quick scan:
nmap -sn xxx.xxx.xxx.0/24

-n Never do name resolving
-s scan

name resolving
nmap -sP xxx.xxx.xxx.0/24

reverse name resolving, (as root: also MAC-addresses)
nmap -R -sP xxx.xxx.xxx.0/24

# # #

arp -a

arp -an


# # #

https://www.cyberciti.biz/networking/nmap-command-examples-tutorials/