Lecture 16: Denial of Service

Intro to DoS




Application-Level DoS





Network-Level DoS



How might modern websites defend against DDoS attacks?




Amplification


In the DNS amplification attack, what packets are sent across the network? For each packet, what are the source and destination fields set to?




TCP SYN Flooding



When using SYN cookies, after a legitimate client sends the ACK packet, how does the server know: 1) the client sequence number x, 2) the server sequence number y, and 3) any extra state that would have been stored after a SYN?




Application-Layer DoS




Algorithmic Complexity Attacks


How are algorithmic complexity attacks related to amplification attacks?




DoS Conclusion