Abstract

In multi-controller Software-Defined Networking (SDN), Distributed Denial-of-Service (DDoS) attacks exhibit a dispersed source, concentrated target pattern across domains, i.e., attack traffic originates from multiple edge-controller domains but converges on a victim in a single aggregation controller domain. While entropy-based DDoS detectors are effective in single-controller settings, their direct application in multi-controller SDN reveals a previously overlooked anomaly. Through systematic experiments, we identify an aggregation bias : during the post-attack transition phase, the aggregation controller continues to generate excessive false positives, while edge controllers have already returned to normal. We attribute this phenomenon to the coupled effects of OpenFlow statistics lag and unconstrained dynamic-threshold drift. To address this issue, we propose a cross-domain confidence-fusion framework that leverages lightweight edge-side messages to calibrate aggregation-controller decisions without sharing raw traffic data. The framework is non-intrusive, communicationefficient, and incrementally deployable. Experiments on a threecontroller linear Mininet testbed with 24 hosts over 10 runs show that the method preserves edge-controller performance while reducing the aggregation false positive rate from 8.87% to 1.96% and increasing the F1 score from 89.04% to 96.89%.