It sounds like what you'd like to do is use tcpdump to discover the hostnames of machines within a particular subnet. If you use the -n flag it's going to display IPs and not perform the lookup to resolve the hostname and display that if the hostname exists in local DNS. Because you're using a private subnet you'd have to have some internal DNS server that mapped those private IPs to hostnames, otherwise it doesn't matter what those machines call themselves - the hostname of a machine isn't communicated within the packet, just the src and destination IPs.
A tool you could use, if you were interested in mapping a subnet, is nmap. Or, if you're motivated, a tool like OpenNMS.
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