Network forensics fundamentals involve the capture, recording, and analysis of network traffic and logs to reconstruct security incidents, identify intrusions, and gather admissible evidence in computer and cyber forensics investigations.
This discipline examines data in transit—such as packets, flows, and protocol behaviors—revealing attacker communications, data exfiltration, and command-and-control channels that persist beyond host compromise.
By monitoring volatile network events, it complements endpoint forensics, providing context for breaches in distributed environments like enterprises and clouds.
Core Concepts and Objectives
Network forensics aims to establish timelines, attribute actions, and detect anomalies through systematic traffic examination.
Primary objectives include intrusion detection, malware communication tracing, and performance troubleshooting.
It operates in two modes: proactive (real-time monitoring via NIDS) and reactive (post-incident reconstruction). Evidence must meet admissibility standards: authentic, complete, reliable, and believable.
Packet Capture and Analysis
Packets form the basic unit, dissected layer-by-layer (Ethernet → IP → TCP/UDP → Application).
1. Full capture (PCAP): Wireshark/tcpdump records raw traffic for deep inspection.
2. Flow data (NetFlow/IPFIX): Summarizes sessions (source/dest IP, ports, bytes) without payloads.
3. Deep Packet Inspection (DPI): Reassembles streams for content (HTTP, DNS).
Analysis reveals C2 beacons, port scans, or encrypted tunnels via entropy/traffic volume.
Log Sources and Correlation
Device logs provide supplementary evidence. Network devices generate structured records correlating with captures.
1. Firewall/IDS logs: Blocked connections, signature alerts (Snort rules).
2. Proxy/DNS logs: Queried domains, URLs revealing phishing/malware callbacks.
3. Router/Switch logs: ARP tables, VLAN changes indicating lateral movement.
4. SIEM aggregation: Normalized events across sources.
Correlation: DNS query → Connection in PCAP → Payload strings.
Common Network Attack Indicators
Patterns distinguish malicious from benign traffic.
Baselines establish norms; anomalies trigger deep dives.
Tools and Methodologies
Frameworks guide structured investigations.
1. OSCAR model: Obtain info → Strategize hypotheses → Collect evidence → Analyze → Report.
2. Wireshark: Filter (ip.src==suspect), dissectors for protocols.
3. Zeek (Bro): Scriptable parsing for custom detections.
4. NetworkMiner: GUI for artifacts (files, certs).
Workflow: Span/mirror ports → Capture → Filter time window → Reconstruct sessions → Timeline.
Challenges and Best Practices
Encryption and volume pose hurdles.
1. TLS/traffic obfuscation: Metadata (volumes, domains) still reveals patterns.
2. High throughput: Sampling or flow exports; retain 90+ days.
3. Legal compliance: Warrants for ISP taps; anonymization review.
Best practices: Full-mesh spanning, retention policies, multi-tool validation. In ransomware, traces C2 → Lateral → Encryption waves.
