A
ping sweep sends ICMP Echo requests to every IP in a range — identifying live hosts without port scanning. 'nmap -sn 192.168.1.0/24'.
Many hosts block ICMP — Nmap -sn also uses ARP (on local subnet) and TCP SYN/ACK probes to detect hosts blocking ping. Nmap -PR (ARP scan) is the most reliable on local subnets. Ping sweeps are active reconnaissance — they appear in firewall logs. Use for internal recon during authorized pen tests.