How to Install and Use Wireshark on Ubuntu

https://linuxhint.com/install_wireshark_ubuntu/

How to find which machines occupying the most bandwidth in LAN?

Telnet to the firewall.
Log in.

Run the 'login' command.
>login
Password:

Run the following command -

#sh conn

Copy all the output to Notepad.
Open the txt file in Excel delimited by space.

Order them by 'Bytes'.