What is a DNS flood attack?
A DNS flood is a type of distributed denial-of-service (DDoS) attack in which an attacker overwhelms a domain's DNS servers so that they can't resolve DNS requests anymore. This causes critical connectivity issues because connecting to websites is possible only when DNS requests are properly handled. DNS acts as the internet's phonebook that translates human-friendly domain names (like nordvpn.com) into machine-readable IP addresses (such as 000.000.0.0). When the DNS server can't connect the domain name with the IP address it has in its DNS records, users can't reach the website.
Consequently, when cybercriminals overwhelm a domain's DNS servers with large volumes of traffic, users may find it hard or even impossible to reach any of the websites related to that domain.
How does a DNS flood attack work?
DNS flood attacks work by overwhelming DNS servers with high volumes of traffic, typically generated by botnets. These botnets are often made of compromised Internet of Things (IoT) devices, which are a key characteristic of DNS flood attacks. IoT devices are easy targets for attackers to exploit because they are often left unsecured and can create large traffic volumes. Using IoT botnets to target DNS servers is what distinguishes DNS flooding from typical DNS amplification attacks, which use publicly available DNS servers to increase the overwhelming traffic.
Attacks targeting DNS servers work on a network layer (Layer 3) and exhaust the server’s bandwidth, processing power, and memory. DNS flood attacks are hard to detect because DNS servers can’t distinguish between malicious and legitimate requests, and when overwhelmed, they fail to resolve requests from both bots and legitimate users. DNS flooding causes website timeouts, server crashes, or worsens website performance.
How to prevent DNS flood attacks
You can lower the chances of falling victim to DNS flood attacks in several ways. Some of the most effective strategies are:
- 1.Use DNS security extensions (DNSSEC) that prevent spoofing and man-in-the-middle attacks.
- 2.Limit the number of DNS queries a single IP address can send to a DNS server in a specific period of time. This will help reduce the impact of a single botnet in case of a large-scale flooding attack.
- 3.Use DDoS protection services that filter malicious traffic before it reaches your DNS servers.
- 4.Distribute DNS traffic across multiple geographically distributed servers, which will help spread the traffic load and reduce the risk of overwhelming a particular DNS server.
- 5.Use DNS filtering to prevent potentially malicious traffic from reaching your servers.
- 6.Set up real-time traffic monitoring, which can help identify unusual patterns or spikes in DNS queries that often indicate flood attacks.
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