 In this lecture, we have discussed about distributed denial of service attacks. We have explored the basic ideas behind how DDoS attacks works, and saw a few examples from operational networks. Also, it is important to remember that DDoS attacks can negatively affect not only the target, but also the monitoring infrastructure itself, which would imply the side effect that an attack can blind your observation point. We have then surveyed a few mitigation techniques, such as BCP38 and the recently introduced DDoS protection services. Finally, we have provided in this course two additional videos, covering two focus topics regarding denial of service attacks. The first video is a review of reflection on mitigation and DDoS attacks. The second video covers the topic of booters, web services that offer DDoS as a service for as little as a few dollars, and the implication of lowering the threshold for this type of attacks, such that anyone is in practice able to launch an attack at any time.