How to determine if an IP address is being used or not?

Question

Computer networks

Goodnight! Gentlemen, tell me, the provider gives 5 ip addresses. Two of them are in use and I know by whom, the question is how do I know if the other addresses are in use or free? Ping is not an option, can be disabled. What other ways to check if there is activity on a specific IP?

Answer 1

If the addresses are on the same broadcast network, ping the WXYZ address from a router connected directly to the network, then use the
arp -a WXYZ (Linux, Windows)
show ip arp WXYZ (Cisco) command to see
if there is an entry in the arp table with a non-zero MAC- address. Even if someone filters the IP packet (ping), it will still be visible inside the local network by arp.

Answer 2

go to the router that distributes the IP