What is Denial of Service (DoS) and how does it work ?

How long have you been using the internet ? And what services do you use over the internet ? I bet you are latched to at lease one of these services Email, World Wide Web, etc. Understanding how these services work is an adventure on it’s own. We will be looking at something that will make sure you are deprived of the services you access over the internet. Today we will be looking at something known as Denial of Service ( DoS ). What it is and how it works and what are the affects of DoS.

At the time of writing this article. The largest ever DoS attack in history has taken place. This attack targeted none other than Amazon, on of the biggest retailer and tech giant on the planet. A huge amount of internet traffic was aimed at Amazon. And by huge I mean 2.3 Tb worth of bandwidth. And to put that into perspective. It is worth 2,528,877 GB of data for Amazon servers to handle.

NOTE: I have used Tb and GB side by side but it cannot be used like this. Because the former is used for data transfer and the latter one is used for digital storage. I will explain about this later on it’s very own post. I have used it just toto paint a clear picture in your head.

What is Denial of Service (DoS) ?

Denial of Service is the condition when the server doesn’t have any more resource to handle all the request from client.


The servers are just computers which are accessible over the internet from anywhere in the world. And when the computer is accessible over the internet. The intention behind doing so is to serve something of value to whoever is requesting the service. On a regular day and normal usage we request something from server and it serves our request back to us. But what if a lot of users send request to the server ?

The answer to the above question is what DoS is. Denial of Service is simply keeping server super occupied so that it can no longer serve any more content. Any request made by the server doesn’t yield any content back because now the server doesn’t have any more resource ( CPU, Ram, etc. ) to reply to the client. So simply put, Denial of Service is the point when the server doesn’t have any more resource to handle all the request from client.

Also Read: Tycoon : A New Java ransomware targets Linux and Windows


What about DDoS ?

Now that you’ve understood what DoS is. It is very much easy to grasp the concept of Distributed Denial of Service (DDoS). And to clarify things up I must say. It is nothing but the DoS attack from multiple attack machines. It’s just amplified DoS performed with the help of compromised systems. Sometimes referred to as Botnet.

Normally vulnerable servers and user’s devices are infected with a Trojan. Which leaves a backdoor open for to the attacker for getting in later. These machines are then configured to send requests to the target all at the same time. Hence, the result is DDoS.

How does Denial of Service (DoS) work ?

The attacker has already setup a Botnet for such task. What is botnet you ask ? Botnet is a series of compromised computers. It doesn’t matter what kind of computer it is. It can be a server or a regular user’s PC / Laptop or even an IoT device. If the has access to the internet. It can be part of the Botnet.

And so it brings us to the types of DoS attacks. There are a number of types of DoS attacks based on how it is carried out. And we will leave the technical details for another article perhaps. But we will only talk about DoS on a high level abstraction here. Because the principal is basically the same in variations of DoS attacks.

Courtesy: Wikimedia Commons

The attack scenario you can paint the picture. The botnet(s) starts to request resources from the server. And at the rate which is faster than the server can handle it. It is because of the volume of the requests is so much that the server is unable to process any more new queries.

Imagine that if the server has 1 MB of RAM allocated for serving. That is 1000 KB worth of memory. And if each request uses 1 KB of memory space. The server can only serve 1000 clients at max. In this configuration if the 1001st client requests something from server. The server will not be even to acknowledge the request because the memory is full.

In an DDoS attack the attackers occupy whole 1000 KB of memory with bogus requests. Making the server unavailable for actual users. And that is how a denial of service (dos) attack works. I have left out the technical bits but you can easily find it over Wikipedia or other sites.

The motivation behind such attacks

After learning about DoS and DDoS. You might be wondering well that might be powerful. But it might come as a surprise to you that. DoS doesn’t really achieve anything. The attacker cannot gain access to the servers and steal data. Or perform any other shady tricks with the server. They just make the server unresponsive for legitimate users.

We might have to look at it as a revenge / disagreement between who the attacker is and the targeted party. Or it can simply be serious flexing over the internet. Because it truly takes great effort to pull such a task. It purely is targeted to disrupt the service of any target. The attacker gains nothing from DDoSing any system over the internet. Except the satisfaction and happiness when the server actually goes down.


Regardless of the nature of the attack. It should not be considered as something that is not fatal. Because it can seriously lead to some great fatality. If the servers on medical field are targeted the outcome will be deadly. If the financial sectors are targeted there will be loss of hundreds and thousands. Disruption of service may prove fatal to any field connected to IT. And in our modern world that is almost every field.

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