If you’re using nmap, MAC addresses are only available if you’re on the same network segment as the target. Newer versions of nmap will only show the MAC address to you if you’re running as root. i.e.: sudo nmap -sP -n 192.168.0.0/24
This was a bug. These lines together result in i being unchanged, so they shouldn’t have been there. The linked article that introduced nmap was published on September 1 1997. If you look at the SVN repository for nmap at https://svn.nmap.org/nmap, the initial revision checked in on February 10 1998 does not have those lines: … Read more
Install nmap, sudo apt-get install nmap then nmap -sP 192.168.1.* or more commonly nmap -sn 192.168.1.0/24 will scan the entire .1 to .254 range This does a simple ping scan in the entire subnet to see which hosts are online.