1NMAP(1) Nmap Reference Guide NMAP(1)
2
6 nmap - Network exploration tool and security / port scanner
7
9 nmap [Scan Type...] [Options] {target specification}
10
12 Nmap (“Network Mapper”) is an open source tool for network exploration
13 and security auditing. It was designed to rapidly scan large networks,
14 although it works fine against single hosts. Nmap uses raw IP packets
15 in novel ways to determine what hosts are available on the network,
16 what services (application name and version) those hosts are offering,
17 what operating systems (and OS versions) they are running, what type of
18 packet filters/firewalls are in use, and dozens of other
19 characteristics. While Nmap is commonly used for security audits, many
20 systems and network administrators find it useful for routine tasks
21 such as network inventory, managing service upgrade schedules, and
22 monitoring host or service uptime.
23 The output from Nmap is a list of scanned targets, with supplemental
25 information on each depending on the options used. Key among that
26 information is the “interesting ports table”.. That table lists the
27 port number and protocol, service name, and state. The state is either
28 open, filtered, closed, or unfiltered. Open. means that an
29 application on the target machine is listening for connections/packets
30 on that port. Filtered. means that a firewall, filter, or other
31 network obstacle is blocking the port so that Nmap cannot tell whether
32 it is open or closed. Closed. ports have no application listening on
33 them, though they could open up at any time. Ports are classified as
34 unfiltered. when they are responsive to Nmap's probes, but Nmap cannot
35 determine whether they are open or closed. Nmap reports the state
36 combinations open|filtered. and closed|filtered. when it cannot
37 determine which of the two states describe a port. The port table may
38 also include software version details when version detection has been
39 requested. When an IP protocol scan is requested (-sO), Nmap provides
40 information on supported IP protocols rather than listening ports.
41 In addition to the interesting ports table, Nmap can provide further
43 information on targets, including reverse DNS names, operating system
44 guesses, device types, and MAC addresses.
45 A typical Nmap scan is shown in Example 1. The only Nmap arguments used
47 in this example are -A, to enable OS and version detection, script
48 scanning, and traceroute; -T4 for faster execution; and then the two
49 target hostnames.
50 Example 1. A representative Nmap scan
52 # nmap -A -T4 scanme.nmap.org
54 Nmap scan report for scanme.nmap.org (74.207.244.221)
56 Host is up (0.029s latency).
57 rDNS record for 74.207.244.221: li86-221.members.linode.com
58 Not shown: 995 closed ports
59 PORT STATE SERVICE VERSION
60 22/tcp open ssh OpenSSH 5.3p1 Debian 3ubuntu7 (protocol 2.0)
61 | ssh-hostkey: 1024 8d:60:f1:7c:ca:b7:3d:0a:d6:67:54:9d:69:d9:b9:dd (DSA)
62 |_2048 79:f8:09:ac:d4:e2:32:42:10:49:d3:bd:20:82:85:ec (RSA)
63 80/tcp open http Apache httpd 2.2.14 ((Ubuntu))
64 |_http-title: Go ahead and ScanMe!
65 646/tcp filtered ldp
66 1720/tcp filtered H.323/Q.931
67 9929/tcp open nping-echo Nping echo
68 Device type: general purpose
69 Running: Linux 2.6.X
70 OS CPE: cpe:/o:linux:linux_kernel:2.6.39
71 OS details: Linux 2.6.39
72 Network Distance: 11 hops
73 Service Info: OS: Linux; CPE: cpe:/o:linux:kernel
74 TRACEROUTE (using port 53/tcp)
76 HOP RTT ADDRESS
77 [Cut first 10 hops for brevity]
78 11 17.65 ms li86-221.members.linode.com (74.207.244.221)
79 Nmap done: 1 IP address (1 host up) scanned in 14.40 seconds
81 The newest version of Nmap can be obtained from http://nmap.org. The
83 newest version of this man page is available at
84 http://nmap.org/book/man.html. It is also included as a chapter of
85 Nmap Network Scanning: The Official Nmap Project Guide to Network
86 Discovery and Security Scanning (see http://nmap.org/book/).
87
89 This options summary is printed when Nmap is run with no arguments, and
90 the latest version is always available at
91 https://svn.nmap.org/nmap/docs/nmap.usage.txt. It helps people remember
92 the most common options, but is no substitute for the in-depth
93 documentation in the rest of this manual. Some obscure options aren't
94 even included here.
95 Nmap 6.40 ( http://nmap.org )
97 Usage: nmap [Scan Type(s)] [Options] {target specification}
98 TARGET SPECIFICATION:
99 Can pass hostnames, IP addresses, networks, etc.
100 Ex: scanme.nmap.org, 192.168.0.1; 10.0.0-255.1-254
101 -iL <inputfilename>: Input from list of hosts/networks
102 -iR <num hosts>: Choose random targets
103 --exclude <host1[,host2][,host3],...>: Exclude hosts/networks
104 --excludefile <exclude_file>: Exclude list from file
105 HOST DISCOVERY:
106 -sL: List Scan - simply list targets to scan
107 -sn: Ping Scan - disable port scan
108 -Pn: Treat all hosts as online -- skip host discovery
109 -PS/PA/PU/PY[portlist]: TCP SYN/ACK, UDP or SCTP discovery to given ports
110 -PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes
111 -PO[protocol list]: IP Protocol Ping
112 -n/-R: Never do DNS resolution/Always resolve [default: sometimes]
113 --dns-servers <serv1[,serv2],...>: Specify custom DNS servers
114 --system-dns: Use OS's DNS resolver
115 --traceroute: Trace hop path to each host
116 SCAN TECHNIQUES:
117 -sS/sT/sA/sW/sM: TCP SYN/Connect()/ACK/Window/Maimon scans
118 -sU: UDP Scan
119 -sN/sF/sX: TCP Null, FIN, and Xmas scans
120 --scanflags <flags>: Customize TCP scan flags
121 -sI <zombie host[:probeport]>: Idle scan
122 -sY/sZ: SCTP INIT/COOKIE-ECHO scans
123 -sO: IP protocol scan
124 -b <FTP relay host>: FTP bounce scan
125 PORT SPECIFICATION AND SCAN ORDER:
126 -p <port ranges>: Only scan specified ports
127 Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080,S:9
128 -F: Fast mode - Scan fewer ports than the default scan
129 -r: Scan ports consecutively - don't randomize
130 --top-ports <number>: Scan <number> most common ports
131 --port-ratio <ratio>: Scan ports more common than <ratio>
132 SERVICE/VERSION DETECTION:
133 -sV: Probe open ports to determine service/version info
134 --version-intensity <level>: Set from 0 (light) to 9 (try all probes)
135 --version-light: Limit to most likely probes (intensity 2)
136 --version-all: Try every single probe (intensity 9)
137 --version-trace: Show detailed version scan activity (for debugging)
138 SCRIPT SCAN:
139 -sC: equivalent to --script=default
140 --script=<Lua scripts>: <Lua scripts> is a comma separated list of
141 directories, script-files or script-categories
142 --script-args=<n1=v1,[n2=v2,...]>: provide arguments to scripts
143 --script-args-file=filename: provide NSE script args in a file
144 --script-trace: Show all data sent and received
145 --script-updatedb: Update the script database.
146 --script-help=<Lua scripts>: Show help about scripts.
147 <Lua scripts> is a comma separated list of script-files or
148 script-categories.
149 OS DETECTION:
150 -O: Enable OS detection
151 --osscan-limit: Limit OS detection to promising targets
152 --osscan-guess: Guess OS more aggressively
153 TIMING AND PERFORMANCE:
154 Options which take <time> are in seconds, or append 'ms' (milliseconds),
155 's' (seconds), 'm' (minutes), or 'h' (hours) to the value (e.g. 30m).
156 -T<0-5>: Set timing template (higher is faster)
157 --min-hostgroup/max-hostgroup <size>: Parallel host scan group sizes
158 --min-parallelism/max-parallelism <numprobes>: Probe parallelization
159 --min-rtt-timeout/max-rtt-timeout/initial-rtt-timeout <time>: Specifies
160 probe round trip time.
161 --max-retries <tries>: Caps number of port scan probe retransmissions.
162 --host-timeout <time>: Give up on target after this long
163 --scan-delay/--max-scan-delay <time>: Adjust delay between probes
164 --min-rate <number>: Send packets no slower than <number> per second
165 --max-rate <number>: Send packets no faster than <number> per second
166 FIREWALL/IDS EVASION AND SPOOFING:
167 -f; --mtu <val>: fragment packets (optionally w/given MTU)
168 -D <decoy1,decoy2[,ME],...>: Cloak a scan with decoys
169 -S <IP_Address>: Spoof source address
170 -e <iface>: Use specified interface
171 -g/--source-port <portnum>: Use given port number
172 --data-length <num>: Append random data to sent packets
173 --ip-options <options>: Send packets with specified ip options
174 --ttl <val>: Set IP time-to-live field
175 --spoof-mac <mac address/prefix/vendor name>: Spoof your MAC address
176 --badsum: Send packets with a bogus TCP/UDP/SCTP checksum
177 OUTPUT:
178 -oN/-oX/-oS/-oG <file>: Output scan in normal, XML, s|<rIpt kIddi3,
179 and Grepable format, respectively, to the given filename.
180 -oA <basename>: Output in the three major formats at once
181 -v: Increase verbosity level (use -vv or more for greater effect)
182 -d: Increase debugging level (use -dd or more for greater effect)
183 --reason: Display the reason a port is in a particular state
184 --open: Only show open (or possibly open) ports
185 --packet-trace: Show all packets sent and received
186 --iflist: Print host interfaces and routes (for debugging)
187 --log-errors: Log errors/warnings to the normal-format output file
188 --append-output: Append to rather than clobber specified output files
189 --resume <filename>: Resume an aborted scan
190 --stylesheet <path/URL>: XSL stylesheet to transform XML output to HTML
191 --webxml: Reference stylesheet from Nmap.Org for more portable XML
192 --no-stylesheet: Prevent associating of XSL stylesheet w/XML output
193 MISC:
194 -6: Enable IPv6 scanning
195 -A: Enable OS detection, version detection, script scanning, and traceroute
196 --datadir <dirname>: Specify custom Nmap data file location
197 --send-eth/--send-ip: Send using raw ethernet frames or IP packets
198 --privileged: Assume that the user is fully privileged
199 --unprivileged: Assume the user lacks raw socket privileges
200 -V: Print version number
201 -h: Print this help summary page.
202 EXAMPLES:
203 nmap -v -A scanme.nmap.org
204 nmap -v -sn 192.168.0.0/16 10.0.0.0/8
205 nmap -v -iR 10000 -Pn -p 80
206 SEE THE MAN PAGE (http://nmap.org/book/man.html) FOR MORE OPTIONS AND EXAMPLES
207
209 Everything on the Nmap command-line that isn't an option (or option
210 argument) is treated as a target host specification. The simplest case
211 is to specify a target IP address or hostname for scanning.
212 Sometimes you wish to scan a whole network of adjacent hosts. For this,
214 Nmap supports CIDR-style. addressing. You can append /numbits to an
215 IPv4 address or hostname and Nmap will scan every IP address for which
216 the first numbits are the same as for the reference IP or hostname
217 given. For example, 192.168.10.0/24 would scan the 256 hosts between
218 192.168.10.0 (binary: 11000000 10101000 00001010 00000000) and
219 192.168.10.255 (binary: 11000000 10101000 00001010 11111111),
220 inclusive. 192.168.10.40/24 would scan exactly the same targets. Given
221 that the host scanme.nmap.org. is at the IP address 64.13.134.52, the
222 specification scanme.nmap.org/16 would scan the 65,536 IP addresses
223 between 64.13.0.0 and 64.13.255.255. The smallest allowed value is /0,
224 which targets the whole Internet. The largest value is /32, which scans
225 just the named host or IP address because all address bits are fixed.
226 CIDR notation is short but not always flexible enough. For example, you
228 might want to scan 192.168.0.0/16 but skip any IPs ending with .0 or
229 .255 because they may be used as subnet network and broadcast
230 addresses. Nmap supports this through octet range addressing. Rather
231 than specify a normal IP address, you can specify a comma-separated
232 list of numbers or ranges for each octet. For example,
233 192.168.0-255.1-254 will skip all addresses in the range that end in .0
234 or .255, and 192.168.3-5,7.1 will scan the four addresses 192.168.3.1,
235 192.168.4.1, 192.168.5.1, and 192.168.7.1. Either side of a range may
236 be omitted; the default values are 0 on the left and 255 on the right.
237 Using - by itself is the same as 0-255, but remember to use 0- in the
238 first octet so the target specification doesn't look like a
239 command-line option. Ranges need not be limited to the final octets:
240 the specifier 0-255.0-255.13.37 will perform an Internet-wide scan for
241 all IP addresses ending in 13.37. This sort of broad sampling can be
242 useful for Internet surveys and research.
243 IPv6 addresses can only be specified by their fully qualified IPv6
245 address or hostname. CIDR and octet ranges aren't yet supported for
246 IPv6.
247 IPv6 addresses with non-global scope need to have a zone ID suffix. On
249 Unix systems, this is a percent sign followed by an interface name; a
250 complete address might be fe80::a8bb:ccff:fedd:eeff%eth0. On Windows,
251 use an interface index number in place of an interface name:
252 fe80::a8bb:ccff:fedd:eeff%1. You can see a list of interface indexes by
253 running the command netsh.exe interface ipv6 show interface.
254 Nmap accepts multiple host specifications on the command line, and they
256 don't need to be the same type. The command nmap scanme.nmap.org
257 192.168.0.0/8 10.0.0,1,3-7.- does what you would expect.
258 While targets are usually specified on the command lines, the following
260 options are also available to control target selection:
261 -iL inputfilename (Input from list) .
263 Reads target specifications from inputfilename. Passing a huge list
264 of hosts is often awkward on the command line, yet it is a common
265 desire. For example, your DHCP server might export a list of 10,000
266 current leases that you wish to scan. Or maybe you want to scan all
267 IP addresses except for those to locate hosts using unauthorized
268 static IP addresses. Simply generate the list of hosts to scan and
269 pass that filename to Nmap as an argument to the -iL option.
270 Entries can be in any of the formats accepted by Nmap on the
271 command line (IP address, hostname, CIDR, IPv6, or octet ranges).
272 Each entry must be separated by one or more spaces, tabs, or
273 newlines. You can specify a hyphen (-) as the filename if you want
274 Nmap to read hosts from standard input rather than an actual file.
275 The input file may contain comments that start with # and extend to
277 the end of the line.
278 -iR num hosts (Choose random targets) .
280 For Internet-wide surveys and other research, you may want to
281 choose targets at random. The num hosts argument tells Nmap how
282 many IPs to generate. Undesirable IPs such as those in certain
283 private, multicast, or unallocated address ranges are automatically
284 skipped. The argument 0 can be specified for a never-ending scan.
285 Keep in mind that some network administrators bristle at
286 unauthorized scans of their networks and may complain. Use this
287 option at your own risk! If you find yourself really bored one
288 rainy afternoon, try the command nmap -Pn -sS -p 80 -iR 0 --open.
289 to locate random web servers for browsing.
290 --exclude host1[,host2[,...]] (Exclude hosts/networks) .
292 Specifies a comma-separated list of targets to be excluded from the
293 scan even if they are part of the overall network range you
294 specify. The list you pass in uses normal Nmap syntax, so it can
295 include hostnames, CIDR netblocks, octet ranges, etc. This can be
296 useful when the network you wish to scan includes untouchable
297 mission-critical servers, systems that are known to react adversely
298 to port scans, or subnets administered by other people.
299 --excludefile exclude_file (Exclude list from file) .
301 This offers the same functionality as the --exclude option, except
302 that the excluded targets are provided in a newline-, space-, or
303 tab-delimited exclude_file rather than on the command line.
304 The exclude file may contain comments that start with # and extend
306 to the end of the line.
307
309 One of the very first steps in any network reconnaissance mission is to
310 reduce a (sometimes huge) set of IP ranges into a list of active or
311 interesting hosts. Scanning every port of every single IP address is
312 slow and usually unnecessary. Of course what makes a host interesting
313 depends greatly on the scan purposes. Network administrators may only
314 be interested in hosts running a certain service, while security
315 auditors may care about every single device with an IP address. An
316 administrator may be comfortable using just an ICMP ping to locate
317 hosts on his internal network, while an external penetration tester may
318 use a diverse set of dozens of probes in an attempt to evade firewall
319 restrictions.
320 Because host discovery needs are so diverse, Nmap offers a wide variety
322 of options for customizing the techniques used. Host discovery is
323 sometimes called ping scan, but it goes well beyond the simple ICMP
324 echo request packets associated with the ubiquitous ping tool. Users
325 can skip the ping step entirely with a list scan (-sL) or by disabling
326 ping (-Pn), or engage the network with arbitrary combinations of
327 multi-port TCP SYN/ACK, UDP, SCTP INIT and ICMP probes. The goal of
328 these probes is to solicit responses which demonstrate that an IP
329 address is actually active (is being used by a host or network device).
330 On many networks, only a small percentage of IP addresses are active at
331 any given time. This is particularly common with private address space
332 such as 10.0.0.0/8. That network has 16 million IPs, but I have seen it
333 used by companies with less than a thousand machines. Host discovery
334 can find those machines in a sparsely allocated sea of IP addresses.
335 If no host discovery options are given, Nmap sends an ICMP echo
337 request, a TCP SYN packet to port 443, a TCP ACK packet to port 80, and
338 an ICMP timestamp request. (For IPv6, the ICMP timestamp request is
339 omitted because it is not part of ICMPv6.) These defaults are
340 equivalent to the -PE -PS443 -PA80 -PP options. The exceptions to this
341 are the ARP (for IPv4) and Neighbor Discovery. (for IPv6) scans which
342 are used for any targets on a local ethernet network. For unprivileged
343 Unix shell users, the default probes are a SYN packet to ports 80 and
344 443 using the connect system call.. This host discovery is often
345 sufficient when scanning local networks, but a more comprehensive set
346 of discovery probes is recommended for security auditing.
347 The -P* options (which select ping types) can be combined. You can
349 increase your odds of penetrating strict firewalls by sending many
350 probe types using different TCP ports/flags and ICMP codes. Also note
351 that ARP/Neighbor Discovery (-PR). is done by default against targets
352 on a local ethernet network even if you specify other -P* options,
353 because it is almost always faster and more effective.
354 By default, Nmap does host discovery and then performs a port scan
356 against each host it determines is online. This is true even if you
357 specify non-default host discovery types such as UDP probes (-PU). Read
358 about the -sn option to learn how to perform only host discovery, or
359 use -Pn to skip host discovery and port scan all target hosts. The
360 following options control host discovery:
361 -sL (List Scan) .
363 The list scan is a degenerate form of host discovery that simply
364 lists each host of the network(s) specified, without sending any
365 packets to the target hosts. By default, Nmap still does
366 reverse-DNS resolution on the hosts to learn their names. It is
367 often surprising how much useful information simple hostnames give
368 out. For example, fw.chi is the name of one company's Chicago
369 firewall. Nmap also reports the total number of IP addresses at
370 the end. The list scan is a good sanity check to ensure that you
371 have proper IP addresses for your targets. If the hosts sport
372 domain names you do not recognize, it is worth investigating
373 further to prevent scanning the wrong company's network.
374 Since the idea is to simply print a list of target hosts, options
376 for higher level functionality such as port scanning, OS detection,
377 or ping scanning cannot be combined with this. If you wish to
378 disable ping scanning while still performing such higher level
379 functionality, read up on the -Pn (skip ping) option.
380 -sn (No port scan) .
382 This option tells Nmap not to do a port scan after host discovery,
383 and only print out the available hosts that responded to the scan.
384 This is often known as a “ping scan”, but you can also request that
385 traceroute and NSE host scripts be run. This is by default one step
386 more intrusive than the list scan, and can often be used for the
387 same purposes. It allows light reconnaissance of a target network
388 without attracting much attention. Knowing how many hosts are up is
389 more valuable to attackers than the list provided by list scan of
390 every single IP and host name.
391 Systems administrators often find this option valuable as well. It
393 can easily be used to count available machines on a network or
394 monitor server availability. This is often called a ping sweep, and
395 is more reliable than pinging the broadcast address because many
396 hosts do not reply to broadcast queries.
397 The default host discovery done with -sn consists of an ICMP echo
399 request, TCP SYN to port 443, TCP ACK to port 80, and an ICMP
400 timestamp request by default. When executed by an unprivileged
401 user, only SYN packets are sent (using a connect call) to ports 80
402 and 443 on the target. When a privileged user tries to scan targets
403 on a local ethernet network, ARP requests are used unless --send-ip
404 was specified. The -sn option can be combined with any of the
405 discovery probe types (the -P* options, excluding -Pn) for greater
406 flexibility. If any of those probe type and port number options are
407 used, the default probes are overridden. When strict firewalls are
408 in place between the source host running Nmap and the target
409 network, using those advanced techniques is recommended. Otherwise
410 hosts could be missed when the firewall drops probes or their
411 responses.
412 In previous releases of Nmap, -sn was known as -sP..
414 -Pn (No ping) .
416 This option skips the Nmap discovery stage altogether. Normally,
417 Nmap uses this stage to determine active machines for heavier
418 scanning. By default, Nmap only performs heavy probing such as port
419 scans, version detection, or OS detection against hosts that are
420 found to be up. Disabling host discovery with -Pn causes Nmap to
421 attempt the requested scanning functions against every target IP
422 address specified. So if a class B target address space (/16) is
423 specified on the command line, all 65,536 IP addresses are scanned.
424 Proper host discovery is skipped as with the list scan, but instead
425 of stopping and printing the target list, Nmap continues to perform
426 requested functions as if each target IP is active. To skip ping
427 scan and port scan, while still allowing NSE to run, use the two
428 options -Pn -sn together.
429 For machines on a local ethernet network, ARP scanning will still
431 be performed (unless --disable-arp-ping or --send-ip is specified)
432 because Nmap needs MAC addresses to further scan target hosts. In
433 previous versions of Nmap, -Pn was -P0. and -PN..
434 -PS port list (TCP SYN Ping) .
436 This option sends an empty TCP packet with the SYN flag set. The
437 default destination port is 80 (configurable at compile time by
438 changing DEFAULT_TCP_PROBE_PORT_SPEC. in nmap.h).. Alternate
439 ports can be specified as a parameter. The syntax is the same as
440 for the -p except that port type specifiers like T: are not
441 allowed. Examples are -PS22 and -PS22-25,80,113,1050,35000. Note
442 that there can be no space between -PS and the port list. If
443 multiple probes are specified they will be sent in parallel.
444 The SYN flag suggests to the remote system that you are attempting
446 to establish a connection. Normally the destination port will be
447 closed, and a RST (reset) packet sent back. If the port happens to
448 be open, the target will take the second step of a TCP
449 three-way-handshake. by responding with a SYN/ACK TCP packet. The
450 machine running Nmap then tears down the nascent connection by
451 responding with a RST rather than sending an ACK packet which would
452 complete the three-way-handshake and establish a full connection.
453 The RST packet is sent by the kernel of the machine running Nmap in
454 response to the unexpected SYN/ACK, not by Nmap itself.
455 Nmap does not care whether the port is open or closed. Either the
457 RST or SYN/ACK response discussed previously tell Nmap that the
458 host is available and responsive.
459 On Unix boxes, only the privileged user root. is generally able to
461 send and receive raw TCP packets.. For unprivileged users, a
462 workaround is automatically employed. whereby the connect system
463 call is initiated against each target port. This has the effect of
464 sending a SYN packet to the target host, in an attempt to establish
465 a connection. If connect returns with a quick success or an
466 ECONNREFUSED failure, the underlying TCP stack must have received a
467 SYN/ACK or RST and the host is marked available. If the connection
468 attempt is left hanging until a timeout is reached, the host is
469 marked as down.
470 -PA port list (TCP ACK Ping) .
472 The TCP ACK ping is quite similar to the just-discussed SYN ping.
473 The difference, as you could likely guess, is that the TCP ACK flag
474 is set instead of the SYN flag. Such an ACK packet purports to be
475 acknowledging data over an established TCP connection, but no such
476 connection exists. So remote hosts should always respond with a RST
477 packet, disclosing their existence in the process.
478 The -PA option uses the same default port as the SYN probe (80) and
480 can also take a list of destination ports in the same format. If an
481 unprivileged user tries this, the connect workaround discussed
482 previously is used. This workaround is imperfect because connect is
483 actually sending a SYN packet rather than an ACK.
484 The reason for offering both SYN and ACK ping probes is to maximize
486 the chances of bypassing firewalls. Many administrators configure
487 routers and other simple firewalls to block incoming SYN packets
488 except for those destined for public services like the company web
489 site or mail server. This prevents other incoming connections to
490 the organization, while allowing users to make unobstructed
491 outgoing connections to the Internet. This non-stateful approach
492 takes up few resources on the firewall/router and is widely
493 supported by hardware and software filters. The Linux
494 Netfilter/iptables. firewall software offers the --syn convenience
495 option to implement this stateless approach. When stateless
496 firewall rules such as this are in place, SYN ping probes (-PS) are
497 likely to be blocked when sent to closed target ports. In such
498 cases, the ACK probe shines as it cuts right through these rules.
499 Another common type of firewall uses stateful rules that drop
501 unexpected packets. This feature was initially found mostly on
502 high-end firewalls, though it has become much more common over the
503 years. The Linux Netfilter/iptables system supports this through
504 the --state option, which categorizes packets based on connection
505 state. A SYN probe is more likely to work against such a system, as
506 unexpected ACK packets are generally recognized as bogus and
507 dropped. A solution to this quandary is to send both SYN and ACK
508 probes by specifying -PS and -PA.
509 -PU port list (UDP Ping) .
511 Another host discovery option is the UDP ping, which sends a UDP
512 packet to the given ports. For most ports, the packet will be
513 empty, though for a few a protocol-specific payload will be sent
514 that is more likely to get a response.. The --data-length. option
515 can be used to send a fixed-length random payload to every port or
516 (if you specify a value of 0) to disable payloads. You can also
517 disable payloads by specifying --data-length 0.
518 The port list takes the same format as with the previously
520 discussed -PS and -PA options. If no ports are specified, the
521 default is 40125.. This default can be configured at compile-time
522 by changing DEFAULT_UDP_PROBE_PORT_SPEC. in nmap.h.. A highly
523 uncommon port is used by default because sending to open ports is
524 often undesirable for this particular scan type.
525 Upon hitting a closed port on the target machine, the UDP probe
527 should elicit an ICMP port unreachable packet in return. This
528 signifies to Nmap that the machine is up and available. Many other
529 types of ICMP errors, such as host/network unreachables or TTL
530 exceeded are indicative of a down or unreachable host. A lack of
531 response is also interpreted this way. If an open port is reached,
532 most services simply ignore the empty packet and fail to return any
533 response. This is why the default probe port is 40125, which is
534 highly unlikely to be in use. A few services, such as the Character
535 Generator (chargen) protocol, will respond to an empty UDP packet,
536 and thus disclose to Nmap that the machine is available.
537 The primary advantage of this scan type is that it bypasses
539 firewalls and filters that only screen TCP. For example, I once
540 owned a Linksys BEFW11S4 wireless broadband router. The external
541 interface of this device filtered all TCP ports by default, but UDP
542 probes would still elicit port unreachable messages and thus give
543 away the device.
544 -PY port list (SCTP INIT Ping) .
546 This option sends an SCTP packet containing a minimal INIT chunk.
547 The default destination port is 80 (configurable at compile time by
548 changing DEFAULT_SCTP_PROBE_PORT_SPEC. in nmap.h). Alternate ports
549 can be specified as a parameter. The syntax is the same as for the
550 -p except that port type specifiers like S: are not allowed.
551 Examples are -PY22 and -PY22,80,179,5060. Note that there can be no
552 space between -PY and the port list. If multiple probes are
553 specified they will be sent in parallel.
554 The INIT chunk suggests to the remote system that you are
556 attempting to establish an association. Normally the destination
557 port will be closed, and an ABORT chunk will be sent back. If the
558 port happens to be open, the target will take the second step of an
559 SCTP four-way-handshake. by responding with an INIT-ACK chunk. If
560 the machine running Nmap has a functional SCTP stack, then it tears
561 down the nascent association by responding with an ABORT chunk
562 rather than sending a COOKIE-ECHO chunk which would be the next
563 step in the four-way-handshake. The ABORT packet is sent by the
564 kernel of the machine running Nmap in response to the unexpected
565 INIT-ACK, not by Nmap itself.
566 Nmap does not care whether the port is open or closed. Either the
568 ABORT or INIT-ACK response discussed previously tell Nmap that the
569 host is available and responsive.
570 On Unix boxes, only the privileged user root. is generally able to
572 send and receive raw SCTP packets.. Using SCTP INIT Pings is
573 currently not possible for unprivileged users..
574 -PE; -PP; -PM (ICMP Ping Types) .
576 In addition to the unusual TCP, UDP and SCTP host discovery types
577 discussed previously, Nmap can send the standard packets sent by
578 the ubiquitous ping program. Nmap sends an ICMP type 8 (echo
579 request) packet to the target IP addresses, expecting a type 0
580 (echo reply) in return from available hosts.. Unfortunately for
581 network explorers, many hosts and firewalls now block these
582 packets, rather than responding as required by RFC 1122[2].. For
583 this reason, ICMP-only scans are rarely reliable enough against
584 unknown targets over the Internet. But for system administrators
585 monitoring an internal network, they can be a practical and
586 efficient approach. Use the -PE option to enable this echo request
587 behavior.
588 While echo request is the standard ICMP ping query, Nmap does not
590 stop there. The ICMP standards (RFC 792[3]. and RFC 950[4]. “a
591 host SHOULD NOT implement these messages”. Timestamp and address
592 mask queries can be sent with the -PP and -PM options,
593 respectively. A timestamp reply (ICMP code 14) or address mask
594 reply (code 18) discloses that the host is available. These two
595 queries can be valuable when administrators specifically block echo
596 request packets while forgetting that other ICMP queries can be
597 used for the same purpose.
598 -PO protocol list (IP Protocol Ping) .
600 One of the newer host discovery options is the IP protocol ping,
601 which sends IP packets with the specified protocol number set in
602 their IP header. The protocol list takes the same format as do port
603 lists in the previously discussed TCP, UDP and SCTP host discovery
604 options. If no protocols are specified, the default is to send
605 multiple IP packets for ICMP (protocol 1), IGMP (protocol 2), and
606 IP-in-IP (protocol 4). The default protocols can be configured at
607 compile-time by changing DEFAULT_PROTO_PROBE_PORT_SPEC. in nmap.h.
608 Note that for the ICMP, IGMP, TCP (protocol 6), UDP (protocol 17)
609 and SCTP (protocol 132), the packets are sent with the proper
610 protocol headers. while other protocols are sent with no
611 additional data beyond the IP header (unless the --data-length.
612 option is specified).
613 This host discovery method looks for either responses using the
615 same protocol as a probe, or ICMP protocol unreachable messages
616 which signify that the given protocol isn't supported on the
617 destination host. Either type of response signifies that the target
618 host is alive.
619 -PR (ARP Ping) .
621 One of the most common Nmap usage scenarios is to scan an ethernet
622 LAN. On most LANs, especially those using private address ranges
623 specified by RFC 1918[5], the vast majority of IP addresses are
624 unused at any given time. When Nmap tries to send a raw IP packet
625 such as an ICMP echo request, the operating system must determine
626 the destination hardware (ARP) address corresponding to the target
627 IP so that it can properly address the ethernet frame. This is
628 often slow and problematic, since operating systems weren't written
629 with the expectation that they would need to do millions of ARP
630 requests against unavailable hosts in a short time period.
631 ARP scan puts Nmap and its optimized algorithms in charge of ARP
633 requests. And if it gets a response back, Nmap doesn't even need to
634 worry about the IP-based ping packets since it already knows the
635 host is up. This makes ARP scan much faster and more reliable than
636 IP-based scans. So it is done by default when scanning ethernet
637 hosts that Nmap detects are on a local ethernet network. Even if
638 different ping types (such as -PE or -PS) are specified, Nmap uses
639 ARP instead for any of the targets which are on the same LAN. If
640 you absolutely don't want to do an ARP scan, specify
641 --disable-arp-ping.
642 For IPv6 (-6 option), -PR uses ICMPv6 Neighbor Discovery instead of
644 ARP. Neighbor Discovery, defined in RFC 4861, can be seen as the
645 IPv6 equivalent of ARP.
646 --disable-arp-ping (No ARP or ND Ping) .
648 Nmap normally does ARP or IPv6 Neighbor Discovery (ND) discovery of
649 locally connected ethernet hosts, even if other host discovery
650 options such as -Pn or -PE are used. To disable this implicit
651 behavior, use the --disable-arp-ping option.
652 The default behavior is normally faster, but this option is useful
654 on networks using proxy ARP, in which a router speculatively
655 replies to all ARP requests, making every target appear to be up
656 according to ARP scan.
657 --traceroute (Trace path to host) .
659 Traceroutes are performed post-scan using information from the scan
660 results to determine the port and protocol most likely to reach the
661 target. It works with all scan types except connect scans (-sT) and
662 idle scans (-sI). All traces use Nmap's dynamic timing model and
663 are performed in parallel.
664 Traceroute works by sending packets with a low TTL (time-to-live)
666 in an attempt to elicit ICMP Time Exceeded messages from
667 intermediate hops between the scanner and the target host. Standard
668 traceroute implementations start with a TTL of 1 and increment the
669 TTL until the destination host is reached. Nmap's traceroute starts
670 with a high TTL and then decrements the TTL until it reaches zero.
671 Doing it backwards lets Nmap employ clever caching algorithms to
672 speed up traces over multiple hosts. On average Nmap sends 5–10
673 fewer packets per host, depending on network conditions. If a
674 single subnet is being scanned (i.e. 192.168.0.0/24) Nmap may only
675 have to send two packets to most hosts.
676 -n (No DNS resolution) .
678 Tells Nmap to never do reverse DNS resolution on the active IP
679 addresses it finds. Since DNS can be slow even with Nmap's built-in
680 parallel stub resolver, this option can slash scanning times.
681 -R (DNS resolution for all targets) .
683 Tells Nmap to always do reverse DNS resolution on the target IP
684 addresses. Normally reverse DNS is only performed against
685 responsive (online) hosts.
686 --system-dns (Use system DNS resolver) .
688 By default, Nmap resolves IP addresses by sending queries directly
689 to the name servers configured on your host and then listening for
690 responses. Many requests (often dozens) are performed in parallel
691 to improve performance. Specify this option to use your system
692 resolver instead (one IP at a time via the getnameinfo call). This
693 is slower and rarely useful unless you find a bug in the Nmap
694 parallel resolver (please let us know if you do). The system
695 resolver is always used for IPv6 scans.
696 --dns-servers server1[,server2[,...]] (Servers to use for reverse DNS
698 queries) .
699 By default, Nmap determines your DNS servers (for rDNS resolution)
700 from your resolv.conf file (Unix) or the Registry (Win32).
701 Alternatively, you may use this option to specify alternate
702 servers. This option is not honored if you are using --system-dns
703 or an IPv6 scan. Using multiple DNS servers is often faster,
704 especially if you choose authoritative servers for your target IP
705 space. This option can also improve stealth, as your requests can
706 be bounced off just about any recursive DNS server on the Internet.
707 This option also comes in handy when scanning private networks.
709 Sometimes only a few name servers provide proper rDNS information,
710 and you may not even know where they are. You can scan the network
711 for port 53 (perhaps with version detection), then try Nmap list
712 scans (-sL) specifying each name server one at a time with
713 --dns-servers until you find one which works.
714
716 While Nmap has grown in functionality over the years, it began as an
717 efficient port scanner, and that remains its core function. The simple
718 command nmap target scans 1,000 TCP ports on the host target. While
719 many port scanners have traditionally lumped all ports into the open or
720 closed states, Nmap is much more granular. It divides ports into six
721 states: open, closed, filtered, unfiltered, open|filtered, or
722 closed|filtered.
723 These states are not intrinsic properties of the port itself, but
725 describe how Nmap sees them. For example, an Nmap scan from the same
726 network as the target may show port 135/tcp as open, while a scan at
727 the same time with the same options from across the Internet might show
728 that port as filtered.
729 The six port states recognized by Nmap
731 An application is actively accepting TCP connections, UDP datagrams
733 or SCTP associations on this port. Finding these is often the
734 primary goal of port scanning. Security-minded people know that
735 each open port is an avenue for attack. Attackers and pen-testers
736 want to exploit the open ports, while administrators try to close
737 or protect them with firewalls without thwarting legitimate users.
738 Open ports are also interesting for non-security scans because they
739 show services available for use on the network.
740 A closed port is accessible (it receives and responds to Nmap probe
742 packets), but there is no application listening on it. They can be
743 helpful in showing that a host is up on an IP address (host
744 discovery, or ping scanning), and as part of OS detection. Because
745 closed ports are reachable, it may be worth scanning later in case
746 some open up. Administrators may want to consider blocking such
747 ports with a firewall. Then they would appear in the filtered
748 state, discussed next.
749 Nmap cannot determine whether the port is open because packet
751 filtering prevents its probes from reaching the port. The filtering
752 could be from a dedicated firewall device, router rules, or
753 host-based firewall software. These ports frustrate attackers
754 because they provide so little information. Sometimes they respond
755 with ICMP error messages such as type 3 code 13 (destination
756 unreachable: communication administratively prohibited), but
757 filters that simply drop probes without responding are far more
758 common. This forces Nmap to retry several times just in case the
759 probe was dropped due to network congestion rather than filtering.
760 This slows down the scan dramatically.
761 The unfiltered state means that a port is accessible, but Nmap is
763 unable to determine whether it is open or closed. Only the ACK
764 scan, which is used to map firewall rulesets, classifies ports into
765 this state. Scanning unfiltered ports with other scan types such as
766 Window scan, SYN scan, or FIN scan, may help resolve whether the
767 port is open.
768 Nmap places ports in this state when it is unable to determine
770 whether a port is open or filtered. This occurs for scan types in
771 which open ports give no response. The lack of response could also
772 mean that a packet filter dropped the probe or any response it
773 elicited. So Nmap does not know for sure whether the port is open
774 or being filtered. The UDP, IP protocol, FIN, NULL, and Xmas scans
775 classify ports this way.
776 This state is used when Nmap is unable to determine whether a port
778 is closed or filtered. It is only used for the IP ID idle scan.
779
781 As a novice performing automotive repair, I can struggle for hours
782 trying to fit my rudimentary tools (hammer, duct tape, wrench, etc.) to
783 the task at hand. When I fail miserably and tow my jalopy to a real
784 mechanic, he invariably fishes around in a huge tool chest until
785 pulling out the perfect gizmo which makes the job seem effortless. The
786 art of port scanning is similar. Experts understand the dozens of scan
787 techniques and choose the appropriate one (or combination) for a given
788 task. Inexperienced users and script kiddies,. on the other hand, try
789 to solve every problem with the default SYN scan. Since Nmap is free,
790 the only barrier to port scanning mastery is knowledge. That certainly
791 beats the automotive world, where it may take great skill to determine
792 that you need a strut spring compressor, then you still have to pay
793 thousands of dollars for it.
794 Most of the scan types are only available to privileged users.. This
796 is because they send and receive raw packets,. which requires root
797 access on Unix systems. Using an administrator account on Windows is
798 recommended, though Nmap sometimes works for unprivileged users on that
799 platform when WinPcap has already been loaded into the OS. Requiring
800 root privileges was a serious limitation when Nmap was released in
801 1997, as many users only had access to shared shell accounts. Now, the
802 world is different. Computers are cheaper, far more people have
803 always-on direct Internet access, and desktop Unix systems (including
804 Linux and Mac OS X) are prevalent. A Windows version of Nmap is now
805 available, allowing it to run on even more desktops. For all these
806 reasons, users have less need to run Nmap from limited shared shell
807 accounts. This is fortunate, as the privileged options make Nmap far
808 more powerful and flexible.
809 While Nmap attempts to produce accurate results, keep in mind that all
811 of its insights are based on packets returned by the target machines
812 (or firewalls in front of them). Such hosts may be untrustworthy and
813 send responses intended to confuse or mislead Nmap. Much more common
814 are non-RFC-compliant hosts that do not respond as they should to Nmap
815 probes. FIN, NULL, and Xmas scans are particularly susceptible to this
816 problem. Such issues are specific to certain scan types and so are
817 discussed in the individual scan type entries.
818 This section documents the dozen or so port scan techniques supported
820 by Nmap. Only one method may be used at a time, except that UDP scan
821 (-sU) and any one of the SCTP scan types (-sY, -sZ) may be combined
822 with any one of the TCP scan types. As a memory aid, port scan type
823 options are of the form -sC, where C is a prominent character in the
824 scan name, usually the first. The one exception to this is the
825 deprecated FTP bounce scan (-b). By default, Nmap performs a SYN Scan,
826 though it substitutes a connect scan if the user does not have proper
827 privileges to send raw packets (requires root access on Unix). Of the
828 scans listed in this section, unprivileged users can only execute
829 connect and FTP bounce scans.
830 -sS (TCP SYN scan) .
832 SYN scan is the default and most popular scan option for good
833 reasons. It can be performed quickly, scanning thousands of ports
834 per second on a fast network not hampered by restrictive firewalls.
835 It is also relatively unobtrusive and stealthy since it never
836 completes TCP connections. SYN scan works against any compliant TCP
837 stack rather than depending on idiosyncrasies of specific platforms
838 as Nmap's FIN/NULL/Xmas, Maimon and idle scans do. It also allows
839 clear, reliable differentiation between the open, closed, and
840 filtered states.
841 This technique is often referred to as half-open scanning, because
843 you don't open a full TCP connection. You send a SYN packet, as if
844 you are going to open a real connection and then wait for a
845 response. A SYN/ACK indicates the port is listening (open), while a
846 RST (reset) is indicative of a non-listener. If no response is
847 received after several retransmissions, the port is marked as
848 filtered. The port is also marked filtered if an ICMP unreachable
849 error (type 3, code 1, 2, 3, 9, 10, or 13) is received. The port is
850 also considered open if a SYN packet (without the ACK flag) is
851 received in response. This can be due to an extremely rare TCP
852 feature known as a simultaneous open or split handshake connection
853 (see http://nmap.org/misc/split-handshake.pdf).
854 -sT (TCP connect scan) .
856 TCP connect scan is the default TCP scan type when SYN scan is not
857 an option. This is the case when a user does not have raw packet
858 privileges. Instead of writing raw packets as most other scan types
859 do, Nmap asks the underlying operating system to establish a
860 connection with the target machine and port by issuing the connect
861 system call. This is the same high-level system call that web
862 browsers, P2P clients, and most other network-enabled applications
863 use to establish a connection. It is part of a programming
864 interface known as the Berkeley Sockets API. Rather than read raw
865 packet responses off the wire, Nmap uses this API to obtain status
866 information on each connection attempt.
867 When SYN scan is available, it is usually a better choice. Nmap has
869 less control over the high level connect call than with raw
870 packets, making it less efficient. The system call completes
871 connections to open target ports rather than performing the
872 half-open reset that SYN scan does. Not only does this take longer
873 and require more packets to obtain the same information, but target
874 machines are more likely to log the connection. A decent IDS will
875 catch either, but most machines have no such alarm system. Many
876 services on your average Unix system will add a note to syslog, and
877 sometimes a cryptic error message, when Nmap connects and then
878 closes the connection without sending data. Truly pathetic services
879 crash when this happens, though that is uncommon. An administrator
880 who sees a bunch of connection attempts in her logs from a single
881 system should know that she has been connect scanned.
882 -sU (UDP scans) .
884 While most popular services on the Internet run over the TCP
885 protocol, UDP[6] services are widely deployed. DNS, SNMP, and DHCP
886 (registered ports 53, 161/162, and 67/68) are three of the most
887 common. Because UDP scanning is generally slower and more difficult
888 than TCP, some security auditors ignore these ports. This is a
889 mistake, as exploitable UDP services are quite common and attackers
890 certainly don't ignore the whole protocol. Fortunately, Nmap can
891 help inventory UDP ports.
892 UDP scan is activated with the -sU option. It can be combined with
894 a TCP scan type such as SYN scan (-sS) to check both protocols
895 during the same run.
896 UDP scan works by sending a UDP packet to every targeted port. For
898 some common ports such as 53 and 161, a protocol-specific payload
899 is sent, but for most ports the packet is empty.. The
900 --data-length option can be used to send a fixed-length random
901 payload to every port or (if you specify a value of 0) to disable
902 payloads. If an ICMP port unreachable error (type 3, code 3) is
903 returned, the port is closed. Other ICMP unreachable errors (type
904 3, codes 1, 2, 9, 10, or 13) mark the port as filtered.
905 Occasionally, a service will respond with a UDP packet, proving
906 that it is open. If no response is received after retransmissions,
907 the port is classified as open|filtered. This means that the port
908 could be open, or perhaps packet filters are blocking the
909 communication. Version detection (-sV) can be used to help
910 differentiate the truly open ports from the filtered ones.
911 A big challenge with UDP scanning is doing it quickly. Open and
913 filtered ports rarely send any response, leaving Nmap to time out
914 and then conduct retransmissions just in case the probe or response
915 were lost. Closed ports are often an even bigger problem. They
916 usually send back an ICMP port unreachable error. But unlike the
917 RST packets sent by closed TCP ports in response to a SYN or
918 connect scan, many hosts rate limit. ICMP port unreachable
919 messages by default. Linux and Solaris are particularly strict
920 about this. For example, the Linux 2.4.20 kernel limits destination
921 unreachable messages to one per second (in net/ipv4/icmp.c).
922 Nmap detects rate limiting and slows down accordingly to avoid
924 flooding the network with useless packets that the target machine
925 will drop. Unfortunately, a Linux-style limit of one packet per
926 second makes a 65,536-port scan take more than 18 hours. Ideas for
927 speeding your UDP scans up include scanning more hosts in parallel,
928 doing a quick scan of just the popular ports first, scanning from
929 behind the firewall, and using --host-timeout to skip slow hosts.
930 -sY (SCTP INIT scan) .
932 SCTP[7] is a relatively new alternative to the TCP and UDP
933 protocols, combining most characteristics of TCP and UDP, and also
934 adding new features like multi-homing and multi-streaming. It is
935 mostly being used for SS7/SIGTRAN related services but has the
936 potential to be used for other applications as well. SCTP INIT scan
937 is the SCTP equivalent of a TCP SYN scan. It can be performed
938 quickly, scanning thousands of ports per second on a fast network
939 not hampered by restrictive firewalls. Like SYN scan, INIT scan is
940 relatively unobtrusive and stealthy, since it never completes SCTP
941 associations. It also allows clear, reliable differentiation
942 between the open, closed, and filtered states.
943 This technique is often referred to as half-open scanning, because
945 you don't open a full SCTP association. You send an INIT chunk, as
946 if you are going to open a real association and then wait for a
947 response. An INIT-ACK chunk indicates the port is listening (open),
948 while an ABORT chunk is indicative of a non-listener. If no
949 response is received after several retransmissions, the port is
950 marked as filtered. The port is also marked filtered if an ICMP
951 unreachable error (type 3, code 1, 2, 3, 9, 10, or 13) is received.
952 -sN; -sF; -sX (TCP NULL, FIN, and Xmas scans) .
954 These three scan types (even more are possible with the --scanflags
955 option described in the next section) exploit a subtle loophole in
956 the TCP RFC[8] to differentiate between open and closed ports. Page
957 65 of RFC 793 says that “if the [destination] port state is CLOSED
958 .... an incoming segment not containing a RST causes a RST to be
959 sent in response.” Then the next page discusses packets sent to
960 open ports without the SYN, RST, or ACK bits set, stating that:
961 “you are unlikely to get here, but if you do, drop the segment, and
962 return.”
963 When scanning systems compliant with this RFC text, any packet not
965 containing SYN, RST, or ACK bits will result in a returned RST if
966 the port is closed and no response at all if the port is open. As
967 long as none of those three bits are included, any combination of
968 the other three (FIN, PSH, and URG) are OK. Nmap exploits this with
969 three scan types:
970 Null scan (-sN)
972 Does not set any bits (TCP flag header is 0)
973 FIN scan (-sF)
975 Sets just the TCP FIN bit.
976 Xmas scan (-sX)
978 Sets the FIN, PSH, and URG flags, lighting the packet up like a
979 Christmas tree.
980 These three scan types are exactly the same in behavior except for
982 the TCP flags set in probe packets. If a RST packet is received,
983 the port is considered closed, while no response means it is
984 open|filtered. The port is marked filtered if an ICMP unreachable
985 error (type 3, code 1, 2, 3, 9, 10, or 13) is received.
986 The key advantage to these scan types is that they can sneak
988 through certain non-stateful firewalls and packet filtering
989 routers. Another advantage is that these scan types are a little
990 more stealthy than even a SYN scan. Don't count on this though—most
991 modern IDS products can be configured to detect them. The big
992 downside is that not all systems follow RFC 793 to the letter. A
993 number of systems send RST responses to the probes regardless of
994 whether the port is open or not. This causes all of the ports to be
995 labeled closed. Major operating systems that do this are Microsoft
996 Windows, many Cisco devices, BSDI, and IBM OS/400. This scan does
997 work against most Unix-based systems though. Another downside of
998 these scans is that they can't distinguish open ports from certain
999 filtered ones, leaving you with the response open|filtered.
1000 -sA (TCP ACK scan) .
1002 This scan is different than the others discussed so far in that it
1003 never determines open (or even open|filtered) ports. It is used to
1004 map out firewall rulesets, determining whether they are stateful or
1005 not and which ports are filtered.
1006 The ACK scan probe packet has only the ACK flag set (unless you use
1008 --scanflags). When scanning unfiltered systems, open and closed
1009 ports will both return a RST packet. Nmap then labels them as
1010 unfiltered, meaning that they are reachable by the ACK packet, but
1011 whether they are open or closed is undetermined. Ports that don't
1012 respond, or send certain ICMP error messages back (type 3, code 1,
1013 2, 3, 9, 10, or 13), are labeled filtered.
1014 -sW (TCP Window scan) .
1016 Window scan is exactly the same as ACK scan except that it exploits
1017 an implementation detail of certain systems to differentiate open
1018 ports from closed ones, rather than always printing unfiltered when
1019 a RST is returned. It does this by examining the TCP Window field
1020 of the RST packets returned. On some systems, open ports use a
1021 positive window size (even for RST packets) while closed ones have
1022 a zero window. So instead of always listing a port as unfiltered
1023 when it receives a RST back, Window scan lists the port as open or
1024 closed if the TCP Window value in that reset is positive or zero,
1025 respectively.
1026 This scan relies on an implementation detail of a minority of
1028 systems out on the Internet, so you can't always trust it. Systems
1029 that don't support it will usually return all ports closed. Of
1030 course, it is possible that the machine really has no open ports.
1031 If most scanned ports are closed but a few common port numbers
1032 (such as 22, 25, 53) are filtered, the system is most likely
1033 susceptible. Occasionally, systems will even show the exact
1034 opposite behavior. If your scan shows 1,000 open ports and three
1035 closed or filtered ports, then those three may very well be the
1036 truly open ones.
1037 -sM (TCP Maimon scan) .
1039 The Maimon scan is named after its discoverer, Uriel Maimon.. He
1040 described the technique in Phrack Magazine issue #49 (November
1041 1996).. Nmap, which included this technique, was released two
1042 issues later. This technique is exactly the same as NULL, FIN, and
1043 Xmas scans, except that the probe is FIN/ACK. According to RFC
1044 793[8] (TCP), a RST packet should be generated in response to such
1045 a probe whether the port is open or closed. However, Uriel noticed
1046 that many BSD-derived systems simply drop the packet if the port is
1047 open.
1048 --scanflags (Custom TCP scan) .
1050 Truly advanced Nmap users need not limit themselves to the canned
1051 scan types offered. The --scanflags option allows you to design
1052 your own scan by specifying arbitrary TCP flags.. Let your
1053 creative juices flow, while evading intrusion detection systems.
1054 whose vendors simply paged through the Nmap man page adding
1055 specific rules!
1056 The --scanflags argument can be a numerical flag value such as 9
1058 (PSH and FIN), but using symbolic names is easier. Just mash
1059 together any combination of URG, ACK, PSH, RST, SYN, and FIN. For
1060 example, --scanflags URGACKPSHRSTSYNFIN sets everything, though
1061 it's not very useful for scanning. The order these are specified in
1062 is irrelevant.
1063 In addition to specifying the desired flags, you can specify a TCP
1065 scan type (such as -sA or -sF). That base type tells Nmap how to
1066 interpret responses. For example, a SYN scan considers no-response
1067 to indicate a filtered port, while a FIN scan treats the same as
1068 open|filtered. Nmap will behave the same way it does for the base
1069 scan type, except that it will use the TCP flags you specify
1070 instead. If you don't specify a base type, SYN scan is used.
1071 -sZ (SCTP COOKIE ECHO scan) .
1073 SCTP COOKIE ECHO scan is a more advanced SCTP scan. It takes
1074 advantage of the fact that SCTP implementations should silently
1075 drop packets containing COOKIE ECHO chunks on open ports, but send
1076 an ABORT if the port is closed. The advantage of this scan type is
1077 that it is not as obvious a port scan than an INIT scan. Also,
1078 there may be non-stateful firewall rulesets blocking INIT chunks,
1079 but not COOKIE ECHO chunks. Don't be fooled into thinking that this
1080 will make a port scan invisible; a good IDS will be able to detect
1081 SCTP COOKIE ECHO scans too. The downside is that SCTP COOKIE ECHO
1082 scans cannot differentiate between open and filtered ports, leaving
1083 you with the state open|filtered in both cases.
1084 -sI zombie host[:probeport] (idle scan) .
1086 This advanced scan method allows for a truly blind TCP port scan of
1087 the target (meaning no packets are sent to the target from your
1088 real IP address). Instead, a unique side-channel attack exploits
1089 predictable IP fragmentation ID sequence generation on the zombie
1090 host to glean information about the open ports on the target. IDS
1091 systems will display the scan as coming from the zombie machine you
1092 specify (which must be up and meet certain criteria). This
1093 fascinating scan type is too complex to fully describe in this
1094 reference guide, so I wrote and posted an informal paper with full
1095 details at http://nmap.org/book/idlescan.html.
1096 Besides being extraordinarily stealthy (due to its blind nature),
1098 this scan type permits mapping out IP-based trust relationships
1099 between machines. The port listing shows open ports from the
1100 perspective of the zombie host. So you can try scanning a target
1101 using various zombies that you think might be trusted. (via
1102 router/packet filter rules).
1103 You can add a colon followed by a port number to the zombie host if
1105 you wish to probe a particular port on the zombie for IP ID
1106 changes. Otherwise Nmap will use the port it uses by default for
1107 TCP pings (80).
1108 -sO (IP protocol scan) .
1110 IP protocol scan allows you to determine which IP protocols (TCP,
1111 ICMP, IGMP, etc.) are supported by target machines. This isn't
1112 technically a port scan, since it cycles through IP protocol
1113 numbers rather than TCP or UDP port numbers. Yet it still uses the
1114 -p option to select scanned protocol numbers, reports its results
1115 within the normal port table format, and even uses the same
1116 underlying scan engine as the true port scanning methods. So it is
1117 close enough to a port scan that it belongs here.
1118 Besides being useful in its own right, protocol scan demonstrates
1120 the power of open-source software. While the fundamental idea is
1121 pretty simple, I had not thought to add it nor received any
1122 requests for such functionality. Then in the summer of 2000,
1123 Gerhard Rieger. conceived the idea, wrote an excellent patch
1124 implementing it, and sent it to the announce mailing list. (then
1125 called nmap-hackers).. I incorporated that patch into the Nmap
1126 tree and released a new version the next day. Few pieces of
1127 commercial software have users enthusiastic enough to design and
1128 contribute their own improvements!
1129 Protocol scan works in a similar fashion to UDP scan. Instead of
1131 iterating through the port number field of a UDP packet, it sends
1132 IP packet headers and iterates through the eight-bit IP protocol
1133 field. The headers are usually empty, containing no data and not
1134 even the proper header for the claimed protocol. The exceptions are
1135 TCP, UDP, ICMP, SCTP, and IGMP. A proper protocol header for those
1136 is included since some systems won't send them otherwise and
1137 because Nmap already has functions to create them. Instead of
1138 watching for ICMP port unreachable messages, protocol scan is on
1139 the lookout for ICMP protocol unreachable messages. If Nmap
1140 receives any response in any protocol from the target host, Nmap
1141 marks that protocol as open. An ICMP protocol unreachable error
1142 (type 3, code 2) causes the protocol to be marked as closed Other
1143 ICMP unreachable errors (type 3, code 1, 3, 9, 10, or 13) cause the
1144 protocol to be marked filtered (though they prove that ICMP is open
1145 at the same time). If no response is received after
1146 retransmissions, the protocol is marked open|filtered
1147 -b FTP relay host (FTP bounce scan) .
1149 An interesting feature of the FTP protocol (RFC 959[9]) is support
1150 for so-called proxy FTP connections. This allows a user to connect
1151 to one FTP server, then ask that files be sent to a third-party
1152 server. Such a feature is ripe for abuse on many levels, so most
1153 servers have ceased supporting it. One of the abuses this feature
1154 allows is causing the FTP server to port scan other hosts. Simply
1155 ask the FTP server to send a file to each interesting port of a
1156 target host in turn. The error message will describe whether the
1157 port is open or not. This is a good way to bypass firewalls because
1158 organizational FTP servers are often placed where they have more
1159 access to other internal hosts than any old Internet host would.
1160 Nmap supports FTP bounce scan with the -b option. It takes an
1161 argument of the form username:password@server:port. Server is the
1162 name or IP address of a vulnerable FTP server. As with a normal
1163 URL, you may omit username:password, in which case anonymous login
1164 credentials (user: anonymous password:-wwwuser@) are used. The port
1165 number (and preceding colon) may be omitted as well, in which case
1166 the default FTP port (21) on server is used.
1167 This vulnerability was widespread in 1997 when Nmap was released,
1169 but has largely been fixed. Vulnerable servers are still around, so
1170 it is worth trying when all else fails. If bypassing a firewall is
1171 your goal, scan the target network for port 21 (or even for any FTP
1172 services if you scan all ports with version detection) and use the
1173 ftp-bounce. NSE script. Nmap will tell you whether the host is
1174 vulnerable or not. If you are just trying to cover your tracks, you
1175 don't need to (and, in fact, shouldn't) limit yourself to hosts on
1176 the target network. Before you go scanning random Internet
1177 addresses for vulnerable FTP servers, consider that sysadmins may
1178 not appreciate you abusing their servers in this way.
1179
1181 In addition to all of the scan methods discussed previously, Nmap
1182 offers options for specifying which ports are scanned and whether the
1183 scan order is randomized or sequential. By default, Nmap scans the most
1184 common 1,000 ports for each protocol.
1185 -p port ranges (Only scan specified ports) .
1187 This option specifies which ports you want to scan and overrides
1188 the default. Individual port numbers are OK, as are ranges
1189 separated by a hyphen (e.g. 1-1023). The beginning and/or end
1190 values of a range may be omitted, causing Nmap to use 1 and 65535,
1191 respectively. So you can specify -p- to scan ports from 1 through
1192 65535. Scanning port zero. is allowed if you specify it
1193 explicitly. For IP protocol scanning (-sO), this option specifies
1194 the protocol numbers you wish to scan for (0–255).
1195 When scanning a combination of protocols (e.g. TCP and UDP), you
1197 can specify a particular protocol by preceding the port numbers by
1198 T: for TCP, U: for UDP, S: for SCTP, or P: for IP Protocol. The
1199 qualifier lasts until you specify another qualifier. For example,
1200 the argument -p U:53,111,137,T:21-25,80,139,8080 would scan UDP
1201 ports 53, 111,and 137, as well as the listed TCP ports. Note that
1202 to scan both UDP and TCP, you have to specify -sU and at least one
1203 TCP scan type (such as -sS, -sF, or -sT). If no protocol qualifier
1204 is given, the port numbers are added to all protocol lists. Ports
1205 can also be specified by name according to what the port is
1206 referred to in the nmap-services. You can even use the wildcards *
1207 and ? with the names. For example, to scan FTP and all ports whose
1208 names begin with “http”, use -p ftp,http*. Be careful about shell
1209 expansions and quote the argument to -p if unsure.
1210 Ranges of ports can be surrounded by square brackets to indicate
1212 ports inside that range that appear in nmap-services. For example,
1213 the following will scan all ports in nmap-services equal to or
1214 below 1024: -p [-1024]. Be careful with shell expansions and quote
1215 the argument to -p if unsure.
1216 -F (Fast (limited port) scan) .
1218 Specifies that you wish to scan fewer ports than the default.
1219 Normally Nmap scans the most common 1,000 ports for each scanned
1220 protocol. With -F, this is reduced to 100.
1221 Nmap needs an nmap-services file with frequency information in
1223 order to know which ports are the most common. If port frequency
1224 information isn't available, perhaps because of the use of a custom
1225 nmap-services file, Nmap scans all named ports plus ports 1-1024.
1226 In that case, -F means to scan only ports that are named in the
1227 services file.
1228 -r (Don't randomize ports) .
1230 By default, Nmap randomizes the scanned port order (except that
1231 certain commonly accessible ports are moved near the beginning for
1232 efficiency reasons). This randomization is normally desirable, but
1233 you can specify -r for sequential (sorted from lowest to highest)
1234 port scanning instead.
1235 --port-ratio ratio<decimal number between 0 and 1>
1237 Scans all ports in nmap-services file with a ratio greater than the
1238 one given. ratio must be between 0.0 and 1.1.
1239 --top-ports n
1241 Scans the n highest-ratio ports found in nmap-services file. n
1242 must be 1 or greater.
1243
1245 Point Nmap at a remote machine and it might tell you that ports 25/tcp,
1246 80/tcp, and 53/udp are open. Using its nmap-services. database of
1247 about 2,200 well-known services,. Nmap would report that those ports
1248 probably correspond to a mail server (SMTP), web server (HTTP), and
1249 name server (DNS) respectively. This lookup is usually accurate—the
1250 vast majority of daemons listening on TCP port 25 are, in fact, mail
1251 servers. However, you should not bet your security on this! People can
1252 and do run services on strange ports..
1253 Even if Nmap is right, and the hypothetical server above is running
1255 SMTP, HTTP, and DNS servers, that is not a lot of information. When
1256 doing vulnerability assessments (or even simple network inventories) of
1257 your companies or clients, you really want to know which mail and DNS
1258 servers and versions are running. Having an accurate version number
1259 helps dramatically in determining which exploits a server is vulnerable
1260 to. Version detection helps you obtain this information.
1261 After TCP and/or UDP ports are discovered using one of the other scan
1263 methods, version detection interrogates those ports to determine more
1264 about what is actually running. The nmap-service-probes. database
1265 contains probes for querying various services and match expressions to
1266 recognize and parse responses. Nmap tries to determine the service
1267 protocol (e.g. FTP, SSH, Telnet, HTTP), the application name (e.g. ISC
1268 BIND, Apache httpd, Solaris telnetd), the version number, hostname,
1269 device type (e.g. printer, router), the OS family (e.g. Windows,
1270 Linux). When possible, Nmap also gets the Common Platform Enumeration
1271 (CPE). representation of this information. Sometimes miscellaneous
1272 details like whether an X server is open to connections, the SSH
1273 protocol version, or the KaZaA user name, are available. Of course,
1274 most services don't provide all of this information. If Nmap was
1275 compiled with OpenSSL support, it will connect to SSL servers to deduce
1276 the service listening behind that encryption layer.. Some UDP ports
1277 are left in the open|filtered state after a UDP port scan is unable to
1278 determine whether the port is open or filtered. Version detection will
1279 try to elicit a response from these ports (just as it does with open
1280 ports), and change the state to open if it succeeds. open|filtered TCP
1281 ports are treated the same way. Note that the Nmap -A option enables
1282 version detection among other things. A paper documenting the
1283 workings, usage, and customization of version detection is available at
1284 http://nmap.org/book/vscan.html.
1285 When RPC services are discovered, the Nmap RPC grinder. is
1287 automatically used to determine the RPC program and version numbers. It
1288 takes all the TCP/UDP ports detected as RPC and floods them with SunRPC
1289 program NULL commands in an attempt to determine whether they are RPC
1290 ports, and if so, what program and version number they serve up. Thus
1291 you can effectively obtain the same info as rpcinfo -p even if the
1292 target's portmapper is behind a firewall (or protected by TCP
1293 wrappers). Decoys do not currently work with RPC scan..
1294 When Nmap receives responses from a service but cannot match them to
1296 its database, it prints out a special fingerprint and a URL for you to
1297 submit if to if you know for sure what is running on the port. Please
1298 take a couple minutes to make the submission so that your find can
1299 benefit everyone. Thanks to these submissions, Nmap has about 6,500
1300 pattern matches for more than 650 protocols such as SMTP, FTP, HTTP,
1301 etc..
1302 Version detection is enabled and controlled with the following options:
1304 -sV (Version detection) .
1306 Enables version detection, as discussed above. Alternatively, you
1307 can use -A, which enables version detection among other things.
1308 -sR. is an alias for -sV. Prior to March 2011, it was used to
1310 active the RPC grinder separately from version detection, but now
1311 these options are always combined.
1312 --allports (Don't exclude any ports from version detection) .
1314 By default, Nmap version detection skips TCP port 9100 because some
1315 printers simply print anything sent to that port, leading to dozens
1316 of pages of HTTP GET requests, binary SSL session requests, etc.
1317 This behavior can be changed by modifying or removing the Exclude
1318 directive in nmap-service-probes, or you can specify --allports to
1319 scan all ports regardless of any Exclude directive.
1320 --version-intensity intensity (Set version scan intensity) .
1322 When performing a version scan (-sV), Nmap sends a series of
1323 probes, each of which is assigned a rarity value between one and
1324 nine. The lower-numbered probes are effective against a wide
1325 variety of common services, while the higher-numbered ones are
1326 rarely useful. The intensity level specifies which probes should be
1327 applied. The higher the number, the more likely it is the service
1328 will be correctly identified. However, high intensity scans take
1329 longer. The intensity must be between 0 and 9.. The default is 7..
1330 When a probe is registered to the target port via the
1331 nmap-service-probesports directive, that probe is tried regardless
1332 of intensity level. This ensures that the DNS probes will always be
1333 attempted against any open port 53, the SSL probe will be done
1334 against 443, etc.
1335 --version-light (Enable light mode) .
1337 This is a convenience alias for --version-intensity 2. This light
1338 mode makes version scanning much faster, but it is slightly less
1339 likely to identify services.
1340 --version-all (Try every single probe) .
1342 An alias for --version-intensity 9, ensuring that every single
1343 probe is attempted against each port.
1344 --version-trace (Trace version scan activity) .
1346 This causes Nmap to print out extensive debugging info about what
1347 version scanning is doing. It is a subset of what you get with
1348 --packet-trace.
1349
1351 One of Nmap's best-known features is remote OS detection using TCP/IP
1352 stack fingerprinting. Nmap sends a series of TCP and UDP packets to the
1353 remote host and examines practically every bit in the responses. After
1354 performing dozens of tests such as TCP ISN sampling, TCP options
1355 support and ordering, IP ID sampling, and the initial window size
1356 check, Nmap compares the results to its nmap-os-db. database of more
1357 than 2,600 known OS fingerprints and prints out the OS details if there
1358 is a match. Each fingerprint includes a freeform textual description of
1359 the OS, and a classification which provides the vendor name (e.g. Sun),
1360 underlying OS (e.g. Solaris), OS generation (e.g. 10), and device type
1361 (general purpose, router, switch, game console, etc). Most fingerprints
1362 also have a Common Platform Enumeration (CPE). representation, like
1363 cpe:/o:linux:linux_kernel:2.6.
1364 If Nmap is unable to guess the OS of a machine, and conditions are good
1366 (e.g. at least one open port and one closed port were found), Nmap will
1367 provide a URL you can use to submit the fingerprint if you know (for
1368 sure) the OS running on the machine. By doing this you contribute to
1369 the pool of operating systems known to Nmap and thus it will be more
1370 accurate for everyone.
1371 OS detection enables some other tests which make use of information
1373 that is gathered during the process anyway. One of these is TCP
1374 Sequence Predictability Classification. This measures approximately how
1375 hard it is to establish a forged TCP connection against the remote
1376 host. It is useful for exploiting source-IP based trust relationships
1377 (rlogin, firewall filters, etc) or for hiding the source of an attack.
1378 This sort of spoofing is rarely performed any more, but many machines
1379 are still vulnerable to it. The actual difficulty number is based on
1380 statistical sampling and may fluctuate. It is generally better to use
1381 the English classification such as “worthy challenge” or “trivial
1382 joke”. This is only reported in normal output in verbose (-v) mode.
1383 When verbose mode is enabled along with -O, IP ID sequence generation
1384 is also reported. Most machines are in the “incremental” class, which
1385 means that they increment the ID field in the IP header for each packet
1386 they send. This makes them vulnerable to several advanced information
1387 gathering and spoofing attacks.
1388 Another bit of extra information enabled by OS detection is a guess at
1390 a target's uptime. This uses the TCP timestamp option (RFC 1323[10]) to
1391 guess when a machine was last rebooted. The guess can be inaccurate due
1392 to the timestamp counter not being initialized to zero or the counter
1393 overflowing and wrapping around, so it is printed only in verbose mode.
1394 A paper documenting the workings, usage, and customization of OS
1396 detection is available at http://nmap.org/book/osdetect.html.
1397 OS detection is enabled and controlled with the following options:
1399 -O (Enable OS detection) .
1401 Enables OS detection, as discussed above. Alternatively, you can
1402 use -A to enable OS detection along with other things.
1403 --osscan-limit (Limit OS detection to promising targets) .
1405 OS detection is far more effective if at least one open and one
1406 closed TCP port are found. Set this option and Nmap will not even
1407 try OS detection against hosts that do not meet this criteria. This
1408 can save substantial time, particularly on -Pn scans against many
1409 hosts. It only matters when OS detection is requested with -O or
1410 -A.
1411 --osscan-guess; --fuzzy (Guess OS detection results) .
1413 When Nmap is unable to detect a perfect OS match, it sometimes
1414 offers up near-matches as possibilities. The match has to be very
1415 close for Nmap to do this by default. Either of these (equivalent)
1416 options make Nmap guess more aggressively. Nmap will still tell you
1417 when an imperfect match is printed and display its confidence level
1418 (percentage) for each guess.
1419 --max-os-tries (Set the maximum number of OS detection tries against a
1421 target) .
1422 When Nmap performs OS detection against a target and fails to find
1423 a perfect match, it usually repeats the attempt. By default, Nmap
1424 tries five times if conditions are favorable for OS fingerprint
1425 submission, and twice when conditions aren't so good. Specifying a
1426 lower --max-os-tries value (such as 1) speeds Nmap up, though you
1427 miss out on retries which could potentially identify the OS.
1428 Alternatively, a high value may be set to allow even more retries
1429 when conditions are favorable. This is rarely done, except to
1430 generate better fingerprints for submission and integration into
1431 the Nmap OS database.
1432
1434 The Nmap Scripting Engine (NSE) is one of Nmap's most powerful and
1435 flexible features. It allows users to write (and share) simple scripts
1436 (using the Lua programming language[11],
1437 Tasks we had in mind when creating the system include network
1439 discovery, more sophisticated version detection, vulnerability
1440 detection. NSE can even be used for vulnerability exploitation.
1441 To reflect those different uses and to simplify the choice of which
1443 scripts to run, each script contains a field associating it with one or
1444 more categories. Currently defined categories are auth, broadcast,
1445 default. discovery, dos, exploit, external, fuzzer, intrusive,
1446 malware, safe, version, and vuln. These are all described at
1447 http://nmap.org/book/nse-usage.html#nse-categories.
1448 Scripts are not run in a sandbox and thus could accidentally or
1450 maliciously damage your system or invade your privacy. Never run
1451 scripts from third parties unless you trust the authors or have
1452 carefully audited the scripts yourself.
1453 The Nmap Scripting Engine is described in detail at
1455 http://nmap.org/book/nse.html and is controlled by the following
1456 options:
1457 -sC .
1459 Performs a script scan using the default set of scripts. It is
1460 equivalent to --script=default. Some of the scripts in this
1461 category are considered intrusive and should not be run against a
1462 target network without permission.
1463 --script filename|category|directory|expression[,...] .
1465 Runs a script scan using the comma-separated list of filenames,
1466 script categories, and directories. Each element in the list may
1467 also be a Boolean expression describing a more complex set of
1468 scripts. Each element is interpreted first as an expression, then
1469 as a category, and finally as a file or directory name.
1470 There are two special features for advanced users only. One is to
1472 prefix script names and expressions with + to force them to run
1473 even if they normally wouldn't (e.g. the relevant service wasn't
1474 detected on the target port). The other is that the argument all
1475 may be used to specify every script in Nmap's database. Be cautious
1476 with this because NSE contains dangerous scripts such as exploits,
1477 brute force authentication crackers, and denial of service attacks.
1478 File and directory names may be relative or absolute. Absolute
1480 names are used directly. Relative paths are looked for in the
1481 scripts of each of the following places until found: --datadir
1482 $NMAPDIR.
1483 ~/.nmap (not searched on Windows).
1484 HOME\AppData\Roaming\nmap (only on Windows).
1485 the directory containing the nmap executable
1486 the directory containing the nmap executable, followed by
1487 ../share/nmap
1488 NMAPDATADIR.
1489 the current directory.
1490 When a directory name is given, Nmap loads every file in the directory
1492 whose name ends with .nse. All other files are ignored and directories
1493 are not searched recursively. When a filename is given, it does not
1494 have to have the .nse extension; it will be added automatically if
1495 necessary. Nmap scripts are stored in a scripts subdirectory of the
1496 Nmap data directory by default (see
1497 http://nmap.org/book/data-files.html). For efficiency, scripts are
1498 indexed in a database stored in scripts/script.db,. which lists the
1499 category or categories in which each script belongs. When referring to
1500 scripts from script.db by name, you can use a shell-style ‘*’ wildcard.
1501 nmap --script "http-*"
1503 Loads all scripts whose name starts with http-, such as http-auth
1504 and http-open-proxy. The argument to --script had to be in quotes
1505 to protect the wildcard from the shell.
1506 More complicated script selection can be done using the and, or, and
1508 not operators to build Boolean expressions. The operators have the same
1509 precedence[12] as in Lua: not is the highest, followed by and and then
1510 or. You can alter precedence by using parentheses. Because expressions
1511 contain space characters it is necessary to quote them.
1512 nmap --script "not intrusive"
1514 Loads every script except for those in the intrusive category.
1515 nmap --script "default or safe"
1517 This is functionally equivalent to nmap --script "default,safe". It
1518 loads all scripts that are in the default category or the safe
1519 category or both.
1520 nmap --script "default and safe"
1522 Loads those scripts that are in both the default and safe
1523 categories.
1524 nmap --script "(default or safe or intrusive) and not http-*"
1526 Loads scripts in the default, safe, or intrusive categories, except
1527 for those whose names start with http-.
1528 --script-args n1=v1,n2={n3=v3},n4={v4,v5} .
1530 Lets you provide arguments to NSE scripts. Arguments are a
1531 comma-separated list of name=value pairs. Names and values may be
1532 strings not containing whitespace or the characters ‘{’, ‘}’, ‘=’,
1533 or ‘,’. To include one of these characters in a string, enclose the
1534 string in single or double quotes. Within a quoted string, ‘\’
1535 escapes a quote. A backslash is only used to escape quotation marks
1536 in this special case; in all other cases a backslash is interpreted
1537 literally. Values may also be tables enclosed in {}, just as in
1538 Lua. A table may contain simple string values or more name-value
1539 pairs, including nested tables. Many scripts qualify their
1540 arguments with the script name, as in xmpp-info.server_name. You
1541 may use that full qualified version to affect just the specified
1542 script, or you may pass the unqualified version (server_name in
1543 this case) to affect all scripts using that argument name. A script
1544 will first check for its fully qualified argument name (the name
1545 specified in its documentation) before it accepts an unqualified
1546 argument name. A complex example of script arguments is
1547 --script-args
1548 'user=foo,pass=",{}=bar",whois={whodb=nofollow+ripe},xmpp-info.server_name=localhost'.
1549 The online NSE Documentation Portal at http://nmap.org/nsedoc/
1550 lists the arguments that each script accepts.
1551 --script-args-file filename .
1553 Lets you load arguments to NSE scripts from a file. Any arguments
1554 on the command line supersede ones in the file. The file can be an
1555 absolute path, or a path relative to Nmap's usual search path
1556 (NMAPDIR, etc.) Arguments can be comma-separated or
1557 newline-separated, but otherwise follow the same rules as for
1558 --script-args, without requiring special quoting and escaping,
1559 since they are not parsed by the shell.
1560 --script-help filename|category|directory|expression|all[,...] .
1562 Shows help about scripts. For each script matching the given
1563 specification, Nmap prints the script name, its categories, and its
1564 description. The specifications are the same as those accepted by
1565 --script; so for example if you want help about the ftp-anon
1566 script, you would run nmap --script-help ftp-anon. In addition to
1567 getting help for individual scripts, you can use this as a preview
1568 of what scripts will be run for a specification, for example with
1569 nmap --script-help default.
1570 --script-trace .
1572 This option does what --packet-trace does, just one ISO layer
1573 higher. If this option is specified all incoming and outgoing
1574 communication performed by a script is printed. The displayed
1575 information includes the communication protocol, the source, the
1576 target and the transmitted data. If more than 5% of all transmitted
1577 data is not printable, then the trace output is in a hex dump
1578 format. Specifying --packet-trace enables script tracing too.
1579 --script-updatedb .
1581 This option updates the script database found in scripts/script.db
1582 which is used by Nmap to determine the available default scripts
1583 and categories. It is only necessary to update the database if you
1584 have added or removed NSE scripts from the default scripts
1585 directory or if you have changed the categories of any script. This
1586 option is generally used by itself: nmap --script-updatedb.
1587
1589 One of my highest Nmap development priorities has always been
1590 performance. A default scan (nmap hostname) of a host on my local
1591 network takes a fifth of a second. That is barely enough time to blink,
1592 but adds up when you are scanning hundreds or thousands of hosts.
1593 Moreover, certain scan options such as UDP scanning and version
1594 detection can increase scan times substantially. So can certain
1595 firewall configurations, particularly response rate limiting. While
1596 Nmap utilizes parallelism and many advanced algorithms to accelerate
1597 these scans, the user has ultimate control over how Nmap runs. Expert
1598 users carefully craft Nmap commands to obtain only the information they
1599 care about while meeting their time constraints.
1600 Techniques for improving scan times include omitting non-critical
1602 tests, and upgrading to the latest version of Nmap (performance
1603 enhancements are made frequently). Optimizing timing parameters can
1604 also make a substantial difference. Those options are listed below.
1605 Some options accept a time parameter. This is specified in seconds by
1607 default, though you can append ‘ms’, ‘s’, ‘m’, or ‘h’ to the value to
1608 specify milliseconds, seconds, minutes, or hours. So the --host-timeout
1609 arguments 900000ms, 900, 900s, and 15m all do the same thing.
1610 --min-hostgroup numhosts; --max-hostgroup numhosts (Adjust parallel
1612 scan group sizes) .
1613 Nmap has the ability to port scan or version scan multiple hosts in
1614 parallel. Nmap does this by dividing the target IP space into
1615 groups and then scanning one group at a time. In general, larger
1616 groups are more efficient. The downside is that host results can't
1617 be provided until the whole group is finished. So if Nmap started
1618 out with a group size of 50, the user would not receive any reports
1619 (except for the updates offered in verbose mode) until the first 50
1620 hosts are completed.
1621 By default, Nmap takes a compromise approach to this conflict. It
1623 starts out with a group size as low as five so the first results
1624 come quickly and then increases the groupsize to as high as 1024.
1625 The exact default numbers depend on the options given. For
1626 efficiency reasons, Nmap uses larger group sizes for UDP or
1627 few-port TCP scans.
1628 When a maximum group size is specified with --max-hostgroup, Nmap
1630 will never exceed that size. Specify a minimum size with
1631 --min-hostgroup and Nmap will try to keep group sizes above that
1632 level. Nmap may have to use smaller groups than you specify if
1633 there are not enough target hosts left on a given interface to
1634 fulfill the specified minimum. Both may be set to keep the group
1635 size within a specific range, though this is rarely desired.
1636 These options do not have an effect during the host discovery phase
1638 of a scan. This includes plain ping scans (-sn). Host discovery
1639 always works in large groups of hosts to improve speed and
1640 accuracy.
1641 The primary use of these options is to specify a large minimum
1643 group size so that the full scan runs more quickly. A common choice
1644 is 256 to scan a network in Class C sized chunks. For a scan with
1645 many ports, exceeding that number is unlikely to help much. For
1646 scans of just a few port numbers, host group sizes of 2048 or more
1647 may be helpful.
1648 --min-parallelism numprobes; --max-parallelism numprobes (Adjust probe
1650 parallelization) .
1651 These options control the total number of probes that may be
1652 outstanding for a host group. They are used for port scanning and
1653 host discovery. By default, Nmap calculates an ever-changing ideal
1654 parallelism based on network performance. If packets are being
1655 dropped, Nmap slows down and allows fewer outstanding probes. The
1656 ideal probe number slowly rises as the network proves itself
1657 worthy. These options place minimum or maximum bounds on that
1658 variable. By default, the ideal parallelism can drop to one if the
1659 network proves unreliable and rise to several hundred in perfect
1660 conditions.
1661 The most common usage is to set --min-parallelism to a number
1663 higher than one to speed up scans of poorly performing hosts or
1664 networks. This is a risky option to play with, as setting it too
1665 high may affect accuracy. Setting this also reduces Nmap's ability
1666 to control parallelism dynamically based on network conditions. A
1667 value of 10 might be reasonable, though I only adjust this value as
1668 a last resort.
1669 The --max-parallelism option is sometimes set to one to prevent
1671 Nmap from sending more than one probe at a time to hosts. The
1672 --scan-delay option, discussed later, is another way to do this.
1673 --min-rtt-timeout time, --max-rtt-timeout time, --initial-rtt-timeout
1675 time (Adjust probe timeouts) .
1676 Nmap maintains a running timeout value for determining how long it
1677 will wait for a probe response before giving up or retransmitting
1678 the probe. This is calculated based on the response times of
1679 previous probes.
1680 If the network latency shows itself to be significant and variable,
1682 this timeout can grow to several seconds. It also starts at a
1683 conservative (high) level and may stay that way for a while when
1684 Nmap scans unresponsive hosts.
1685 Specifying a lower --max-rtt-timeout and --initial-rtt-timeout than
1687 the defaults can cut scan times significantly. This is particularly
1688 true for pingless (-Pn) scans, and those against heavily filtered
1689 networks. Don't get too aggressive though. The scan can end up
1690 taking longer if you specify such a low value that many probes are
1691 timing out and retransmitting while the response is in transit.
1692 If all the hosts are on a local network, 100 milliseconds
1694 (--max-rtt-timeout 100ms) is a reasonable aggressive value. If
1695 routing is involved, ping a host on the network first with the ICMP
1696 ping utility, or with a custom packet crafter such as Nping. that
1697 is more likely to get through a firewall. Look at the maximum round
1698 trip time out of ten packets or so. You might want to double that
1699 for the --initial-rtt-timeout and triple or quadruple it for the
1700 --max-rtt-timeout. I generally do not set the maximum RTT below
1701 100 ms, no matter what the ping times are. Nor do I exceed 1000 ms.
1702 --min-rtt-timeout is a rarely used option that could be useful when
1704 a network is so unreliable that even Nmap's default is too
1705 aggressive. Since Nmap only reduces the timeout down to the minimum
1706 when the network seems to be reliable, this need is unusual and
1707 should be reported as a bug to the nmap-dev mailing list..
1708 --max-retries numtries (Specify the maximum number of port scan probe
1710 retransmissions) .
1711 When Nmap receives no response to a port scan probe, it could mean
1712 the port is filtered. Or maybe the probe or response was simply
1713 lost on the network. It is also possible that the target host has
1714 rate limiting enabled that temporarily blocked the response. So
1715 Nmap tries again by retransmitting the initial probe. If Nmap
1716 detects poor network reliability, it may try many more times before
1717 giving up on a port. While this benefits accuracy, it also lengthen
1718 scan times. When performance is critical, scans may be sped up by
1719 limiting the number of retransmissions allowed. You can even
1720 specify --max-retries 0 to prevent any retransmissions, though that
1721 is only recommended for situations such as informal surveys where
1722 occasional missed ports and hosts are acceptable.
1723 The default (with no -T template) is to allow ten retransmissions.
1725 If a network seems reliable and the target hosts aren't rate
1726 limiting, Nmap usually only does one retransmission. So most target
1727 scans aren't even affected by dropping --max-retries to a low value
1728 such as three. Such values can substantially speed scans of slow
1729 (rate limited) hosts. You usually lose some information when Nmap
1730 gives up on ports early, though that may be preferable to letting
1731 the --host-timeout expire and losing all information about the
1732 target.
1733 --host-timeout time (Give up on slow target hosts) .
1735 Some hosts simply take a long time to scan. This may be due to
1736 poorly performing or unreliable networking hardware or software,
1737 packet rate limiting, or a restrictive firewall. The slowest few
1738 percent of the scanned hosts can eat up a majority of the scan
1739 time. Sometimes it is best to cut your losses and skip those hosts
1740 initially. Specify --host-timeout with the maximum amount of time
1741 you are willing to wait. For example, specify 30m to ensure that
1742 Nmap doesn't waste more than half an hour on a single host. Note
1743 that Nmap may be scanning other hosts at the same time during that
1744 half an hour, so it isn't a complete loss. A host that times out is
1745 skipped. No port table, OS detection, or version detection results
1746 are printed for that host.
1747 --scan-delay time; --max-scan-delay time (Adjust delay between probes)
1749 .
1750 This option causes Nmap to wait at least the given amount of time
1751 between each probe it sends to a given host. This is particularly
1752 useful in the case of rate limiting.. Solaris machines (among many
1753 others) will usually respond to UDP scan probe packets with only
1754 one ICMP message per second. Any more than that sent by Nmap will
1755 be wasteful. A --scan-delay of 1s will keep Nmap at that slow rate.
1756 Nmap tries to detect rate limiting and adjust the scan delay
1757 accordingly, but it doesn't hurt to specify it explicitly if you
1758 already know what rate works best.
1759 When Nmap adjusts the scan delay upward to cope with rate limiting,
1761 the scan slows down dramatically. The --max-scan-delay option
1762 specifies the largest delay that Nmap will allow. A low
1763 --max-scan-delay can speed up Nmap, but it is risky. Setting this
1764 value too low can lead to wasteful packet retransmissions and
1765 possible missed ports when the target implements strict rate
1766 limiting.
1767 Another use of --scan-delay is to evade threshold based intrusion
1769 detection and prevention systems (IDS/IPS)..
1770 --min-rate number; --max-rate number (Directly control the scanning
1772 rate) .
1773 Nmap's dynamic timing does a good job of finding an appropriate
1774 speed at which to scan. Sometimes, however, you may happen to know
1775 an appropriate scanning rate for a network, or you may have to
1776 guarantee that a scan will be finished by a certain time. Or
1777 perhaps you must keep Nmap from scanning too quickly. The
1778 --min-rate and --max-rate options are designed for these
1779 situations.
1780 When the --min-rate option is given Nmap will do its best to send
1782 packets as fast as or faster than the given rate. The argument is a
1783 positive real number representing a packet rate in packets per
1784 second. For example, specifying --min-rate 300 means that Nmap will
1785 try to keep the sending rate at or above 300 packets per second.
1786 Specifying a minimum rate does not keep Nmap from going faster if
1787 conditions warrant.
1788 Likewise, --max-rate limits a scan's sending rate to a given
1790 maximum. Use --max-rate 100, for example, to limit sending to 100
1791 packets per second on a fast network. Use --max-rate 0.1 for a slow
1792 scan of one packet every ten seconds. Use --min-rate and --max-rate
1793 together to keep the rate inside a certain range.
1794 These two options are global, affecting an entire scan, not
1796 individual hosts. They only affect port scans and host discovery
1797 scans. Other features like OS detection implement their own timing.
1798 There are two conditions when the actual scanning rate may fall
1800 below the requested minimum. The first is if the minimum is faster
1801 than the fastest rate at which Nmap can send, which is dependent on
1802 hardware. In this case Nmap will simply send packets as fast as
1803 possible, but be aware that such high rates are likely to cause a
1804 loss of accuracy. The second case is when Nmap has nothing to send,
1805 for example at the end of a scan when the last probes have been
1806 sent and Nmap is waiting for them to time out or be responded to.
1807 It's normal to see the scanning rate drop at the end of a scan or
1808 in between hostgroups. The sending rate may temporarily exceed the
1809 maximum to make up for unpredictable delays, but on average the
1810 rate will stay at or below the maximum.
1811 Specifying a minimum rate should be done with care. Scanning faster
1813 than a network can support may lead to a loss of accuracy. In some
1814 cases, using a faster rate can make a scan take longer than it
1815 would with a slower rate. This is because Nmap's adaptive
1816 retransmission algorithms will detect the network congestion caused
1817 by an excessive scanning rate and increase the number of
1818 retransmissions in order to improve accuracy. So even though
1819 packets are sent at a higher rate, more packets are sent overall.
1820 Cap the number of retransmissions with the --max-retries option if
1821 you need to set an upper limit on total scan time.
1822 --defeat-rst-ratelimit .
1824 Many hosts have long used rate limiting. to reduce the number of
1825 ICMP error messages (such as port-unreachable errors) they send.
1826 Some systems now apply similar rate limits to the RST (reset)
1827 packets they generate. This can slow Nmap down dramatically as it
1828 adjusts its timing to reflect those rate limits. You can tell Nmap
1829 to ignore those rate limits (for port scans such as SYN scan which
1830 don't treat non-responsive ports as open) by specifying
1831 --defeat-rst-ratelimit.
1832 Using this option can reduce accuracy, as some ports will appear
1834 non-responsive because Nmap didn't wait long enough for a
1835 rate-limited RST response. With a SYN scan, the non-response
1836 results in the port being labeled filtered rather than the closed
1837 state we see when RST packets are received. This option is useful
1838 when you only care about open ports, and distinguishing between
1839 closed and filtered ports isn't worth the extra time.
1840 --nsock-engine epoll|kqueue|poll|select .
1842 Enforce use of a given nsock IO multiplexing engine. Only the
1843 select(2)-based fallback engine is guaranteed to be available on
1844 your system. Engines are named after the name of the IO management
1845 facility they leverage. Engines currenty implemented are epoll,
1846 kqueue, poll, and select, but not all will be present on any
1847 platform. Use nmap -V to see which engines are supported.
1848 -T paranoid|sneaky|polite|normal|aggressive|insane (Set a timing
1850 template) .
1851 While the fine-grained timing controls discussed in the previous
1852 section are powerful and effective, some people find them
1853 confusing. Moreover, choosing the appropriate values can sometimes
1854 take more time than the scan you are trying to optimize. So Nmap
1855 offers a simpler approach, with six timing templates. You can
1856 specify them with the -T option and their number (0–5) or their
1857 name. The template names are paranoid (0), sneaky (1), polite (2),
1858 normal (3), aggressive (4), and insane (5). The first two are for
1859 IDS evasion. Polite mode slows down the scan to use less bandwidth
1860 and target machine resources. Normal mode is the default and so -T3
1861 does nothing. Aggressive mode speeds scans up by making the
1862 assumption that you are on a reasonably fast and reliable network.
1863 Finally insane mode. assumes that you are on an extraordinarily
1864 fast network or are willing to sacrifice some accuracy for speed.
1865 These templates allow the user to specify how aggressive they wish
1867 to be, while leaving Nmap to pick the exact timing values. The
1868 templates also make some minor speed adjustments for which
1869 fine-grained control options do not currently exist. For example,
1870 -T4. prohibits the dynamic scan delay from exceeding 10 ms for TCP
1871 ports and -T5 caps that value at 5 ms. Templates can be used in
1872 combination with fine-grained controls, and the fine-grained
1873 controls will you specify will take precedence over the timing
1874 template default for that parameter. I recommend using -T4 when
1875 scanning reasonably modern and reliable networks. Keep that option
1876 even when you add fine-grained controls so that you benefit from
1877 those extra minor optimizations that it enables.
1878 If you are on a decent broadband or ethernet connection, I would
1880 recommend always using -T4. Some people love -T5 though it is too
1881 aggressive for my taste. People sometimes specify -T2 because they
1882 think it is less likely to crash hosts or because they consider
1883 themselves to be polite in general. They often don't realize just
1884 how slow -T polite. really is. Their scan may take ten times
1885 longer than a default scan. Machine crashes and bandwidth problems
1886 are rare with the default timing options (-T3) and so I normally
1887 recommend that for cautious scanners. Omitting version detection is
1888 far more effective than playing with timing values at reducing
1889 these problems.
1890 While -T0. and -T1. may be useful for avoiding IDS alerts, they
1892 will take an extraordinarily long time to scan thousands of
1893 machines or ports. For such a long scan, you may prefer to set the
1894 exact timing values you need rather than rely on the canned -T0 and
1895 -T1 values.
1896 The main effects of T0 are serializing the scan so only one port is
1898 scanned at a time, and waiting five minutes between sending each
1899 probe. T1 and T2 are similar but they only wait 15 seconds and 0.4
1900 seconds, respectively, between probes. T3 is Nmap's default
1901 behavior, which includes parallelization.. does the equivalent of
1902 --max-rtt-timeout 1250ms --initial-rtt-timeout 500ms --max-retries
1903 6 and sets the maximum TCP scan delay to 10 milliseconds. T5 does
1904 the equivalent of --max-rtt-timeout 300ms --min-rtt-timeout 50ms
1905 --initial-rtt-timeout 250ms --max-retries 2 --host-timeout 15m as
1906 well as setting the maximum TCP scan delay to 5 ms.
1907
1909 Many Internet pioneers envisioned a global open network with a
1910 universal IP address space allowing virtual connections between any two
1911 nodes. This allows hosts to act as true peers, serving and retrieving
1912 information from each other. People could access all of their home
1913 systems from work, changing the climate control settings or unlocking
1914 the doors for early guests. This vision of universal connectivity has
1915 been stifled by address space shortages and security concerns. In the
1916 early 1990s, organizations began deploying firewalls for the express
1917 purpose of reducing connectivity. Huge networks were cordoned off from
1918 the unfiltered Internet by application proxies, network address
1919 translation, and packet filters. The unrestricted flow of information
1920 gave way to tight regulation of approved communication channels and the
1921 content that passes over them.
1922 Network obstructions such as firewalls can make mapping a network
1924 exceedingly difficult. It will not get any easier, as stifling casual
1925 reconnaissance is often a key goal of implementing the devices.
1926 Nevertheless, Nmap offers many features to help understand these
1927 complex networks, and to verify that filters are working as intended.
1928 It even supports mechanisms for bypassing poorly implemented defenses.
1929 One of the best methods of understanding your network security posture
1930 is to try to defeat it. Place yourself in the mind-set of an attacker,
1931 and deploy techniques from this section against your networks. Launch
1932 an FTP bounce scan, idle scan, fragmentation attack, or try to tunnel
1933 through one of your own proxies.
1934 In addition to restricting network activity, companies are increasingly
1936 monitoring traffic with intrusion detection systems (IDS). All of the
1937 major IDSs ship with rules designed to detect Nmap scans because scans
1938 are sometimes a precursor to attacks. Many of these products have
1939 recently morphed into intrusion prevention systems (IPS). that
1940 actively block traffic deemed malicious. Unfortunately for network
1941 administrators and IDS vendors, reliably detecting bad intentions by
1942 analyzing packet data is a tough problem. Attackers with patience,
1943 skill, and the help of certain Nmap options can usually pass by IDSs
1944 undetected. Meanwhile, administrators must cope with large numbers of
1945 false positive results where innocent activity is misdiagnosed and
1946 alerted on or blocked.
1947 Occasionally people suggest that Nmap should not offer features for
1949 evading firewall rules or sneaking past IDSs. They argue that these
1950 features are just as likely to be misused by attackers as used by
1951 administrators to enhance security. The problem with this logic is that
1952 these methods would still be used by attackers, who would just find
1953 other tools or patch the functionality into Nmap. Meanwhile,
1954 administrators would find it that much harder to do their jobs.
1955 Deploying only modern, patched FTP servers is a far more powerful
1956 defense than trying to prevent the distribution of tools implementing
1957 the FTP bounce attack.
1958 There is no magic bullet (or Nmap option) for detecting and subverting
1960 firewalls and IDS systems. It takes skill and experience. A tutorial is
1961 beyond the scope of this reference guide, which only lists the relevant
1962 options and describes what they do.
1963 -f (fragment packets); --mtu (using the specified MTU) .
1965 The -f option causes the requested scan (including ping scans) to
1966 use tiny fragmented IP packets. The idea is to split up the TCP
1967 header over several packets to make it harder for packet filters,
1968 intrusion detection systems, and other annoyances to detect what
1969 you are doing. Be careful with this! Some programs have trouble
1970 handling these tiny packets. The old-school sniffer named Sniffit
1971 segmentation faulted immediately upon receiving the first fragment.
1972 Specify this option once, and Nmap splits the packets into eight
1973 bytes or less after the IP header. So a 20-byte TCP header would be
1974 split into three packets. Two with eight bytes of the TCP header,
1975 and one with the final four. Of course each fragment also has an IP
1976 header. Specify -f again to use 16 bytes per fragment (reducing the
1977 number of fragments).. Or you can specify your own offset size
1978 with the --mtu option. Don't also specify -f if you use --mtu. The
1979 offset must be a multiple of eight. While fragmented packets won't
1980 get by packet filters and firewalls that queue all IP fragments,
1981 such as the CONFIG_IP_ALWAYS_DEFRAG option in the Linux kernel,
1982 some networks can't afford the performance hit this causes and thus
1983 leave it disabled. Others can't enable this because fragments may
1984 take different routes into their networks. Some source systems
1985 defragment outgoing packets in the kernel. Linux with the iptables.
1986 connection tracking module is one such example. Do a scan while a
1987 sniffer such as Wireshark. is running to ensure that sent packets
1988 are fragmented. If your host OS is causing problems, try the
1989 --send-eth. option to bypass the IP layer and send raw ethernet
1990 frames.
1991 Fragmentation is only supported for Nmap's raw packet features,
1993 which includes TCP and UDP port scans (except connect scan and FTP
1994 bounce scan) and OS detection. Features such as version detection
1995 and the Nmap Scripting Engine generally don't support fragmentation
1996 because they rely on your host's TCP stack to communicate with
1997 target services.
1998 -D decoy1[,decoy2][,ME][,...] (Cloak a scan with decoys) .
2000 Causes a decoy scan to be performed, which makes it appear to the
2001 remote host that the host(s) you specify as decoys are scanning the
2002 target network too. Thus their IDS might report 5–10 port scans
2003 from unique IP addresses, but they won't know which IP was scanning
2004 them and which were innocent decoys. While this can be defeated
2005 through router path tracing, response-dropping, and other active
2006 mechanisms, it is generally an effective technique for hiding your
2007 IP address.
2008 Separate each decoy host with commas, and you can optionally use
2010 ME. as one of the decoys to represent the position for your real
2011 IP address. If you put ME in the sixth position or later, some
2012 common port scan detectors (such as Solar Designer's. excellent
2013 Scanlogd). are unlikely to show your IP address at all. If you
2014 don't use ME, Nmap will put you in a random position. You can also
2015 use RND. to generate a random, non-reserved IP address, or
2016 RND:number to generate number addresses.
2017 Note that the hosts you use as decoys should be up or you might
2019 accidentally SYN flood your targets. Also it will be pretty easy to
2020 determine which host is scanning if only one is actually up on the
2021 network. You might want to use IP addresses instead of names (so
2022 the decoy networks don't see you in their nameserver logs).
2023 Decoys are used both in the initial ping scan (using ICMP, SYN,
2025 ACK, or whatever) and during the actual port scanning phase. Decoys
2026 are also used during remote OS detection (-O). Decoys do not work
2027 with version detection or TCP connect scan. When a scan delay is in
2028 effect, the delay is enforced between each batch of spoofed probes,
2029 not between each individual probe. Because decoys are sent as a
2030 batch all at once, they may temporarily violate congestion control
2031 limits.
2032 It is worth noting that using too many decoys may slow your scan
2034 and potentially even make it less accurate. Also, some ISPs will
2035 filter out your spoofed packets, but many do not restrict spoofed
2036 IP packets at all.
2037 -S IP_Address (Spoof source address) .
2039 In some circumstances, Nmap may not be able to determine your
2040 source address (Nmap will tell you if this is the case). In this
2041 situation, use -S with the IP address of the interface you wish to
2042 send packets through.
2043 Another possible use of this flag is to spoof the scan to make the
2045 targets think that someone else is scanning them. Imagine a company
2046 being repeatedly port scanned by a competitor! The -e option and
2047 -Pn are generally required for this sort of usage. Note that you
2048 usually won't receive reply packets back (they will be addressed to
2049 the IP you are spoofing), so Nmap won't produce useful reports.
2050 -e interface (Use specified interface) .
2052 Tells Nmap what interface to send and receive packets on. Nmap
2053 should be able to detect this automatically, but it will tell you
2054 if it cannot.
2055 --source-port portnumber; -g portnumber (Spoof source port number) .
2057 One surprisingly common misconfiguration is to trust traffic based
2058 only on the source port number. It is easy to understand how this
2059 comes about. An administrator will set up a shiny new firewall,
2060 only to be flooded with complaints from ungrateful users whose
2061 applications stopped working. In particular, DNS may be broken
2062 because the UDP DNS replies from external servers can no longer
2063 enter the network. FTP is another common example. In active FTP
2064 transfers, the remote server tries to establish a connection back
2065 to the client to transfer the requested file.
2066 Secure solutions to these problems exist, often in the form of
2068 application-level proxies or protocol-parsing firewall modules.
2069 Unfortunately there are also easier, insecure solutions. Noting
2070 that DNS replies come from port 53 and active FTP from port 20,
2071 many administrators have fallen into the trap of simply allowing
2072 incoming traffic from those ports. They often assume that no
2073 attacker would notice and exploit such firewall holes. In other
2074 cases, administrators consider this a short-term stop-gap measure
2075 until they can implement a more secure solution. Then they forget
2076 the security upgrade.
2077 Overworked network administrators are not the only ones to fall
2079 into this trap. Numerous products have shipped with these insecure
2080 rules. Even Microsoft has been guilty. The IPsec filters that
2081 shipped with Windows 2000 and Windows XP contain an implicit rule
2082 that allows all TCP or UDP traffic from port 88 (Kerberos). In
2083 another well-known case, versions of the Zone Alarm personal
2084 firewall up to 2.1.25 allowed any incoming UDP packets with the
2085 source port 53 (DNS) or 67 (DHCP).
2086 Nmap offers the -g and --source-port options (they are equivalent)
2088 to exploit these weaknesses. Simply provide a port number and Nmap
2089 will send packets from that port where possible. Most scanning
2090 operations that use raw sockets, including SYN and UDP scans,
2091 support the option completely. The option notably doesn't have an
2092 effect for any operations that use normal operating system sockets,
2093 including DNS requests, TCP connect scan,. version detection, and
2094 script scanning. Setting the source port also doesn't work for OS
2095 detection, because Nmap must use different port numbers for certain
2096 OS detection tests to work properly.
2097 --data-length number (Append random data to sent packets) .
2099 Normally Nmap sends minimalist packets containing only a header. So
2100 its TCP packets are generally 40 bytes and ICMP echo requests are
2101 just 28. Some UDP ports. and IP protocols. get a custom payload
2102 by default. This option tells Nmap to append the given number of
2103 random bytes to most of the packets it sends, and not to use any
2104 protocol-specific payloads. (Use --data-length 0 for no random or
2105 protocol-specific payloads.. OS detection (-O) packets are not
2106 affected. because accuracy there requires probe consistency, but
2107 most pinging and portscan packets support this. It slows things
2108 down a little, but can make a scan slightly less conspicuous.
2109 --ip-options S|R [route]|L [route]|T|U ... ; --ip-options hex string
2111 (Send packets with specified ip options) .
2112 The IP protocol[13] offers several options which may be placed in
2113 packet headers. Unlike the ubiquitous TCP options, IP options are
2114 rarely seen due to practicality and security concerns. In fact,
2115 many Internet routers block the most dangerous options such as
2116 source routing. Yet options can still be useful in some cases for
2117 determining and manipulating the network route to target machines.
2118 For example, you may be able to use the record route option to
2119 determine a path to a target even when more traditional
2120 traceroute-style approaches fail. Or if your packets are being
2121 dropped by a certain firewall, you may be able to specify a
2122 different route with the strict or loose source routing options.
2123 The most powerful way to specify IP options is to simply pass in
2125 values as the argument to --ip-options. Precede each hex number
2126 with \x then the two digits. You may repeat certain characters by
2127 following them with an asterisk and then the number of times you
2128 wish them to repeat. For example, \x01\x07\x04\x00*36\x01 is a hex
2129 string containing 36 NUL bytes.
2130 Nmap also offers a shortcut mechanism for specifying options.
2132 Simply pass the letter R, T, or U to request record-route,.
2133 record-timestamp,. or both options together, respectively. Loose
2134 or strict source routing. may be specified with an L or S followed
2135 by a space and then a space-separated list of IP addresses.
2136 If you wish to see the options in packets sent and received,
2138 specify --packet-trace. For more information and examples of using
2139 IP options with Nmap, see http://seclists.org/nmap-dev/2006/q3/52.
2140 --ttl value (Set IP time-to-live field) .
2142 Sets the IPv4 time-to-live field in sent packets to the given
2143 value.
2144 --randomize-hosts (Randomize target host order) .
2146 Tells Nmap to shuffle each group of up to 16384 hosts before it
2147 scans them. This can make the scans less obvious to various network
2148 monitoring systems, especially when you combine it with slow timing
2149 options. If you want to randomize over larger group sizes, increase
2150 PING_GROUP_SZ. in nmap.h. and recompile. An alternative solution
2151 is to generate the target IP list with a list scan (-sL -n -oN
2152 filename), randomize it with a Perl script, then provide the whole
2153 list to Nmap with -iL..
2154 --spoof-mac MAC address, prefix, or vendor name (Spoof MAC address) .
2156 Asks Nmap to use the given MAC address for all of the raw ethernet
2157 frames it sends. This option implies --send-eth. to ensure that
2158 Nmap actually sends ethernet-level packets. The MAC given can take
2159 several formats. If it is simply the number 0, Nmap chooses a
2160 completely random MAC address for the session. If the given string
2161 is an even number of hex digits (with the pairs optionally
2162 separated by a colon), Nmap will use those as the MAC. If fewer
2163 than 12 hex digits are provided, Nmap fills in the remainder of the
2164 six bytes with random values. If the argument isn't a zero or hex
2165 string, Nmap looks through nmap-mac-prefixes to find a vendor name
2166 containing the given string (it is case insensitive). If a match is
2167 found, Nmap uses the vendor's OUI (three-byte prefix). and fills
2168 out the remaining three bytes randomly. Valid --spoof-mac argument
2169 examples are Apple, 0, 01:02:03:04:05:06, deadbeefcafe, 0020F2, and
2170 Cisco. This option only affects raw packet scans such as SYN scan
2171 or OS detection, not connection-oriented features such as version
2172 detection or the Nmap Scripting Engine.
2173 --badsum (Send packets with bogus TCP/UDP checksums) .
2175 Asks Nmap to use an invalid TCP, UDP or SCTP checksum for packets
2176 sent to target hosts. Since virtually all host IP stacks properly
2177 drop these packets, any responses received are likely coming from a
2178 firewall or IDS that didn't bother to verify the checksum. For more
2179 details on this technique, see http://nmap.org/p60-12.html
2180 --adler32 (Use deprecated Adler32 instead of CRC32C for SCTP checksums)
2182 .
2183 Asks Nmap to use the deprecated Adler32 algorithm for calculating
2184 the SCTP checksum. If --adler32 is not given, CRC-32C (Castagnoli)
2185 is used. RFC 2960[14] originally defined Adler32 as checksum
2186 algorithm for SCTP; RFC 4960[7] later redefined the SCTP checksums
2187 to use CRC-32C. Current SCTP implementations should be using
2188 CRC-32C, but in order to elicit responses from old, legacy SCTP
2189 implementations, it may be preferable to use Adler32.
2190
2192 Any security tool is only as useful as the output it generates. Complex
2193 tests and algorithms are of little value if they aren't presented in an
2194 organized and comprehensible fashion. Given the number of ways Nmap is
2195 used by people and other software, no single format can please
2196 everyone. So Nmap offers several formats, including the interactive
2197 mode for humans to read directly and XML for easy parsing by software.
2198 In addition to offering different output formats, Nmap provides options
2200 for controlling the verbosity of output as well as debugging messages.
2201 Output types may be sent to standard output or to named files, which
2202 Nmap can append to or clobber. Output files may also be used to resume
2203 aborted scans.
2204 Nmap makes output available in five different formats. The default is
2206 called interactive output,. and it is sent to standard output
2207 (stdout).. There is also normal output,. which is similar to
2208 interactive except that it displays less runtime information and
2209 warnings since it is expected to be analyzed after the scan completes
2210 rather than interactively.
2211 XML output. is one of the most important output types, as it can be
2213 converted to HTML, easily parsed by programs such as Nmap graphical
2214 user interfaces, or imported into databases.
2215 The two remaining output types are the simple grepable output. which
2217 includes most information for a target host on a single line, and
2218 sCRiPt KiDDi3 0utPUt. for users who consider themselves |<-r4d.
2219 While interactive output is the default and has no associated
2221 command-line options, the other four format options use the same
2222 syntax. They take one argument, which is the filename that results
2223 should be stored in. Multiple formats may be specified, but each format
2224 may only be specified once. For example, you may wish to save normal
2225 output for your own review while saving XML of the same scan for
2226 programmatic analysis. You might do this with the options -oX
2227 myscan.xml -oN myscan.nmap. While this chapter uses the simple names
2228 like myscan.xml for brevity, more descriptive names are generally
2229 recommended. The names chosen are a matter of personal preference,
2230 though I use long ones that incorporate the scan date and a word or two
2231 describing the scan, placed in a directory named after the company I'm
2232 scanning.
2233 While these options save results to files, Nmap still prints
2235 interactive output to stdout as usual. For example, the command nmap
2236 -oX myscan.xml target prints XML to myscan.xml and fills standard
2237 output with the same interactive results it would have printed if -oX
2238 wasn't specified at all. You can change this by passing a hyphen
2239 character as the argument to one of the format types. This causes Nmap
2240 to deactivate interactive output, and instead print results in the
2241 format you specified to the standard output stream. So the command nmap
2242 -oX - target will send only XML output to stdout.. Serious errors may
2243 still be printed to the normal error stream, stderr..
2244 Unlike some Nmap arguments, the space between the logfile option flag
2246 (such as -oX) and the filename or hyphen is mandatory. If you omit the
2247 flags and give arguments such as -oG- or -oXscan.xml, a backwards
2248 compatibility feature of Nmap will cause the creation of normal format
2249 output files named G- and Xscan.xml respectively.
2250 All of these arguments support strftime-like. conversions in the
2252 filename. %H, %M, %S, %m, %d, %y, and %Y are all exactly the same as
2253 in strftime. %T is the same as %H%M%S, %R is the same as %H%M, and %D
2254 is the same as %m%d%y. A % followed by any other character just yields
2255 that character (%% gives you a percent symbol). So -oX 'scan-%T-%D.xml'
2256 will use an XML file with a name in the form of scan-144840-121307.xml.
2257 Nmap also offers options to control scan verbosity and to append to
2259 output files rather than clobbering them. All of these options are
2260 described below.
2261 Nmap Output Formats
2263 -oN filespec (normal output) .
2265 Requests that normal output be directed to the given filename. As
2266 discussed above, this differs slightly from interactive output.
2267 -oX filespec (XML output) .
2269 Requests that XML output be directed to the given filename. Nmap
2270 includes a document type definition (DTD) which allows XML parsers
2271 to validate Nmap XML output. While it is primarily intended for
2272 programmatic use, it can also help humans interpret Nmap XML
2273 output. The DTD defines the legal elements of the format, and often
2274 enumerates the attributes and values they can take on. The latest
2275 version is always available from
2276 https://svn.nmap.org/nmap/docs/nmap.dtd.
2277 XML offers a stable format that is easily parsed by software. Free
2279 XML parsers are available for all major computer languages,
2280 including C/C++, Perl, Python, and Java. People have even written
2281 bindings for most of these languages to handle Nmap output and
2282 execution specifically. Examples are Nmap::Scanner[15]. and
2283 Nmap::Parser[16]. in Perl CPAN. In almost all cases that a
2284 non-trivial application interfaces with Nmap, XML is the preferred
2285 format.
2286 The XML output references an XSL stylesheet which can be used to
2288 format the results as HTML. The easiest way to use this is simply
2289 to load the XML output in a web browser such as Firefox or IE. By
2290 default, this will only work on the machine you ran Nmap on (or a
2291 similarly configured one) due to the hard-coded nmap.xsl filesystem
2292 path. Use the --webxml or --stylesheet options to create portable
2293 XML files that render as HTML on any web-connected machine.
2294 -oS filespec (ScRipT KIdd|3 oUTpuT) .
2296 Script kiddie output is like interactive output, except that it is
2297 post-processed to better suit the l33t HaXXorZ who previously
2298 looked down on Nmap due to its consistent capitalization and
2299 spelling. Humor impaired people should note that this option is
2300 making fun of the script kiddies before flaming me for supposedly
2301 “helping them”.
2302 -oG filespec (grepable output) .
2304 This output format is covered last because it is deprecated. The
2305 XML output format is far more powerful, and is nearly as convenient
2306 for experienced users. XML is a standard for which dozens of
2307 excellent parsers are available, while grepable output is my own
2308 simple hack. XML is extensible to support new Nmap features as they
2309 are released, while I often must omit those features from grepable
2310 output for lack of a place to put them.
2311 Nevertheless, grepable output is still quite popular. It is a
2313 simple format that lists each host on one line and can be trivially
2314 searched and parsed with standard Unix tools such as grep, awk,
2315 cut, sed, diff, and Perl. Even I usually use it for one-off tests
2316 done at the command line. Finding all the hosts with the SSH port
2317 open or that are running Solaris takes only a simple grep to
2318 identify the hosts, piped to an awk or cut command to print the
2319 desired fields.
2320 Grepable output consists of comments (lines starting with a pound
2322 (#)). and target lines. A target line includes a combination of
2323 six labeled fields, separated by tabs and followed with a colon.
2324 The fields are Host, Ports, Protocols, Ignored State, OS, Seq
2325 Index, IP ID, and Status.
2326 The most important of these fields is generally Ports, which gives
2328 details on each interesting port. It is a comma separated list of
2329 port entries. Each port entry represents one interesting port, and
2330 takes the form of seven slash (/) separated subfields. Those
2331 subfields are: Port number, State, Protocol, Owner, Service, SunRPC
2332 info, and Version info.
2333 As with XML output, this man page does not allow for documenting
2335 the entire format. A more detailed look at the Nmap grepable output
2336 format is available from
2337 http://nmap.org/book/output-formats-grepable-output.html.
2338 -oA basename (Output to all formats) .
2340 As a convenience, you may specify -oA basename to store scan
2341 results in normal, XML, and grepable formats at once. They are
2342 stored in basename.nmap, basename.xml, and basename.gnmap,
2343 respectively. As with most programs, you can prefix the filenames
2344 with a directory path, such as ~/nmaplogs/foocorp/ on Unix or
2345 c:\hacking\sco on Windows.
2346 Verbosity and debugging options
2348 -v (Increase verbosity level) .
2350 Increases the verbosity level, causing Nmap to print more
2351 information about the scan in progress. Open ports are shown as
2352 they are found and completion time estimates are provided when Nmap
2353 thinks a scan will take more than a few minutes. Use it twice or
2354 more for even greater verbosity: -vv, or give a verbosity level
2355 directly, for example -v3..
2356 Most changes only affect interactive output, and some also affect
2358 normal and script kiddie output. The other output types are meant
2359 to be processed by machines, so Nmap can give substantial detail by
2360 default in those formats without fatiguing a human user. However,
2361 there are a few changes in other modes where output size can be
2362 reduced substantially by omitting some detail. For example, a
2363 comment line in the grepable output that provides a list of all
2364 ports scanned is only printed in verbose mode because it can be
2365 quite long.
2366 -d (Increase debugging level) .
2368 When even verbose mode doesn't provide sufficient data for you,
2369 debugging is available to flood you with much more! As with the
2370 verbosity option (-v), debugging is enabled with a command-line
2371 flag (-d) and the debug level can be increased by specifying it
2372 multiple times,. as in -dd, or by setting a level directly. For
2373 example, -d9 sets level nine. That is the highest effective level
2374 and will produce thousands of lines unless you run a very simple
2375 scan with very few ports and targets.
2376 Debugging output is useful when a bug is suspected in Nmap, or if
2378 you are simply confused as to what Nmap is doing and why. As this
2379 feature is mostly intended for developers, debug lines aren't
2380 always self-explanatory. You may get something like: Timeout vals:
2381 srtt: -1 rttvar: -1 to: 1000000 delta 14987 ==> srtt: 14987 rttvar:
2382 14987 to: 100000. If you don't understand a line, your only
2383 recourses are to ignore it, look it up in the source code, or
2384 request help from the development list (nmap-dev).. Some lines are
2385 self explanatory, but the messages become more obscure as the debug
2386 level is increased.
2387 --reason (Host and port state reasons) .
2389 Shows the reason each port is set to a specific state and the
2390 reason each host is up or down. This option displays the type of
2391 the packet that determined a port or hosts state. For example, A
2392 RST packet from a closed port or an echo reply from an alive host.
2393 The information Nmap can provide is determined by the type of scan
2394 or ping. The SYN scan and SYN ping (-sS and -PS) are very detailed,
2395 but the TCP connect scan (-sT) is limited by the implementation of
2396 the connect system call. This feature is automatically enabled by
2397 the debug option (-d). and the results are stored in XML log files
2398 even if this option is not specified.
2399 --stats-every time (Print periodic timing stats) .
2401 Periodically prints a timing status message after each interval of
2402 time. The time is a specification of the kind described in the
2403 section called “TIMING AND PERFORMANCE”; so for example, use
2404 --stats-every 10s to get a status update every 10 seconds. Updates
2405 are printed to interactive output (the screen) and XML output.
2406 --packet-trace (Trace packets and data sent and received) .
2408 Causes Nmap to print a summary of every packet sent or received.
2409 This is often used for debugging, but is also a valuable way for
2410 new users to understand exactly what Nmap is doing under the
2411 covers. To avoid printing thousands of lines, you may want to
2412 specify a limited number of ports to scan, such as -p20-30. If you
2413 only care about the goings on of the version detection subsystem,
2414 use --version-trace instead. If you only care about script tracing,
2415 specify --script-trace. With --packet-trace, you get all of the
2416 above.
2417 --open (Show only open (or possibly open) ports) .
2419 Sometimes you only care about ports you can actually connect to
2420 (open ones), and don't want results cluttered with closed,
2421 filtered, and closed|filtered ports. Output customization is
2422 normally done after the scan using tools such as grep, awk, and
2423 Perl, but this feature was added due to overwhelming requests.
2424 Specify --open to only see hosts with at least one open,
2425 open|filtered, or unfiltered port, and only see ports in those
2426 states. These three states are treated just as they normally are,
2427 which means that open|filtered and unfiltered may be condensed into
2428 counts if there are an overwhelming number of them.
2429 --iflist (List interfaces and routes) .
2431 Prints the interface list and system routes as detected by Nmap.
2432 This is useful for debugging routing problems or device
2433 mischaracterization (such as Nmap treating a PPP connection as
2434 ethernet).
2435 Miscellaneous output options
2437 --append-output (Append to rather than clobber output files) .
2439 When you specify a filename to an output format flag such as -oX or
2440 -oN, that file is overwritten by default. If you prefer to keep the
2441 existing content of the file and append the new results, specify
2442 the --append-output option. All output filenames specified in that
2443 Nmap execution will then be appended to rather than clobbered. This
2444 doesn't work well for XML (-oX) scan data as the resultant file
2445 generally won't parse properly until you fix it up by hand.
2446 --resume filename (Resume aborted scan) .
2448 Some extensive Nmap runs take a very long time—on the order of
2449 days. Such scans don't always run to completion. Restrictions may
2450 prevent Nmap from being run during working hours, the network could
2451 go down, the machine Nmap is running on might suffer a planned or
2452 unplanned reboot, or Nmap itself could crash. The administrator
2453 running Nmap could cancel it for any other reason as well, by
2454 pressing ctrl-C. Restarting the whole scan from the beginning may
2455 be undesirable. Fortunately, if normal (-oN) or grepable (-oG) logs
2456 were kept, the user can ask Nmap to resume scanning with the target
2457 it was working on when execution ceased. Simply specify the
2458 --resume option and pass the normal/grepable output file as its
2459 argument. No other arguments are permitted, as Nmap parses the
2460 output file to use the same ones specified previously. Simply call
2461 Nmap as nmap --resume logfilename. Nmap will append new results to
2462 the data files specified in the previous execution. Resumption does
2463 not support the XML output format because combining the two runs
2464 into one valid XML file would be difficult.
2465 --stylesheet path or URL (Set XSL stylesheet to transform XML output) .
2467 Nmap ships with an XSL. stylesheet. named nmap.xsl. for viewing
2468 or translating XML output to HTML.. The XML output includes an
2469 xml-stylesheet directive which points to nmap.xml where it was
2470 initially installed by Nmap. Run the XML file through an XSLT
2471 processor such as xsltproc[17]. to produce an HTML file. Directly
2472 opening the XML file in a browser no longer works well because
2473 modern browsers limit the locations a stylesheet may be loaded
2474 from. If you wish to use a different stylesheet, specify it as the
2475 argument to --stylesheet. You must pass the full pathname or URL.
2476 One common invocation is --stylesheet
2477 http://nmap.org/svn/docs/nmap.xsl. This tells an XSLT processor to
2478 load the latest version of the stylesheet from Nmap.Org. The
2479 --webxml option does the same thing with less typing and
2480 memorization. Loading the XSL from Nmap.Org makes it easier to view
2481 results on a machine that doesn't have Nmap (and thus nmap.xsl)
2482 installed. So the URL is often more useful, but the local
2483 filesystem location of nmap.xsl is used by default for privacy
2484 reasons.
2485 --webxml (Load stylesheet from Nmap.Org) .
2487 This is a convenience option, nothing more than an alias for
2488 --stylesheet http://nmap.org/svn/docs/nmap.xsl.
2489 --no-stylesheet (Omit XSL stylesheet declaration from XML) .
2491 Specify this option to prevent Nmap from associating any XSL
2492 stylesheet with its XML output. The xml-stylesheet directive is
2493 omitted.
2494
2496 This section describes some important (and not-so-important) options
2497 that don't really fit anywhere else.
2498 -6 (Enable IPv6 scanning) .
2500 Nmap has IPv6 support for its most popular features. Ping scanning,
2501 port scanning, version detection, and the Nmap Scripting Engine all
2502 support IPv6. The command syntax is the same as usual except that
2503 you also add the -6 option. Of course, you must use IPv6 syntax if
2504 you specify an address rather than a hostname. An address might
2505 look like 3ffe:7501:4819:2000:210:f3ff:fe03:14d0, so hostnames are
2506 recommended. The output looks the same as usual, with the IPv6
2507 address on the “interesting ports” line being the only IPv6
2508 giveaway.
2509 While IPv6 hasn't exactly taken the world by storm, it gets
2511 significant use in some (usually Asian) countries and most modern
2512 operating systems support it. To use Nmap with IPv6, both the
2513 source and target of your scan must be configured for IPv6. If your
2514 ISP (like most of them) does not allocate IPv6 addresses to you,
2515 free tunnel brokers are widely available and work fine with Nmap. I
2516 use the free IPv6 tunnel broker. service at
2517 http://www.tunnelbroker.net. Other tunnel brokers are listed at
2518 Wikipedia[18]. 6to4 tunnels are another popular, free approach.
2519 On Windows, raw-socket IPv6 scans are supported only on ethernet
2521 devices (not tunnels), and only on Windows Vista. and later. Use
2522 the --unprivileged. option in other situations.
2523 -A (Aggressive scan options) .
2525 This option enables additional advanced and aggressive options. I
2526 haven't decided exactly which it stands for yet. Presently this
2527 enables OS detection (-O), version scanning (-sV), script scanning
2528 (-sC) and traceroute (--traceroute).. More features may be added
2529 in the future. The point is to enable a comprehensive set of scan
2530 options without people having to remember a large set of flags.
2531 However, because script scanning with the default set is considered
2532 intrusive, you should not use -A against target networks without
2533 permission. This option only enables features, and not timing
2534 options (such as -T4) or verbosity options (-v) that you might want
2535 as well.
2536 --datadir directoryname (Specify custom Nmap data file location) .
2538 Nmap obtains some special data at runtime in files named
2539 nmap-service-probes, nmap-services, nmap-protocols, nmap-rpc,
2540 nmap-mac-prefixes, and nmap-os-db. If the location of any of these
2541 files has been specified (using the --servicedb or --versiondb
2542 options), that location is used for that file. After that, Nmap
2543 searches these files in the directory specified with the --datadir
2544 option (if any). Any files not found there, are searched for in the
2545 directory specified by the NMAPDIR. environment variable. Next
2546 comes ~/.nmap. for real and effective UIDs; or on Windows,
2547 HOME\AppData\Roaming\nmap (where HOME is the user's home directory,
2548 like C:\Users\user). This is followed by the location of the nmap
2549 executable and the same location with ../share/nmap appended. Then
2550 a compiled-in location such as /usr/local/share/nmap or
2551 /usr/share/nmap.
2552 --servicedb services file (Specify custom services file) .
2554 Asks Nmap to use the specified services file rather than the
2555 nmap-services data file that comes with Nmap. Using this option
2556 also causes a fast scan (-F) to be used. See the description for
2557 --datadir for more information on Nmap's data files.
2558 --versiondb service probes file (Specify custom service probes file) .
2560 Asks Nmap to use the specified service probes file rather than the
2561 nmap-service-probes data file that comes with Nmap. See the
2562 description for --datadir for more information on Nmap's data
2563 files.
2564 --send-eth (Use raw ethernet sending) .
2566 Asks Nmap to send packets at the raw ethernet (data link) layer
2567 rather than the higher IP (network) layer. By default, Nmap chooses
2568 the one which is generally best for the platform it is running on.
2569 Raw sockets (IP layer). are generally most efficient for Unix
2570 machines, while ethernet frames are required for Windows operation
2571 since Microsoft disabled raw socket support. Nmap still uses raw IP
2572 packets on Unix despite this option when there is no other choice
2573 (such as non-ethernet connections).
2574 --send-ip (Send at raw IP level) .
2576 Asks Nmap to send packets via raw IP sockets rather than sending
2577 lower level ethernet frames. It is the complement to the --send-eth
2578 option discussed previously.
2579 --privileged (Assume that the user is fully privileged) .
2581 Tells Nmap to simply assume that it is privileged enough to perform
2582 raw socket sends, packet sniffing, and similar operations that
2583 usually require root privileges. on Unix systems. By default Nmap
2584 quits if such operations are requested but geteuid is not zero.
2585 --privileged is useful with Linux kernel capabilities and similar
2586 systems that may be configured to allow unprivileged users to
2587 perform raw-packet scans. Be sure to provide this option flag
2588 before any flags for options that require privileges (SYN scan, OS
2589 detection, etc.). The NMAP_PRIVILEGED. environment variable may be
2590 set as an equivalent alternative to --privileged.
2591 --unprivileged (Assume that the user lacks raw socket privileges) .
2593 This option is the opposite of --privileged. It tells Nmap to treat
2594 the user as lacking network raw socket and sniffing privileges.
2595 This is useful for testing, debugging, or when the raw network
2596 functionality of your operating system is somehow broken. The
2597 NMAP_UNPRIVILEGED. environment variable may be set as an
2598 equivalent alternative to --unprivileged.
2599 --release-memory (Release memory before quitting) .
2601 This option is only useful for memory-leak debugging. It causes
2602 Nmap to release allocated memory just before it quits so that
2603 actual memory leaks are easier to spot. Normally Nmap skips this as
2604 the OS does this anyway upon process termination.
2605 -V; --version (Print version number) .
2607 Prints the Nmap version number and exits.
2608 -h; --help (Print help summary page) .
2610 Prints a short help screen with the most common command flags.
2611 Running Nmap without any arguments does the same thing.
2612
2614 During the execution of Nmap, all key presses are captured. This allows
2615 you to interact with the program without aborting and restarting it.
2616 Certain special keys will change options, while any other keys will
2617 print out a status message telling you about the scan. The convention
2618 is that lowercase letters increase the amount of printing, and
2619 uppercase letters decrease the printing. You may also press ‘?’ for
2620 help.
2621 v / V
2623 Increase / decrease the verbosity level
2624 d / D
2626 Increase / decrease the debugging Level
2627 p / P
2629 Turn on / off packet tracing
2630 ?
2632 Print a runtime interaction help screen
2633 Anything else
2635 Print out a status message like this:
2636 Stats: 0:00:07 elapsed; 20 hosts completed (1 up), 1 undergoing Service Scan
2638 Service scan Timing: About 33.33% done; ETC: 20:57 (0:00:12 remaining)
2639
2641 Here are some Nmap usage examples, from the simple and routine to a
2642 little more complex and esoteric. Some actual IP addresses and domain
2643 names are used to make things more concrete. In their place you should
2644 substitute addresses/names from your own network. While I don't think
2645 port scanning other networks is or should be illegal, some network
2646 administrators don't appreciate unsolicited scanning of their networks
2647 and may complain. Getting permission first is the best approach.
2648 For testing purposes, you have permission to scan the host
2650 scanme.nmap.org.. This permission only includes scanning via Nmap and
2651 not testing exploits or denial of service attacks. To conserve
2652 bandwidth, please do not initiate more than a dozen scans against that
2653 host per day. If this free scanning target service is abused, it will
2654 be taken down and Nmap will report Failed to resolve given hostname/IP:
2655 scanme.nmap.org. These permissions also apply to the hosts
2656 scanme2.nmap.org, scanme3.nmap.org, and so on, though those hosts do
2657 not currently exist.
2658 This option scans all reserved TCP ports on the machine scanme.nmap.org
2660 . The -v option enables verbose mode.
2661 Launches a stealth SYN scan against each machine that is up out of the
2663 256 IPs on the class C sized network where Scanme resides. It also
2664 tries to determine what operating system is running on each host that
2665 is up and running. This requires root privileges because of the SYN
2666 scan and OS detection.
2667 Launches host enumeration and a TCP scan at the first half of each of
2669 the 255 possible eight-bit subnets in the 198.116 class B address
2670 space. This tests whether the systems run SSH, DNS, POP3, or IMAP on
2671 their standard ports, or anything on port 4564. For any of these ports
2672 found open, version detection is used to determine what application is
2673 running.
2674 Asks Nmap to choose 100,000 hosts at random and scan them for web
2676 servers (port 80). Host enumeration is disabled with -Pn since first
2677 sending a couple probes to determine whether a host is up is wasteful
2678 when you are only probing one port on each target host anyway.
2679 This scans 4096 IPs for any web servers (without pinging them) and
2681 saves the output in grepable and XML formats.
2682
2684 While this reference guide details all material Nmap options, it can't
2685 fully demonstrate how to apply those features to quickly solve
2686 real-world tasks. For that, we released Nmap Network Scanning: The
2687 Official Nmap Project Guide to Network Discovery and Security Scanning.
2688 Topics include subverting firewalls and intrusion detection systems,
2689 optimizing Nmap performance, and automating common networking tasks
2690 with the Nmap Scripting Engine. Hints and instructions are provided for
2691 common Nmap tasks such as taking network inventory, penetration
2692 testing, detecting rogue wireless access points, and quashing network
2693 worm outbreaks. Examples and diagrams show actual communication on the
2694 wire. More than half of the book is available free online. See
2695 http://nmap.org/book for more information.
2696
2698 Like its author, Nmap isn't perfect. But you can help make it better by
2699 sending bug reports or even writing patches. If Nmap doesn't behave the
2700 way you expect, first upgrade to the latest version available from
2701 http://nmap.org. If the problem persists, do some research to determine
2702 whether it has already been discovered and addressed. Try searching for
2703 the error message on our search page at http://insecure.org/search.html
2704 or at Google. Also try browsing the nmap-dev archives at
2705 http://seclists.org/.. Read this full manual page as well. If nothing
2706 comes of this, mail a bug report to <dev@nmap.org>. Please include
2707 everything you have learned about the problem, as well as what version
2708 of Nmap you are running and what operating system version it is running
2709 on. Problem reports and Nmap usage questions sent to <dev@nmap.org> are
2710 far more likely to be answered than those sent to Fyodor directly. If
2711 you subscribe to the nmap-dev list before posting, your message will
2712 bypass moderation and get through more quickly. Subscribe at
2713 http://nmap.org/mailman/listinfo/dev.
2714 Code patches to fix bugs are even better than bug reports. Basic
2716 instructions for creating patch files with your changes are available
2717 at https://svn.nmap.org/nmap/HACKING. Patches may be sent to nmap-dev
2718 (recommended) or to Fyodor directly.
2719
2721 Gordon “Fyodor” Lyon <fyodor@nmap.org> (http://insecure.org)
2722 Hundreds of people have made valuable contributions to Nmap over the
2724 years. These are detailed in the CHANGELOG. file which is distributed
2725 with Nmap and also available from http://nmap.org/changelog.html.
2726
2728 Nmap Copyright and Licensing
2729 The Nmap Security Scanner is (C) 1996–2012 Insecure.Com LLC. Nmap is
2730 also a registered trademark of Insecure.Com LLC. This program is free
2731 software; you may redistribute and/or modify it under the terms of the
2732 GNU General Public License as published by the Free Software
2733 Foundation; Version 2 with the clarifications and exceptions described
2734 below. This guarantees your right to use, modify, and redistribute this
2735 software under certain conditions. If you wish to embed Nmap technology
2736 into proprietary software, we sell alternative licenses (contact
2737 <sales@insecure.com>). Dozens of software vendors already license Nmap
2738 technology such as host discovery, port scanning, OS detection, and
2739 version detection.
2740 Note that the GPL places important restrictions on “derived works”, yet
2742 it does not provide a detailed definition of that term. To avoid
2743 misunderstandings, we consider an application to constitute a
2744 “derivative work” for the purpose of this license if it does any of the
2745 following:
2746 · Integrates source code from Nmap
2748 · Reads or includes Nmap copyrighted data files, such as nmap-os-db
2750 or nmap-service-probes.
2751 · Executes Nmap and parses the results (as opposed to typical shell
2753 or execution-menu apps, which simply display raw Nmap output and so
2754 are not derivative works.)
2755 · Integrates/includes/aggregates Nmap into a proprietary executable
2757 installer, such as those produced by InstallShield.
2758 · Links to a library or executes a program that does any of the
2760 above.
2761 The term “Nmap” should be taken to also include any portions or derived
2763 works of Nmap. This list is not exclusive, but is meant to clarify our
2764 interpretation of derived works with some common examples. Our
2765 interpretation applies only to Nmap—we don't speak for other people's
2766 GPL works.
2767 If you have any questions about the GPL licensing restrictions on using
2769 Nmap in non-GPL works, we would be happy to help. As mentioned above,
2770 we also offer alternative license to integrate Nmap into proprietary
2771 applications and appliances. These contracts have been sold to many
2772 security vendors, and generally include a perpetual license as well as
2773 providing for priority support and updates as well as helping to fund
2774 the continued development of Nmap technology. Please email
2775 <sales@insecure.com> for further information.
2776 As a special exception to the GPL terms, Insecure.Com LLC grants
2778 permission to link the code of this program with any version of the
2779 OpenSSL library which is distributed under a license identical to that
2780 listed in the included COPYING.OpenSSL file, and distribute linked
2781 combinations including the two.. You must obey the GNU GPL in all
2782 respects for all of the code used other than OpenSSL. If you modify
2783 this file, you may extend this exception to your version of the file,
2784 but you are not obligated to do so.
2785 If you received these files with a written license agreement or
2787 contract stating terms other than the terms above, then that
2788 alternative license agreement takes precedence over these comments.
2789 Creative Commons License for this Nmap Guide
2791 This Nmap Reference Guide is (C) 2005–2012 Insecure.Com LLC. It is
2792 hereby placed under version 3.0 of the Creative Commons Attribution
2793 License[19]. This allows you redistribute and modify the work as you
2794 desire, as long as you credit the original source. Alternatively, you
2795 may choose to treat this document as falling under the same license as
2796 Nmap itself (discussed previously).
2797 Source Code Availability and Community Contributions
2799 Source is provided to this software because we believe users have a
2800 right to know exactly what a program is going to do before they run it.
2801 This also allows you to audit the software for security holes (none
2802 have been found so far).
2803 Source code also allows you to port Nmap to new platforms, fix bugs,
2805 and add new features. You are highly encouraged to send your changes to
2806 <dev@nmap.org> for possible incorporation into the main distribution.
2807 By sending these changes to Fyodor or one of the Insecure.Org
2808 development mailing lists, it is assumed that you are offering the Nmap
2809 Project (Insecure.Com LLC) the unlimited, non-exclusive right to reuse,
2810 modify, and relicense the code. Nmap will always be available open
2811 source,. but this is important because the inability to relicense code
2812 has caused devastating problems for other Free Software projects (such
2813 as KDE and NASM). We also occasionally relicense the code to third
2814 parties as discussed above. If you wish to specify special license
2815 conditions of your contributions, just say so when you send them.
2816 No Warranty.
2818 This program is distributed in the hope that it will be useful, but
2819 WITHOUT ANY WARRANTY; without even the implied warranty of
2820 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
2821 General Public License v2.0 for more details at
2822 http://www.gnu.org/licenses/gpl-2.0.html, or in the COPYING file
2823 included with Nmap.
2824 It should also be noted that Nmap has occasionally been known to crash
2826 poorly written applications, TCP/IP stacks, and even operating
2827 systems.. While this is extremely rare, it is important to keep in
2828 mind. Nmap should never be run against mission critical systems unless
2829 you are prepared to suffer downtime. We acknowledge here that Nmap may
2830 crash your systems or networks and we disclaim all liability for any
2831 damage or problems Nmap could cause.
2832 Inappropriate Usage
2834 Because of the slight risk of crashes and because a few black hats like
2835 to use Nmap for reconnaissance prior to attacking systems, there are
2836 administrators who become upset and may complain when their system is
2837 scanned. Thus, it is often advisable to request permission before doing
2838 even a light scan of a network.
2839 Nmap should never be installed with special privileges (e.g. suid
2841 root).. That would open up a major security vulnerability as other
2842 users on the system (or attackers) could use it for privilege
2843 escalation.
2844 Third-Party Software and Funding Notices
2846 This product includes software developed by the Apache Software
2847 Foundation[20]. A modified version of the Libpcap portable packet
2848 capture library[21]. is distributed along with Nmap. The Windows
2849 version of Nmap utilized the Libpcap-derived WinPcap library[22].
2850 instead. Regular expression support is provided by the PCRE
2851 library[23],. which is open-source software, written by Philip Hazel..
2852 Certain raw networking functions use the Libdnet[24]. networking
2853 library, which was written by Dug Song.. A modified version is
2854 distributed with Nma.p Nmap can optionally link with the OpenSSL
2855 cryptography toolkit[25]. for SSL version detection support. The Nmap
2856 Scripting Engine uses an embedded version of the Lua programming
2857 language[26].. The Liblinear linear classification library[27] is used
2858 for our IPv6 OS detection machine learning techniques[28]. All of the
2859 third-party software described in this paragraph is freely
2860 redistributable under BSD-style software licenses.
2861 Binary packages for Windows and Mac OS X include support libraries
2863 necessary to run Zenmap and Ndiff with Python and PyGTK. (Unix
2864 platforms commonly make these libraries easy to install, so they are
2865 not part of the packages.) A listing of these support libraries and
2866 their licenses is included in the LICENSES files.
2867 This software was supported in part through the Google Summer of
2869 Code[29] and the DARPA CINDER program[30] (DARPA-BAA-10-84).
2870 United States Export Control.
2872 Nmap only uses encryption when compiled with the optional OpenSSL
2873 support and linked with OpenSSL. When compiled without OpenSSL support,
2874 Insecure.Com LLC believes that Nmap is not subject to U.S. Export
2875 Administration Regulations (EAR)[31] export control. As such, there is
2876 no applicable ECCN (export control classification number) and
2877 exportation does not require any special license, permit, or other
2878 governmental authorization.
2879 When compiled with OpenSSL support or distributed as source code,
2881 Insecure.Com LLC believes that Nmap falls under U.S. ECCN 5D002[32]
2882 (“Information Security Software”). We distribute Nmap under the TSU
2883 exception for publicly available encryption software defined in EAR
2884 740.13(e)[33].
2885
2887 1. Nmap Network Scanning: The Official Nmap Project Guide to Network
2888 Discovery and Security Scanning
2889 http://nmap.org/book/
2890 2. RFC 1122
2892 http://www.rfc-editor.org/rfc/rfc1122.txt
2893 3. RFC 792
2895 http://www.rfc-editor.org/rfc/rfc792.txt
2896 4. RFC 950
2898 http://www.rfc-editor.org/rfc/rfc950.txt
2899 5. RFC 1918
2901 http://www.rfc-editor.org/rfc/rfc1918.txt
2902 6. UDP
2904 http://www.rfc-editor.org/rfc/rfc768.txt
2905 7. SCTP
2907 http://www.rfc-editor.org/rfc/rfc4960.txt
2908 8. TCP RFC
2910 http://www.rfc-editor.org/rfc/rfc793.txt
2911 9. RFC 959
2913 http://www.rfc-editor.org/rfc/rfc959.txt
2914 10. RFC 1323
2916 http://www.rfc-editor.org/rfc/rfc1323.txt
2917 11. Lua programming language
2919 http://lua.org
2920 12. precedence
2922 http://www.lua.org/manual/5.1/manual.html#2.5.3
2923 13. IP protocol
2925 http://www.rfc-editor.org/rfc/rfc791.txt
2926 14. RFC 2960
2928 http://www.rfc-editor.org/rfc/rfc2960.txt
2929 15. Nmap::Scanner
2931 http://sourceforge.net/projects/nmap-scanner/
2932 16. Nmap::Parser
2934 http://nmapparser.wordpress.com/
2935 17. xsltproc
2937 http://xmlsoft.org/XSLT/
2938 18. listed at Wikipedia
2940 http://en.wikipedia.org/wiki/List_of_IPv6_tunnel_brokers
2941 19. Creative Commons Attribution License
2943 http://creativecommons.org/licenses/by/3.0/
2944 20. Apache Software Foundation
2946 http://www.apache.org
2947 21. Libpcap portable packet capture library
2949 http://www.tcpdump.org
2950 22. WinPcap library
2952 http://www.winpcap.org
2953 23. PCRE library
2955 http://www.pcre.org
2956 24. Libdnet
2958 http://libdnet.sourceforge.net
2959 25. OpenSSL cryptography toolkit
2961 http://www.openssl.org
2962 26. Lua programming language
2964 http://www.lua.org
2965 27. Liblinear linear classification library
2967 http://www.csie.ntu.edu.tw/~cjlin/liblinear/
2968 28. IPv6 OS detection machine learning techniques
2970 http://nmap.org/book/osdetect-guess.html#osdetect-guess-ipv6
2971 29. Google Summer of Code
2973 http://nmap.org/soc/
2974 30. DARPA CINDER program
2976 https://www.fbo.gov/index?s=opportunity&mode=form&id=585e02a51f77af5cb3c9e06b9cc82c48&tab=core&_cview=1
2977 31. Export Administration Regulations (EAR)
2979 http://www.access.gpo.gov/bis/ear/ear_data.html
2980 32. 5D002
2982 http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf
2983 33. EAR 740.13(e)
2985 http://www.access.gpo.gov/bis/ear/pdf/740.pdf
2986Nmap 07/28/2013 NMAP(1)