What is a DDoS Attack?

A DDoS attack, short for distributed denial-of-service attack, is a cyber incident designed to overwhelm a target with traffic or requests, making a website, service, or network unavailable to legitimate users. Unlike a simple DoS attack that comes from a single source, a DDoS attack leverages many sources—often thousands or millions of compromised devices—to flood the victim. The result can be sluggish performance, outages, and lost revenue. For businesses, understanding how a DDoS attack works helps teams prepare, detect, and respond more effectively.

Understanding the basics

At its core, a DDoS attack aims to exhaust the resources of the target. Those resources might be bandwidth, server CPU time, memory, or application limits. Because traffic comes from many different locations, it is harder for defenses to distinguish legitimate users from malicious requests. As a consequence, normal visitors may experience slow pages or complete failures while the attacker’s traffic continues unabated.

How a DDoS attack works

The most common way a DDoS attack is launched is by harnessing a botnet—an army of compromised devices such as personal computers, routers, or Internet of Things (IoT) devices. Each device sends small, sometimes innocuous requests. When thousands of such devices act in unison, the aggregate traffic can exceed the capacity of the target’s network or application layer, spilling into the point where legitimate users cannot connect.

There are several layers at which a DDoS attack can operate. In volumetric attacks, the goal is to saturate the bandwidth by flooding with high-volume traffic. Protocol attacks exploit weaknesses in network protocols to consume server resources or intermediate devices like firewalls and load balancers. Application-layer attacks target specific features of a web application, such as a login page or search function, with a smaller number of requests that nonetheless exhaust resources because each request requires significant processing.

Attackers frequently combine multiple techniques to create a multi-vector assault. A multi-vector approach makes it harder for defenders to keep up and often forces them to weave through a maze of signals to isolate the malicious traffic from legitimate activity. For organizations, this means that passive monitoring is rarely enough; active, adaptive defense is essential.

Common types of DDoS attacks

Volumetric attacks: These aim to saturate bandwidth with huge volumes of data. Examples include UDP floods and ICMP floods that overwhelm the network’s ability to transmit normal traffic.
Protocol attacks: These abuse weaknesses in network protocols (such as TCP, TCP handshakes, or connection-oriented services) to deplete server or device resources. SYN floods are a classic example where half-open connections tie up resources.
Application-layer attacks: These target the logic of an application, often by mimicking legitimate user behavior at a high rate. An attacker might flood a login page or a search endpoint with requests that require substantial processing, leading to slowdowns or outages even when the bandwidth is not saturated.
Amplification and reflection: In these attacks, the attacker leverages misconfigured services (like DNS or NTP servers) to amplify traffic toward the victim, increasing impact while sending requests from spoofed source addresses that make defense harder.

Understanding these types helps security teams prioritize defenses. For instance, volumetric and amplification attacks are often mitigated with network scrubbing and traffic filtering, while application-layer attacks call for more granular controls at the application level and intelligent load balancing.

Why attackers launch DDoS attacks

Motives vary. Some attackers seek reputational impact or exert pressure on a target, while others pursue financial gain through extortion, demanding payment to stop the attack. Competitors or hacktivist groups may also leverage DDoS as a tactic to disrupt services. In some cases, a DDoS attack is a distraction to divert attention while other cyber intrusions occur elsewhere in the network. Regardless of motive, the disruption to users and the potential for collateral damage makes DDoS a persistent threat for online services.

Detecting a DDoS attack

Early detection is critical. Indicators may include a sudden surge in inbound traffic from many sources, abnormal spikes in DNS or application-layer requests, increased latency, or a spike in error rates. Modern monitoring looks beyond raw volume and examines traffic patterns, geographic distribution, and the ratio of legitimate users to attempts to connect. By integrating network telemetry, application logs, and threat intelligence, teams can identify multi-vector DDoS activity more quickly and start mitigation sooner.

Mitigating and defending against DDoS attacks

Mitigation is most effective when built into a layered strategy that combines people, processes, and technology. Consider these core approaches:

Capacity and resilience planning: Over-provision bandwidth and build redundant network paths. Anycast routing and distributed hosting can help distribute traffic and reduce single points of failure.
Traffic filtering and scrubbing: Deploy upstream scrubbing services or on-premises appliances that can filter malicious traffic before it reaches critical infrastructure.
Rate limiting and load balancing: Implement rate limits for API endpoints and use load balancers to distribute legitimate traffic across multiple servers.
Application-layer protections: Harden web applications, implement CAPTCHA where appropriate, and use WAFs (web application firewalls) to filter suspicious requests without impacting real users.
Network hygiene and hardening: Secure IoT devices and endpoint devices to reduce the size of a usable botnet, and keep firmware up to date to prevent devices from becoming unwitting agents.
Incident response planning: Prepare an action plan that includes who to contact, roles and responsibilities, and communication templates for customers and stakeholders.
Collaboration with providers: Build a relationship with your ISP and DDoS mitigation vendors so that you can trigger rapid protections when a flood begins.

When a DDoS attack is underway, speed matters. Organizations often rely on a combination of traffic diversion (redirecting traffic to a scrubbing center), rate-based blocking (temporary throttling of suspicious flows), and application-layer controls to keep essential services online. The right mix depends on the target, the attack type, and the organization’s tolerance for downtime.

Real-world impact and lessons learned

Large-scale DDoS attacks can churn through tens of gigabits of traffic per second, temporarily knocking services offline and forcing costly remediation. Even short outages can damage customer trust and interrupt revenue streams. From small e-commerce sites to large cloud platforms, the critical lesson is not whether an attack will happen, but how prepared you are to respond. Organizations that invest in monitoring, rapid response, and robust mitigation services tend to recover faster and limit reputational harm.

Building a practical defense plan

A sound defense plan balances proactive measures with a tested incident response. Here are practical steps to start:

Map critical assets and dependencies to identify what an attacker would target first.
Baseline normal traffic so anomalies stand out more clearly during an incident.
Deploy a multi-layered defense that includes network-level protections, application protections, and business continuity planning.
Engage a trusted DDoS mitigation service and ensure contracts include clear service levels and response times.
Run regular drills that simulate different attack vectors, including volumetric and application-layer scenarios.
Establish a communication protocol for informing customers, partners, and internal teams during an incident.
Document lessons learned after each event to refine both technology and processes.

Key questions to ask about DDoS protection

Can your network absorb peak traffic typical for your industry, and what is your recovery time objective?
Do your defenses cover all layers—from bandwidth to application logic?
Are you using adaptive, real-time threat intelligence to adjust defenses as the attack evolves?
What is the plan for engaging service providers or mitigation services during a large-scale event?

Conclusion

A DDoS attack is a deliberate effort to disrupt service by overwhelming a target with traffic from many sources. While the threat landscape evolves, the core defense remains consistent: understand your assets, monitor for anomalies, and implement a layered, repeatable response. By combining proactive capacity planning with intelligent filtering, rapid incident response, and ongoing education for staff, organizations can reduce the impact of a DDoS attack and keep essential services accessible to legitimate users. In today’s connected world, a robust defense against DDoS attacks isn’t optional—it’s a foundational part of operating a trustworthy online presence.