DNS Nxdomain Attack

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How can you prevent a DDoS attack against your DNS server?

DNS DDoS Protection DNS Flood is a DDoS attack that targets multiple DNS servers (Domain Name System) within a specific zone. The hacker attempts to block the resolution of resource records.

DNS servers can be described as the “roadmap” to the Internet. This helps requesters find the right server. A DNS zone is an area of domain name space within a particular Domain Name System (DNS). Administrative responsibility for each type of zone is given to a particular cluster of servers.

An attacker attempts to flood a specific DNS server by using valid traffic and impeding its ability. The server resources are used to direct legitimate requests to the zone resources.

Attack Description

DNS flood attacks should be distinguished from multiple DNS amplification attacks. This is an unbalanced DDoS attack where the attacker sends a small query to the wrong target IP. The target becomes the beneficiary of larger DNS responses.

These attacks are designed to overwhelm the network and exhaust the bandwidth capacity.

DDoS attacks that cause DNS flooding are a constant threat. These types of attacks are designed to exhaust server-side resources (such as CPU or memory) through a flood of UDP requests. This is done by scripts that run on compromised botnet machines.

A DNS flood attack can be considered a UDP flood attack because DNS servers use the Layer 7 attack to resolve name resolution. Because the UDP-based issues do not establish an entire circuit, it is easy to spoof.

An attacker must run a script to attack a DNS Server with a DNS flood. Usually, this script comes from multiple servers. These scripts all send malware packets to the wrong IP addresses. Layer 7 attacks don’t require any response. Hackers can send packets that are not correctly formatted or accurate to be effective.

An attacker can easily steal all of the critical information including the source IP address and make it appear like the attack is coming from different sources. The attackers can use the randomized packet data to block common DDoS protection mechanisms such as IP filtering. This is completely useless.

Another common DNS flood attack is the DNS NXDOMAIN flood attack. This involves flooding the DNS Server with requests for records that are non-existent or invalid. The DNS Server uses all its resources to search for records. This includes cache files with bad requests that are not able to fulfill legitimate requests.

How to defend your server from DDoS attacks

DDoS systems have two main goals:

  • Make sure infrastructure and services are always available.
  • Assure that the services are available to legitimate users.

Remember that objective No. 1 must be achieved if object No. 2 cannot be accomplished. Remember that if objective No. Because both objectives are equally important, 2

A good DNS DDoS protection system can reduce false negatives as well as false positives. False positives can lead to a false negative that is not detected and legitimate users are blocked.

Traffic shaping is a feature of most DDoS defense systems. Traffic shaping includes preventing traffic from falling over.

This strategy can cause collateral damage as traffic filters are used to dispose of traffic indiscriminately. This means that legit users are also removed along with malicious traffic.

A DDoS defense system must be capable of distinguishing legitimate and illegitimate users to prevent this from happening. Multi-modal detection and mitigation strategies can help achieve this.

All strategies must be focused on the Source Policy Violation. These strategies maybe some of the most technical. The RFC Check is simple in technical terms, but Destination Protection can have a significant effect on legitimate users.

Another strategy is to identify the attack user’s traffic pattern and create a filter that blocks DDoS traffic without any manual intervention or advanced configuration. This approach is also known as ZAPR and can be:

  • Create a filter automatically to block attacks quickly with surgical precision.
  • Identify common attack vectors or methods of malicious traffic.
  • Analyze the incoming traffic.


DDoS attacks can cause serious damage, so it is up to you to defend your DNS Server against such attacks. Please read this article to learn more about DDoS attacks and how you can protect your server.