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..
Some options require root-privileges.
- Here's a pretty thorough scan recipe:
nmap -T Aggressive -P0 -sT -p 1-65535 <insert host IP here>
- 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
- This command will scan your system for open ports
- This command will see if the default svn port (6963) is open on your system:
nmap localhost -p 6963
- This command will print a list of common options
- 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.