Nmap

Nmap ("Network Mapper") is a well-known utility for network exploration or security auditing. It is distributed under the GPL. It can rapidly scan a large network using raw IP packets "in novel ways" to give feedback about which hosts are active, which OS they are running, which ports/services are open and awaiting connections, etc..

= Tips = Some options require root-privileges. nmap -T Aggressive -P0 -sT -p 1-65535 
 * Here's a pretty thorough scan recipe:


 * Sometimes a host appears down, so the scanning is not done. This can be a problem. To avoid it, use the option -P0. For more information, see the man page.


 * There is also nmapfe, which is a GUI frontend for nmap

= Examples = nmap localhost nmap localhost -p 6963 nmap -h
 * This command will scan your system for open ports
 * This command will see if the default svn port (6963) is open on your system:
 * This command will print a list of common options

= Q&A =
 * Why don't I see a port for ping even though the computer answers on ping requests?
 * The protocols shown by nmap are protocols based on TCP or UDP, while ping's icmp protocol is based on IP.

= See also =
 * Linux security vulnerabilities
 * netstat
 * network
 * diagnostics
 * Nmap home page
 * Nmap docs
 * nmap man page