Which of the following is used by Nmap for identifying live hosts and devices as part of a network sweep?

UDP scanning in Nmap is used for port enumeration on specific services, not as the primary mechanism for sweeping to identify whether hosts are alive.

Nmap's host discovery process (ping scan) sends multiple probe types to detect live hosts, including ICMP Type 13 Timestamp requests (-PP flag). Many hosts respond to timestamp requests even when they block standard ICMP echo requests, making this an effective technique for identifying active devices during a sweep. It is a documented part of Nmap's default and configurable discovery arsenal.

DNS queries resolve hostnames to IP addresses and are used for reverse lookups during scanning, not as the core probe for detecting live hosts in a network sweep.

DHCP Discover packets are broadcast by clients seeking an IP address assignment from a DHCP server and are not used by Nmap as a host discovery technique.