Denial of service attack

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What is DoS, DDoS or DRDoS?

In a DoS attack, a service is so overloaded with requests that it can no longer process regular requests from other users.

A denial of service attack is comparable to a road with so many cars traveling to a destination that it becomes impossible for traffic to flow.

A distributed denial of service attack (DDoS) is a denial of service attack that is carried out by multiple devices on a target. These are usually devices infected by the attacker and controlled as so-called bots via a command and control server.

Denial of service attack
Source: Denial of Service Attack |

How does a DDoS attack work?

Imagine the Internet as a series of pipes. A DDoS attack causes these pipes to become clogged.

In a (Distributed) Reflected Denial of Service attack (DRDoS), the behavior of the UDP protocol is exploited by an attacker requesting other network services - such as DNS or NTP - with the IP address of his victim, after which these services direct their responses to the victim and thus make it unreachable for others.

A reflected denial of service attack is comparable to someone placing orders in your name with delivery services, taxis, and delivery people, and then they all line up at your door with the same statement: “We received an order with your name and yours Address".

Meanwhile, your friends are standing at the front door and can't get in.

Other types of DoS attacks:

Teardrop attack

In a teardrop attack, an attacker overwhelms their victim with fragmented IP packets. When IP packets become too large, they are split into smaller packets and reassembled at the destination. Essential for this is the “Fragment Offset” field, which indicates at which position in the entire data packet this sub-packet is located in order to ensure correct composition. If this field is now manipulated, the victim will no longer be able to assemble these packets correctly and the continued attempt will put the victim in a denial of service state. This primarily affects older operating systems such as Windows 95, NT and devices with a Linux kernel version 2.1.63 and older.

Banana attack

Creating a feedback loop is known as a banana attack. To do this, the attacker must have compromised the outgoing router. The router under the attacker's control sends received frames back to its victim and generates incoming frames from the victim's received frames, into which it writes the address of its victim. The victim is flooded with their own messages and copies of them until they collapse under the weight.


Smurf attacks

In Smurf attacks, the attacker sends ICMP packets to all devices in the network directly or via the broadcast address, listing the victim as the sender. As a result, the victim now receives all the answers and is supposed to collapse under the burden.



A permanent denial of service, or PDoS for short, is an attack that aims to damage an attacked system so severely that it requires a reinstallation of the system or the replacement of system components.

This is achieved, for example, by exploiting a security vulnerability that allows an attacker to replace a device's firmware with a manipulated or defective version, rendering the device unable to perform its intended function until it is fixed or replaced.

Why all this?

The attackers' motivations are usually economic. Companies hire these attackers to cause damage to competitors and thus harm the companies. Due to the Dos attacks, many websites are no longer accessible, which means that companies suffer a loss of sales and/or a loss of image.

Famous examples of DoS attacks:

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