Port Scan is the 1st Stage of any vulnerability assessment done on the orgaization. It can be of two types: Internal & External.Internal Scan: Inside scan of IPs that are private ip & not being natted. External IPs can also be scanned.External Scan: IPs which are being natted to communicate with outside world. Generally, performed from outside the organizaton's network.Pros:1: Finding Threats & Vulnerabilities through IP.2: Services running on those ports & their versions.Cons:1: Firewall will keep logs of the Source_IP from where the scan was initiated.Command : "sudo"(to run as root) nmap -sV -O <target-ip>nmap: Network Mapper is free network scanning tool.-sV: detects target system's service & version-O: detects OS of the target system.N.B: There are many commands even --scripts are there to run along nmap. This is just the basic & most efficient command to remember & does the job.