Nmap Scanning - How?
From time to time people send me questions about the tools that HackerTarget uses to scan internet systems.
Nmap is the best port scanning tool in the world. This is clearly a strong statement. However it is also true. Read on for some interesting tricks you scan do with Nmap scans.
Firstly I would recommend you use a Linux based system to run nmap (not because Windows is for chumps) mostly because running Security tools on Linux is always a more pleasurable experience. If you haven’t used Linux before then try downloading Ubuntu or Knoppix - you dont even have to install it to your hard drive. Run it as a Live distro as it runs straight off the cd.
Nmap 4.20 ( http://insecure.org )
Usage: nmap [Scan Type(s)] [Options] {target specification}
TARGET SPECIFICATION:
Can pass hostnames, IP addresses, networks, etc.
Ex: scanme.nmap.org, microsoft.com/24, 192.168.0.1; 10.0.0-255.1-254
-iL <inputfilename>: Input from list of hosts/networks
-iR <num hosts>: Choose random targets
–exclude <host1[,host2][,host3],…>: Exclude hosts/networks
–excludefile <exclude_file>: Exclude list from file
HOST DISCOVERY:
-sL: List Scan - simply list targets to scan
-sP: Ping Scan - go no further than determining if host is online
-P0: Treat all hosts as online — skip host discovery
-PS/PA/PU [portlist]: TCP SYN/ACK or UDP discovery to given ports
-PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes
-n/-R: Never do DNS resolution/Always resolve [default: sometimes]
–dns-servers <serv1[,serv2],…>: Specify custom DNS servers
–system-dns: Use OS’s DNS resolver
SCAN TECHNIQUES:
-sS/sT/sA/sW/sM: TCP SYN/Connect()/ACK/Window/Maimon scans
-sU: UDP Scan
-sN/sF/sX: TCP Null, FIN, and Xmas scans
–scanflags <flags>: Customize TCP scan flags
-sI <zombie host[:probeport]>: Idlescan
-sO: IP protocol scan
-b <ftp relay host>: FTP bounce scan
PORT SPECIFICATION AND SCAN ORDER:
-p <port ranges>: Only scan specified ports
Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080
-F: Fast - Scan only the ports listed in the nmap-services file)
-r: Scan ports consecutively - don’t randomize
SERVICE/VERSION DETECTION:
-sV: Probe open ports to determine service/version info
–version-intensity <level>: Set from 0 (light) to 9 (try all probes)
–version-light: Limit to most likely probes (intensity 2)
–version-all: Try every single probe (intensity 9)
–version-trace: Show detailed version scan activity (for debugging)
OS DETECTION:
-O: Enable OS detection (try 2nd generation w/fallback to 1st)
-O2: Only use the new OS detection system (no fallback)
-O1: Only use the old (1st generation) OS detection system
–osscan-limit: Limit OS detection to promising targets
–osscan-guess: Guess OS more aggressively
TIMING AND PERFORMANCE:
Options which take <time> are in milliseconds, unless you append ’s’
(seconds), ‘m’ (minutes), or ‘h’ (hours) to the value (e.g. 30m).
-T[0-5]: Set timing template (higher is faster)
–min-hostgroup/max-hostgroup <size>: Parallel host scan group sizes
–min-parallelism/max-parallelism <time>: Probe parallelization
–min-rtt-timeout/max-rtt-timeout/initial-rtt-timeout <time>: Specifies
probe round trip time.
–max-retries <tries>: Caps number of port scan probe retransmissions.
–host-timeout <time>: Give up on target after this long
–scan-delay/–max-scan-delay <time>: Adjust delay between probes
FIREWALL/IDS EVASION AND SPOOFING:
-f; –mtu <val>: fragment packets (optionally w/given MTU)
-D <decoy1,decoy2[,ME],…>: Cloak a scan with decoys
-S <IP_Address>: Spoof source address
-e <iface>: Use specified interface
-g/–source-port <portnum>: Use given port number
–data-length <num>: Append random data to sent packets
–ip-options <options>: Send packets with specified ip options
–ttl <val>: Set IP time-to-live field
–spoof-mac <mac address/prefix/vendor name>: Spoof your MAC address
–badsum: Send packets with a bogus TCP/UDP checksum
OUTPUT:
-oN/-oX/-oS/-oG <file>: Output scan in normal, XML, s|<rIpt kIddi3,
and Grepable format, respectively, to the given filename.
-oA <basename>: Output in the three major formats at once
-v: Increase verbosity level (use twice for more effect)
-d[level]: Set or increase debugging level (Up to 9 is meaningful)
–open: Only show open (or possibly open) ports
–packet-trace: Show all packets sent and received
–iflist: Print host interfaces and routes (for debugging)
–log-errors: Log errors/warnings to the normal-format output file
–append-output: Append to rather than clobber specified output files
–resume <filename>: Resume an aborted scan
–stylesheet <path/URL>: XSL stylesheet to transform XML output to HTML
–webxml: Reference stylesheet from Insecure.Org for more portable XML
–no-stylesheet: Prevent associating of XSL stylesheet w/XML output
MISC:
-6: Enable IPv6 scanning
-A: Enables OS detection and Version detection
–datadir <dirname>: Specify custom Nmap data file location
–send-eth/–send-ip: Send using raw ethernet frames or IP packets
–privileged: Assume that the user is fully privileged
–unprivileged: Assume the user lacks raw socket privileges
-V: Print version number
-h: Print this help summary page.
EXAMPLES:
nmap -v -A scanme.nmap.org
nmap -v -sP 192.168.0.0/16 10.0.0.0/8
nmap -v -iR 10000 -P0 -p 80
SEE THE MAN PAGE FOR MANY MORE OPTIONS, DESCRIPTIONS, AND EXAMPLES
As you can there are a multitude of options available, so let me explain the basics. For an excellent and more indepth guide go to the source http://nmap.org/man/.
As a normal user: nmap 192.168.1.1 — this will scan the specified IP using a TCP connect scan
As a root user: nmap 192.168.1.1 — this will scan the specified IP using a TCP Syn scan
From here you can simply add options to the basic command above to provide different options
such as:
nmap -P0 192.168.1.1 — if the target IP is unpingable then you can do this to tell nmap to ignore the ping check
nmap -p 22 192.168.1.1 — specifiy which ports to scan
nmap -p 22-80 192.168.1.1 — specify a range of ports to scan
nmap -A 192.168.1.1 — scan ports and try to detect the version and service running on the port
nmap -F 192.168.1.1 — a fast scan of common ports
You get the picture, it is not difficult and an excellent tool for security scanning and network diagnosis. Now back to the question of chumps, whether you use Windows or Linux there is no doubt that an nmap gui is for chumps. 
