3. 定义

SNMPv2-PDU DEFINITIONS ::= BEGIN

-- Protocol Data Units

PDUs ::=
    CHOICE {
        get-request
            GetRequest-PDU,
        get-next-request
            GetNextRequest-PDU,
        get-bulk-request
            GetBulkRequest-PDU,
        response
            Response-PDU,
        set-request
            SetRequest-PDU,
        inform-request
            InformRequest-PDU,
        snmpV2-trap
            SNMPv2-Trap-PDU,
        report
            Report-PDU
    }

-- PDU Types

GetRequest-PDU ::=
    [0]
        IMPLICIT PDU

GetNextRequest-PDU ::=
    [1]
        IMPLICIT PDU

Response-PDU ::=
    [2]
        IMPLICIT PDU

SetRequest-PDU ::=
    [3]
        IMPLICIT PDU

-- [4] is obsolete

GetBulkRequest-PDU ::=
    [5]
        IMPLICIT BulkPDU

InformRequest-PDU ::=
    [6]
        IMPLICIT PDU

SNMPv2-Trap-PDU ::=
    [7]
        IMPLICIT PDU

-- Usage and precise semantics of Report-PDU are not presently defined.
-- Any SNMP administrative framework making use of this PDU must define its usage and semantics.

Report-PDU ::=
    [8]
        IMPLICIT PDU

max-bindings
    INTEGER ::= 2147483647

PDU ::=
    SEQUENCE {
        request-id
            Integer32,
        error-status            -- sometimes ignored
            INTEGER {
                noError(0),
                tooBig(1),
                noSuchName(2),      -- for proxy compatibility
                badValue(3),        -- for proxy compatibility
                readOnly(4),        -- for proxy compatibility
                genErr(5),
                noAccess(6),
                wrongType(7),
                wrongLength(8),
                wrongEncoding(9),
                wrongValue(10),
                noCreation(11),
                inconsistentValue(12),
                resourceUnavailable(13),
                commitFailed(14),
                undoFailed(15),
                authorizationError(16),
                notWritable(17),
                inconsistentName(18)
            },
        error-index             -- sometimes ignored
            INTEGER (0..max-bindings),
        variable-bindings       -- values are sometimes ignored
            VarBindList
    }

BulkPDU ::=                     -- MUST be identical in structure to PDU
    SEQUENCE {
        request-id
            Integer32,
        non-repeaters
            INTEGER (0..max-bindings),
        max-repetitions
            INTEGER (0..max-bindings),
        variable-bindings       -- values are ignored
            VarBindList
    }

-- Variable Binding

VarBind ::=
    SEQUENCE {
        name
            ObjectName,
        CHOICE {
            value
                ObjectSyntax,
            unSpecified         -- in retrieval requests
                NULL,
                                -- exceptions in responses
            noSuchObject[0]
                IMPLICIT NULL,
            noSuchInstance[1]
                IMPLICIT NULL,
            endOfMibView[2]
                IMPLICIT NULL
        }
    }

-- Variable Binding List

VarBindList ::=
    SEQUENCE (SIZE (0..max-bindings)) OF
        VarBind

-- Definitions from other modules

Integer32 ::= [UNIVERSAL 2] IMPLICIT INTEGER (-2147483648..2147483647)

ObjectName ::= [UNIVERSAL 6] IMPLICIT OBJECT IDENTIFIER

ObjectSyntax ::= CHOICE {
    simple
        SimpleSyntax,
    application-wide
        ApplicationSyntax
}

SimpleSyntax ::= CHOICE {
    integer-value
        INTEGER (-2147483648..2147483647),
    string-value
        OCTET STRING (SIZE (0..65535)),
    objectID-value
        OBJECT IDENTIFIER
}

ApplicationSyntax ::= CHOICE {
    ipAddress-value
        IpAddress,
    counter-value
        Counter32,
    timeticks-value
        TimeTicks,
    arbitrary-value
        Opaque,
    big-counter-value
        Counter64,
    unsigned-integer-value
        Unsigned32
}

IpAddress ::=
    [APPLICATION 0]
        IMPLICIT OCTET STRING (SIZE (4))

Counter32 ::=
    [APPLICATION 1]
        IMPLICIT INTEGER (0..4294967295)

Unsigned32 ::=
    [APPLICATION 2]
        IMPLICIT INTEGER (0..4294967295)

Gauge32 ::= Unsigned32

TimeTicks ::=
    [APPLICATION 3]
        IMPLICIT INTEGER (0..4294967295)

Opaque ::=
    [APPLICATION 4]
        IMPLICIT OCTET STRING

Counter64 ::=
    [APPLICATION 6]
        IMPLICIT INTEGER (0..18446744073709551615)

END

此 ASN.1 模块定义 SNMP 版本 2 协议数据单元 (Protocol Data Unit, PDU) 的结构. 该模块包括:

• PDU 类型: GetRequest, GetNextRequest, GetBulkRequest, Response, SetRequest, InformRequest, SNMPv2-Trap 和 Report
• 错误状态码: 在 Response-PDU 中用于指示处理结果
• 变量绑定: 将对象名称与其值或异常配对的机制
• 数据类型: 包括简单类型 (INTEGER, OCTET STRING, OBJECT IDENTIFIER) 和应用范围类型 (IpAddress, Counter32, Counter64, Gauge32, TimeTicks, Opaque, Unsigned32)