currently I have a problem. I have a switch and have no idea, what port is connected to what PoE device. Now I'd like to solve this issue. My idea is to disable a PoE port on the switch and wait what IP went down.

But how can I do this? Is there a tool, that can ping all IPs in the net and show what IP just went down?

1 Answer 1


For an IPv4 LAN try arp-scan. It sends arp packets and collects the responses.

Install it e.g. via apt:

sudo apt install arp-scan

Here is an example to scan all IPs in your LAN connected to the interface eth0:

sudo arp-scan --interface=eth0 --localnet

Pipe the output of the scans to two files before.dat and after.dat and compare them via

diff before.dat after.dat
  • And how can I get, what device went down? I have to compare the output manually. And with 200+ IPs it's quite annoying.
    – user39063
    Jul 17, 2019 at 18:40
  • pipe the result before and after to files and compare the files.
    – oh.dae.su
    Jul 17, 2019 at 18:41

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