The DNP3 protocol is widely used in SCADA systems (particularly electrical power) as a means of communicating observed sensor state information back to a control center. Typical architectures using DNP3 have a two level hierarchy, where a specialized data aggregator receives observed state from devices within a local region, and the control center collects the aggregated state from the data aggregator. The DNP3 communications are asynchronous across the two levels; this leads to the possibility of completely filling a data aggregator's buffer of pending events, when a compromised relay sends overly many (false) events to the data aggregator. This paper investigates the attack by implementing the attack using real SCADA system hardware and software. A Discrete-Time Markov Chain (DTMC) model is developed for understanding conditions under which the attack is successful and effective. The model is validated by a Möbius simulation model and data collected on a real SCADA testbed.