nmap
scan for IPs and ports
nmap -PR -oN /tmp/nmap.out 192.168.1.0/24
search hosts
nmap -sP 192.168.1.*
nmap -PR -oN /tmp/nmap.out 192.168.1.0/24
scan for open ports
nmap -T4 -sS 192.168.1.100
get more detailed information
sudo nmap -O 192.168.1.100 -T4
scan one port
nmap -sV -P0 -p 22 -vv 192.168.1.100
LINKS
http://linuxwiki.de/nmap