DDoS attacks aim to disrupt the normal functioning of a network, service, or server by overwhelming it with a flood of internet traffic. These attacks are “distributed” because they originate from multiple sources, often thousands of devices in a botnet, which makes them difficult to stop. The sheer volume of traffic can exceed the processing capacity of the target system, causing it to slow down or even crash.
In a typical DDoS attack, the attacker begins by exploiting a vulnerability in one computer system and making it the DDoS master. The attack master, also known as the botmaster, identifies and infects other vulnerable systems with malware. These infected systems, often referred to as ‘zombies’, are then remotely controlled by the botmaster, forming a network of compromised systems, or a ‘botnet’.
The botmaster then commands this network of bots to send a flood of requests to a specific target. This could be a single target, such as a website, or multiple targets within a network. The flood of incoming messages to the target system essentially forces it to shut down, denying service to the system's legitimate users. This is achieved by exhausting the target’s resources such as bandwidth, processing power, or memory.
In this article:
Volume of Traffic
The sheer scale of traffic in a DDoS attack is the primary challenge for prevention. Modern attacks can generate traffic surges reaching into the hundreds of gigabits or even terabits per second, easily overwhelming the target’s bandwidth. This sheer volume often causes network congestion, forcing routers and switches to drop packets indiscriminately, including those from legitimate users.
Since many organizations do not have the infrastructure to handle such massive surges, relying on upstream providers or cloud-based mitigation services becomes essential. Identifying and filtering malicious traffic from legitimate traffic at this scale requires sophisticated solutions capable of deep packet inspection and dynamic traffic analysis.
Distributed Nature
DDoS attacks are difficult to prevent because of their distributed nature, leveraging botnets with potentially millions of infected devices. These devices, ranging from personal computers to IoT gadgets like cameras and smart thermostats, are often spread across numerous geographic regions. Blocking traffic from individual IP addresses is insufficient because attackers can rotate between different sources, often spoofing IPs to mask their origin.
The decentralized aspect of DDoS attacks means that defenders need to implement network-wide, global solutions, such as using anycast routing to distribute incoming traffic across multiple data centers, or working with ISPs to block malicious traffic before it reaches the target.
Variety of Attack Types
DDoS attacks can vary significantly in how they are executed, targeting different aspects of a network or application:
- Volumetric attacks, such as UDP floods, aim to overwhelm the bandwidth of the target by sending an excessive amount of data.
- Protocol attacks, like SYN floods, target weaknesses in network protocols by consuming server resources and preventing legitimate connections.
- Application-layer attacks, which are harder to detect, overwhelm specific services, such as HTTP, DNS, or SMTP, with legitimate-looking requests.
Because of this variety, organizations need to adopt a layered defense strategy, using tools like web application firewalls (WAFs), rate limiting, and DNS-based traffic management, while also ensuring they have protection across the network, transport, and application layers.
Sophistication of Attacks
DDoS attacks have become increasingly sophisticated, with attackers employing a combination of techniques to evade detection and maximize damage. Multi-vector attacks are especially challenging as they combine volumetric, protocol, and application-layer attacks, forcing defenders to address multiple attack surfaces simultaneously.
Attackers are also using advanced evasion techniques such as dynamic traffic patterns and encrypted attack traffic to bypass traditional defenses. For instance, encrypted attacks flood networks with SSL/TLS traffic, overwhelming the server’s ability to process encryption requests. As attackers evolve their tactics, organizations must employ advanced solutions such as behavioral analysis, AI-driven anomaly detection, and automated mitigation tools.
Differentiating between normal traffic surges and potential DDoS activity can be challenging. However, there are a few key differences. Normal traffic surges typically occur sporadically and are often tied to specific events or times of day. DDoS traffic, on the other hand, is usually more sustained and doesn't follow typical user behavior patterns.
Recognizing a DDoS attack involves continuous monitoring, understanding your network’s normal behavior, and being able to identify anomalies such as:
- Slow Network Performance: DDoS attacks often cause network performance to degrade, resulting in slow loading times or difficulty accessing network resources. While this could be due to a variety of reasons, a sustained slowdown could indicate a DDoS attack. It’s important to note that not all performance issues are indicative of a DDoS attack. However, if the slowdown is severe and persists despite your best troubleshooting efforts, it may be time to consider the possibility of a DDoS attack.
- Unusual Traffic Patterns: A sudden, unexpected surge in network traffic is often the first sign of a DDoS attack. This could manifest as an unusual spike in requests to a particular server or service. Monitoring traffic patterns and understanding your network’s baseline is crucial for detecting these anomalies. Network monitoring tools can provide real-time analysis of your network traffic and alert you to any significant deviations from the norm.
- Unavailability of a Particular Service: If a specific service or website becomes unavailable, it could be under a DDoS attack. This is especially true if the service remains inaccessible despite repeated attempts to connect. Regularly testing your services for availability can help you detect a potential DDoS attack early.
- Increase in Spam Emails: Some DDoS attacks are preceded by a spike in spam emails. This could be an attempt to distract IT staff while the actual DDoS attack is launched. Therefore, a sudden increase in spam could be indicative of a brewing DDoS attack.
- Disproportionate Increase in Requests: During a DDoS attack, you may notice a disproportionate increase in requests to a single endpoint or service. This could be a sign that attackers are trying to overwhelm a specific part of your network.
- Unusual Device Behavior: Devices on your network may start to behave unusually during a DDoS attack. For example, if your routers or firewalls are processing more network traffic than usual, this could be a sign of a DDoS attack.
- Network Bottlenecks: DDoS attacks can cause network bottlenecks, which can slow down your entire network. If you notice that certain parts of your network are slower than others, this could be a sign of a DDoS attack.
1. Start With Traditional Security Measures
Traditional security measures such as firewalls with Access Control Lists (ACLs) and static signature-based protections are the first line of defense against DDoS attacks.
However, these measures alone are not always sufficient as DDoS attacks often target applications and services at the application layer (Layer 4-7 of the OSI model). Therefore, it’s crucial to ensure protections are in place for non-firewall protected services like HTTP, FTP, and SMTP.
2. Follow Network & Application Security Best Practices
Implementing best practices for network and application security can significantly reduce the risk of a DDoS attack. These include changing passwords frequently to reduce the risk of unauthorized access, regularly scanning for vulnerabilities and patching any that are found promptly, deploying anti-malware and additional DDoS protection solutions/services, and implementing firewalls with up-to-date access control lists.
3. Stay Current on System Updates & Patches
Keeping all networks and system operating systems up to date with the latest security patches is crucial. Many DDoS attacks exploit known vulnerabilities in software that have already been patched by the software provider.
Therefore, regular updates and patches can protect your systems from these types of attacks. Be mindful of attacks that consume resources of stateful devices; implement solutions minimizing allocated resources close to completion information/threat state of each client connection.
4. Create a DDoS Attack Threat Model and Response Plan
Creating a DDoS attack threat model involves analyzing your network and application infrastructure to identify potential vulnerabilities and how they might be exploited by attackers. This process helps in understanding the most critical assets within your organization, such as web servers, DNS infrastructure, and databases, which are common targets of DDoS attacks. The threat model should cover different attack vectors, from volumetric attacks to sophisticated application-layer attacks, and outline the likely scenarios under which each type of attack could occur.
In addition, a comprehensive response plan for DDoS attacks is essential. This plan should outline the steps to take in the event of an attack to minimize damage and downtime. It should include procedures for identifying the attack, notifying the appropriate personnel, isolating affected systems, and implementing mitigation strategies. Regular testing and updating of this plan are also crucial to ensure its effectiveness.
5. Set DDoS Priority Buckets
Not all traffic or services are of equal importance during a DDoS attack, and establishing DDoS priority buckets can help you maintain the availability of mission-critical services even under attack. Priority buckets categorize different types of traffic based on their importance to your organization. High-priority buckets may include traffic to core services like authentication servers, DNS servers, and transaction systems, which must remain available at all times. Low-priority traffic, such as traffic to non-essential services, can be deprioritized or even dropped entirely in the event of an attack.
This approach allows your network infrastructure to continue servicing high-priority requests while discarding less critical traffic to conserve resources. Traffic management rules can be applied using firewalls, load balancers, or even at the ISP level, where lower-priority traffic is throttled or blocked during an attack.
6. Apply Rate Limiting
Rate limiting is a basic defense mechanism that can help with lower-scale DoS and DDOS attacks. It controls the volume of incoming requests a server or application will process within a set period. By imposing limits on the number of requests allowed from a single IP or user session, rate limiting can mitigate volumetric DDoS attacks, where attackers flood the system with excessive traffic. For example, an API endpoint could be configured to only accept a certain number of requests per minute from each IP address.
This strategy is effective at reducing the impact of low-and-slow attacks, which aim to fly under the radar by sending legitimate-looking but high-volume traffic to exhaust server resources. Implementing rate limiting at various levels—such as the application layer, API gateway, and web server—ensures that traffic is managed holistically. Rate limits can be dynamic, adjusting based on the real-time load on the system.
7. Prepare for Surges
Preparing for traffic surges involves building scalable, resilient infrastructure capable of handling both anticipated and unanticipated spikes in traffic. Whether traffic increases are due to organic growth, seasonal demand, or malicious DDoS attacks, your infrastructure needs to be flexible enough to absorb these surges without compromising service quality.
Cloud-based solutions, particularly Infrastructure-as-a-Service (IaaS) platforms, allow you to scale resources up or down as needed. By leveraging auto-scaling features in cloud environments, you can dynamically add more computing power, bandwidth, or server instances when traffic spikes occur.
Content Delivery Networks (CDNs) and load balancers play a crucial role in distributing traffic efficiently. A CDN caches content at multiple geographically dispersed locations, reducing the load on your origin servers by serving requests from closer network nodes. Load balancers intelligently route incoming traffic across multiple servers to prevent any single server from becoming overwhelmed.
8. Monitor and Analyze Logs
Constantly monitoring and analyzing network and application logs is vital for detecting and responding to DDoS attacks early. Logs provide insights into traffic patterns, resource utilization, and user behavior, helping you identify anomalies that may indicate an ongoing or impending attack. Using advanced logging tools such as Security Information and Event Management (SIEM) systems, you can aggregate logs from various parts of your network, including firewalls, routers, web servers, and applications, and analyze them in real-time.
Anomalies such as unexpected traffic spikes, repeated requests to specific endpoints, or sudden drops in service availability are all potential indicators of a DDoS attack. By setting up automated alerts based on log analysis, your team can respond quickly to suspicious activity, investigating and mitigating threats before they escalate.
9. Implement CAPTCHA Challenge
CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) challenges are widely used to differentiate between legitimate users and automated bots. During a DDoS attack, implementing CAPTCHA challenges can prevent botnets from overwhelming your web services with traffic by forcing each incoming user to complete a task—such as identifying objects in an image or solving a simple puzzle—that is easy for humans but difficult for automated systems.
This method is particularly effective at stopping application-layer DDoS attacks, where bots attempt to mimic legitimate user behavior. CAPTCHA challenges are usually applied at the login, registration, or form submission stages of web applications, preventing malicious bots from abusing these services. Additionally, CAPTCHAs can be integrated with rate limiting to further slow down bot traffic, ensuring that human users maintain access while bot traffic is filtered out.
10. Consider Using a Crypto Challenge
A crypto challenge forces clients to expend computational resources before they can establish a connection with your server, making it more difficult for bots to overwhelm your infrastructure. Techniques such as Proof of Work (PoW) require clients to solve a cryptographic puzzle before being allowed to proceed with their requests. While legitimate users can solve these puzzles relatively quickly, bots operating within a DDoS attack, especially those orchestrated from a large botnet, must solve millions of such puzzles, slowing down their attack considerably.
Deploying crypto challenges helps limit the number of requests malicious actors can make, especially in application-layer attacks targeting login forms or APIs. This technique works well in conjunction with other defenses, such as rate limiting and CAPTCHA, to ensure that the attack surface is minimized. However, it should be noted that crypto challenges introduce a small delay for legitimate users.
11. Implement Multi-Layer Anti-DDoS Protection
Deploying a combination of DDoS protection services, firewalls, web application firewalls, routers, and switches can help mitigate threats. This multi-layered approach ensures that even if one layer is compromised, others remain to protect the system. Consider solutions that offer real-time monitoring capabilities to detect malicious requests or data before they reach your application or service.
12. Outsource DDoS Mitigation
Outsourcing DDoS protection to specialized service providers can offer a robust defense against large-scale and sophisticated attacks that may exceed the capabilities of in-house infrastructure. Third-party DDoS mitigation services are equipped with massive, globally distributed networks designed to absorb and neutralize even the most intense DDoS attacks. These providers have dedicated resources and expertise to continuously monitor, analyze, and mitigate traffic in real-time.
By leveraging outsourced protection, your organization benefits from advanced traffic filtering, deep packet inspection, and anomaly detection that can adapt quickly to evolving threats. Additionally, these services often include multi-layered defenses that can mitigate attacks at the network, transport, and application layers, providing comprehensive protection.
Radware offers a suite of advanced DDoS prevention tools that play a crucial role in safeguarding digital assets against the evolving landscape of DDoS threats. These tools are designed to provide comprehensive protection against a wide range of DDoS attacks, ensuring the resilience and availability of your online operations.
Emergency Response Team
Radware’s Emergency Response Team (ERT) is a dedicated group of security experts providing round-the-clock support and mitigation services for a wide range of application and network-layer DDoS attacks. With a team of experienced security engineers, the ERT offers immediate assistance and specialized mitigation techniques for organizations under threat from DoS, DDoS attacks, or malware outbreaks.
The team handles various security events, including malware outbreaks and application exploits, and uses their industry-leading expertise, best practices, and deep knowledge of threats, attack tools, intelligence, and mitigation technologies to combat common and emerging attacks daily. During prolonged, complex attacks, the ERT provides the necessary expertise and service to quickly restore operations by swiftly mitigating DDoS attacks.
Continuous Innovation and 24/7 Support
At Radware, we are committed to continuous innovation, constantly updating our tools and technologies to stay ahead of the evolving threat landscape. We offer 24/7 support, ensuring that organizations have the help they need, when they need it. With Radware’s advanced DDoS prevention tools and dedicated support, organizations can stay ahead of the curve in DDoS threat prevention and response.
By leveraging these tools and following the best practices outlined in this article, businesses can significantly enhance their defenses against DDoS attacks and ensure the resilience and availability of their online operations.
Specific Tools and Technologies
Among Radware’s suite of tools, DefensePro stands out for its advanced DDoS prevention and protection capabilities. DefensePro uses patented, behavioral-based algorithms to automatically block the most advanced threats in real-time. It is capable of handling a wide range of attacks, including volumetric attacks, application-layer attacks, and ‘low-and-slow’ attack tactics.
In addition to DefensePro, Radware also offers cloud-based DDoS protection services. These services use advanced behavioral algorithms to detect and mitigate DDoS attacks at any level, providing infrastructure DDoS protection and web DDoS protection. They offer an additional layer dedicated to detecting and mitigating sophisticated application-layer DDoS attacks.
Comprehensive Defense Mechanism
Radware’s solutions offer a comprehensive defense mechanism, integrating adaptive behavioral-based detection with real-time signature recognition to effectively mitigate attacks. This unique approach allows Radware’s tools to accurately detect and block even the most advanced threats in real-time, including burst and DNS attacks, web DDoS attacks, IoT botnets, and ransom DDoS.