How to find unknown ip address of a device?

Question

Computer networks

There is a piece of iron with an unknown ip address, even a subnet that is generally unknown.
It can respond to echo requests, telnet, ssh and web ports are open.
The piece of iron is directly plugged into the network card of the laptop. The mac of the network interface is known.
The question is how to find out the ip address of the device without running a scan on 0.0.0.0/0 or how to do it in a few hours.

Answer 1

Hard-reset and default in the documentation to look.

Answer 2

If the piece of iron has some kind of default ip address and responds to icmp echo, then sorting through all the ip ranges takes 10-15 minutes maximum. The scanner moves easily.

Answer 3

If the piece of hardware tries to send packets, then you can wireshark / tcpdump in promiscuous mode, a
rare chance that it can even light up in "arp -a"