INTRODUCTION
A key technique for maintaining networks’ effectiveness and safety is packet capture. It can also be used to steal private information, such as usernames and passwords, in the wrong hands. In this article, we’ll examine what a packet capture is, how it operates, what tools are employed, and a few hypothetical use cases.
The process of capturing Internet Protocol (IP) packets for examination or analysis is referred to as packet capture. The phrase is also applicable to the files produced by packet capture programs, which are frequently saved in the.pcap format. Network administrators frequently utilize packet capture as a tool for troubleshooting, as well as for scanning network traffic for security risks. Packet captures after a data breach or other incident offer crucial forensic hints that help investigations. Packet captures could be used by threat actors to obtain passwords and other private information. In contrast to active reconnaissance methods like port scanning, packet capture can be carried out with no traces left behind for investigators.
Understanding a Packet Capture
You’ll need a rudimentary understanding of core networking ideas, particularly the OSI model, in order to comprehend and analyze a packet capture. Although there could be variations among particular tools, a payload and a few headers are usually present in a packet capture. The actual material being delivered is known as the payload; examples include emails, malware, and small portions of streaming movies.
The essential data that network equipment needs to decide what to do with each packet is all contained in the packet headers. The source and destination addresses are the most crucial, but IP packets have a total of 14 headers that range from the Class of Service to the Protocol Type.
Libraries, Formats, and Filters Oh My!
There are several terms that are linked to packet captures that can rapidly become confused. Here are some of the most crucial and typical terminology you might hear, explained:
Formats for Packet Captures
Although real-time traffic inspection is possible with packet capture tools like Wireshark, it’s more typical to store captures to a file for later examination. The most popular format for saving these files is.pcap, which is generally compatible with a variety of network analyzers and other applications.Pcapng, which adds extra features and capabilities to the straightforward.pcap format, has replaced.pcap as the default file format in Wireshark.
Libraries
The actual stars of the packet capture show are libraries like libpcap, winpcap, and npcap since they can peer into packets flowing across interfaces by hooking into an operating system’s networking stack. Since many of these libraries are open-source initiatives, they can be found in a wide range of packet capture programs, both paid and unpaid.
Filtering
Full packet capture might consume a lot of storage space and put extra demands on the capturing device’s resources. Additionally, it’s usually overkill because the most interesting data only makes up a small part of the observed traffic overall. To remove the pertinent material, they frequently screened. The payload, IP address, or a combination of factors may all play a role in this.
Tools for packet capture
There are numerous tools available to collect and examine the packets moving via your network. These devices are also referred to as packet sniffers. Here are a few of the most well-known:
Wireshark
Wireshark, the standard packet tool, is preferred by many network managers, security experts, and home computer geeks. Wireshark combines usability and power with a simple GUI and a ton of functionality for sorting, analyzing, and making sense of traffic. The tshark command-line tool is also part of the Wireshark package.
Network Performance Monitor, SolarWinds
The simplicity of use, the graphics, and the option to categorize traffic by application have made this commercial tool a longtime favorite. Despite only being compatible with Windows platforms, the tool can sniff and analyze communications from any kind of device.
Capsa ColaSoft
ColaSoft creates a for-profit packet sniffer geared toward businesses, but it also provides a condensed version for novice networkers and students. The tool offers a wide range of monitoring functions to help with analysis and troubleshooting in real-time.
Kismet
Kismet is a tool used to monitor wireless activity and identify wireless networks and gadgets. This application supports a wide variety of capture sources, including Bluetooth and Zigbee radios, and is accessible for Linux, Mac, and Windows platforms.
Advantages and Disadvantages of Packet Capture
As was already said, network managers and security teams greatly benefit from packet captures. However, they are not the only option, and there may be circumstances in which SNMP or NetFlow are preferable options for monitoring network traffic. Here are a few benefits and drawbacks of employing packet captures:
Most Comprehensive View of Network Traffic
By definition, packet capture is a copy of the actual packets that are traveling across a network or network link. As a result, it offers the most complete examination of network traffic. Other monitoring methods do not provide the amount of detail found in packet captures, which include the whole payload, all IP header data, and frequently even information about the capture interface.
Can be saved for later examination
Packet captures can be recorded in the widely used.pcap and.pcapng formats for later analysis or inspection. This enables, for instance, a network engineer to record suspicious traffic for subsequent analysis by a security expert. This format is supported by many tools. Additionally, a packet capture including many hours’ worth of data can be saved and later reviewed.
Hardware Agnostic
Both Hardware Agnostic SNMP and NetFlow demand network hardware support. Despite having widespread support, neither technology is available everywhere. On the other hand, packet capture can be performed from any device that has network access and does not need particular hardware support.
Disadvantages
Large files.
Full packet capture can use up to 20 times as much disk space as other solutions, which is a significant amount of storage. A single capture file may consume many gigabytes of storage, even after filtering. As a result, packet captures might not be acceptable for long-term archiving. When opening a.pcap in a network analysis tool, these high file sizes can also cause protracted waiting times.
Excessive Information
Although packet captures offer a highly thorough view of network traffic, they are frequently overly thorough. Large data sets frequently make it difficult to find pertinent information. Although analysis programs include the ability to organise, sort, and filter capture files, there may be other solutions that are more suitable for certain use situations.
Conclusion
Although packet capture is a crucial tool for security and troubleshooting, a network administrator or security expert should never rely only on it. The effectiveness of tools like Wireshark is constrained by the rise in the usage of encryption for both legal and illegal purposes. Additionally, packet captures do not provide incident responders with a clear picture of the activities that have been conducted on a host. Without producing a single packet, files could have been changed, processes could have been concealed, and new user accounts could have been made.
