Protecting the critical backbone of the internet against DDoS threats.
DNS Amplification is one of the most effective and widely-used forms of Distributed Denial-of-Service (DDoS) attacks. It exploits vulnerabilities in the Domain Name System (DNS) infrastructure to flood a target with massive volumes of traffic, often overwhelming network bandwidth and causing catastrophic service outages. Understanding the mechanics of this attack is the first step toward building truly resilient infrastructure.
What is a DNS Amplification Attack?
This is a type of reflection attack where the attacker leverages legitimate, misconfigured DNS servers—known as **open DNS resolvers**—to magnify the volume of malicious traffic. The goal is to generate a disproportionately large response for a small initial query, effectively turning hundreds or thousands of DNS servers into unwilling attack agents.
The Amplification Mechanism
- Spoofing: The attacker sends a small DNS query to numerous open DNS resolvers. Crucially, they forge the source IP address, replacing it with the victim’s IP address.
- Amplification: The query typically requests a large amount of DNS data (e.g., a query for all records using the
ANYparameter). - Reflection: The unaware open resolvers send the large response packets back to the *spoofed* source—the victim—magnifying the traffic volume by a factor of up to 70 times the initial query size.
- Impact: The victim’s network is saturated with unwanted DNS response traffic, leading to service disruption.
Essential Strategies for Mitigation and Defense
Preventing and mitigating these attacks requires a layered approach, combining network policy best practices with secure server configurations.
1. Disable Open Recursion on DNS Servers
Your authoritative DNS servers should only respond to queries for domains they host. Disabling recursion ensures your server cannot be used by external, unauthorized IPs to perform recursive lookups, drastically reducing its potential for abuse as an amplification reflector.
2. Implement Source IP Verification (BCP 38)
The simplest way to break the attack chain is to prevent spoofing. **Ingress and Egress Filtering**, as outlined in Best Current Practice 38 (BCP 38), should be implemented at the network perimeter (routers). This ensures that IP packets entering or leaving your network must have a source address reachable via that interface, effectively blocking forged source IPs.
3. Apply Response Rate Limiting (RRL)
RRL caps the number of identical DNS responses your server sends to a single source IP per second. This prevents attackers from receiving the massive volume of amplified traffic they need to cripple a target, protecting both your infrastructure and external victims from abuse.
4. Leverage Anycast DNS and DDoS Mitigation Services
For high-volume services, partnering with a reputable DNS provider that uses an **Anycast network** is vital. This distributes the authoritative servers across multiple geographic locations, diffusing attack traffic and preventing any single server from being overwhelmed. These services also provide specialized filtering at the edge of the network.
5. Conduct Regular DNS Infrastructure Audits
Proactive auditing using tools like dig, nslookup, and Nmap scripts is essential to detect misconfigurations, such as accidentally leaving recursion enabled on authoritative servers, before they can be exploited by attackers.
Building Long-Term Resilience
Early detection and swift mitigation are key to minimizing the impact of these attacks. By adopting these multi-layered strategies—focusing on configuration hardening, rate limiting, and network filtering—organizations can significantly reduce the risk of denial-of-service incidents and ensure the continued availability of their critical internet services.
About SafeDNS
SafeDNS breathes to make the internet safer for people all over the world with solutions ranging from AI & ML-powered web filtering, cybersecurity to threat intelligence. Moreover, we strive to create the next generation of safer and more affordable web filtering products. Endlessly working to improve our users’ online protection, SafeDNS has also launched an innovative system powered by continuous machine learning and user behavior analytics to detect botnets and malicious websites.
About Version 2 Digital
Version 2 Digital is one of the most dynamic IT companies in Asia. The company distributes a wide range of IT products across various areas including cyber security, cloud, data protection, end points, infrastructures, system monitoring, storage, networking, business productivity and communication products.
Through an extensive network of channels, point of sales, resellers, and partnership companies, Version 2 offers quality products and services which are highly acclaimed in the market. Its customers cover a wide spectrum which include Global 1000 enterprises, regional listed companies, different vertical industries, public utilities, Government, a vast number of successful SMEs, and consumers in various Asian cities.
