the Application Layer, Transport Layer, Network Layer or by profiling allowed traffic and filtering the traffic as per the profiling.

Profiling Application-Layer Traffic

DoS Attacks can be defended in the Application Layer by profiling incoming traffic to distinguish between humans, human bots, or hijacked web browsers and filtering traffic based on that. Several techniques can be used to profile the incoming traffic. Various attributes like IP and ASN information, HTTP headers, cookie support variation, JavaScript footprint, etc can be used to classify client requests and filter out bots. Often, fingerprinting is used to separate good bots from bad bots. Some DoS defense solutions also maintain visitor state across sessions within an application and isolate real users from repeat offenders.

Using Progressive Challenges

A set of progressive challenges can isolate a legitimate human user from a malicious bot. Transparent challenges like cookie support or JavaScript execution can be used for this purpose. CAPTCHA can also be used so that a human can complete a CAPTCHA test and move ahead.

Behavioral Anomaly Detection

Anomaly detection rules can analyze behavioral patterns of incoming traffic and detect non-human traffic or traffic from hijacked or malware-infected computers, which are often used to carry out a DDoS attack.

Web Application Firewall

Application-layer firewalls can examine a packet’s payload and filter traffic based on that. They can also allow or deny certain application-layer requests from a user and create firewall rules to block malicious traffic on allowed ports. (What are Web Application Firewalls?)

Deep Packet Inspection

Deep Packet Inspection, or DPI, can examine the data part of a network packet and filter traffic accordingly. It can monitor the payload of each packet and detect protocols, applications, inappropriate URLs, and intrusion attempts. DPI can also produce much more detailed logs, which can help in dealing with security incidents. DPI can eliminate unwanted traffic before it can attack the entire network. (What is Deep Packet Inspection?)

Using IDS/IPS

IDS/IPS can match the packet signature with existing attack signatures present in a database and filter traffic accordingly. If a database is adequately populated, it can detect and prevent network attacks with much less false positives. (What is IDS? and What is IPS?)

High Capacity Network Bandwidth

High-capacity network bandwidth helps prevent Layer 3 and Layer 4 DDoS attacks to a great extent. Layer 3 or Layer 4 DDoS attacks are usually possible if the attackers’ network bandwidth is more than that of the attacked network. Hence, increasing the capacity of the network bandwidth does help.

Security Fundamentals Practice Tests

The Security Fundamentals Practice Tests test one’s fundamental knowledge of cyber security. They are good for those preparing for various certification exams, such as the CCNA, CCNP, or CompTIA, and for students and IT/security professionals who want to improve their understanding of cybersecurity.