What Is PCAP? Packet Capture Explained – Forbes Advisor

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Published: Aug 25, 2023, 12:00pm

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Do you ever wonder what is happening on your network? Packet capture (PCAP) can help you find out.

Packet capture is a networking practice in which the data packets traveling across your network are intercepted and captured. This is typically performed by your information technology department utilizing an application programming interface. Once captured, the IT team can analyze the data to identify any potential problems on the network that require troubleshooting, identify malicious activity or better understand network behavior.

How PCAP Works

PCAP is a multi-step process that utilizes a number of tools that enable both packet capture and packet analysis. The process of packet capture starts with packet sniffers, which are tools that are used to conduct the process. Packet sniffers can be physical hardware devices, typically known as taps. More commonly, they are software tools that run on a computer or other device that is connected to the network. Once connected, the packet sniffer creates a PCAP file that will contain the packets that it intercepts. The file should include timestamps of each capture as well as details about the data that has been caught in the process. Once the packet capture process starts, the sniffer will copy packets of data as they move across the network and then store those copies for analysis.

That data can be stored in a number of different formats. The most common are:

  • Libpcap: Compatible with macOS and Linux devices
  • WinPcap: Made for Windows machines and supports remote use
  • Npcap: Used with Windows machines and supports external PCAP analysis tools
  • PCAPng: A next-generation capture file format that supports additional scripting and extensions

Once packets have been captured, PCAP analysis tools such as Wireshark, Windump or tcpdump provide an interface to interact with the captured data. Some PCAP analysis tools—Wireshark and tcpdump included—are open source, making them cost-effective and accessible. Some IT departments prefer to use proprietary tools to accomplish more specific tasks and analyses based on their needs. There are also paid tools that may offer more specific, high-level features that some security situations may require.

Why Do I Need To Use PCAP?

PCAP is a valuable tool that can be used to monitor and observe traffic on your network. It’s ideal for responding to an alert or event that requires a deeper understanding, such as a breach or an intrusion. PCAP is an ideal technique to utilize when your intention is to monitor bandwidth usage across the network, detect malware or other malicious activity, or monitor domain name system (DNS) resolution to make sure the network is operating as expected. If there is something fishy happening on your network or if there are issues that you can’t quite identify, PCAP is a technique that can help you look into traffic and see where the problem is occurring and what is causing it.

Network administrators and IT professionals including security researchers often use PCAP because of the insight that packet file analysis allows them. By capturing data as it moves across the network and then analyzing the activity using PCAP analysis tools, IT experts can see malicious traffic, identify where it is coming from and take action to stop the activity and prevent further intrusions. PCAP may not always be the first line of defense that a security team chooses to utilize, as simpler techniques such as log reviews and network flows from routers and servers on the network can provide a decent overview. But when additional information is needed, PCAP is a worthy solution.

Advantages of PCAP

PCAP is a technique that system administrators and security teams count on to get more insight into what is happening on their network. While it is not necessarily the first line of defense, it is an important forensic tool that provides IT professionals a number of benefits.

  • Increased visibility into the network: The primary benefit of packet capture is the ability to get a clear insight into activity on the network by monitoring where traffic is coming from and what applications and devices it is interacting with. Packet capture provides the ability to spot specific problematic activity and address it.
  • Real-time monitoring: Because PCAP collects and copies data packets as they move across the network, the IT team can get real-time insight into activity. There is minimal delay, allowing for rapid identification and response of breaches, leaks, packet loss and other potential problems that may plague the network.
  • Simplicity and compatibility: While PCAP is a powerful tool, it is also a simple one that produces file formats that are widely compatible with readily accessible packet sniffing programs and PCAP analysis tools. You can find compatible tools for Windows, Linux, and macOS network architectures, including open source tools.

Disadvantages of PCAP

While PCAP is a valuable technique for IT teams and system administrators, it is not the perfect tool for every situation. You and your team will want to consider what your goals are before deploying PCAP and consider where the technique might fall short of your needs depending on the situation that you are facing.

  • Won’t identify non-network threats: Packet capturing and analysis is a technique for monitoring the activity that occurs across your network, which means if an attack is launched in a way that does not originate through network traffic, such as a hardware-based attack or an attack that compromises a USB drive, then it will not necessarily appear in PCAP analysis. These types of attacks require other types of security measures in order to identify and protect against them.
  • Unable to defeat encryption: While PCAP provides visibility into your network activity, it cannot provide visibility into encrypted communications, which attackers will often utilize when launching attacks in order to prevent being identified. For this reason, packet sniffers may be able to collect the data being transmitted across your network but will not be able to let you see the details of the network traffic if it is encrypted.
  • Location matters: While PCAP is a great way to get insight into what is happening across your network, it can’t see everything, and where you place your packet sniffer will play a role in what kind of data you gain access to. A packet sniffer connected to a device on the edge of your network may miss some activity, while one placed in the center of your network may collect significantly more noise and information than your IT team has the capacity to reasonably sort through and utilize.

Bottom Line

PCAP is an essential tool that security teams including system administrators should feel comfortable deploying when they need to get insight and visibility into the activity that is taking place across the company’s network. The ability to collect data packets and quickly analyze the data in easily readable formats using open source or proprietary tools makes PCAP one of the most accessible and essential tools for network security. But it should not be the only line of defense as it does have limitations in its ability to protect against outside attacks.

Frequently Asked Questions (FAQs)

What is the purpose of PCAP?

The purpose of PCAP is to copy data packets as they move across your network and allow the network administrator or other IT professional to analyze the activity. PCAP is an essential tool for identifying issues on the network ranging from attacks and malicious activity to packet loss and network congestion. Because of the visibility into the network traffic that packet capture offers, the IT team will be able to respond to incidents and issues precisely and efficiently, which makes PCAP a valuable technique to utilize when there are known issues across the network.

What does PCAP mean in Wireshark?

Wireshark is a popular packet analysis tool that is free and open source. It is utilized after a packet sniffer is deployed to capture data and provides a software-based interface for reading the information from the data packets that are captured. Wireshark is capable of creating .pcap files, which can come in a number of formats depending on the network architecture and operating system that you are running on. The most common PCAP file formats that are compatible with Wireshark include Libpcap, WinPcap, and PCAPng.

What is PCAP in security?

In network security, PCAP refers to packet capture, a technique of capturing data packets as they travel across the network in order to analyze them and understand problems that may be affecting the network. PCAP is a technique that is utilized by security teams including IT professionals and system administrators by deploying packet sniffers that can capture or copy data packets in transit. Packet analysis tools are then used to process that data, allowing security professionals to see where data originated from, where it is going and what the packet contains. PCAP is a technique that is used to identify problems within a network, from breaches and malicious software to packet loss and network traffic congestion.

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AJ Dellinger

AJ Dellinger is a writer, reporter, and editor based in Madison, Wisconsin. He has been published in Wired, Gizmodo, CNET, and a variety of other publications. He has covered small business and technology and cybersecurity solutions for publications like Bankrate, Digital.com, and others.

Kiran Aditham

For over 15 years, Kiran has served as an editor, writer and reporter for publications covering fields including advertising, technology, business, entertainment and new media.He has served as a reporter for AdAge/Creativity and spent several years as an edito and writer at Adweek. Along the way, he has also served in managing editor roles at the likes of PSFK and Ladders, worked in PR as a director of content, and most recently served as a Senior Editor at Dotdash Meredith for personal finance brand The Balance and then Entertainment Weekly. At Forbes Advisor, Kiran brings his experience and expertise to reinforce the brand’s reputation as the most informative, accessible and trusted resource in small business.

Matt Hoeper

Matt is a proven leader in IT, combining a master’s degree in Management Information Systems and solid experience with a proven track record in IT, leading business initiatives to help organizations meet their goals. He has led the security practices at 2 different MSPs, been a Health IT Director, a project manager, business analyst, system administrator, systems architect…if it has to do with IT, he’s probably done it. He helped author the CMMC Certified Professional and CMMC Certified Assessor field guides and has spoken at conferences all over the country regarding CMMC, IT security, risk. Matt has worked with Fortune 500 companies and small businesses, in areas ranging from engineering to marketing and supply chain to health care.

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