Overview
This lecture explains denial of service (DOS) and distributed denial of service (DDoS) attacks, their mechanisms, and their impact on network services.
Denial of Service (DOS) Attacks
- DOS attacks overwhelm networks or servers to prevent legitimate user access.
- Attacks work by occupying all available service slots, blocking real users from connecting.
- Websites with limited capacity are especially vulnerable to resource exhaustion.
Common Types of DOS Attacks
- Ping of Death (PoD): Sends oversized, malformed ping packets to cause buffer overflows and system crashes.
- Ping Flood: Overloads a target with ICMP echo requests (pings) until it cannot respond, disrupting service.
- SYN Flood: Bombards a server with TCP SYN packets, leaving many half-open connections and wasting server resources.
- SYN floods are also known as half-open attacks due to incomplete TCP handshakes.
Distributed Denial of Service (DDoS) Attacks
- DDoS attacks use multiple compromised machines to amplify the attack's scale and impact.
- Attackers often use botnets (networks of hijacked computers) to launch massive, coordinated assaults.
- DDoS attacks can quickly overwhelm even large, robust services.
Notable Example
- In October 2016, a major DDoS attack targeted DNS provider Dyn using fake DNS requests and SYN floods.
- The attack disrupted major websites like Reddit, GitHub, and Twitter by making their domains unreachable.
Key Terms & Definitions
- Denial of Service (DOS) Attack — An attack that prevents legitimate users from accessing a service by overwhelming it.
- Distributed Denial of Service (DDoS) Attack — A DOS attack using multiple computers to increase its scale and effectiveness.
- Ping of Death (PoD) — A DOS attack using oversized ping packets to crash systems.
- Ping Flood — DoS attack sending massive ICMP echo requests to overwhelm a target.
- SYN Flood — Attack that exploits the TCP handshake by sending SYN packets and not completing connections.
- Botnet — A network of hijacked computers used to perform coordinated attacks.
Action Items / Next Steps
- Review examples of DOS and DDoS attacks.
- Understand TCP handshake and how SYN floods disrupt it.
- Prepare for questions on attack mechanisms and prevention strategies.