What is a DOS Attack Denial of Service

March 18, 2024
| Ethical Hacking

After a short period of decline in incidences, denial of service (DoS), and Distributed denial of service attacks (DDoS) have become rampant once more. Whenever there is a major internet security incident, it mostly means that a DDoS attack occurred. These cybercriminals often target websites, personal accounts, servers, and other services to overload its internet traffic until the victim’s system becomes impassive to legitimate requests.

Virtually every business organization and governmental agencies consistently need the services of ethical hackers to tackle the mounting threats to Cybersecurity. In the modern-day of IT security, Certified Ethical Hackers are invaluable, which is why they work alongside some of the best and largest organizations across industries such as ICT, financial, healthcare, energy, and government, among several others!

Ethical Hacking is a standard requirement for handling DDoS and DoS attacks. The Certified Ethical Hacker (C|EH) training and credentialing program is an esteemed and reliable Ethical Hacking program offered by EC-Council and teaches you everything you need to know about DoS attacks and how to conduct one ethically.

What Is a Denial-Of-Service Attack?

A denial-of-service attack or DoS attack is a type of cyber-attack that occurs when an attacker seeks to render a computer or other networks inaccessible to its authorized users by momentarily or permanently interrupting the normal operations of a host linked to the Internet. Simply put, a denial-of-service (DoS) attack occurs when a cybercriminal prevents an authorized user from retrieving their personal data or files.

Typically, in a DoS attack, a single or group of computers are used to launch an attack. When these attacks are launched, they negatively affect an extensive array of services, including online accounts, private data, emails, websites, and other platforms that depend on the compromised computer or network.

How Do Denial of Service Attacks Work?

A denial of Service attack is often achieved using TCP and UDP packets. In a DoS attack, the perpetrators flood the user’s system with illegal traffic or service requests to inundate its resources and stop it from executing intended tasks.

A DoS attack can target distinct computers or a whole network system. These attacks can be costly for a company, both in terms of finance and timewise, until their services and other affected resources are restored or become accessible.

To learn how a DoS attack works, sign-up for the Certified Ethical Hacker course!

How to Tell if You are Experiencing a DoS Attack

The following are some pointers that you are experiencing a DoS attack:
Some of the symptoms of a DoS attack often appear as a non-malicious accessibility problem. The most effective method of identifying and detecting a DoS attack is through network traffic monitoring and testing. Network traffic can be scrutinized through an intrusion detection system or a firewall. The network manager or the owner of the device may even establish some instructions that create warnings when an irregular traffic load is detected and also recognize the source of the traffic or leaves network packets that match a certain criterion.

What Is the Most Common Form of DoS attacks?

DoS attacks are simple, yet effective. They can cause the most overwhelming loss to the target. There are different forms of DoS attacks. Different networks may be compromised by DoS attacks without being openly targeted. There are different forms of DoS, but the following are the most common ones:

Smurf Attack :

Here, the perpetrator exploits the broadcast address of a weak network by distributing spoofed packets that belong to the aimed device. Once the receivers of these spoofed packets respond, their Internet Protocol (IP) address is then flooded with those responses.

Considering the fact that a particular Internet Broadcast Address can sustain at most 255 hosts, a smurf attack works by intensifying each ping by 255. The outcome is that the network becomes slow to a level where it becomes difficult to use and discarded.

SYN Flood :

SYN Flood attacks occur when a cyber-attacker sends a request to connect to a server but does not complete the connection known as the three-way-handshake. This type of connection is a technique utilized in a Transmission Control Protocol (TCP)/IP network to form a connection between the server and local host/client. The outcome of the uncompleted handshake is that the network becomes overwhelmed with connection requests, making the connected port inaccessible to others. The malicious hacker will keep on sending requests, flooding all available ports until the authorized users are unable to connect.
Ping of Death or ICMP Flood :
ICMP flood attack is utilized to take misconfigured or unconfigured network and implement them in distributing spoof packets to ping all the system within that network. The ping of death attack is often merged together with ICMP flood.
Buffer Overflow Attacks :
This is one of the most widespread DoS attacks. A buffer is a momentary storage location in the random access memory (RAM) utilized for holding data to facilitate its use by the CPU prior to writing it back to the disc. Buffer has a size constraint and the aim of this type of attack is to overload it with more data than it can handle. Buffer overflow attacks allow a cyber-attacker to overflow a network address with traffic so as to make it discarded or unusable.
Teardrop Attack :
In a teardrop attack, the malicious hacker distributes fragments of an IP address packet to a targeted network. In turn, the network tries to reassemble these fragments to its initial packets. The method of assembling all these fragments to their initial packets wears out the system and as a result, it collapses. The system collapse or breakdown is due to the fact that the fields are created to obscure the system to the point where it is unable to assemble them together.

What Is Distributed denial of service (DDoS) Attack With Example?

Distributed denial of service (DDoS) attack is a malicious effort to render an online service or website inaccessible to users, typically by momentarily disrupting or appending the services of the host server. A Distributed denial of service attack naturally comprises of above 3 to 5 nodes on diverse networks, anything lesser may serve as a denial of service attack.
The aim of this attack is to make the website or online service impracticable. The traffic can involve fake packets, incoming mails, or requests for connections. Sometimes the target is compromised at a low level or threatened with a DDoS attack. This may be joined with blackmail and threats of more overwhelming attacks except the organization meets the set ransom. DDoS typically uses botnets to execute these malicious tasks.

What is a DDoS Botnet?

The term “botnet” refers to a group of hijacked internet-connected devices that are operated remotely from a Command & Control Center (C&C) by a malicious attacker. A botnet is a combination of the word network and robot and each compromised computer is referred to as a bot. These attacks characteristically comprise of unsecured IoT devices, PCs, smartphones, and sometimes resources from public cloud services.

A botnet is designed by a malicious hacker to achieve malicious tasks or execute illegal actions, such as stealing data, sending spam, fraudulently clicking on ads, ransomware, or Distributed denial of service (DDoS) attacks. Botnets work by allowing attackers to execute DDoS attacks by seizing the control of several computers and disrupting the traffic source of the traffic. It is often hard for security teams and other security applications to identify a DDoS attack until it is too late.

Malicious hackers use malware and other methods to infect a device, rendering it into a “zombie” in the perpetrator’s botnet. Although some malware may have an immediate effect on the device or network owners, DDoS botnet malware can have diverse stages of visibility. Some of this malware is intended to run mutely as a background while mutely awaiting commands from the “bot herder” or attacker. Other malware is intended to take absolute control of the device or network.

Self-circulating botnets engage other bots through a number of different pathways including Trojan horse malware, the exploitation of website weaknesses, and cracking scrawny verification to obtain remote admission. The moment access has been gained, all these infection techniques lead to the installation of malware on the aimed device. This grants the botnet operator a remote control of the device.

What Is the Difference Between DoS and DDoS Attack?

DDoS and DoS differ in that the latter uses a single internet connection (that is one internet-connected device or network) to flood the victim’s computer or other networks with malicious traffic, while the former uses multiple internet connections to render the victim’s network or device inaccessible to them. Hence, a DoS attack can be obstructed by blocking the single IP address.
DDoS attacks are the most powerful internet attacks and also the most difficult to detect. The reason being that they are introduced from several locations to hide their identities and prevent the victim from easily identifying the main source of the attack. As a result, it is unfeasible to distinguish between genuine and counterfeit network traffic.
Another difference between DDoS and DoS attacks lies in the volume of the attack being launched. While DDoS attacks give room for the cyber-attacker to introduce enormous volumes of traffic to the user’s computer or network, DoS cannot afford the attacker with such excesses. Additionally, you should also note that their mode of execution varies as well. While DoS attacks are executed using a script or DoS tool, such as Low Orbit Ion Cannon, DDoS attacks are usually launched using botnets or through the networks of the devices infiltrated by the attacker.

Broad Categories of DDoS and DoS attacks

Generally, there are two forms of DoS attacks including those that flood services and those that crash services. All other categories fall under these two. However, the most severe attacks are those that are distributed.

Application Layer Attacks

applications to try to exhaust resources, by generating as many transactions and processes as possible. The reason for this approach is, to make the operations initially seem like legitimate requests from users, pending the time when it will be too late, and the victim is inundated and incapable of responding.

These attacks are targeted at the layer where a server creates web pages and reacts to Http requests. The size of this attack is usually calculated in requests per second (RPS), with merely 50 to 100 RPS often needed to bring down a number of mid-sized websites. These attacks involve GET/POST floods, low-and-slow attacks, attacks that target Apache, Windows or OpenBSD vulnerabilities, and Http floods, among others.

Volumetric Attacks

Volumetric attacks are any type of attack where the bandwidth resources of a network are intentionally used up by a malicious hacker. The moment these bandwidth resources have been used up, they are rendered inaccessible to authorized devices and users within that network. This attack occurs when a cybercriminal, who often exploits a bot, distributes enormous false requests for every single open port connection. Two forms of volumetric attacks exist, including UDP flood and ICMP flood.

Fragmentation Attacks

These types of attacks pressurize a network to restore maneuvered packets. In the curse of the fragmentation attack, the cybercriminal distributes maneuvered packets to a target network with the intention of making them unfeasible to restore. When these fake data packets are incapable of being reassembled, they become overwhelming for the server.

Protocol-Based Attack

Protocol-based attacks target parts of the network. The cybercriminal deliberately distributes slow and abnormal pings that uses voluminous memory while attempting to authenticate the incoming pings. This type of attack uses up real server resources, or those belonging to transitional communication devices, including load balancers and firewalls. It is computed in packets per second (Pps). Protocol-based attack comprises of fragmented packet attacks, SYN floods, Smurf DDoS, and Ping of Death, among others.

What Causes Denial of service attacks and
Distributed denial of service attacks?

DDoS attacks are fast becoming the most threatening attacks in the Cybersecurity industry. In recent years, DDoS attacks have grown in volume and number, exceeding a terabit per second in 2016. Whether it’s a DDoS or a DoS, there are different malicious reasons why cybercriminals execute DoS and DDoS attacks. Businesses, individuals, and even nation-states have different motivations for these cybercrimes. However, the most common include:
Extorsion or Ransom

The most popular motivation for DDoS and DoS attacks is to extort money. The cyber-attacker demands a ransom after sending a crippling DDoS attack. Then, the attacker will promise to halt the attack and restore back the network once a certain amount has been paid. This type of attack is facilitated by the presence of booter services and stresser.

More than a few well-known online software companies have fallen victim to these DDoS attacks, including Vimeo, MeetUp, Basecamp, and Bitly. Some even went temporarily offline, declining the requests of the extortioner.


This is used by an ideological movement or group to launch personal and political attacks. Hacktivists use DDoS attacks to express their criticisms for everything, ranging from politics to current events. When these groups dislike your ideology, they take down your site. It isn’t unheard of for hacktivists to put the websites of political organizations or businesses they disagree with offline to stress their antagonism. One of the popular hacktivist groups is anonymous. Anonymous is accountable for the cyber-attack against ISIS that occurred in 2015. Also, they are responsible for the attack against the Brazilian government and World Cup promoters that occurred in 2014.
Dissatisfied Worker
A Dissatisfied worker can launch a DDoS attack against their former employers particularly if they perceive they have been unjustly laid off, unpaid, or if there’s a breach of contract. Although some employees handle these objections more sensibly, others resort to cyber-attacks to take down the organization.
Cyber Warfare
Government sanctioned DDoS attacks can be exploited to cripple the infrastructure of a rival nation and to bring down the websites of an opposition group. These attacks are well funded and orchestrated by the government of a country. The aim of this type of attack is, to silent some internal antagonists and other government criticizers. It also serves as a means to upset serious health, economic, and organizational services in their rival countries.
Business Feuds

Businesses are now using these tools to settle business feuds. Sometimes these attacks are launched to keep a competitor from partaking in a significant business venture. Whereas, other attacks are introduced to completely cripple a business and keep them offline indefinitely.

The motivation for this is to keep the competitor out of service so that their consumers would rush to the opposition. While this is taking place the reputation of the company would be tampered with and they will also encounter huge financial losses.

Business motivated attacks are often well-sponsored and accomplished by experts in the fields. These hackers perform timely investigation and exploit proprietary applications as well as resources to endure tremendously destructive and tenacious DDoS attacks.

How Can Denial of Service (DoS) Affect You

Distributed denial of service and Denial of service attacks are two of the most frightening threats faced by modern-day organizations. Only a few types of attacks can have such detrimental financial impacts as that of a successfully executed DDoS and DoS attack. A recent survey suggested that the average cost of a DDoS attack ranges between 20,000 dollars to 40,000 dollars per hour.

Not only will you be put out of action for a considerable period of time, but a successful DDoS attack can also cause some of your systems to start acting up. With each day you are unable to access your computer and other devices, you begin to incur costs you would otherwise have been spared. This is why you need a Certified Ethical Hacker to safeguard your systems and networks.

How to Stop DDoS and DoS attacks

You can’t prevent a DDoS attack and you can’t completely keep cyber-attackers from launching an attack. However, recognizing how to detect and mitigate a DDoS and DoS attack can be the difference between your company flourishing or going out of business. The impact of a successful attack can be so detrimental to the point that your business may be obliterated from the internet and your consumers inaccessible.

Monitor Your Traffic

You need to keep an eye on your traffic for signs of abnormalities, such as a mysterious spike in traffic and suspicious IP address and geolocation visits. If you are the administrator of your own servers, it is important that you are able to identify when an attack is happening. The more you know about your inbound traffic, the easier it is to spot an attack.

Nearly all DDoS attacks begin with sharp traffic spikes. All these could be symptoms of hackers executing “dry runs” to test your defenses before launching a full-sized attack. So, it would be helpful if you’re able to differentiate between an abrupt surge of genuine visitors and the beginning of a DDoS attack.

Even though your overprovision attempt may not necessarily avert an attack, it will give you some extra time to take deliberate actions before your website become completely saturated.

Make more Bandwidth Available

It is often advisable to make provisions for more bandwidths to your server than you would normally exhaust. By making overprovision bandwidth for your web servers, you can easily handle rapid and unanticipated surges in traffic that could arise due to a special offer, advertising crusade, or a mention of your organization in the media.

Monitor your Social media Pages and Public Waste Bins

It is vital for you to monitor your social media pages, particularly your Twitter account, and other public waste bins, including Pastebin.com for conversations, surges, and threats that may indicate a possible inbound attack. You should consider using third-party DDoS testing, to imitate possible DDoS assaults against your IT infrastructure. This way your incident responder or IRT can be prepared to tackle any level of assault.

Consult a Cybersecurity Expert

You need to consult a cybersecurity expert, particularly one that specializes in DDoS attacks. For large attacks, the ability to get your business back online may depend on a Cybersecurity expert. When you consult a cybersecurity expert, particularly a Certified Ethical Hacker, they test a wide range of assaults and not only those with which you are acquainted.

Create an Effective Incident Response Plan

You can prepare for uncertain attacks by creating a practical incident response (IR) plan. You need something like a DDoS attack playbook that thoroughly records every phase of a pre-planned incident response so that every attack can be easily detected and immediately responded to. Plan for what to do and who would handle the incidence response in case of an attack. That is, have a designated group of people such as an incidence response team (IRT) to reduce the effect of the assault. Ensure you update your plan every time you perform a dry run.
A vital part of your incidence response plan is to have a plan for how to communicate you’re the attack to your consumers. Since these attacks can last for up to 24 hours, having a good communication plan would minimize the cost to your business. When you are prepared for an attack, including having an updated incident response plan, this will boost the trust of your customers.

Managing DoS and DDoS attacks

Only a few attacks are as concerning for organizations as DoS and DDoS attacks. Not only do you have to deal with stolen data, but even a day worth of downtime can be costly for you to handle. You can always use a Vulnerability Assessment and Penetration Testing (VAPT) to detect unusual traffic that hints at a potential threat.
Another effective alternative is to familiarize yourself with everything there is to know about these types of attacks. This can go a long way in preventing and mitigating further attacks. What better way to gain ample knowledge about DDoS, DoS, and other related attacks than to become a Certified Ethical Hacker (CEH)

How to Get the CEH (Master) Credential

C|EH Master is the next progression for the world-recognized Certified Ethical Hacker credential and a logical ‘next step’ for those holding the prestigious certification. Earning the C|EH Master designation is your way of learning, understanding, and putting your knowledge about Ethical Hacking to work.

EC-Council will award the C|EH (Master) certification to you if you clear the C|EH certification and the C|EH (Practical) credential. Ready to become a Certified Ethical Hacker? Click here to complete the C|EH (Practical) exam.

"*" indicates required fields

Share this Article
You may also like
Recent Articles
Become a
Certified Ethical Hacker (C|EH)

"*" indicates required fields