A distributed denial-of-service (DDoS) attack makes a web application unavailable by sending requests simultaneously from thousands of servers and different Internet Protocol addresses. Unlike an ordinary denial-of-service attack, it is harder to block by source. section 1.2
The Dyn outage
In 2016, DNS provider Dyn suffered a major DDoS attack. Popular websites including Amazon.com and Zillow.com became unavailable in the United States for much of the day. section 1.2
The attack does not need to penetrate a security perimeter; overwhelming servers with requests can consume the computing resources available to legitimate visitors. section 1.2


