What are Denial of Service (DoS) attacks? How to Prevent It?

What is Denial of Service (DoS)?

A Denial of Service (DoS) event is a cyber attack in which hackers or cybercriminals seek to make a host machine, online service, or network resource unavailable to targeted users.

Distributed denial of service attacks may be the most well-known type of hacking incident – with GitHub 2018 and Dyn DDoS 2016 being the most prominent – but there are many other types of denial of service attacks that don’t. do not necessarily involve the distributed attacks or botnet approach. In virtually all cases, however, denial of service events are characterized by the fact that the target machine or service is inundated with inbound traffic to the point where processing or bandwidth resources are overwhelmed and taken offline.

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Types of DoS attacks

Over the years, denial of service attacks have evolved to encompass a number of attack vectors and mechanisms.

Distributed Denial of Service (DDoS)

Originally, DoS attacks involved one system while attacking another. Although a DoS attack can be conducted in the same way today, the majority of DoS attacks today involve a number of systems (even hundreds of thousands) under the attacker’s control, all simultaneously attacking the target.

Network-targeted denial of service

Referred to as a “bandwidth consumption attack”, the attacker will attempt to use all available network bandwidth (“flood”) so that legitimate traffic can no longer pass to / from the targeted systems.

Denial of service targeted by the system

These attacks aim to compromise the usability of the targeted systems. Resource depletion is a common attack vector, where limited system resources (eg, memory, processor, disk space) are intentionally “used” by the attacker in order to cripple the normal operations of the system. target.

Application-targeted denial of service

Application targeting is a popular vector for DoS attacks. Some of these attacks use the existing usual behavior of the application to create a denial of service situation.

How do you know you’ve suffered a DoS attack?

The most obvious sign of a DoS attack is prolonged network problems. However, there are other signs to watch out for:

  • A higher volume of spam than normal.
  • Sudden loss of connectivity between devices on the same network.
  • Slow website performance, pages not loading.
  • Staff are unable to open files stored on the network or when accessing websites.

What are common denial-of-service attacks?

There are many different methods to conduct a DoS attack. The most common attack method occurs when an attacker floods a network server with traffic. In this type of DoS attack, the attacker sends several requests to the target server, overloading it with traffic.

In a Smurf attack, the attacker sends Internet Control Message Protocol broadcast packets to a number of hosts with a spoofed source Internet Protocol (IP) address that belongs to the target machine. The recipients of these spoofed packets will then respond, and the targeted host will be inundated with these responses.

A SYN flood occurs when an attacker sends a connection request to the target server but does not terminate the connection through what is known as a three-way negotiation, a method used in a TCP / IP network to create a connection between a local host / client and a server. The incomplete handshake leaves the connected port in a busy state and unavailable for further requests. An attacker will continue to send queries, saturating all open ports, so that legitimate users cannot connect.

How a DoS attack works

A DoS attack prevents users from accessing a service by overloading its physical resources or network connections. The attack essentially floods the service with so much traffic or data that no one else can use it until the malicious stream has been processed. One way to overload a service’s physical resources is to send it so many requests in such a short time that it overwhelms all available memory, processing, or storage space. In extreme cases, it can even lead to damage to the physical components of these resources.

Likewise, to interrupt a service’s network connections, a DoS attack can send it invalid, malformed, or simply overwhelming connection requests. While these are being processed, login requests from legitimate users cannot be processed. Sometimes a DoS attack exploits a vulnerability in a program or website to force misuse its resources or network connections, which also leads to denial of service.

Some malware also includes the ability to launch DoS attacks. When infecting a computer or device, these threats can use the resources of the infected machines to carry out the attack. If several infected machines launch attacks against the same target, it is called a DDoS (Distributed-Denial-of-Service) attack. The volume of data used in a DoS or DDoS attack can be enormous, up to a rate of several gigabits per second. Botnets are quite often used to perform DDoS attacks because many services do not have the resources to counter an attack of thousands or even hundreds of thousands of infected devices.

What is the Difference Between a DoS and a DDoS Attack?

A denial of service (DoS) attack includes many types of attacks, all designed to interrupt services. In addition to DDoS, you can have Application Layer DoS, Advanced Persistent DoS, and DoS as a Service. Companies will use DoS as a service to test their networks.

In short, DDoS is a type of DoS attack – however, DoS can also mean that the attacker used a single node to initiate the attack, instead of using a botnet. Both definitions are correct.

How to prevent a DoS attack

It is difficult to prevent DoS attacks, but there are steps you can take to mitigate the threat. Here are three ways to get started:

  • Increase your bandwidth

The easiest thing you can do is buy more bandwidth. This allows you to handle a greater amount of traffic, reducing the risk of bottlenecks that could disrupt your service. This is a particularly good solution for growing businesses as it also helps them deal with an increased amount of legitimate traffic and is something they might eventually have to do anyway. The only downside is that increasing your bandwidth won’t protect you from downtime attacks, which exploit weaknesses in the system instead of flooding your server.

  • Build more complex servers

You should consider spreading your servers across multiple data centers to make it as difficult as possible for cybercriminals to target you. These servers should ideally be located in different locations, in different premises or in different countries. For this strategy to work, you will need a load balancing system to distribute traffic between the servers. Segregating your servers in this manner means that criminals face a daunting task in flooding your systems. Their attack can compromise one server, but the rest will not be affected and should be able to take at least some of the additional traffic.

  • Reconfigure your network hardware

You should adjust or harden your hardware configurations to reduce the risk of malicious traffic. For example, your network and web application firewalls can be modified to check for incoming packets against predefined rules (such as allow / deny protocols, ports, and IP addresses) and block the incoming malicious traffic.

This article covers the answers to some of your frequently asked questions:

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