The document summarizes research on using client puzzles as a proof-of-work to mitigate volumetric distributed denial of service (DDoS) attacks. It proposes a multi-level defense approach that detects attacks, challenges attacking sources with puzzles, suppresses malicious packets, and diverts excess traffic. The approach is evaluated through simulations that show it can successfully prioritize legitimate connections over malicious ones under different attack loads. The research concludes the method authenticates authorized clients while activating defenses only during attacks to reduce costs, and future work could focus on real-world testing and investigating financial incentives for helpers in defense.