Explanation
The best option when stealth is not a concern and the task is time sensitive is to use the command: Nmap -sV
--script=smb* 172.21.0.0/16. This command will use version detection and SMB scripts to scan for port 445 on the given IP range. The -sV option will cause Nmap to detect the version of services running on the ports, which is helpful for identifying vulnerabilities, and the --script=smb* option will cause Nmap to run all of the SMB related scripts. The -T4 option can be used to speed up the scan, as it increases the timing probes.