From “Using nmap for Linux administration and security” at http://searchenterpriselinux.techtarget.com/tip/Using-nmap-for-Linux-administration-and-security
nmap “Network Mapper” is a free and open source utility for network exploration or security auditing.
Ping scan to inventory network
nmap -sP -n 192.168.1.0/24
What changed since the last inventory scan?
diff monday.scan tuesday.scan | grep “> Host”
nmap -n -sV 192.168.1.5
Who has ports 80 or 443 open on the network?
nmap -n -p 80,443 192.168.1.0/24 | egrep “ports|open”
What is the state of port 139 on the network?
nmap -n -sV -p 139 192.168.1.0/24 | egrep “ports|139”
Run and test nmap
nmap –A –T4 scanme.insecure.org
Articles about nmap from searchsecurity.techtarget.com:
Video demo: How to use nmap to scan a network
Nmap: A valuable open source tool for network security
How to install and configure Nmap for Windows
How to install and configure Nmap on Linux
How to scan ports and services
Firewall configuration testing
Techniques for improving Nmap scan times
Interpreting and acting on Nmap scan results
Nmap and the open source debate
Nmap tutorial: How to use the open source network scanner
Detecting irregular programs and services installed in your network