Please note that for clarity, I have removed the interface filter in the examples below. Tcpdump: verbose output suppressed, use -v. Then, it is possible to use the interface name or number, still with the -i argument, like: $ sudo tcpdump -i 1 The other method is to use tcpdump to get the interfaces list, with the command: tcpdump -D, this can be useful on systems that don’t have other command to list them: $ sudo tcpdump -D 1.enp0s3 Ģ.any (Pseudo-device that captures on all interfaces) Ĥ.bluetooth-monitor (Bluetooth Linux Monitor) ĥ.nflog (Linux netfilter log (NFLOG) interface) Ħ.nfqueue (Linux netfilter queue (NFQUEUE) interface) Ĩ.dbus-session (D-Bus session bus) Then, for this example, here is how to capture packets from the Ethernet interface enp0s3: $ sudo tcpdump -i enp0s3 Type ip link show up to see your current up interfaces of your system, for example: $ ip link show upġ: lo: mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000 We saw this in this article: Basic Linux Networking tips and tricks part-1: ip and nmcli commands. So we will start with the fact that tcpdump is installed and working.īasics Capture all packets from specific interface (-i interface_name_or_id)įirst, you have to know the name of the local interfaces. Moreover, there are already thousands of guides on the Internet about it. So the installation is very straightforward. It depends on the Linux distribution you are using and it is available as a standard package on almost all of them. However, I won’t explain how to install it. From the basics to everyday examples, including the much more advanced filtering options. Here, I tried to write a complete tcpdump tutorial with many examples and filtering details. Tcpdump prints out a description of the contents of packets on a network interface that matches an expression the description is preceded by a time stamp, printed, by default, as hours, minutes, seconds, and fractions of a second since midnight. I think the most essential element to debug a network problem is a packet capture tool or sniffer, and the most common one on Linux distributions is tcpdump. This post is part of a series of basic Linux Networking tips and tricks. Here is another post of the series on basic network troubleshooting and tools under Linux.
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