What Is DNP3?

DNP3, the Distributed Network Protocol version 3, is an open communication protocol for SCADA and telemetry. A master station in a control room exchanges data with outstations in the field: an RTU at a pumping station, a protection relay in a substation or a controller on a pipeline. It was designed for links that are slow, noisy and expensive, such as leased lines and radio, so it squeezes as much as possible into each message.

DNP3 was developed by Westronic, later part of GE Harris, and released in 1993. Ownership passed to the DNP Users Group, which still maintains it, and it was adopted as IEEE Std 1815 in 2010. Its message structure is based on the IEC 60870-5 telecontrol standards, with three layers: data link, a light transport function and application.

The outstation keeps two kinds of data. Static data is the present value of each point. Event data is a buffered record of every change, each with a time stamp and quality flags, so the master can rebuild exactly what happened during an outage instead of seeing only the latest value.

DNP3 describes data with a shared library of objects, organized into groups and variations, which is why masters and outstations from different vendors interoperate without custom mapping.

DNP3 began on serial links, RS-232 to modems and radios and multi-drop RS-485, with 16-bit addresses that allow thousands of outstations on one network. Today most new links carry the same application messages over TCP or UDP, on port 20000 by default. Many sites run both: serial outstations on a shared radio channel, and IP outstations on fiber or cellular, collected by a front end or gateway in between.

On a shared multi-drop serial channel, unsolicited responses can collide, so they are often disabled there and the master polls instead. On TCP each outstation has its own connection, so unsolicited reporting works well and keeps polling traffic low.

DNP3 is usually compared with Modbus, the simpler protocol most instruments and PLCs speak, and with IEC 60870-5-104, its European counterpart for electricity telecontrol.

In practice, Modbus suits short, reliable links to local devices, while DNP3 suits wide-area telemetry where links drop and every change must be logged in order. Gateways and RTUs often poll Modbus meters locally and report the same values upstream over DNP3.

Original DNP3 has no authentication, so a device that could reach an outstation could send it commands. Secure Authentication, added in IEEE 1815-2012 as version 5, uses a challenge and response with keyed hashes to prove that critical requests such as controls come from an authorized master. For DNP3 over TCP, TLS can also be added following IEC 62351-3. Many utilities also keep DNP3 traffic inside segmented networks with firewalls at the boundaries.

DNP3 is common in North American and Australian electricity networks and in water and wastewater telemetry, including in the USA, where IEC 60870-5-101 and 104 are also widely used. It runs in RTUs, protection relays, reclosers and the data concentrators that sit between them and the control centre.

The DNP3 stack itself is software, so it often runs on a small industrial computer that also polls Modbus devices locally. Our industrial IoT gateways carry RS-232 and RS-485 COM ports alongside Ethernet and cellular options for that role. On the network side, two of the Antaira managed industrial switches we list include OpenDNP3 among their supported protocols, alongside ERPS ring recovery and IEEE 1588 PTP.

We supply gateways, DIN rail computers and managed switches for telemetry and substation projects with the operating system, network settings and your protocol software installed as standard. Tell us your outstations, links and protocols, and we will specify the hardware to match.