performing-network-traffic-analysis-with-zeek

name	performing-network-traffic-analysis-with-zeek
description	Deploy Zeek (formerly Bro) as a passive network security monitor to generate structured logs of protocol metadata (HTTP, DNS, TLS, SSH, SMTP, FTP, and more), write custom detection scripts, and integrate outputs with SIEM platforms. Use when standing up continuous, high-fidelity network traffic monitoring for threat detection, anomaly identification, or forensic investigation beyond what raw PCAP analysis provides.
domain	cybersecurity
subdomain	network-security
tags	["zeek","network-monitoring","traffic-analysis","ids","nids","pcap","threat-detection","forensics","siem-integration"]
version	1.0
author	mahipal
license	Apache-2.0
nist_csf	["PR.IR-01","DE.CM-01","ID.AM-03","PR.DS-02"]
mitre_attack	["T1046","T1040","T1557","T1071","T1685.002"]

Performing Network Traffic Analysis with Zeek

Overview

Zeek (formerly Bro) is an open-source network analysis framework that operates as a passive network security monitor. Unlike traditional signature-based IDS tools, Zeek generates high-fidelity structured logs from observed network traffic, capturing detailed metadata for protocols including HTTP, DNS, TLS, SSH, SMTP, FTP, and dozens more. Zeek's extensible scripting language enables custom detection logic, behavioral analysis, and automated response. This skill covers deploying Zeek, understanding its log architecture, writing custom detection scripts, and integrating outputs with SIEM platforms.

When to Use

• When conducting security assessments that involve performing network traffic analysis with zeek
• When following incident response procedures for related security events
• When performing scheduled security testing or auditing activities
• When validating security controls through hands-on testing

Prerequisites

• Linux server (Ubuntu 22.04+ or CentOS 8+) with 4+ CPU cores and 8GB+ RAM
• Network TAP or SPAN port mirroring configured for traffic capture
• Zeek 6.0+ installed (via package manager or source compilation)
• Root or capture group privileges for packet capture
• SIEM platform (Splunk, ELK Stack, or QRadar) for log ingestion

Core Concepts

Zeek Architecture

Zeek operates in two main modes:

1. Live Capture - Monitors traffic in real-time on one or more network interfaces
2. Offline Analysis - Processes saved PCAP files for retrospective analysis

The processing pipeline consists of:

• Packet Capture Layer - Reads raw packets from interfaces or PCAP files
• Event Engine - Reassembles TCP streams and generates protocol events
• Script Interpreter - Executes Zeek scripts that process events and generate logs
• Log Framework - Writes structured logs in TSV, JSON, or custom formats

Log Architecture

Zeek generates protocol-specific log files:

Log File	Description
conn.log	TCP/UDP/ICMP connection summaries with duration, bytes, state
dns.log	DNS queries and responses with query type, answers, TTL