Nmap (“Network Mapper”) is a free and open source (license) utility for network exploration or security auditing. Many systems and network administrators also find it useful for tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime.



In addition to my list you can also check out this Comprehensive Guide to Nmap here and of course the man pages

Here are some really cool scanning techniques using Nmap

nmap -sS -P0 -sV -O <target>

Where < target > may be a single IP, a hostname or a subnet -sS TCP SYN scanning (also known as half-open, or stealth scanning) -P0 option allows you to switch off ICMP pings. -sV option enables version detection -O flag attempt to identify the remote operating system Other option: -A option enables both OS fingerprinting and version detection -v use -v twice for more verbosity. nmap -sS -P0 -A -v < target >

2) Get list of servers with a specific port open

nmap -sT -p 80 -oG – 192.168.1.* | grep open

Change the -p argument for the port number. See “man nmap” for different ways to specify address ranges.

3) Find all active IP addresses in a network

nmap -sP 192.168.0.*

There are several other options. This one is plain and simple.

Another option is:

nmap -sP 192.168.0.0/24

for specific subnets

4) Ping a range of IP addresses

nmap -sP 192.168.1.100-254

nmap accepts a wide variety of addressing notation, multiple targets/ranges, etc.

5) Find unused IPs on a given subnet

nmap -T4 -sP 192.168.2.0/24 && egrep “00:00:00:00:00:00” /proc/net/arp

6) Scan for the Conficker virus on your LAN ect.

nmap -PN -T4 -p139,445 -n -v –script=smb-check-vulns –script-args safe=1 192.168.0.1-254

replace 192.168.0.1-256 with the IP’s you want to check.

7) Scan Network for Rogue APs.

nmap -A -p1-85,113,443,8080-8100 -T4 –min-hostgroup 50 –max-rtt-timeout 2000 –initial-rtt-timeout 300 –max-retries 3 –host-timeout 20m –max-scan-delay 1000 -oA wapscan 10.0.0.0/8

I’ve used this scan to successfully find many rogue APs on a very, very large network.

8) Use a decoy while scanning ports to avoid getting caught by the sys admin

sudo nmap -sS 192.168.0.10 -D 192.168.0.2

Scan for open ports on the target device/computer (192.168.0.10) while setting up a decoy address (192.168.0.2). This will show the decoy ip address instead of your ip in targets security logs. Decoy address needs to be alive. Check the targets security log at /var/log/secure to make sure it worked.

9) List of reverse DNS records for a subnet

nmap -R -sL 209.85.229.99/27 | awk ‘{if($3==”not”)print”(“$2″) no PTR”;else print$3″ is “$2}’ | grep ‘(‘