Packet capture or PCAP is also referred to as libpcap, and it’s an application programming interface (API), capable of capturing live packet data on the network.
It does so in the OSI Layer 2-7 model. Network analysers or packet sniffers such as Wireshark will create .pcap (packet capture file) files when they read data from a network.
PCAP files are used for viewing TCP/IP and UDP network packet data, and therefore if you want to log network traffic, you will have to create files with a .pcap file extension.
Here you can learn more about what a PCAP file is and how it works.
How Does a Packet Sniffer Work?
To capture PCAP files, you need to use a packet sniffer, which captures packets and presents them in an easy to understand manner.
When you use a PCAP sniffer, you will need to identify the interface you wish to sniff. If you are using Linux based devices, these can be eth0 or wlan0. You can also select the interface using the ifconfig command.
Once you know the interface, you will be sniffing; you can choose the type of traffic you wish to monitor.
For example, many of the tools allow you to choose the different packet types such as TCP/IP, and thus, it will only collect this type.
You can use Wireshark for PCAP file capture and network analysis. here it allows you to filter traffic type you see in the capture filters and display filters.
The capture filters are the traffic you capture, and the display is the data you see. For instance, it is possible to filter protocols, flows, or hosts.
With filtered traffic, you can check for performance issues. You can also filer on source ports to target your analysis as well as destination ports. All of this can be used to test network performance. (Read Online Safety for Kids)
Why Would I Need PCAP?
PCAP can provide a rich resource for analysing files and for monitoring network traffic.
Packet collection tools, including Wireshark, enable you to gather network traffic and convert it into a human-readable open file format.
For many reasons, PCAP is widely used to monitor networks. Among the more common, are monitoring bandwidth usage, identification of rogue DHCP servers, detecting malware, resolving DNS and reacting to incidents.
For the network administrator or security researchers, PCAP packet file analysis is a useful way of detecting network intrusions and any suspicious activity.
For instance, if an open source sends large amounts of malicious traffic on the network, you can use the PCAP software agent to identify such traffic and apply corrective measures to resolve the file attack.
What are the Versions of PCAP?
You can find various versions of PCAP files, including:
Each PCAP version offers its use case and various network-monitoring tools with support. Libpcap, for example, is a portable open-source c/C++ library designed for Linux and Mac OS.
It enables admin to filter and capture packets with tools like tcpdump, which use Libpcap file format.
For Windows, you have WinPcap format, which is another portable packet capture library, which captures and filters packets. Wireshark, Nmap, and Snort are popular and use WinPCap for device monitoring, although the protocol has ended.
Pcapng or .pcap Next Generation Capture File Format is an advanced version of PCAP and is the default in Wireshark. Pcapng captures and stores data.
Pcapng collects extended timestamp precision, user comments, and capture stats for more information.
Wireshark uses PCAPng as it records more info than PCAP, even when it lacks compatibility with some tools.
Npcap is a Windows portable packet sniffer library, which is faster and secure than WinpCap. Npcap has Windows 10 support and (127.0.0.1) loopback packet capture injection. It also has support for Wireshark.
PCAP Packet Capturing Advantages
The main advantage of packet capturing is visibility. You use packet data to pinpoint root causes of network issues.
You can monitor traffic sources and understand application and device usage data. PCAP offers real-time file info to locate and resolve network performance issues so you can maintain network function after security events and an open network.
It is possible to recognise where malware entered an open network by tracing the flow of malicious traffic and malicious file communications.
Without PCAP and packet sniffers, this would be more of a challenge. As an easy to use and read file format, PCAP is advantageous of being compatible with nearly all packet sniffers on any OS such as Windows, macOS and Linux.
Disadvantages of PCAP Packet Capture
While it is great to be able to record network traffic and understanding packet captures and using the information the PCAP file supply.
However, there are some limitations. Apps such as Wireshark on Windows or the other OS do not allow PCAP to capture everything.
For example, you can still find some cyber-attacks that do not stem from the network traffic to open or access files.
Hardware attacks and from USB drives can be physical attacks, and this information is hidden from the likes of Wireshark until it affects the network, and even then, it can be hard for the software or admin to determine the root cause.
One thing often an oversight is the way attackers get around Wireshark on Windows or other OS and hide their information.
Encryption hides your data and makes it impossible for apps like Wireshark to read your information.
You can use Wireshark to create a PCAP file extension file, and it won’t be readable, and you can’t open the PCAP file as the contents are encrypted. One way they do this may be the use of a VPN.
A virtual private network uses encrypted tunnels to send their files, and no one on the outside can open the file.
Users should know that network admin are wise to use PCAP as a base form of security. On the other hand, hackers can use such tools like Wireshark on Wi-Fi connections, and thus to be safe, any user should employ the services of a premium VPN provider.
If a VPN can hide the hackers, then you can hide your information from everyone else as well.