Daniel, a SOC analyst, detects multiple incoming TCP requests to the organization’s mail server from...

Comprehensive and Detailed Explanation (ECIH-aligned):

This scenario describes a SYN flood attack, a classic protocol-level Denial-of-Service technique covered in the ECIH Network Security Incidents module. In a SYN flood, attackers send a large volume of TCP SYN packets but never complete the three-way handshake, leaving the server waiting for responses and exhausting connection resources.

Option D is correct because incomplete TCP handshakes, half-open connections, and resource exhaustion are defining characteristics of SYN flood attacks. The presence of multiple source IPs further suggests a distributed attack.

Option A involves taking over an existing session, not exhausting resources. Option B applies to UDP-based amplification attacks. Option C affects DNS resolution, not TCP handshakes.

ECIH stresses that early identification of SYN floods allows defenders to deploy SYN cookies, rate limiting, and upstream filtering. Recognizing handshake anomalies is therefore critical in protecting service availability.