Lesson 5.9: Discovering hosts and services with nmap, within scope
What network scanning is, why defenders do it on their own networks and why doing it to others without permission is illegal; host discovery, port scanning and version detection with nmap; saving results; and comparing what you find with what should be there. In the lab you scan the office network under a written authorisation, save the results, find the one device that isn't in the inventory, identify what it runs, review the NAS's services and see the lab refuse an out-of-scope target.
19 min
You will learn to
- Explain host discovery, port scanning and version detection
- Scan only within a written scope
- Save and compare scan results
- Find unknown devices against an inventory
- Interpret open, closed and filtered ports
Key terms
- Network scanning
- Sending probes to many addresses and ports to find which hosts are up and which services they run.
- nmap
- The best-known free network scanner: host discovery, port scanning, service and version detection, and more.
- Host discovery
- Finding which addresses in a range have a live host (nmap -sn).
- Port scan
- Checking which ports on a host are open, closed or filtered.
- Version detection
- Asking each open service what software and version it runs (nmap -sV), so known vulnerabilities can be checked.
- Asset inventory
- The list of devices and services that should be on a network; the baseline a scan is compared against.
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