This document discusses detecting distributed denial-of-service (DDoS) attacks on software defined networks (SDNs). It first provides background on SDNs and DDoS attacks. It then reviews related research on DDoS detection methods for SDNs. The document evaluates these methods based on results using the KDD99 dataset in a simulated SDN environment. It finds that the Double P-value of Transductive Confidence Machines for K-Nearest Neighbors (DPTCM-KNN) method achieved the highest true positive rate and lowest false positive rate, making it the most efficient approach for detecting anomalous flows in SDNs.