What is a DoS (Denial of Service) attack, and how can it be mitigated?

A Denial of Service (DoS) attack is a malicious attempt to disrupt the normal functioning of a targeted system, network, or service by overwhelming it with a flood of illegitimate requests or traffic. The primary goal of a DoS attack is to make the targeted resource unavailable to its intended users, causing a denial of service. There are various techniques employed in DoS attacks, and they can target different layers of the technology stack.

Types of DoS Attacks:

1. Flooding Attacks:
   • TCP/IP-based attacks: Attackers send a high volume of TCP, UDP, or ICMP packets to overwhelm network resources.
   • Bandwidth attacks: Overwhelm network links with a flood of traffic, consuming the available bandwidth.
   • Application layer attacks: Overload application resources by sending a high volume of requests, often using HTTP or DNS.
2. Resource Depletion Attacks:
   • Exhausting system resources such as CPU, memory, or disk space to render the system non-responsive.
3. Distributed Denial of Service (DDoS) Attacks:
   • Coordinated attacks from multiple sources to amplify the volume of the attack and make it harder to trace and mitigate.

Mitigation Techniques:

1. Network-Level Mitigation:
   • Firewalls and Intrusion Prevention Systems (IPS): Configuring firewalls and IPS to filter and block malicious traffic based on predefined rules.
   • Rate Limiting: Limiting the number of incoming requests from a single source to prevent overwhelming the network.
2. Traffic Filtering:
   • Access Control Lists (ACLs): Filtering traffic based on source IP addresses, protocols, or ports to block malicious traffic.
   • Ingress and Egress Filtering: Configuring routers to filter incoming and outgoing traffic based on specified criteria.
3. Load Balancing:
   • Distributing incoming network traffic across multiple servers to ensure that no single server becomes a bottleneck and is overwhelmed.
4. Scrubbing Centers:
   • Employing services that can clean and filter traffic before it reaches the target network, mitigating the impact of DDoS attacks.
5. Content Delivery Network (CDN):
   • Distributing content across geographically dispersed servers to reduce the impact of regional attacks and improve overall availability.
6. Anomaly Detection and Intrusion Prevention:
   • Implementing systems that can detect unusual patterns in network traffic and automatically block or mitigate suspicious activities.
7. Cloud-Based Services:
   • Leveraging cloud-based DDoS protection services that can absorb and filter malicious traffic before it reaches the target network.
8. Incident Response Planning:
   • Developing and implementing an incident response plan to quickly identify and mitigate the impact of a DoS attack.