rfc1442.txt

<VC++网络游戏建摸与实现>源代码

          RFC 1442                SMI for SNMPv2              April 1993


          7.  Mapping of the OBJECT-TYPE macro

          The OBJECT-TYPE macro is used to define a managed object.  It
          should be noted that the expansion of the OBJECT-TYPE macro is
          something which conceptually happens during implementation and
          not during run-time.


          7.1.  Mapping of the SYNTAX clause

          The SYNTAX clause, which must be present, defines the abstract
          data structure corresponding to that object.  The data
          structure must be one of the alternatives defined in the
          ObjectSyntax CHOICE.

          Full ASN.1 sub-typing is allowed, as appropriate to the
          underingly ASN.1 type, primarily as an aid to implementors in
          understanding the meaning of the object.  Any such restriction
          on size, range, enumerations or repertoire specified in this
          clause represents the maximal level of support which makes
          "protocol sense".  Of course, sub-typing is not allowed for
          the Counter32 or Counter64 types, but is allowed for the
          Gauge32 type.

          The semantics of ObjectSyntax are now described.


          7.1.1.  Integer32 and INTEGER

          The Integer32 type represents integer-valued information
          between -2^31 and 2^31-1 inclusive (-2147483648 to 2147483647
          decimal).  This type is indistinguishable from the INTEGER
          type.

          The INTEGER type may also be used to represent integer-valued
          information, if it contains named-number enumerations, or if
          it is sub-typed to be more constrained than the Integer32
          type.  In the former case, only those named-numbers so
          enumerated may be present as a value.  Note that although it
          is recommended that enumerated values start at 1 and be
          numbered contiguously, any valid value for Integer32 is
          allowed for an enumerated value and, further, enumerated
          values needn't be contiguously assigned.







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          Finally, the hyphen character is not allowed as a part of the
          label name for any named-number enumeration.


          7.1.2.  OCTET STRING

          The OCTET STRING type represents arbitrary binary or textual
          data.  Although there is no SMI-specified size limitation for
          this type, MIB designers should realize that there may be
          implementation and interoperability limitations for sizes in
          excess of 255 octets.


          7.1.3.  OBJECT IDENTIFIER

          The OBJECT IDENTIFIER type represents administratively
          assigned names.  Any instance of this type may have at most
          128 sub-identifiers.  Further, each sub-identifier must not
          exceed the value 2^32-1 (4294967295 decimal).


          7.1.4.  BIT STRING

          The BIT STRING type represents an enumeration of named bits.
          This collection is assigned non-negative, contiguous values,
          starting at zero.  Only those named-bits so enumerated may be
          present in a value.

          A requirement on "standard" MIB modules is that the hyphen
          character is not allowed as a part of the label name for any
          named-bit enumeration.


          7.1.5.  IpAddress

          The IpAddress type represents a 32-bit internet address.  It
          is represented as an OCTET STRING of length 4, in network
          byte-order.

          Note that the IpAddress type is a tagged type for historical
          reasons.  Network addresses should be represented using an
          invocation of the TEXTUAL-CONVENTION macro [3].








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          7.1.6.  Counter32

          The Counter32 type represents a non-negative integer which
          monotonically increases until it reaches a maximum value of
          2^32-1 (4294967295 decimal), when it wraps around and starts
          increasing again from zero.

          Counters have no defined "initial" value, and thus, a single
          value of a Counter has (in general) no information content.
          Discontinuities in the monotonically increasing value normally
          occur at re-initialization of the management system, and at
          other times as specified in the description of an object-type
          using this ASN.1 type.  If such other times can occur, for
          example, the creation of an object instance at times other
          than re-initialization, then a corresponding object should be
          defined with a SYNTAX clause value of TimeStamp (a textual
          convention defined in [3]) indicating the time of the last
          discontinuity.

          The value of the MAX-ACCESS clause for objects with a SYNTAX
          clause value of Counter32 is always "read-only".

          A DEFVAL clause is not allowed for objects with a SYNTAX
          clause value of Counter32.


          7.1.7.  Gauge32

          The Gauge32 type represents a non-negative integer, which may
          increase or decrease, but shall never exceed a maximum value.
          The maximum value can not be greater than 2^32-1 (4294967295
          decimal).  The value of a Gauge has its maximum value whenever
          the information being modeled is greater or equal to that
          maximum value; if the information being modeled subsequently
          decreases below the maximum value, the Gauge also decreases.


          7.1.8.  TimeTicks

          The TimeTicks type represents a non-negative integer which
          represents the time, modulo 2^32 (4294967296 decimal), in
          hundredths of a second between two epochs.  When objects are
          defined which use this ASN.1 type, the description of the
          object identifies both of the reference epochs.






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          For example, [3] defines the TimeStamp textual convention
          which is based on the TimeTicks type.  With a TimeStamp, the
          first reference epoch is defined as when MIB-II's sysUpTime
          [7] was zero, and the second reference epoch is defined as the
          current value of sysUpTime.


          7.1.9.  Opaque

          The Opaque type is provided solely for backward-compatibility,
          and shall not be used for newly-defined object types.

          The Opaque type supports the capability to pass arbitrary
          ASN.1 syntax.  A value is encoded using the ASN.1 Basic
          Encoding Rules [4] into a string of octets.  This, in turn, is
          encoded as an OCTET STRING, in effect "double-wrapping" the
          original ASN.1 value.

          Note that a conforming implementation need only be able to
          accept and recognize opaquely-encoded data.  It need not be
          able to unwrap the data and then interpret its contents.

          A requirement on "standard" MIB modules is that no object may
          have a SYNTAX clause value of Opaque.


          7.1.10.  NsapAddress

          The NsapAddress type represents an OSI address as a variable-
          length OCTET STRING.  The first octet of the string contains a
          binary value in the range of 0..20, and indicates the length
          in octets of the NSAP.  Following the first octet, is the
          NSAP, expressed in concrete binary notation, starting with the
          most significant octet.  A zero-length NSAP is used as a
          "special" address meaning "the default NSAP" (analogous to the
          IP address of 0.0.0.0).  Such an NSAP is encoded as a single
          octet, containing the value 0.  All other NSAPs are encoded in
          at least 4 octets.

          Note that the NsapAddress type is a tagged type for historical
          reasons.  Network addresses should be represented using an
          invocation of the TEXTUAL-CONVENTION macro [3].








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          7.1.11.  Counter64

          The Counter64 type represents a non-negative integer which
          monotonically increases until it reaches a maximum value of
          2^64-1 (18446744073709551615 decimal), when it wraps around
          and starts increasing again from zero.

          Counters have no defined "initial" value, and thus, a single
          value of a Counter has (in general) no information content.
          Discontinuities in the monotonically increasing value normally
          occur at re-initialization of the management system, and at
          other times as specified in the description of an object-type
          using this ASN.1 type.  If such other times can occur, for
          example, the creation of an object instance at times other
          than re-initialization, then a corresponding object should be
          defined with a SYNTAX clause value of TimeStamp (a textual
          convention defined in [3]) indicating the time of the last
          discontinuity.

          The value of the MAX-ACCESS clause for objects with a SYNTAX
          clause value of Counter64 is always "read-only".

          A requirement on "standard" MIB modules is that the Counter64
          type may be used only if the information being modeled would
          wrap in less than one hour if the Counter32 type was used
          instead.

          A DEFVAL clause is not allowed for objects with a SYNTAX
          clause value of Counter64.


          7.1.12.  UInteger32

          The UInteger32 type represents integer-valued information
          between 0 and 2^32-1 inclusive (0 to 4294967295 decimal).


          7.2.  Mapping of the UNITS clause

          This UNITS clause, which need not be present, contains a
          textual definition of the units associated with that object.









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          7.3.  Mapping of the MAX-ACCESS clause

          The MAX-ACCESS clause, which must be present, defines whether
          it makes "protocol sense" to read, write and/or create an
          instance of the object.  This is the maximal level of access
          for the object.  (This maximal level of access is independent
          of any administrative authorization policy.)

          The value "read-write" indicates that read and write access
          make "protocol sense", but create does not.  The value "read-
          create" indicates that read, write and create access make
          "protocol sense".  The value "not-accessible" indicates either
          an auxiliary object (see Section 7.7) or an object which is
          accessible only via a notificationn (e.g., snmpTrapOID [5]).

          These values are ordered, from least to greatest: "not-
          accessible", "read-only", "read-write", "read-create".

          If any columnar object in a conceptual row has "read-create"
          as its maximal level of access, then no other columnar object
          of the same conceptual row may have a maximal access of
          "read-write".  (Note that "read-create" is a superset of
          "read-write".)


          7.4.  Mapping of the STATUS clause

          The STATUS clause, which must be present, indicates whether
          this definition is current or historic.

          The values "current", and "obsolete" are self-explanatory.
          The "deprecated" value indicates that the object is obsolete,
          but that an implementor may wish to support that object to
          foster interoperability with older implementations.


          7.5.  Mapping of the DESCRIPTION clause

          The DESCRIPTION clause, which must be present, contains a
          textual definition of that object which provides all semantic
          definitions necessary for implementation, and should embody
          any information which would otherwise be communicated in any
          ASN.1 commentary annotations associated with the object.







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          7.6.  Mapping of the REFERENCE clause

          The REFERENCE clause, which need not be present, contains a
          textual cross-reference to an object defined in some other
          information module.  This is useful when de-osifying a MIB
          module produced by some other organization.


          7.7.  Mapping of the INDEX clause

          The INDEX clause, which must be present if that object
          corresponds to a conceptual row (unless an AUGMENTS clause is
          present instead), and must be absent otherwise, defines
          instance identification information for the columnar objects
          subordinate to that object.

          Management operations apply exclusively to scalar objects.
          However, it is convenient for developers of management
          applications to impose imaginary, tabular structures on the
          ordered collection of objects that constitute the MIB.  Each
          such conceptual table contains zero or more rows, and each row
          may contain one or more scalar objects, termed columnar
          objects.  This conceptualization is formalized by using the
          OBJECT-TYPE macro to define both an object which corresponds
          to a table and an object which corresponds to a row in that
          table.  A conceptual table has SYNTAX of the form:

               SEQUENCE OF <EntryType>

          where <EntryType> refers to the SEQUENCE type of its
          subordinate conceptual row.  A conceptual row has SYNTAX of
          the form:

               <EntryType>

          where <EntryType> is a SEQUENCE type defined as follows:

               <EntryType> ::= SEQUENCE { <type1>, ... , <typeN> }

          where there is one <type> for each subordinate object, and
          each <type> is of the form:

               <descriptor> <syntax>

          where <descriptor> is the descriptor naming a subordinate





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          object, and <syntax> has the value of that subordinate
          object's SYNTAX clause, optionally omitting the sub-typing
          information.  Further, these ASN.1 types are always present
          (the DEFAULT and OPTIONAL clauses are disallowed in the
          SEQUENCE definition).  The MAX-ACCESS clause for conceptual
          tables and rows is "not-accessible".

          For leaf objects which are not columnar objects, instances of
          the object are identified by appending a sub-identifier of
          zero to the name of that object.  Otherwise, the INDEX clause
          of the conceptual row object superior to a columnar object
          defines instance identification information.

          The instance identification information in an INDEX clause
          must specify object(s) such that value(s) of those object(s)
          will unambiguously distinguish a conceptual row.  The syntax
          of those objects indicate how to form the instance-identifier:

          (1)  integer-valued: a single sub-identifier taking the
               integer value (this works only for non-negative
               integers);

          (2)  string-valued, fixed-length strings (or variable-length
               preceded by the IMPLIED keyword): `n' sub-identifiers,
               where `n' is the length of the string (each octet of the
               string is encoded in a separate sub-identifier);

          (3)  string-valued, variable-length strings (not preceded by
               the IMPLIED keyword): `n+1' sub-identifiers, where `n' is
               the length of the string (the first sub-identifier is `n'
               itself, following this, each octet of the string is
               encoded in a separate sub-identifier);

          (4)  object identifier-valued: `n+1' sub-identifiers, where
               `n' is the number of sub-identifiers in the value (the
               first sub-identifier is `n' itself, following this, each