rfc2982.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

     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