PART 3: ZEEK IN THE NETWORK SECURITY TOOL ECOSYSTEM
Understanding Where Zeek Fits
Now that you understand Zeek’s philosophical approach and architecture, it’s important to understand where it fits in the broader ecosystem of network security tools. Zeek isn’t meant to replace every other security tool in your environment-it’s designed to complement other systems and fill specific gaps that other tools don’t address well.
The network security monitoring landscape includes several categories of tools: signature-based intrusion detection systems, packet capture and analysis tools, network flow analyzers, and security information and event management platforms. Each has its strengths and ideal use cases. Understanding where Zeek excels - and where other tools might be more appropriate - will help you architect comprehensive security monitoring solutions.
Zeek and Signature-Based IDS: Complementary, Not Competing
Let’s start by examining the relationship between Zeek and signature-based intrusion detection systems like Snort and Suricata. At first glance, these might seem like competing technologies - they all monitor network traffic looking for threats. But in practice, they’re highly complementary, and mature security operations centres often deploy both.
Snort, which has been around since 1998 and is one of the most widely deployed open-source IDS systems, excels at real-time detection of known threats. It processes packets at line rate, comparing them against thousands of signatures that describe known attacks. When traffic matches a signature, Snort generates an alert immediately. It can also operate in prevention mode, sitting inline and actively blocking traffic that matches malicious signatures. This makes Snort excellent for defending against commodity attacks and known threats.
Snort’s strength is also its limitation. Because it relies on signatures, it needs to know what to look for. When a new vulnerability is discovered and exploited in the wild, there’s a window of time before signatures are developed and deployed. During this window, Snort will be blind to the attack. Similarly, when attackers customize malware or use novel techniques, they may evade signature-based detection entirely.
This is where Zeek shines. Because Zeek focuses on behavioural analysis and generates comprehensive logs of network activity, it can detect suspicious patterns even when no signature exists. More importantly, when an incident occurs, Zeek’s detailed logs provide the forensic data needed to understand what happened. You can reconstruct the attacker’s actions, identify the scope of a compromise, and gather the intelligence needed to improve your defenses.
In a well-designed security architecture, Snort and Zeek work together. Snort provides the first line of defense against known threats, generating real-time alerts and optionally blocking malicious traffic. Zeek provides deep visibility into network behaviour, enabling the detection of sophisticated threats and providing the rich forensic data needed for investigation and response. When Snort generates an alert, you can pivot to Zeek’s logs to get the full context of what was happening on the network at that time.
Suricata represents an interesting middle ground. Originally developed as a modernized alternative to Snort, Suricata includes many improvements over traditional signature-based IDS. It has native multi-threading support, can generate rich JSON logs, and includes some protocol analysis capabilities that go beyond simple signature matching. In some ways, Suricata tries to bridge the gap between Snort’s signature-based approach and Zeek’s behavioural analysis.
However, Suricata’s protocol analysis capabilities, while improving, don’t match Zeek’s depth. Zeek was designed from the ground up for protocol analysis and behavioural monitoring, with a full-featured scripting language that gives you complete control over detection logic. Suricata’s scripting capabilities are more limited, primarily using Lua for simple programmatic rules. For complex behavioral analysis, custom protocol parsers, or sophisticated statistical detection, Zeek remains the better choice.
Zeek and Packet Capture: Different Layers of Abstraction
Another important comparison is between Zeek and traditional packet capture tools like tcpdump and Wireshark. These tools serve very different purposes, but they’re often used together in complementary ways.
Tools like tcpdump and Wireshark capture complete packets from the network and allow you to examine them in detail. This is incredibly valuable when you need to perform deep forensic analysis of specific network activity. You can see exactly what bytes were sent, examine protocol headers at the lowest level, and track the precise sequence of network events.
However, packet capture tools have significant limitations when it comes to continuous network monitoring. Capturing full packets requires enormous amounts of storage, especially on high-bandwidth networks. A one-gigabit network generating even modest traffic can produce terabytes of packet capture data per day. This makes long-term storage impractical for most organizations. Additionally, analyzing packet captures is largely a manual process. While you can write display filters in Wireshark or process captures with command-line tools, you’re still working at a very low level of abstraction.
Zeek takes a completely different approach. Rather than capturing complete packets, Zeek extracts high-level information and generates structured logs. An HTTP transaction that might consume megabytes in a packet capture might be represented by a few hundred bytes in Zeek’s HTTP log, containing all the important details-source and destination, requested URL, response code, content type, sizes, and timing information-but discarding the raw packet bytes.
This approach provides several enormous advantages. First, Zeek’s logs are compact enough that you can realistically store months or even years of network activity. This long-term retention is crucial for threat hunting and incident investigation. Second, Zeek’s logs are structured and easily searchable, enabling rapid analysis of large time periods. Third, Zeek’s automated analysis can identify suspicious patterns across millions of connections, something that would be impossible with manual packet analysis.
The typical deployment pattern is to use Zeek for continuous monitoring and automated analysis, while using targeted packet capture for specific investigations. Zeek can trigger packet capture when it detects something suspicious, giving you the best of both worlds: efficient long-term monitoring with detailed packet-level data available when needed. Many organizations use Zeek’s notice framework to automatically initiate packet capture whenever high-priority alerts are generated, ensuring that the raw packet data is available for deep forensic analysis.
Zeek and SIEM: Complementary Components of a Security Architecture
Perhaps the most important relationship to understand is between Zeek and Security Information and Event Management (SIEM) platforms like Splunk, Elastic Stack, or commercial solutions like QRadar and ArcSight. This relationship is often misunderstood, with people sometimes asking whether they should deploy Zeek or a SIEM. The answer is that they serve fundamentally different purposes and are most powerful when used together.
A SIEM platform is designed to aggregate security data from many different sources across your environment - firewalls, intrusion detection systems, endpoint security tools, authentication logs, application logs, and more. The SIEM normalizes this data into common formats, stores it in a searchable database, provides correlation capabilities to identify patterns across different data sources, and offers dashboards and alerting to help analysts make sense of it all.
Zeek is not a SIEM. Zeek is a network visibility tool that generates structured data about network activity. It’s one of the sources that feeds data into your SIEM. In a typical architecture, Zeek sits at strategic points in your network, analyzing traffic and generating logs. These logs are then forwarded to your SIEM, where they’re combined with data from other sources for comprehensive security monitoring.
This architecture is powerful because it combines Zeek’s deep network visibility with the SIEM’s ability to correlate across multiple data sources. For example, Zeek might detect a host making a suspicious outbound connection. That information flows into your SIEM, which correlates it with endpoint logs showing the initial infection vector, authentication logs showing subsequent lateral movement, and firewall logs showing data exfiltration attempts. The SIEM gives you the complete picture of the attack campaign, while Zeek provides the critical network component of that picture.
Many organizations structure their Zeek-to-SIEM pipeline using log shipping tools like Filebeat or Logstash. Zeek generates its logs in tab-separated or JSON format, a log shipper monitors these files and forwards them to the SIEM in real-time, and the SIEM ingests and indexes them. This provides near-real-time visibility into network activity within your central security monitoring platform.
It’s worth noting that for organizations without a SIEM, Zeek’s logs can still be incredibly valuable. You can analyze them directly using command-line tools, Python scripts, or even spreadsheet software. However, as your Zeek deployment grows and you begin generating significant volumes of data, having a proper SIEM or log management platform becomes increasingly important for making that data actionable.