Wireshark on Linux: Capture Network Traffic with dumpcap

Capturing network traffic is an essential task for network administrators and security professionals. Wireshark is a popular network protocol analyzer that provides a comprehensive suite of tools for capturing, filtering, and analyzing network packets. One of the key components of Wireshark is dumpcap, which allows users to capture packets without the graphical user interface (GUI). In this article, we will explore how to use dumpcap on Linux systems.

Basic Options

Dumpcap provides several basic options that can be used to customize the capture process. The `-w` option specifies the output file name and location. For example, `-w mycapture.pcapng` will write the captured packets to a file named `mycapture.pcapng`.

The `-b` option is used to specify the number of files to capture before overwriting the oldest file. This can be achieved by using the `-b files` option followed by the desired number. For example, `-b files:20` will capture 20 files before overwriting the oldest one.

Another important option is `-b filesize`, which specifies the file size in kilobytes (KB) before starting a new file. This allows users to capture large amounts of data without exhausting disk space. For instance, `-b filesize:100000` will start a new file when it reaches 100 MB in size.

Interface Selection

When capturing network traffic, it is essential to specify the interface number that you want to monitor. The interface number can be listed using the `dumpcap -D` command. Once you have identified the desired interface, you can use the `-i` option followed by the interface number. For example, `-i 1` will capture packets on interface 1.

Example Command

Here is an example command that demonstrates how to use dumpcap to capture network traffic:

```bash

dumpcap -i 1 -b filesize:100000 -b files:20 -w mycapture.pcapng

```

This command captures packets on interface 1, writes the output to a file named `mycapture.pcapng`, and captures 20 files before overwriting the oldest one. Each file will be limited to 100 MB in size.

Advanced Options

Dumpcap provides several advanced options that can be used to customize the capture process. For example, you can use the `-h` flag to see all available options and their descriptions.

If you want to filter traffic based on specific criteria, you can use display filters. Display filters allow you to specify conditions for which packets should be included or excluded from the capture. For example, `ip.addr = 1.2.3.4` will only show packets with a destination IP address of `1.2.3.4`.

In this article, we have explored how to use dumpcap on Linux systems to capture network traffic without the GUI. We discussed basic options such as output file selection and interface selection, as well as advanced options like display filters and capture filter syntax. By mastering these tools, you can effectively monitor and analyze network traffic to troubleshoot issues, identify security threats, and optimize network performance.

References

* `wireshark-filter(4)`: Display Filter Syntax

* `pcap-filter(7)`: Capture Filter Syntax

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