What Is a DDoS Attack?

A distributed denial of service (DDoS) attack is a cyber threat that overwhelms an online resource with traffic, causing the web service to fail to operate normally and possibly even go offline. This threat can significantly harm a business, preventing users from gaining access to sites or slowing down the web server to the point it becomes inaccessible.

Attacks can last several hours and, in severe cases, persist for multiple days. Many businesses and organisations rely heavily on online platforms so a DDoS attack can have significant consequences. 

Attackers may strategically time DDoS attacks during critical periods. For example, an online retailer could suffer an attack on a high-volume shopping day, such as Black Friday, when its website becomes inaccessible, causing it to lose a considerable amount of business. In some cases, attackers may infiltrate databases during DDoS attacks and gain access to sensitive information due to security vulnerabilities being exploited. 

How to prevent DDoS attacks

Preventing and identifying DDoS attacks can come with challenges since it may be difficult to differentiate genuine traffic from attack traffic. One strategy for preventing DDoS attacks is rate limiting. Rate limiting puts a limit on the number of requests a server will accept over a given period of time. Web application firewalls (WAFs) are especially useful in preventing application layer attacks by protecting the server from illegitimate traffic. 

Types of DDoS attacks

Three main types of DDoS attacks are:

• Application layer attacks: These attacks target the software that provides the web service. They typically exhaust the target’s resources, making this type of DDoS attack challenging to defend against.

• Protocol attacks: Protocol attacks, also known as state-exhaustion attacks, target firewalls or the device's operating system. This consumes the resources of these network-based devices and servers, causing the inaccessibility of web services.

• Volumetric attacks: Volumetric attacks use extreme traffic to congest the target. This overwhelming traffic flood consumes all the available bandwidth, and services become unavailable. 

Related terms

• Social engineering

• Operating system

• Access control

• Physical security

Get started with Coursera.

A DDoS attack overwhelms a website with traffic, causing it to crash and become inaccessible.  These attacks come in different forms and can cripple online businesses. You can employ methods to mitigate DDoS attacks, such as rate limiting and firewalls.

If you’re ready to start a cybersecurity career, consider enrolling in the Google Cybersecurity Professional Certificate on Coursera, where you can learn how to use job-essential tools like Splunk, Chronicle, a cybersecurity playbook, and more. You're not required to have previous experience to enroll, and learning these skills can help you find your first job in the cybersecurity field.