Techniques for detecting and responding to attacks on computer and network systems including denial-of-service (DoS) attacks. A packet is classified as potentially being an attack packet if it matches an access control list (ACL) specifying one or more conditions. One or more actions may be performed responsive to packets identified as potential attack packets. These actions may include dropping packets identified as potential attack packets for a period of time, rate limiting a port over which the potential attack packets are received for a period of time, and other actions.