With tools such as Fing (Android app) and netdiscover (Kali Linux tool) its possible to get all connected devices in network.
How it's possible to prevent host discovery in a network?
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There are multiple approaches an attacker can use for host discovery. I believe
netdiscover uses ARP requests for host discovery, which operates on the Ethernet protocol (see https://github.com/alexxy/netdiscover). Other tools like
nmap operate at higher protocol layers (ICMP, TCP/IP, UDP/IP, see https://nmap.org/book/man-host-discovery.html). A solution which prevents host discovery at higher protocol layers may not prevent host discovery at lower layers, and vice versa.
A firewall is a common solution for preventing host discovery. For example, Linux can use
iptables to prevent host discovery at higher layers and
arptables at the lower layers. This doesn't protect against sniffing of traffic by a passive attacker (
netdiscover can do this).
Network segmentation or VLANs could further protect against host discovery at the Ethernet layer.