Nmap
Nmap maps which hosts are alive on a network and which TCP/UDP services they expose, including software versions and operating-system hints.
What it is used for
- Inventory the services running in your own lab or company network
- Check that a firewall change really closed a port
- Find forgotten internet-facing services during an authorised assessment
Key features
- Host discovery and port scanning
- Service and version detection (-sV)
- OS fingerprinting
- Nmap Scripting Engine (NSE) for extra checks
Installation
Linux: install from your distribution (for example `sudo apt install nmap`). Windows/macOS: use the installers on nmap.org/download.
Beginner usage guide
Start with a ping/host-discovery sweep of your lab subnet, then run a service-version scan against the hosts you found and read the output line by line: each open port shows its state, protocol and (with -sV) the detected product.
Example commands
Run these only against your own lab or authorised targets. Placeholder addresses such as 192.0.2.x are documentation ranges.
nmap -sV --top-ports 100 192.0.2.10Scans the 100 most common ports on one lab host and tries to identify each service version. 192.0.2.0/24 is a documentation range — replace it with a host you own.
nmap -sn 192.168.56.0/24Ping sweep of a lab subnet; lists hosts that respond.