Inside DNP3: Building an Outstation from the Ground Up
In my previous article, Inside DNP3’s Event-Driven Telemetry Model , we explored how DNP3 (IEEE 1815) organizes information through object groups, event classes, and Internal Indications (IIN). That discussion focused on the protocol's architecture and how an outstation exposes operational state to a SCADA master.
Understanding the specification, however, is only half of the story.
The more interesting question is what happens inside an implementation when frames begin arriving on the wire. How does an outstation process malformed transport fragments? What state transitions occur when control commands arrive out of sequence? How are administrative function codes handled internally? What actually changes when Secure Authentication (SA v5) is introduced?
To answer those questions, I built an isolated DNP3 research laboratory entirely in Python. Rather than relying on vendor implementations or third-party protocol libraries, I implemented custom outstation targets, protocol parsers, and master-side test harnesses to observe protocol behavior from the raw...
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