What are Denial of Service Attacks?

Denial of Service (DoS) Attacks are meant to shut down a network, making it inaccessible to intended users. Often, systems are shut down due to malicious traffic meant to overload and cause congestion. This creates a large window for attack without detection. Services affected may include email, websites, online accounts (e.g., banking), or other services that rely on the affected computer or network.

Types of DoS Attacks

DoS attacks generally have two methods: flooding or crashing servers. When systems receive too much traffic for the server to buffer, slow down, and stop. This is called flooding. More specific types of attacks include the following:

Application Layer: used to create imitation traffic to web servers, including DNS servers or HTTP servers. This includes flooding targeted servers with network data, while other application layers target the party’s protocol or server.

• Buffer Overflow: This attack is designed to generate multitudes of traffic to a network that cannot handle more than capacity.
• State Exhaustion: The attacker aims at the state tables that are in firewalls and other network devices, such as routers and loads them with attack information. When incorporating stateful inspection of network circuits, these devices fill the state tables by opening more TCP (Transmission Control Protocol) circuits than the target’s network can handle. This prevents real users from reaching network resources.
• Teardrop: Attacks like these recognize and exploit flaws, much like old OS’es handled fragmented IP packets. Packet fragmentation happens when they are too big to be picked up by routers and it needs PF’s to specify fragment offsets. Teardrop attacks are when the fragment offsets are overlapping. Hosts configuring operating systems can’t put fragments back together, which causes the system to crash from the attack.
• Volume Based: Large amounts of imitation traffic overwhelms an online server, resource or website. Volume is measured in bps (bits per second).

How to Prevent DoS Attacks

Companies and organizations need to take the following steps toward DoS attack prevention and protection.

• Monitor Traffic: Companies can subscribe to a service that recognizes or redirects suspicious traffic flows usually seen with DoS attacks, while recognizing normal traffic to go forward on the network.
• Make security posture stronger: Fortify all internet devices to prevent compromise, downloading and keeping up with antivirus software, configuring firewalls to defend against DoS attacks and following security practices to manage and monitor unwarranted traffic.
• Configure a DoS attack response protocol: It is imperative to have a disaster recovery plan for DoS attack that involves mitigation, communication, and recovery.
• Monitor and Analyze network traffic: Use a firewall or intrusion detection system to supervise network traffic. Administrators can program rules that alert when unusual traffic is detected. They can also identify traffic sources or drop network packets that meet specific criteria.

How to Know if an Attack is Happening 

Symptoms of a DoS attack can look like non-malicious activity, such as technical problems with certain networks or systems administrator performing upkeep. The following could be precursors to DoS or DDoS attacks.

• Inability to access websites
• Slow network performance
• Unavailability of certain websites

Detecting and identifying D0S attacks work best through network traffic monitoring and analysis. NT can be watched via firewalls or intrusion detection systems. It is again, possible for admins to program rules that alert upon detection of anomalous traffic loads.

Protecting From DoS Attacks

Fortunately, there are methods to protect agains denial of service attacks. These include:

• Blackhole routing: When blackhole filtering is achieved without specific restriction standards, both actual and dangerous network traffic is routed to a void route, hence blackhole, and terminated from the network. Internet properties that witness a DOS attack, may send all website’s traffic in a blackhole to defend against the attack. While effective, this is not an ideal outcome, as it does exactly what the attackers were trying to achieve by making the network inaccessible.
• Web application firewall: This is a tool that can assist in mitigating layer 7 DOS attacks. It acts as a reverse proxy by placing a WAF in between the web and an origin server. This protects the server from malicious traffic. Layer 7 attacks will be impeded by filtering requests based on series of rules set up to locate DOS tools.
• Rate Limiting: The number of requests a server can accept over a specific frame of time can be limited in regards to mitigating DOS attacks. It can be used to slow web scrapers from stealing bulk amounts of content and constant log in attempts.

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