Scan for HOSTNAME

NMAP

If you on Ubuntu, Centos, or Fedora, you will need to run as sudo

Ubuntu, Centos, Fedora will need your authentication 

sudo nmap -sP <gw ip>/24 | grep '<name>'

<name> might be a group name or person name

<gw ip> is the gateway

To scan for all host,

sudo nmap -sP <gw ip>/24

Backtrack, Backbox

nmap -sP <gw ip>/24 | grep 'name'

To scan for all host,

nmap -sP <gw ip>/24