What is a DDoS Attack?

On this day, several telephone companies have presented service failures in the United States, and some versions point to a DDoS attack as the origin of these failures.

So, What is a DDoS Attack?

A distributed denial-of-service (DDoS) attack is a malicious attempt to disrupt normal traffic of a targeted server, service or network by overwhelming the target or its surrounding infrastructure with a flood of Internet traffic. DDoS attacks achieve effectiveness by utilizing multiple compromised computer systems as sources of attack traffic. Exploited machines can include computers and other networked resources such as IoT devices. From a high level, a DDoS attack is like a traffic jam clogging up with highway, preventing regular traffic from arriving at its desired destination.

How does a DDoS attack work?

A DDoS attack requires an attacker to gain control of a network of online machines in order to carry out an attack. Computers and other machines (such as IoT devices) are infected with malware, turning each one into a bot (or zombie). The attacker then has remote control over the group of bots, which is called a botnet.

Once a botnet has been established, the attacker is able to direct the machines by sending updated instructions to each bot via a method of remote control. When the IP address of a victim is targeted by the botnet, each bot will respond by sending requests to the target, potentially causing the targeted server or network to overflow capacity, resulting in a denial-of-service to normal traffic. Because each bot is a legitimate Internet device, separating the attack traffic from normal traffic can be difficult.

What are common types of DDoS attacks?

Different DDoS attack vectors target varying components of a network connection. In order to understand how different DDoS attacks work, it is necessary to know how a network connection is made. A network connection on the Internet is composed of many different components or “layers”. Like building a house from the ground up, each step in the model has a different purpose. The OSI model, shown below, is a conceptual framework used to describe network connectivity in 7 distinct layers.

While nearly all DDoS attacks involve overwhelming a target device or network with traffic, attacks can be divided into three categories. An attacker may make use one or multiple different attack vectors, or cycle attack vectors potentially based on counter measures taken by the target.

Application Layer Attacks

The Goal of the Attack:

Sometimes referred to as a layer 7 DDoS attack (in reference to the 7th layer of the OSI model), the goal of these attacks is to exhaust the resources of the target. The attacks target the layer where web pages are generated on the server and delivered in response to HTTP requests. A single HTTP request is cheap to execute on the client side, and can be expensive for the target server to respond to as the server often must load multiple files and run database queries in order to create a web page. Layer 7 attacks are difficult to defend as the traffic can be difficult to flag as malicious.