DNP3 (Distributed Network Protocol 3)

DNP3, the Distributed Network Protocol version 3, carries commands and readings between the master station in a utility’s control centre and the outstations in the field. It is used mainly in electric power and water systems as part of supervisory control and data acquisition (SCADA), and is standardised as IEEE 1815. It was designed for serial links, with its own data link, transport and application layers, and is now commonly carried inside TCP and IP.

That layering is why study sources commonly use DNP3 as the example of a multilayer protocol. A complete protocol stack is wrapped inside another by encapsulation, which lets control traffic cross ordinary IP networks, but a firewall that sees only the outer headers cannot judge the command inside. The original protocol also had no authentication or encryption. Later editions of the standard added Secure Authentication, which lets a device verify that a critical command is genuine but does not encrypt it; confidentiality has to come from a wrapper such as TLS or an encrypted tunnel.

Exam relevance: a scenario is likely to describe an industrial protocol carried over IP and ask for the risk this creates. Candidates are expected to connect DNP3 with multilayer encapsulation, weak native authentication, and the need for segmentation and protocol-aware filtering.