Command Line Fu - Use tcpdump to capture traffic for wireshark

If there's some problem regarding any network-facing services, it can be useful to capture the traffic of the server's interfaces. A nice graphical environment for analyzing these traffic-dumps is Wireshark.

First, make sure tcpdump is installed on your server:
Note: yum is symlinked on CentOS 8 so this command will work.

 [archy@server ~]$ sudo yum -y install tcpdump

Now that tcpdump is installed, you can start capturing traffic.

 [archy@server ~]$ sudo tcpdump -i eth0 -nn -c 10000 -Z $(whoami) -w tcpdump_$(date +%Y-%m-%d).pcapng 'dst net 172.31.10.0/24'

-i the interface of the server from which to capture traffic

-nn disables name resolution for ip addresses and ports

-c specifies the number of packages before the capture is stopped automatically

-Z specifies the user which will be the owner of the captured file

-w specifies the file to which the capture should be written

The last argument will be the filter expression, in my case 'dst net 172.31.10.0/24'

Once you copied the file over to your Desktop, you can simply open it in Wireshark.

Feel free to comment and / or suggest a topic.

Comments

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