Zeek — Powerful Network Analysis Framework for Security Monitoring

Introduction

Zeek (formerly Bro) is a passive network traffic analyzer that produces detailed, structured logs of network activity. Unlike signature-based IDS tools, Zeek focuses on understanding what is happening on a network by parsing protocols and generating rich event data for security analysts.

What Zeek Does

• Parses 30+ network protocols (HTTP, DNS, TLS, SMB, SSH, etc.) into structured logs
• Generates connection summaries, file extraction, and certificate inventories
• Provides a domain-specific scripting language for custom analysis logic
• Produces JSON or TSV logs consumable by SIEMs and log platforms
• Detects anomalies through protocol analysis rather than signature matching

Architecture Overview

Zeek runs as a cluster of worker processes supervised by a manager node. Each worker receives raw packets from a network tap or mirror port via a packet capture library (libpcap or AF_PACKET). Workers parse protocol state machines and emit events, which Zeek scripts process to generate log entries and raise notices.

Self-Hosting & Configuration

• Install from binary packages for major Linux distributions or build from source
• Configure monitored interfaces and cluster topology in node.cfg
• Customize analysis by writing or loading Zeek scripts (.zeek files)
• Use zeekctl to deploy, start, stop, and manage cluster nodes
• Forward logs to Elasticsearch, Splunk, or any SIEM via JSON output or Kafka

Key Features

• Protocol-level visibility into HTTP headers, DNS queries, TLS certificates, and more
• Automatic file extraction from network traffic (binaries, documents, images)
• Extensible scripting language for writing custom detectors and log enrichment
• Cluster mode for monitoring multi-gigabit network links
• Community-maintained package ecosystem via the Zeek Package Manager

Comparison with Similar Tools

• Suricata — Signature-based IDS/IPS; Zeek focuses on protocol analysis and logging
• Wireshark — Interactive packet inspector; Zeek is designed for continuous automated monitoring
• Snort — Classic signature-based IDS; less protocol parsing depth than Zeek
• Arkime (Moloch) — Full packet capture and search; complements Zeek logs with raw pcap storage
• NetworkMiner — Forensic analysis tool; GUI-based, not designed for continuous operation

FAQ

Q: Is Zeek an IDS? A: Zeek is a network analysis framework, not a traditional signature-based IDS. It excels at protocol parsing and log generation, which analysts use for detection and investigation.

Q: Can Zeek handle high-speed links? A: Yes. In cluster mode, Zeek distributes traffic across workers and can monitor 10 Gbps+ links with appropriate hardware.

Q: What happened to Bro? A: Zeek was renamed from Bro in 2018. The software and community are the same; only the name changed.

Q: Can I write custom detections? A: Yes. Zeek includes a full scripting language for writing custom protocol analyzers, detectors, and log generators.

Sources

• https://github.com/zeek/zeek
• https://docs.zeek.org