What You Should Know About Application Layer DDoS Attacks

DDoS attacks are a threat that constantly lurks beneath the surface for website administrators. We have gotten used to DDoS attacks as headline news due to the damage and downtime wrought. However, we often miss the details that might clue us in on how to avoid such attacks.

Investigating the OSI Model

To get a firm grasp on the various DDoS attacks which are perpetrated, it might help to first understand how data travels within a network connection. The OSI Model (Open Systems Interconnection) is the process of coming to terms with the different levels within a network connection.

The levels of the OSI Model are as follows:

Application – The layer where partners are identified.
Presentation – Is usually part of an Operating System and converts data into various formats.
Session – Establishes, coordinates, and terminates conversations.
Transport – Turns data into packets for easy sending.
Network – Handles addressing and routing data.
Data Link – Sets up links across a physical network.
Physical – Conveys the stream of data, also called bitstream.
Keep in mind that data begins at the bottom of the OSI Model and works its way up towards the top. If you would like more information about the OSI Model, take a look at this post for a basic rundown in terms we can all understand.
To put it simply, data travels through the levels of the OSI Model until it reaches its intended destination. The uppermost level communicates only through the layer below until the data request is complete. Keep in mind that these connections are happening at lightning speed whenever you send a request by clicking a link on the web. If data should become lost at any level, the connection ends and the connection is lost. DDoS attacks look to disrupt these communications at various levels to overwhelm the network and end connectivity.

Entering Layer 7: Application Level Attacks

While there are a variety of DDoS attacks, there has been a surge of Application Level, or Layer 7, attacks. If you look at the OSI Model above, the Application Level is the topmost section of the data connection. This type of DDoS attacks are typically much more sophisticated and require fewer resources to disrupt the targeted website’s connectivity. Because fewer resources are necessary, Layer 7 attacks are less expensive to create. And due to the various sources of disruption, they are also harder to mitigate.
Layer 7 attacks can slow websites to a crawl and can often take them offline completely. Downtime happens when an attacker aims to exploit a system’s resources with an overwhelming number of HTTP requests. Bots and infected computer systems send single HTTP requests to the targeted network. One HTTP request is fairly easy to combat, however, when the requests are fired in rapid succession the network is quickly overloaded.
CDN experts at Cloudflare wrote that the only way “to combat Level 7 DDoS attacks, applications and websites must upgrade their networks to handle the load.” This translates to increased resources and redundancy at the server level. For VPS hosting, many administrators will scale up and add extra nodes to ensure that connection is not lost in the event of a large-scale DDoS attack.

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