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SYNTAX Clause

  • Artykuł

The OBJECT-TYPE macro contains a SYNTAX clause that defines the data and type for the MIB object. While the SNMP Provider observes general rules for mapping SYNTAX clauses, the provider also follows rules specific to several data types.

Note

For more information about installing the provider, see Setting up the WMI SNMP Environment.

The following mapping rules apply to all of the data types described in the table below:

  • The textual representation of the SYNTAX clause maps to the CIM property qualifier textual_convention.
  • The named type definition in the SYNTAX clause maps to the CIM property qualifier object_syntax. This mapping differs depending on the data type. For more information, see the mapping descriptions.
  • The SNMP type used when encoding SNMPv1 and SNMPv2C protocol frames maps to the CIM property qualifier encoding.
  • The CIM property qualifier cimtype contains the textual representation that formats the underlying CIM protocol value.

The following table lists data types that have specific rules that govern the provider mapping behavior.

SNMP data type Description
Primitive type One of the basic data types defined in the Structure of Management Information (SMI) documents RFC 1213 and RFC 1903.
Textual convention Type definition generated through the explicit use of the SNMPv2C TEXTUAL-CONVENTION macro or generated through the use of a named type. A textual convention assigns a name and, in some cases, a range of values to an existing data type.
Named type Named reference to a primitive type, textual convention, or constrained type.
Constrained type Primitive type, named type, or textual convention that has been constrained by some subtyping mechanism defined in the SMI documents RFC 1213 and RFC 1903.

Primitive Type

The primitive type is one of the basic data types defined in the Structure of Management Information (SMI) documents RFC 1213 and RFC 1903. SNMP primitive types map to CIM-defined types. The following table lists the mapping that occurs when the SYNTAX clause explicitly refers to a primitive type for SNMPv1. The textual_convention, encoding, and object_syntax qualifiers are always the same as the MIB type and the default value is always NULL.

MIB type CIM variant type cimtype value
INTEGER VT_I4 sint32
OCTETSTRING VT_BSTR string
OBJECTIDENTIFIER VT_BSTR string
NULL VT_NULL Not supported
IpAddress VT_BSTR string
Counter VT_I4 uint32
Gauge VT_I4 uint32
TimeTicks VT_I4 uint32
Opaque VT_BSTR string
NetworkAddress VT_BSTR string

The provider ignores the OBJECT-TYPE macro when the SYNTAX clause refers to NULL, either explicitly or through a named type assignment. The following table lists the mapping that occurs when the SYNTAX clause explicitly refers to a primitive type for SNMPv2. The textual_convention, encoding, and object_syntax qualifiers are always the same as the MIB type and the default value is always NULL.

MIB type CIM variant type cimtype value
INTEGER VT_I4 sint32
OCTET STRING VT_BSTR string
OBJECT IDENTIFIER VT_BSTR string
IpAddress VT_BSTR string
Counter32 VT_I4 uint32
Gauge32 VT_I4 uint32
Unsigned32 VT_I4 uint32
Integer32 VT_I4 sint32
Counter64 VT_BSTR uint64
TimeTicks VT_I4 uint32
Opaque VT_BSTR string

Named Type

SNMP named types map to CIM-defined types. When the SYNTAX clause refers to a primitive type, textual convention, or constrained type through a type assignment derivation, use the those types to determine which mapping procedures apply.

  • If, through derivation of the type assignment rules, you encounter a constrained type definition:

    • And if, through further derivation, you encounter one of the textual conventions listed in TEXTUAL-CONVENTION Macro, then apply the mapping rules for constrained types and textual conventions.
    • Otherwise, if you encounter one of the primitive types listed in either primitive type table, apply the mapping rules for primitive types and constrained types.

  • If you encounter one of the textual conventions listed in TEXTUAL_CONVENTION Macro, apply the mapping rules for textual conventions.

  • If you encounter one of the primitive types listed in either primitive type table, apply the mapping rules for primitive types.

Note

Classes containing property types that do not conform to the mapping described above are not valid. In this case, the provider returns an error if and when the provider requests the retrieval of a class definition while executing an instance retrieval function.

Constrained Type

A constrained type is a primitive type, named type, or textual convention that has been constrained by some subtyping mechanism defined in the SMI documents RFC 1213 and RFC 1903. When subtyping occurs, additional CIM qualifiers are required to specify the subtype values. The named-type definition in the SYNTAX clause maps verbatim to the CIM property qualifier object_syntax up to, but not including the constraints of the subtype.

Subtypes may follow any of the following formats:

  • Enumerated INTEGER

    The CIM property qualifier enumeration specifies the enumerated values. This qualifier is represented as a string containing a comma-separated list of signed 32-bit integer values. The following table lists the mapping types. The default value is always NULL.

Constrained MIB type CIM variant type CIM qualifiers
Enumerated INTEGER VT_BSTR textual_convention: enumeratedinteger
encoding: INTEGER
cimtype: string

  • BITS

    The CIM property qualifier bits specifies the enumerated values. This qualifier is represented as a string containing a comma-separated list of signed 32-bit integer values. The following table lists the mapping types. The default value is always NULL.

Constrained MIB type CIM variant type CIM qualifiers
BITS VT_ARRAY | VT_BSTR textual_convention: bits
encoding: OCTETSTRING
cimtype: string

  • Variable-length

    When the SYNTAX clause refers to a primitive type, named type, or textual convention that is subtyped as a variable-length OCTET STRING or Opaque, the CIM property qualifier variable_length specifies the minimum, maximum, and fixed-length values associated with the type definition. This qualifier is implemented as a string in the following format where the variable-length values are represented as unsigned 32-bit integers.

    (((0.9) .. (0.9)) | (0.9))(, (((0.9) .. (0.9)) | (0.9)))*

  • Fixed-length

    When the SYNTAX clause refers to a primitive type, named type, or textual convention that is subtyped as a fixed-length OCTET STRING or Opaque, the CIM property qualifier fixed_length specifies the fixed-length value. This qualifier is represented as an unsigned 32-bit integer value.

  • Range

    When the SYNTAX clause refers to a primitive type, named type, or textual convention that is subtyped as a ranged or fixed-value INTEGER or Gauge, the CIM property qualifier variable_value specifies the ranged and fixed values associated with the type definition. This qualifier is implemented as a string in the following format where the range and fixed-length values are represented as unsigned 32-bit integers.

    (((0.9)..(0.9))|(0.9))(,(((0.9)..(0.9))|(0.9)))*

Example Code

The following example describes an enumerated INTEGER subtype.

Status := INTEGER {
up(1),
down(2),
testing(3)
}

This example maps to:

enumeration("up(1),down(2),testing(3)")

The following code example describes a BITS subtype.

Status := BITS {
up(1),
down(2), 
testing(3)
}

The following code example maps to:

bits("up(1),down(2),testing(3)")

The following code example describes a variable-length subtype.

MySnmpOSIAddress ::=  TEXTUAL-CONVENTION

    DISPLAY-HINT    "*1x:/1x:"
    STATUS        current
    DESCRIPTION
            "Represents an OSI transport-address:

            octets    contents         encoding
              1        length of NSAP   'n' as an unsigned-integer
                                        (either 0 or from 3 to 20)
              2..(n+1)  NSAP          concrete binary representation
              (n+2)..m  TSEL             string of (up to 64) octets
            "
    SYNTAX         OCTET STRING (SIZE (1|4..85))

This example maps to:

display_hint("*1x:/1x:"),
encoding("OCTETSTRING"),
textual_convention("OCTETSTRING"),
variable_length ("1,4..85")

The following example describes a fixed-length subtype.

IPXADDRESS := OCTET STRING (SIZE (6))

This example maps to:

fixed_length(6)

The following example describes a range subtype.

Status := INTEGER (10..20|8)

This example maps to:

variable_value("10..20,8")