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What is Network Packet Capture?

Network packet capture is the process of recording data packets as they travel across a network. It is used to troubleshoot performance issues, monitor traffic, and detect security threats.

What is an IP Packet?

Networks communicate by transmitting data in small units called packets. One of the most common types is the IPv4 packet, typically carried inside Ethernet frames. An IPv4 packet contains two key parts:
  • Header: Includes essential routing information like source and destination IP addresses, protocol type, packet length, and other metadata used for proper delivery.
  • Payload: This is the actual data being sent, whether it’s part of a file, email, video stream, or web page.
By examining these packets, we can answer vital questions like:
  • Who sent the packet?
  • Where is it going?
  • What data is being transmitted?
Thankfully, packet analysis tools decode these packets, making complex protocol information readable to humans.

What is Packet Capture?

Packet capture refers to recording and analyzing packets that travel across a network. Every packet, including its header and payload, can be saved in files like .pcap, .pcapng, or. erf. Security teams and network engineers use this data to investigate threats or resolve performance problems.

Packet captures act as digital CCTV footage for networks providing a complete and reliable record of what happened.

How Does Packet Capture Work?

Advanced deployments use specialized hardware or virtual appliances, known as packet capture systems or network analyzers, to capture all network traffic, regardless of its destination.

This is called passive monitoring since it does not interfere with other network devices. It captures traffic silently, writing every packet to disk.

Accessing Network Traffic: SPAN, TAP, and NPB

To capture traffic, you need access to a copy of it:

  • SPAN (Switched Port Analyzer): Also called port mirroring, SPAN ports are configured on switches or routers to send a copy of traffic. They are easy to use but can drop packets under high loads.
  • TAP (Test Access Point): Hardware devices inserted between network links that provide an exact replica of traffic. They do not drop packets and are ideal for high-fidelity recording.
  • NPB (Network Packet Broker): Specialized devices that aggregate traffic from multiple sources, filter, balance, and forward it to capture systems. They enable efficient, flexible monitoring across many network segments.

Packet Capture File Formats

  • .pcap: Most generic formats, including timestamps and lengths.
  • .pcapng: Next-generation format with extended metadata.
  • .erf: High-fidelity format with rich metadata and in-band loss detection, ideal for forensics.

Types of Packet Capture

  • On-Demand: Good for quick diagnostics, but ineffective for intermittent or retrospective issues.
  • Continuous Capture: Records traffic 24/7 using a rolling buffer, overwriting oldest data when full. Ideal for security, troubleshooting, and compliance.
  • Triggered Capture: Stores packets only when specific events happen. Useful in low-storage environments but risky for detecting unknown threats.
  • Truncated Capture: Saves only part of each packet (usually just the header) to reduce storage. May miss critical data unless done intelligently.
  • Filtered Capture: Captures only selected types of traffic, based on criteria like IP, port, or application. Useful for focusing on key areas and extending retention.

Why Use Packet Capture?

Cybersecurity

Packet capture helps analysts see what really happened during an attack. Logs can be altered or erased by attackers, and metadata lacks full detail. Continuous packet capture provides the truth — letting teams investigate everything from zero-day exploits to insider threats.

Network Performance

Packet capture allows teams to diagnose issues like poor application performance or network outages. It helps answer questions such as:
  • Was the problem caused by the app or the network?
  • Where exactly did the delays occur?
  • What data was lost or retransmitted?

Tools for Packet Analysis

  • Wireshark: Popular open-source tool for decoding and analyzing packets. It has a user-friendly GUI and supports many protocols.
  • tcpdump: Command-line packet analyzer suitable for smaller captures or live filtering.

While great for small-scale captures, tools like Wireshark struggle with files larger than 1GB. Enterprise-grade systems like EndaceProbe handle terabytes to petabytes of traffic, supporting fast search and integration with other tools. 

Packet Metadata and Deep Packet Inspection (DPI)

Metadata summarizes packet contents and aids in search and analysis. Common fields include: 

  • IP addresses and ports
  • Protocol type
  • Timestamps
  • Application identifiers

DPI goes further, analyzing payloads to identify specific applications or behavior — even within encrypted or tunneled traffic.

Indexed Metadata and Fast Search

Effective packet capture systems generate and index metadata, allowing for rapid queries. This is essential for: 
  • Tracking malware communication with external IPs
  • Investigating data breaches
  • Identifying lateral movement within the network
Without indexed metadata, analyzing large-scale captures is slow and painful. 

Integration with SIEM, SOAR, and Other Tools

Packet capture solutions should integrate with your existing cybersecurity stack (e.g., SIEM, SOAR, IDS, NDR, NPM). This enables instant access to relevant packet data during investigations or incident response. 

Look for integrations that allow “right-click to view packets” directly from your alert or event. 

NDR and Packet Capture: A Unified Approach to Threat Detection

NDR solutions continuously monitor network traffic by analyzing flow records (NetFlow, IPFIX), metadata, and raw packet data. While flow records provide a high-level summary, such as who communicated, when, and how much data was exchanged. Packet capture delivers granular, packet-level visibility essential for deep forensic analysis and detecting advanced threats.

Packet capture can be Full Packet Capture (FPC), which records all data but is storage-heavy, or Smart Packet Capture (SPC), which selectively records relevant packets based on NDR-detected anomalies. SPC reduces data volume while preserving critical information.

This packet-level insight enables NDR tools to detect advanced threats like C2 communications, data exfiltration, malware, insider threats, and zero-day attacks—often missed by perimeter defenses. When threats are detected, packet data becomes the source of truth for incident response, allowing investigators to trace events, identify affected systems, and understand the full scope of breaches.

Beyond detection, packet capture supports proactive threat hunting by enabling analysts to search historical data for indicators of compromise (IoCs) or suspicious behavior.

In short, NDR delivers intelligence, and packet capture delivers evidence. Together, they offer powerful, context-rich security critical for defending against today’s sophisticated cyber threats.

Conclusion

Packet capture is a vital capability for modern IT, networking, and cybersecurity teams. Whether used for investigating security incidents, resolving performance problems, or auditing data flows, packet capture provides indisputable, packet-level evidence. Continuous, enterprise-class solutions provide deep visibility, rapid search, and the confidence to resolve incidents quickly and accurately.

 

Contact us for a live demo and discover how Vehere NDR can strengthen your network security posture and give your team the edge it needs.

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