In the CEH Denial-of-Service and Network Attacks coverage, a SYN flood is a classic TCP-based DoS technique that exploits the TCP connection establishment process. In a normal handshake, the client sends SYN, the server replies SYN/ACK, and the client completes with ACK. A SYN flood deliberately sends a high volume of SYN packets (often spoofed) but never completes the final ACK. As CEH describes, this leaves the server holding many half-open connections in SYN_RECEIVED, consuming memory and connection table resources (backlog queue). When the backlog fills, legitimate clients cannot establish connections, degrading availability.
The indicators in your scenario align exactly with CEH’s SYN flood fingerprints: incomplete handshakes and accumulation of half-open connections. The goal is resource exhaustion at the connection-management layer rather than bandwidth saturation.
Option B (Ping of Death) involves malformed/oversized ICMP packets and does not match SYN_RECEIVED behavior. Option C (UDP flood) targets UDP services/ports and creates different symptoms (high UDP traffic, ICMP unreachable messages, service degradation) without half-open TCP states. Option D (Smurf) is ICMP-based amplification via broadcast addresses—again unrelated to incomplete TCP handshakes.
CEH also notes mitigations such as SYN cookies, increasing backlog, reducing SYN-RECEIVED timers, rate limiting, and upstream filtering—further reinforcing that the described event is a SYN flood.
