How does a Distributed Denial-of-Service (DDoS) attack work?

A Distributed Denial-of-Service (DDoS) attack overwhelms a network, service, or server with traffic to cause disruption or unavailability.

In more detail, a DDoS attack is a malicious attempt to disrupt the normal functioning of a network, service, or server by overwhelming it with a flood of internet traffic. These attacks are carried out using multiple computers or other devices, often ones that have been infected with malware and are under the control of the attacker. This network of infected devices, known as a botnet, can be used to generate an overwhelming amount of traffic to target and disrupt a specific service.

The primary aim of a DDoS attack is not to gain unauthorised access or to steal data, but rather to cause disruption. The targeted service is flooded with requests, far beyond what it can handle. This causes the service to slow down significantly or even crash, denying service to legitimate users.

There are several types of DDoos attacks. Volume-based attacks aim to consume the bandwidth of the targeted site, and include ICMP floods and UDP floods. Protocol attacks, including SYN floods, Ping of Death, and Smurf DDoS, aim to consume actual server resources, or those of intermediate communication equipment, such as firewalls. Lastly, application layer attacks, including GET/POST floods, target the layer where web pages are generated on the server and delivered in response to HTTP requests.

DDoS attacks can be difficult to defend against, as it can be hard to distinguish between legitimate traffic and attack traffic. However, there are measures that can be taken to mitigate the effects of an attack. These include rate limiting, IP address filtering, and overprovisioning bandwidth to handle unexpected traffic surges.

In summary, a DDoS attack is a significant threat to online services, capable of causing major disruption by overwhelming a service with traffic. Understanding how these attacks work is the first step in defending against them.