 11] Internet Draft Expression MIB 4 November 1998 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 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. Because of the relationships among the multiple tables for an expression (expExpressionTable, expObjectTable, and Expires 4 November 1998+6 months [Page 12] Internet Draft Expression MIB 4 November 1998 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. If the subsequent expression includes objects with expObjectSampleType 'deltaValue' the evaluation of that expression takes place under the security credentials of the creator of its expExpressionEntry. Values of read-write objects in this table may be changed at any time." INDEX { IMPLIED expExpressionName } ::= { expExpressionTable 1 } ExpExpressionEntry ::= SEQUENCE { expExpressionName SnmpAdminString, expExpression OCTET STRING, expExpressionValueType INTEGER, expExpressionComment DisplayString, expExpressionDeltaInterval Integer32, expExpressionPrefix OBJECT IDENTIFIER, expExpressionErrors Counter32, expExpressionErrorTime TimeStamp, expExpressionErrorIndex Integer32, expExpressionError INTEGER, expExpressionInstance OBJECT IDENTIFIER, expExpressionOwner OwnerString, expExpressionRowStatus RowStatus } expExpressionName OBJECT-TYPE SYNTAX SnmpAdminString (SIZE (1..64)) MAX-ACCESS not-accessible STATUS current DESCRIPTION "The name of the expression. Choosing names with useful lexical ordering supports using GetNext or GetBulk to retrieve a useful subset of the table or to provide instance- level access control for security purposes." Expires 4 November 1998+6 months [Page 13] Internet Draft Expression MIB 4 November 1998 ::= { expExpressionEntry 1 } expExpression OBJECT-TYPE SYNTAX OCTET STRING (SIZE (1..1024)) MAX-ACCESS read-write 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 integer that corresponds to an expObjectIndex. An example of a valid expression is: ($1-$5)*100 Expressions may not be recursive, that is although an expression may use the results of another expression, it may not contain any variable that is directly or indirectly a result of its own evaluation. 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 Expires 4 November 1998+6 months [Page 14] Internet Draft Expression MIB 4 November 1998 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 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 1-based 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: Expires 4 November 1998+6 months [Page 15] Internet Draft Expression MIB 4 November 1998 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. 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 >= also work with TimeTicks. The operators &, |, and ^ also work with IpAddress. The operators << and >> also 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. Expires 4 November 1998+6 months [Page 16] Internet Draft Expression MIB 4 November 1998 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 sum exists The following function definitions indicate their 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 (1-based) 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 1-based index where the match began. A return value of 0 indicates no match (i.e. boolean false). Expires 4 November 1998+6 months [Page 17] Internet Draft Expression MIB 4 November 1998 oidBegins/Ends/Contains(oid, oid) - looks for the second OID (which can be an OID constant) in the first and returns the the 1-based index where the match began. A return value of 0 indicates no match (i.e. boolean false). sum(integerObject*) - sums all availiable 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)." ::= { expExpressionEntry 2 } expExpressionValueType OBJECT-TYPE SYNTAX INTEGER { counter32(1), unsignedOrGauge32(2), timeTicks(3), integer32(4), ipAddress(5), octetString(6), objectId(7), counter64(8) } MAX-ACCESS read-write 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 3 } expExpressionComment OBJECT-TYPE SYNTAX DisplayString MAX-ACCESS read-write STATUS current DESCRIPTION "A comment to explain the use or meaning of the expression." DEFVAL { ''H } ::= { expExpressionEntry 4 } expExpressionDeltaInterval OBJECT-TYPE SYNTAX Integer32 (0..86400) UNITS "seconds" MAX-ACCESS read-write STATUS current Expires 4 November 1998+6 months [Page 18] Internet Draft Expression MIB 4 November 1998 DESCRIPTION "Sampling interval for objects in this expression with expObjectSampleType 'deltaValue'. This object is 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 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." DEFVAL { 0 } ::= { expExpressionEntry 5 } 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. Expires 4 November 1998+6 months [Page 19] Internet Draft Expression MIB 4 November 1998 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 6 } expExpressionErrors OBJECT-TYPE 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. It is a legitimate condition that causes the corresponding expression value not to be instantiated." ::= { expExpressionEntry 7 } expExpressionErrorTime 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. This object is not instantiated if there have been no errors." ::= { expExpressionEntry 8 } expExpressionErrorIndex OBJECT-TYPE SYNTAX Integer32 MAX-ACCESS read-only STATUS current DESCRIPTION Expires 4 November 1998+6 months [Page 20] Internet Draft Expression MIB 4 November 1998 "The 1-based character index into expExpression for where the error occurred. The value zero indicates irrelevance. This object is not instantiated if there have been no errors." ::= { expExpressionEntry 9 } expExpressionError 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 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) Expires 4 November 1998+6 months [Page 21] Internet Draft Expression MIB 4 November 1998 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 evalutaion for a Get* operation return the SNMP error code 'genErr' except for 'tooManyWildcardValues' and 'resourceUnavailable' which return the SNMP error code 'resourceUnavailable'. This object is not instantiated if there have been no errors." ::= { expExpressionEntry 10 } expExpressionInstance OBJECT-TYPE SYNTAX OBJECT IDENTIFIER MAX-ACCESS read-only STATUS current DESCRIPTION "The expValueInstance being evaluated when the error occurred. A zero-length indicates irrelevance. This object is not instantiated if there have been no errors." ::= { expExpressionEntry 11 } expExpressionOwner OBJECT-TYPE SYNTAX OwnerString MAX-ACCESS read-write Expires 4 November 1998+6 months [Page 22] Internet Draft Expression MIB 4 November 1998 STATUS current DESCRIPTION "The entity that configured this entry and is therefore using the resources assigned to it." DEFVAL { "" } ::= { expExpressionEntry 12 } expExpressionRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The control that allows creation and deletion of entries." ::= { expExpressionEntry 13 } -- -- 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 2 } expObjectEntry OBJECT-TYPE SYNTAX ExpObjectEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION Expires 4 November 1998+6 months [Page 23] Internet Draft Expression MIB 4 November 1998 "Information about an object. An application uses expObjectRowStatus 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 { expExpressionName, expObjectIndex } ::= { expObjectTable 1 } ExpObjectEntry ::= SEQUENCE { expObjectIndex Unsigned32, expObjectID OBJECT IDENTIFIER, expObjectIDWildcard TruthValue, expObjectSampleType INTEGER, expObjectDeltaDiscontinuityID OBJECT IDENTIFIER, expObjectDiscontinuityIDWildcard TruthValue, expObjectDiscontinuityIDType INTEGER, expObjectConditional OBJECT IDENTIFIER, expObjectConditionalWildcard TruthValue, expObjectRowStatus 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. Expires 4 November 1998+6 months [Page 24] Internet Draft Expression MIB 4 November 1998 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, expExpressionPrefix will reflect a scalar object (ie 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 Expires 4 November 1998+6 months [Page 25] Internet Draft Expression MIB 4 November 1998 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 } expObjectDeltaDiscontinuityID OBJECT-TYPE SYNTAX OBJECT IDENTIFIER MAX-ACCESS read-create STATUS current DESCRIPTION "The OBJECT IDENTIFIER (OID) of a TimeTicks or TimeStamp object that indicates a discontinuity in the value at expObjectID. This object is not instantiated if expObject is not 'deltaValue'. 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 { sysUpTime 0 } ::= { 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 not instantiated if expObject is not 'deltaValue'. NOTE: The simplest implementations of this MIB may not allow Expires 4 November 1998+6 months [Page 26] Internet Draft Expression MIB 4 November 1998 wildcards." DEFVAL { false } ::= { expObjectEntry 6 } expObjectDiscontinuityIDType OBJECT-TYPE SYNTAX INTEGER { timeTicks(1), timeStamp(2) } MAX-ACCESS read-create STATUS current DESCRIPTION "The value 'timeTicks' indicates the expObjectDeltaDiscontinuityID of this row is of syntax TimeTicks. The value 'timeStamp' indicates that expObjectDeltaDiscontinuityID is of syntax TimeStamp. This object is not instantiated if expObject is not 'deltaValue'." DEFVAL { timeTicks } ::= { expObjectEntry 7 } 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 Expires 4 November 1998+6 months [Page 27] Internet Draft Expression MIB 4 November 1998 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 } expObjectRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The control that allows creation/deletion of entries. Objects in this table may be changed while expObjectRowStatus 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 Expires 4 November 1998+6 months [Page 28] Internet Draft Expression MIB 4 November 1998 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', reading a value from the table causes the evaluation of the expression for that value. For those that contain a 'deltaValue' the value read is as of the last delta 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, expression evaluation must take place using security credentials for the implied Gets of the objects in the expression. For expressions with no deltaValue those security credentials are the ones that came with the Get* for the value. For expressions with a deltaValue the ongoing expression evaluation is under the security credentials of the creator of the corresponding expNameEntry." INDEX { 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 Expires 4 November 1998+6 months [Page 29] Internet Draft Expression MIB 4 November 1998 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 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 'unsignedOrGauge32'." ::= { 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 } Expires 4 November 1998+6 months [Page 30] Internet Draft Expression MIB 4 November 1998 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 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 -- expressionMIBConformance OBJECT IDENTIFIER ::= { expressionMIB 3 } expressionMIBCompliances OBJECT IDENTIFIER ::= { expressionMIBConformance 1 } expressionMIBGroups OBJECT IDENTIFIER ::= { expressionMIBConformance 2 } -- Compliance expressionMIBCompliance MODULE-COMPLIANCE Expires 4 November 1998+6 months [Page 31] Internet Draft Expression MIB 4 November 1998 STATUS current DESCRIPTION "The compliance statement for entities which implement the Expression MIB." MODULE -- this module MANDATORY-GROUPS { expressionResourceGroup, expressionDefinitionGroup, expressionValueGroup } 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 not allow deltas." ::= { expressionMIBCompliances 1 } -- Units of Conformance expressionResourceGroup OBJECT-GROUP OBJECTS { expResourceDeltaMinimum, expResourceDeltaWildcardInstanceMaximum, expResourceDeltaWildcardInstances, expResourceDeltaWildcardInstancesHigh, expResourceDeltaWildcardInstanceResourceLacks } STATUS current DESCRIPTION "Expression definition resource management." ::= { expressionMIBGroups 1 } expressionDefinitionGroup OBJECT-GROUP OBJECTS { expExpression, expExpressionValueType, expExpressionComment, expExpressionDeltaInterval, Expires 4 November 1998+6 months [Page 32] Internet Draft Expression MIB 4 November 1998 expExpressionPrefix, expExpressionErrors, expExpressionErrorTime, expExpressionErrorIndex, expExpressionError, expExpressionInstance, expExpressionOwner, expExpressionRowStatus, expObjectID, expObjectIDWildcard, expObjectSampleType, expObjectDeltaDiscontinuityID, expObjectDiscontinuityIDWildcard, expObjectDiscontinuityIDType, expObjectConditional, expObjectConditionalWildcard, expObjectRowStatus } STATUS current DESCRIPTION "Expression definition." ::= { expressionMIBGroups 2 } expressionValueGroup OBJECT-GROUP OBJECTS { expValueCounter32Val, expValueUnsigned32Val, expValueTimeTicksVal, expValueInteger32Val, expValueIpAddressVal, expValueOctetStringVal, expValueOidVal, expValueCounter64Val } STATUS current DESCRIPTION "Expression value." ::= { expressionMIBGroups 3 } END Expires 4 November 1998+6 months [Page 33] Internet Draft Expression MIB 4 November 1998 5. 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. Expires 4 November 1998+6 months [Page 34] Internet Draft Expression MIB 4 November 1998 6. 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 implemenation. Expires 4 November 1998+6 months [Page 35] Internet Draft Expression MIB 4 November 1998 7. References [1] Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for Describing SNMP Management Frameworks", RFC 2271, Cabletron Systems, Inc., BMC Software, Inc., IBM T. J. Watson Research, January 1998. [2] Rose, M. and K. McCloghrie, "Structure and Identification of Management Information for TCP/IP-based Internets", RFC 1155, Performance Systems International, Hughes LAN Systems, May 1990. [3] Rose, M. and K. McCloghrie, "Concise MIB Definitions", RFC 1212, Performance Systems International, Hughes LAN Systems, March 1991. [4] M. Rose, "A Convention for Defining Traps for use with the SNMP", RFC 1215, Performance Systems International, March 1991. [5] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Structure of Management Information for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1902, SNMP Research,Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc., International Network Services, January 1996. [6] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Textual Conventions for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1903, SNMP Research, Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc., International Network Services, January 1996. [7] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Conformance Statements for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1904, SNMP Research, Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc., International Network Services, January 1996. [8] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple Network Management Protocol", RFC 1157, SNMP Research, Performance Systems International, Performance Systems International, MIT Laboratory for Computer Science, May 1990. [9] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Introduction to Community-based SNMPv2", RFC 1901, SNMP Research, Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc., International Network Services, January 1996. Expires 4 November 1998+6 months [Page 36] Internet Draft Expression MIB 4 November 1998 [10] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Transport Mappings for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1906, SNMP Research, Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc., International Network Services, January 1996. [11] Case, J., Harrington D., Presuhn R. and B. Wijnen, "Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)", RFC 2272, SNMP Research, Inc., Cabletron Systems, Inc., BMC Software, Inc., IBM T. J. Watson Research, January 1998. [12] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)", RFC 2274, IBM T. J. Watson Research, January 1998. [13] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1905, SNMP Research, Inc., Cisco Systems, Inc., Dover Beach Consulting, Inc., International Network Services, January 1996. [14] Levi, D., Meyer, P. and B. Stewart, "SNMPv3 Applications", RFC 2273, SNMP Research, Inc., Secure Computing Corporation, Cisco Systems, January 1998. [15] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)", RFC 2275, IBM T. J. Watson Research, BMC Software, Inc., Cisco Systems, Inc., January 1998. [16] Stewart, B., "Event MIB", RFC ????, Cisco Systems, Inc., ?Month? 1998. Expires 4 November 1998+6 months [Page 37] Internet Draft Expression MIB 4 November 1998 8. 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. Security of expression definitions and results depends on the expression name. With view-based access control [16] and expression names with hierarchical structure a network manager can control who has what level of access to what expressions. Access control for the objects within the expression depends on when the expression is evaluated. For expressions of all absolute values the security credentials used to get to the necessary objects are those of the reader of the expression value. For expressions containing delta or changed values, the security credentials used at each polling period to get the necessary objects are those used to set the expression definition's RowStatus object to 'active'. 9. Author's Address Bob Stewart Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134-1706 U.S.A. Phone: +1 408 526 4527 Email: bstewart@cisco.com Expires 4 November 1998+6 months [Page 38] Internet Draft Expression MIB 4 November 1998 10. Full Copyright Statement Copyright (C) The Internet Society (1998). 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. Expires 4 November 1998+6 months [Page 39] Internet Draft Expression MIB 4 November 1998 Table of Contents 1 Abstract ........................................................ 2 2 The SNMP Management Framework ................................... 2 3 Overview ........................................................ 4 3.1 Usage ......................................................... 4 3.2 Operation ..................................................... 5 3.2.1 Sampling .................................................... 5 3.2.2 Wildcards ................................................... 5 3.2.3 Evaluation .................................................. 6 3.3 Structure ..................................................... 6 3.3.1 Resource .................................................... 6 3.3.2 Definition .................................................. 7 3.3.3 Value ....................................................... 7 4 Definitions ..................................................... 8 5 Intellectual Property ........................................... 34 6 Acknowledgements ................................................ 35 7 References ...................................................... 36 8 Security Considerations ......................................... 38 9 Author's Address ................................................ 38 10 Full Copyright Statement ....................................... 39 Expires 4 November 1998+6 months [Page 40]