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1. Introduction

The DNP3 connector extracts values from DNP3 outstations and forwards the data to gRPC_kafka.
Configuration is JSON-based, enabling clear, repeatable deployments for DNP3 environments.

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Key Features

  • DNP3 client (Master) support – communicate with one or more outstations.
  • Class-based scanning – mirror data by DNP3 class (0–3) instead of single indices.
  • Flexible configuration – per-class or per-index configuration available.
  • Comprehensive logging – log rotation, file templates, and log levels for easy troubleshooting.

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2. Configuration

The DNP3 connector is configured through a JSON file composed of a logSettings object and a tagConfiguration array.
Each element of the array defines one DNP3 class or index group to poll and forward. There are two ways to configure tags in the connector:
  1. Class-based configuration
    • The simplest approach.
    • You configure the connector to poll entire DNP3 classes (0–3).
    • All indices belonging to the class are collected automatically and forwarded to the cloud.
    • Useful when you want complete mirroring of all data points without manually listing them.
  2. Per-index configuration
    • A more granular approach.
    • You can specify a list of exact indices (tags) to poll within a class.
    • Only those data points are read and forwarded.
    • Useful for optimizing bandwidth or focusing on a subset of values.

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logSettings

FieldTypeDescription
logFilePathstringPath template for log files (the % is replaced with the device ID)
logFileMaxMBSizenumberMaximum size per log file in MB before rotation
logFileMaxFilesnumberNumber of rotated files to keep
logLevelstringLogging level (trace, debug, info, etc.)

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tagConfiguration entries

Each entry describes either a DNP3 class or a set of specific indices.

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Common fields

FieldTypeDescription
deviceModelstringDevice model identifier
classIDnumberDNP3 class ID (0–3)
triggerTypestringWhen to send data: changed, cyclic-N (N seconds), or percentage-N (N %)
metaDataobjectProtocol-specific communication parameters

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Optional per-index field

FieldTypeDescription
dataPointsstring[]List of specific data points (e.g. "Binary/1", "Analog/3")

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Example 1: Class-based configuration

{
    "logSettings": {
        "logFilePath": "./log_files/test_dnp3_log_file.log",
        "logFileMaxMBSize": 1,
        "logFileMaxFiles": 3,
        "logLevel": "debug"
    },
    "tagConfiguration": [
        {
            "deviceModel": "dnp3_model",
            "classID": 0,
            "triggerType": "cyclic-1000",
            "metaData": {
            "cyclicPeriod": 1
            }
        },
        {
            "deviceModel": "dnp3_model",
            "classID": 1,
            "triggerType": "changed",
            "metaData": {
            "cyclicPeriod": 1
            }
        },
        {
            "deviceModel": "dnp3_model",
            "classID": 2,
            "triggerType": "percentage-5",
            "metaData": {
            "cyclicPeriod": 1
            }
        },
        {
            "deviceModel": "DNP3 device model",
            "classID": 3,
            "triggerType": "cyclic-5",
            "metaData": {
            "cyclicPeriod": 1
            }
        }
    ]
}

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Example 2: Per-index configuration

{
    "logSettings": {
        "logFilePath": "./log_files/test_dnp3_log_file.log",
        "logFileMaxMBSize": 1,
        "logFileMaxFiles": 3,
        "logLevel": "debug"
    },
    "tagConfiguration": [
        {
            "deviceModel": "DNP3 device model",
            "classID": 1,
            "triggerType": "changed",
            "metaData": {
                "cyclicPeriod": 2
            },
            "dataPoints": [
                "Binary/1",
                "Analog/1",
                "DoubleBitBinary/1",
                "Binary/4",
                "Analog/4",
                "DoubleBitBinary/4"
            ]
        },
        {
            "deviceModel": "DNP3 device model",
            "classID": 2,
            "triggerType": "changed",
            "metaData": {
                "cyclicPeriod": 4
            },
            "dataPoints": [
                "Binary/2",
                "Analog/2",
                "DoubleBitBinary/2",
                "Binary/5",
                "Analog/5",
                "DoubleBitBinary/5"
            ]
        },
        {
            "deviceModel": "DNP3 device model",
            "classID": 3,
            "triggerType": "changed",
            "metaData": {
                "cyclicPeriod": 6
            },
            "dataPoints": [
                "Binary/3",
                "Analog/3",
                "DoubleBitBinary/3",
                "Binary/6",
                "Analog/6",
                "DoubleBitBinary/6"
            ]
        }
    ]
}

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3. Message format sent to Nexalis Cloud

{
    "dataPoint": "Analog/0",
    "description": "DNP3 data point",
    "deviceID": "test device",
    "deviceModel": "DNP3 device model",
    "metaData": {
        "class": 0,
        "nx-agent-id": "fb9cf8e6-xxxx-xxxx-xxxx-be2aea9631d8",
        "registerType": "Analog",
        "type": "double"
    },
    "protocol": "DNP3",
    "qualitySource": "RESTART",
    "siteName": "test site",
    "triggerType": "changed",
    "tsConnector": 1754003248853,
    "tsSource": 0,
    "unit": null,
    "value": 0.0
}

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4. Running the Connector

The DNP3 connector is launched automatically by the Nexalis Agent.
For debugging only, it can be started manually: 
./dnp3_connector --siteName SITE_1 --deviceID 100 --communicationAddress 127.0.0.1:502 --deviceModel /path/to/device_config/dnp3_model.json
Default gRPC forwarding: localhost:50051
Use --grpcAddress to override.

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5. Supported DNP3 Data Types

DataPoint PrefixDescriptionData Type in Cloud
BinaryBinary input (status)bool
DoubleBitBinaryDouble-bit inputuint8_t
AnalogAnalog inputdouble
CounterCounter inputuint32_t
FrozenCounterSnapshot counteruint32_t
BinaryOutputStatusStatus of binary outputbool
AnalogOutputStatusStatus of analog outputdouble
TimeAndIntervalTimestamped interval valuesTimeAndInterval
OctetStringBinary/string datastring
DNPTimeDNP3 time valueDNPTime

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6. DNP3 General Information

The DNP3 protocol does not support reading individual object indices for reading specific data points. Instead, it uses polling or scanning methods that discovers and reads multiple object indices grouped by class.

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Classes

  • Class 0 Integrity Poll: Purpose: Retrieves all current values data points at the outstation. Usage: Typically performed at startup or at cyclic periods to get a complete snapshot of the current state of all data points.
  • Class 1 Poll: Purpose: Retrieves a list of all changes in data from the last poll. Usage: Used to monitor and retrieve updates for high-priority data points.
  • Class 2 Poll: Purpose: Retrieves a list of all changes in data from the last poll. Usage: Used to monitor and retrieve updates for medium-priority data points.
  • Class 3 Poll: Purpose: Retrieves a list of all changes in data from the last poll. Usage: Used to monitor and retrieve updates for low-priority data points.
Recommendation: By using a combination of an initial Integrity Poll (i.e., Class 0) and periodic Class 1-3 polls, the Nexalis DNP3 connector ensures comprehensive monitoring and efficient real-time data updating in Nexalis Cloud.

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DNP3 Object Variations

In DNP3, each object type (such as Binary, Analog, or Counter) can be represented in different variations.
A variation defines the format and level of detail used when encoding and transmitting data from the outstation (DNP3 server) to the master.
  • Binary Inputs
    • Packed format: multiple inputs encoded in a single byte (bit-packed).
    • With flags: includes additional status flags such as online/offline or communication quality.
  • Analog Inputs
    • 16-bit integer values.
    • 32-bit integer values.
    • 16-bit with status flags.
    • 32-bit with status flags.
  • Counters
    • 16-bit counter values.
    • 32-bit counter values.
    • 16-bit counters with status flags.
    • 32-bit counters with status flags.

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Important Notes

  • Variations are configured on the DNP3 outstation (server side), not in the Nexalis DNP3 connector.
  • The connector does not select or override variations; it polls classes and mirrors the data exactly as provided by the outstation.
  • This means the same type of data (e.g., an analog input) may arrive with different precision or with/without flags, depending on the device configuration.
  • The Nexalis connector’s role is to interpret the incoming format correctly and forward it in JSON, preserving the raw information without transformation.