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How to Detect Unauthorized Devices on a Network Using Linux Tools
Detecting Unauthorized Devices on a Network: A Practical Linux Guide
When I first started learning network security, one of the things that surprised me was how easy it could be for an unknown device to appear on a network.
A phone, laptop, router, IoT device, or even a virtual machine can connect to a network without immediately being obvious to someone managing it. If you don’t regularly check what’s connected, you may not notice an unfamiliar device until there is already a problem.
That made me realize something important: you can’t secure a network properly if you don’t know what’s connected to it.
In this guide, I’ll walk through some of the practical techniques I use to discover devices on a network using Linux. We’ll look at ARP tables, DHCP information, active connections, nmap, and arp-scan.
Important: Only scan networks and devices that you own or have explicit permission to administer.
Why Unknown Devices Matter
An unknown device isn’t automatically a malicious device.
It could simply be a new employee’s laptop, someone’s phone, a smart TV, a printer, or another device that you…
