Hello again world! This week I am relaxing with my family in the beautiful Blue Ridge Mountains of North Carolina! However, I still found time to play with tcpdump a little bit and wanted to share how to open tcpdump captures using Wireshark.
tcpdump is a Linux/Unix command line utility that allows you to capture network packets, similar to Wireshark’s command line capture utility named tshark. Running tcpdump without any parameters will simply cause it to print out a basic description of the captured packets using one line per packet in the current shell. Redirecting the output of the command to a file isn’t very useful since it’s not really packet data that’s being captured, just the descriptions. If we want to capture the entire contents of each packet for later analysis, we will need to use the -w parameter and supply a filename. In our example, we’ll go ahead and append a file extension of “.pcap” to the filename so that Wireshark will recognize the filetype in our GUI, whether we are opening the file on the current system or transferring it to a Windows system. And depending on our OS, we might need to run tcpdump as root so we’ll use sudo:
sudo tcpdump -w capture.pcap
This will cause tcpdump to write all captured packets to capture.pcap in the current working directory. If you don’t specify any limiting factors like a maximum packet capture count or a maximum file size, the capture session will run until you press Ctrl+C. After tcpdump is stopped, you can view the trace file using Wireshark on a system of your choice. Best of luck!