NMAP 帮助手册

PORT SCANNING TECHNIQUES
       As a novice performing automotive repair, I can struggle for hours trying to fit my rudimentary tools (hammer, duct tape, wrench, etc.) to the task at hand. When I fail miserably and tow my jalopy to a real mechanic, he
       invariably fishes around in a huge tool chest until pulling out the perfect gizmo which makes the job seem effortless. The art of port scanning is similar. Experts understand the dozens of scan techniques and choose the
       appropriate one (or combination) for a given task. Inexperienced users and script kiddies,.  on the other hand, try to solve every problem with the default SYN scan. Since Nmap is free, the only barrier to port scanning mastery
       is knowledge. That certainly beats the automotive world, where it may take great skill to determine that you need a strut spring compressor, then you still have to pay thousands of dollars for it.

       Most of the scan types are only available to privileged users..  This is because they send and receive raw packets,.  which requires root access on Unix systems. Using an administrator account on Windows is recommended, though
       Nmap sometimes works for unprivileged users on that platform when WinPcap has already been loaded into the OS. Requiring root privileges was a serious limitation when Nmap was released in 1997, as many users only had access to
       shared shell accounts. Now, the world is different. Computers are cheaper, far more people have always-on direct Internet access, and desktop Unix systems (including Linux and Mac OS X) are prevalent. A Windows version of Nmap
       is now available, allowing it to run on even more desktops. For all these reasons, users have less need to run Nmap from limited shared shell accounts. This is fortunate, as the privileged options make Nmap far more powerful
       and flexible.

       While Nmap attempts to produce accurate results, keep in mind that all of its insights are based on packets returned by the target machines (or firewalls in front of them). Such hosts may be untrustworthy and send responses
       intended to confuse or mislead Nmap. Much more common are non-RFC-compliant hosts that do not respond as they should to Nmap probes. FIN, NULL, and Xmas scans are particularly susceptible to this problem. Such issues are
       specific to certain scan types and so are discussed in the individual scan type entries.

       This section documents the dozen or so port scan techniques supported by Nmap. Only one method may be used at a time, except that UDP scan (-sU) and any one of the SCTP scan types (-sY, -sZ) may be combined with any one of the
       TCP scan types. As a memory aid, port scan type options are of the form -sC, where C is a prominent character in the scan name, usually the first. The one exception to this is the deprecated FTP bounce scan (-b). By default,
       Nmap performs a SYN Scan, though it substitutes a connect scan if the user does not have proper privileges to send raw packets (requires root access on Unix). Of the scans listed in this section, unprivileged users can only
       execute connect and FTP bounce scans.

       -sS (TCP SYN scan) .
           SYN scan is the default and most popular scan option for good reasons. It can be performed quickly, scanning thousands of ports per second on a fast network not hampered by restrictive firewalls. It is also relatively
           unobtrusive and stealthy since it never completes TCP connections. SYN scan works against any compliant TCP stack rather than depending on idiosyncrasies of specific platforms as Nmap's FIN/NULL/Xmas, Maimon and idle scans
           do. It also allows clear, reliable differentiation between the open, closed, and filtered states.

           This technique is often referred to as half-open scanning, because you don't open a full TCP connection. You send a SYN packet, as if you are going to open a real connection and then wait for a response. A SYN/ACK indicates
           the port is listening (open), while a RST (reset) is indicative of a non-listener. If no response is received after several retransmissions, the port is marked as filtered. The port is also marked filtered if an ICMP
           unreachable error (type 3, code 1, 2, 3, 9, 10, or 13) is received. The port is also considered open if a SYN packet (without the ACK flag) is received in response. This can be due to an extremely rare TCP feature known as
           a simultaneous open or split handshake connection (see http://nmap.org/misc/split-handshake.pdf).

       -sT (TCP connect scan) .
           TCP connect scan is the default TCP scan type when SYN scan is not an option. This is the case when a user does not have raw packet privileges. Instead of writing raw packets as most other scan types do, Nmap asks the
           underlying operating system to establish a connection with the target machine and port by issuing the connect system call. This is the same high-level system call that web browsers, P2P clients, and most other
           network-enabled applications use to establish a connection. It is part of a programming interface known as the Berkeley Sockets API. Rather than read raw packet responses off the wire, Nmap uses this API to obtain status
           information on each connection attempt.

           When SYN scan is available, it is usually a better choice. Nmap has less control over the high level connect call than with raw packets, making it less efficient. The system call completes connections to open target ports
           rather than performing the half-open reset that SYN scan does. Not only does this take longer and require more packets to obtain the same information, but target machines are more likely to log the connection. A decent IDS
           will catch either, but most machines have no such alarm system. Many services on your average Unix system will add a note to syslog, and sometimes a cryptic error message, when Nmap connects and then closes the connection
           without sending data. Truly pathetic services crash when this happens, though that is uncommon. An administrator who sees a bunch of connection attempts in her logs from a single system should know that she has been connect
           scanned.

       -sU (UDP scans) .
           While most popular services on the Internet run over the TCP protocol, UDP[6] services are widely deployed. DNS, SNMP, and DHCP (registered ports 53, 161/162, and 67/68) are three of the most common. Because UDP scanning is
           generally slower and more difficult than TCP, some security auditors ignore these ports. This is a mistake, as exploitable UDP services are quite common and attackers certainly don't ignore the whole protocol. Fortunately,
           Nmap can help inventory UDP ports.

           UDP scan is activated with the -sU option. It can be combined with a TCP scan type such as SYN scan (-sS) to check both protocols during the same run.

           UDP scan works by sending a UDP packet to every targeted port. For some common ports such as 53 and 161, a protocol-specific payload is sent, but for most ports the packet is empty..  The --data-length option can be used to
           send a fixed-length random payload to every port or (if you specify a value of 0) to disable payloads. If an ICMP port unreachable error (type 3, code 3) is returned, the port is closed. Other ICMP unreachable errors (type
           3, codes 1, 2, 9, 10, or 13) mark the port as filtered. Occasionally, a service will respond with a UDP packet, proving that it is open. If no response is received after retransmissions, the port is classified as
           open|filtered. This means that the port could be open, or perhaps packet filters are blocking the communication. Version detection (-sV) can be used to help differentiate the truly open ports from the filtered ones.

           A big challenge with UDP scanning is doing it quickly. Open and filtered ports rarely send any response, leaving Nmap to time out and then conduct retransmissions just in case the probe or response were lost. Closed ports
           are often an even bigger problem. They usually send back an ICMP port unreachable error. But unlike the RST packets sent by closed TCP ports in response to a SYN or connect scan, many hosts rate limit.  ICMP port
           unreachable messages by default. Linux and Solaris are particularly strict about this. For example, the Linux 2.4.20 kernel limits destination unreachable messages to one per second (in net/ipv4/icmp.c).

           Nmap detects rate limiting and slows down accordingly to avoid flooding the network with useless packets that the target machine will drop. Unfortunately, a Linux-style limit of one packet per second makes a 65,536-port
           scan take more than 18 hours. Ideas for speeding your UDP scans up include scanning more hosts in parallel, doing a quick scan of just the popular ports first, scanning from behind the firewall, and using --host-timeout to
           skip slow hosts.

       -sY (SCTP INIT scan) .
           SCTP[7] is a relatively new alternative to the TCP and UDP protocols, combining most characteristics of TCP and UDP, and also adding new features like multi-homing and multi-streaming. It is mostly being used for
           SS7/SIGTRAN related services but has the potential to be used for other applications as well. SCTP INIT scan is the SCTP equivalent of a TCP SYN scan. It can be performed quickly, scanning thousands of ports per second on a
           fast network not hampered by restrictive firewalls. Like SYN scan, INIT scan is relatively unobtrusive and stealthy, since it never completes SCTP associations. It also allows clear, reliable differentiation between the
           open, closed, and filtered states.

           This technique is often referred to as half-open scanning, because you don't open a full SCTP association. You send an INIT chunk, as if you are going to open a real association and then wait for a response. An INIT-ACK
           chunk indicates the port is listening (open), while an ABORT chunk is indicative of a non-listener. If no response is received after several retransmissions, the port is marked as filtered. The port is also marked filtered
           if an ICMP unreachable error (type 3, code 1, 2, 3, 9, 10, or 13) is received.

       -sN; -sF; -sX (TCP NULL, FIN, and Xmas scans) .
           These three scan types (even more are possible with the --scanflags option described in the next section) exploit a subtle loophole in the TCP RFC[8] to differentiate between open and closed ports. Page 65 of RFC 793 says
           that "if the [destination] port state is CLOSED .... an incoming segment not containing a RST causes a RST to be sent in response."  Then the next page discusses packets sent to open ports without the SYN, RST, or ACK bits
           set, stating that: "you are unlikely to get here, but if you do, drop the segment, and return."

           When scanning systems compliant with this RFC text, any packet not containing SYN, RST, or ACK bits will result in a returned RST if the port is closed and no response at all if the port is open. As long as none of those
           three bits are included, any combination of the other three (FIN, PSH, and URG) are OK. Nmap exploits this with three scan types:

           Null scan (-sN)
               Does not set any bits (TCP flag header is 0)

           FIN scan (-sF)
               Sets just the TCP FIN bit.

           Xmas scan (-sX)
               Sets the FIN, PSH, and URG flags, lighting the packet up like a Christmas tree.

           These three scan types are exactly the same in behavior except for the TCP flags set in probe packets. If a RST packet is received, the port is considered closed, while no response means it is open|filtered. The port is
           marked filtered if an ICMP unreachable error (type 3, code 1, 2, 3, 9, 10, or 13) is received.

           The key advantage to these scan types is that they can sneak through certain non-stateful firewalls and packet filtering routers. Another advantage is that these scan types are a little more stealthy than even a SYN scan.
           Don't count on this though--most modern IDS products can be configured to detect them. The big downside is that not all systems follow RFC 793 to the letter. A number of systems send RST responses to the probes regardless
           of whether the port is open or not. This causes all of the ports to be labeled closed. Major operating systems that do this are Microsoft Windows, many Cisco devices, BSDI, and IBM OS/400. This scan does work against most
           Unix-based systems though. Another downside of these scans is that they can't distinguish open ports from certain filtered ones, leaving you with the response open|filtered.

       -sA (TCP ACK scan) .
           This scan is different than the others discussed so far in that it never determines open (or even open|filtered) ports. It is used to map out firewall rulesets, determining whether they are stateful or not and which ports
           are filtered.

           The ACK scan probe packet has only the ACK flag set (unless you use --scanflags). When scanning unfiltered systems, open and closed ports will both return a RST packet. Nmap then labels them as unfiltered, meaning that they
           are reachable by the ACK packet, but whether they are open or closed is undetermined. Ports that don't respond, or send certain ICMP error messages back (type 3, code 1, 2, 3, 9, 10, or 13), are labeled filtered.

       -sW (TCP Window scan) .
           Window scan is exactly the same as ACK scan except that it exploits an implementation detail of certain systems to differentiate open ports from closed ones, rather than always printing unfiltered when a RST is returned. It
           does this by examining the TCP Window field of the RST packets returned. On some systems, open ports use a positive window size (even for RST packets) while closed ones have a zero window. So instead of always listing a
           port as unfiltered when it receives a RST back, Window scan lists the port as open or closed if the TCP Window value in that reset is positive or zero, respectively.

           This scan relies on an implementation detail of a minority of systems out on the Internet, so you can't always trust it. Systems that don't support it will usually return all ports closed. Of course, it is possible that the
           machine really has no open ports. If most scanned ports are closed but a few common port numbers (such as 22, 25, 53) are filtered, the system is most likely susceptible. Occasionally, systems will even show the exact
           opposite behavior. If your scan shows 1,000 open ports and three closed or filtered ports, then those three may very well be the truly open ones.

       -sM (TCP Maimon scan) .
           The Maimon scan is named after its discoverer, Uriel Maimon..  He described the technique in Phrack Magazine issue #49 (November 1996)..  Nmap, which included this technique, was released two issues later. This technique is
           exactly the same as NULL, FIN, and Xmas scans, except that the probe is FIN/ACK. According to RFC 793[8] (TCP), a RST packet should be generated in response to such a probe whether the port is open or closed. However, Uriel
           noticed that many BSD-derived systems simply drop the packet if the port is open.

       --scanflags (Custom TCP scan) .
           Truly advanced Nmap users need not limit themselves to the canned scan types offered. The --scanflags option allows you to design your own scan by specifying arbitrary TCP flags..  Let your creative juices flow, while
           evading intrusion detection systems.  whose vendors simply paged through the Nmap man page adding specific rules!

           The --scanflags argument can be a numerical flag value such as 9 (PSH and FIN), but using symbolic names is easier. Just mash together any combination of URG, ACK, PSH, RST, SYN, and FIN. For example, --scanflags
           URGACKPSHRSTSYNFIN sets everything, though it's not very useful for scanning. The order these are specified in is irrelevant.

           In addition to specifying the desired flags, you can specify a TCP scan type (such as -sA or -sF). That base type tells Nmap how to interpret responses. For example, a SYN scan considers no-response to indicate a filtered
           port, while a FIN scan treats the same as open|filtered. Nmap will behave the same way it does for the base scan type, except that it will use the TCP flags you specify instead. If you don't specify a base type, SYN scan is
           used.

       -sZ (SCTP COOKIE ECHO scan) .
           SCTP COOKIE ECHO scan is a more advanced SCTP scan. It takes advantage of the fact that SCTP implementations should silently drop packets containing COOKIE ECHO chunks on open ports, but send an ABORT if the port is closed.
           The advantage of this scan type is that it is not as obvious a port scan than an INIT scan. Also, there may be non-stateful firewall rulesets blocking INIT chunks, but not COOKIE ECHO chunks. Don't be fooled into thinking
           that this will make a port scan invisible; a good IDS will be able to detect SCTP COOKIE ECHO scans too. The downside is that SCTP COOKIE ECHO scans cannot differentiate between open and filtered ports, leaving you with the
           state open|filtered in both cases.

       -sI zombie host[:probeport] (idle scan) .
           This advanced scan method allows for a truly blind TCP port scan of the target (meaning no packets are sent to the target from your real IP address). Instead, a unique side-channel attack exploits predictable IP
           fragmentation ID sequence generation on the zombie host to glean information about the open ports on the target. IDS systems will display the scan as coming from the zombie machine you specify (which must be up and meet
           certain criteria).  This fascinating scan type is too complex to fully describe in this reference guide, so I wrote and posted an informal paper with full details at http://nmap.org/book/idlescan.html.

           Besides being extraordinarily stealthy (due to its blind nature), this scan type permits mapping out IP-based trust relationships between machines. The port listing shows open ports from the perspective of the zombie host.
           So you can try scanning a target using various zombies that you think might be trusted.  (via router/packet filter rules).

           You can add a colon followed by a port number to the zombie host if you wish to probe a particular port on the zombie for IP ID changes. Otherwise Nmap will use the port it uses by default for TCP pings (80).

       -sO (IP protocol scan) .
           IP protocol scan allows you to determine which IP protocols (TCP, ICMP, IGMP, etc.) are supported by target machines. This isn't technically a port scan, since it cycles through IP protocol numbers rather than TCP or UDP
           port numbers. Yet it still uses the -p option to select scanned protocol numbers, reports its results within the normal port table format, and even uses the same underlying scan engine as the true port scanning methods. So
           it is close enough to a port scan that it belongs here.

           Besides being useful in its own right, protocol scan demonstrates the power of open-source software. While the fundamental idea is pretty simple, I had not thought to add it nor received any requests for such functionality.
           Then in the summer of 2000, Gerhard Rieger.  conceived the idea, wrote an excellent patch implementing it, and sent it to the announce mailing list.  (then called nmap-hackers)..  I incorporated that patch into the Nmap
           tree and released a new version the next day. Few pieces of commercial software have users enthusiastic enough to design and contribute their own improvements!

           Protocol scan works in a similar fashion to UDP scan. Instead of iterating through the port number field of a UDP packet, it sends IP packet headers and iterates through the eight-bit IP protocol field. The headers are
           usually empty, containing no data and not even the proper header for the claimed protocol. The exceptions are TCP, UDP, ICMP, SCTP, and IGMP. A proper protocol header for those is included since some systems won't send them
           otherwise and because Nmap already has functions to create them. Instead of watching for ICMP port unreachable messages, protocol scan is on the lookout for ICMP protocol unreachable messages. If Nmap receives any response
           in any protocol from the target host, Nmap marks that protocol as open. An ICMP protocol unreachable error (type 3, code 2) causes the protocol to be marked as closed Other ICMP unreachable errors (type 3, code 1, 3, 9, 10,
           or 13) cause the protocol to be marked filtered (though they prove that ICMP is open at the same time). If no response is received after retransmissions, the protocol is marked open|filtered

       -b FTP relay host (FTP bounce scan) .
           An interesting feature of the FTP protocol (RFC 959[9]) is support for so-called proxy FTP connections. This allows a user to connect to one FTP server, then ask that files be sent to a third-party server. Such a feature is
           ripe for abuse on many levels, so most servers have ceased supporting it. One of the abuses this feature allows is causing the FTP server to port scan other hosts. Simply ask the FTP server to send a file to each
           interesting port of a target host in turn. The error message will describe whether the port is open or not. This is a good way to bypass firewalls because organizational FTP servers are often placed where they have more
           access to other internal hosts than any old Internet host would. Nmap supports FTP bounce scan with the -b option. It takes an argument of the form username:password@server:port.  Server is the name or IP address of a
           vulnerable FTP server. As with a normal URL, you may omit username:password, in which case anonymous login credentials (user: anonymous password:-wwwuser@) are used. The port number (and preceding colon) may be omitted as
           well, in which case the default FTP port (21) on server is used.

           This vulnerability was widespread in 1997 when Nmap was released, but has largely been fixed. Vulnerable servers are still around, so it is worth trying when all else fails. If bypassing a firewall is your goal, scan the
           target network for port 21 (or even for any FTP services if you scan all ports with version detection) and use the ftp-bounce.  NSE script. Nmap will tell you whether the host is vulnerable or not. If you are just trying to
           cover your tracks, you don't need to (and, in fact, shouldn't) limit yourself to hosts on the target network. Before you go scanning random Internet addresses for vulnerable FTP servers, consider that sysadmins may not
           appreciate you abusing their servers in this way.

PORT SPECIFICATION AND SCAN ORDER
       In addition to all of the scan methods discussed previously, Nmap offers options for specifying which ports are scanned and whether the scan order is randomized or sequential. By default, Nmap scans the most common 1,000 ports
       for each protocol.

       -p port ranges (Only scan specified ports) .
           This option specifies which ports you want to scan and overrides the default. Individual port numbers are OK, as are ranges separated by a hyphen (e.g.  1-1023). The beginning and/or end values of a range may be omitted,
           causing Nmap to use 1 and 65535, respectively. So you can specify -p- to scan ports from 1 through 65535. Scanning port zero.  is allowed if you specify it explicitly. For IP protocol scanning (-sO), this option specifies
           the protocol numbers you wish to scan for (0-255).

           When scanning a combination of protocols (e.g. TCP and UDP), you can specify a particular protocol by preceding the port numbers by T: for TCP, U: for UDP, S: for SCTP, or P: for IP Protocol. The qualifier lasts until you
           specify another qualifier. For example, the argument -p U:53,111,137,T:21-25,80,139,8080 would scan UDP ports 53, 111,and 137, as well as the listed TCP ports. Note that to scan both UDP and TCP, you have to specify -sU and
           at least one TCP scan type (such as -sS, -sF, or -sT). If no protocol qualifier is given, the port numbers are added to all protocol lists.  Ports can also be specified by name according to what the port is referred to in
           the nmap-services. You can even use the wildcards * and ?  with the names. For example, to scan FTP and all ports whose names begin with "http", use -p ftp,http*. Be careful about shell expansions and quote the argument to
           -p if unsure.

           Ranges of ports can be surrounded by square brackets to indicate ports inside that range that appear in nmap-services. For example, the following will scan all ports in nmap-services equal to or below 1024: -p [-1024]. Be
           careful with shell expansions and quote the argument to -p if unsure.

       -F (Fast (limited port) scan) .
           Specifies that you wish to scan fewer ports than the default. Normally Nmap scans the most common 1,000 ports for each scanned protocol. With -F, this is reduced to 100.

           Nmap needs an nmap-services file with frequency information in order to know which ports are the most common. If port frequency information isn't available, perhaps because of the use of a custom nmap-services file, Nmap
           scans all named ports plus ports 1-1024. In that case, -F means to scan only ports that are named in the services file.

       -r (Don't randomize ports) .
           By default, Nmap randomizes the scanned port order (except that certain commonly accessible ports are moved near the beginning for efficiency reasons). This randomization is normally desirable, but you can specify -r for
           sequential (sorted from lowest to highest) port scanning instead.

       --port-ratio ratio<decimal number between 0 and 1>
           Scans all ports in nmap-services file with a ratio greater than the one given.  ratio must be between 0.0 and 1.1.

       --top-ports n
           Scans the n highest-ratio ports found in nmap-services file.  n must be 1 or greater.

SERVICE AND VERSION DETECTION
       Point Nmap at a remote machine and it might tell you that ports 25/tcp, 80/tcp, and 53/udp are open. Using its nmap-services.  database of about 2,200 well-known services,.  Nmap would report that those ports probably
       correspond to a mail server (SMTP), web server (HTTP), and name server (DNS) respectively. This lookup is usually accurate--the vast majority of daemons listening on TCP port 25 are, in fact, mail servers. However, you should
       not bet your security on this! People can and do run services on strange ports..

       Even if Nmap is right, and the hypothetical server above is running SMTP, HTTP, and DNS servers, that is not a lot of information. When doing vulnerability assessments (or even simple network inventories) of your companies or
       clients, you really want to know which mail and DNS servers and versions are running. Having an accurate version number helps dramatically in determining which exploits a server is vulnerable to. Version detection helps you
       obtain this information.

       After TCP and/or UDP ports are discovered using one of the other scan methods, version detection interrogates those ports to determine more about what is actually running. The nmap-service-probes.  database contains probes for
       querying various services and match expressions to recognize and parse responses. Nmap tries to determine the service protocol (e.g. FTP, SSH, Telnet, HTTP), the application name (e.g. ISC BIND, Apache httpd, Solaris telnetd),
       the version number, hostname, device type (e.g. printer, router), the OS family (e.g. Windows, Linux). When possible, Nmap also gets the Common Platform Enumeration (CPE).  representation of this information. Sometimes
       miscellaneous details like whether an X server is open to connections, the SSH protocol version, or the KaZaA user name, are available. Of course, most services don't provide all of this information. If Nmap was compiled with
       OpenSSL support, it will connect to SSL servers to deduce the service listening behind that encryption layer..  Some UDP ports are left in the open|filtered state after a UDP port scan is unable to determine whether the port is
       open or filtered. Version detection will try to elicit a response from these ports (just as it does with open ports), and change the state to open if it succeeds.  open|filtered TCP ports are treated the same way. Note that the
       Nmap -A option enables version detection among other things.  A paper documenting the workings, usage, and customization of version detection is available at http://nmap.org/book/vscan.html.

       When RPC services are discovered, the Nmap RPC grinder.  is automatically used to determine the RPC program and version numbers. It takes all the TCP/UDP ports detected as RPC and floods them with SunRPC program NULL commands
       in an attempt to determine whether they are RPC ports, and if so, what program and version number they serve up. Thus you can effectively obtain the same info as rpcinfo -p even if the target's portmapper is behind a firewall
       (or protected by TCP wrappers). Decoys do not currently work with RPC scan..

       When Nmap receives responses from a service but cannot match them to its database, it prints out a special fingerprint and a URL for you to submit if to if you know for sure what is running on the port. Please take a couple
       minutes to make the submission so that your find can benefit everyone. Thanks to these submissions, Nmap has about 6,500 pattern matches for more than 650 protocols such as SMTP, FTP, HTTP, etc..

       Version detection is enabled and controlled with the following options:

       -sV (Version detection) .
           Enables version detection, as discussed above. Alternatively, you can use -A, which enables version detection among other things.

           -sR.  is an alias for -sV. Prior to March 2011, it was used to active the RPC grinder separately from version detection, but now these options are always combined.

       --allports (Don't exclude any ports from version detection) .
           By default, Nmap version detection skips TCP port 9100 because some printers simply print anything sent to that port, leading to dozens of pages of HTTP GET requests, binary SSL session requests, etc. This behavior can be
           changed by modifying or removing the Exclude directive in nmap-service-probes, or you can specify --allports to scan all ports regardless of any Exclude directive.

       --version-intensity intensity (Set version scan intensity) .
           When performing a version scan (-sV), Nmap sends a series of probes, each of which is assigned a rarity value between one and nine. The lower-numbered probes are effective against a wide variety of common services, while
           the higher-numbered ones are rarely useful. The intensity level specifies which probes should be applied. The higher the number, the more likely it is the service will be correctly identified. However, high intensity scans
           take longer. The intensity must be between 0 and 9..  The default is 7..  When a probe is registered to the target port via the nmap-service-probesports directive, that probe is tried regardless of intensity level. This
           ensures that the DNS probes will always be attempted against any open port 53, the SSL probe will be done against 443, etc.

       --version-light (Enable light mode) .
           This is a convenience alias for --version-intensity 2. This light mode makes version scanning much faster, but it is slightly less likely to identify services.

       --version-all (Try every single probe) .
           An alias for --version-intensity 9, ensuring that every single probe is attempted against each port.

       --version-trace (Trace version scan activity) .
           This causes Nmap to print out extensive debugging info about what version scanning is doing. It is a subset of what you get with --packet-trace.

OS DETECTION
       One of Nmap's best-known features is remote OS detection using TCP/IP stack fingerprinting. Nmap sends a series of TCP and UDP packets to the remote host and examines practically every bit in the responses. After performing
       dozens of tests such as TCP ISN sampling, TCP options support and ordering, IP ID sampling, and the initial window size check, Nmap compares the results to its nmap-os-db.  database of more than 2,600 known OS fingerprints and
       prints out the OS details if there is a match. Each fingerprint includes a freeform textual description of the OS, and a classification which provides the vendor name (e.g. Sun), underlying OS (e.g. Solaris), OS generation
       (e.g. 10), and device type (general purpose, router, switch, game console, etc). Most fingerprints also have a Common Platform Enumeration (CPE).  representation, like cpe:/o:linux:linux_kernel:2.6.

       If Nmap is unable to guess the OS of a machine, and conditions are good (e.g. at least one open port and one closed port were found), Nmap will provide a URL you can use to submit the fingerprint if you know (for sure) the OS
       running on the machine. By doing this you contribute to the pool of operating systems known to Nmap and thus it will be more accurate for everyone.

       OS detection enables some other tests which make use of information that is gathered during the process anyway. One of these is TCP Sequence Predictability Classification. This measures approximately how hard it is to establish
       a forged TCP connection against the remote host. It is useful for exploiting source-IP based trust relationships (rlogin, firewall filters, etc) or for hiding the source of an attack. This sort of spoofing is rarely performed
       any more, but many machines are still vulnerable to it. The actual difficulty number is based on statistical sampling and may fluctuate. It is generally better to use the English classification such as "worthy challenge" or
       "trivial joke". This is only reported in normal output in verbose (-v) mode. When verbose mode is enabled along with -O, IP ID sequence generation is also reported. Most machines are in the "incremental" class, which means that
       they increment the ID field in the IP header for each packet they send. This makes them vulnerable to several advanced information gathering and spoofing attacks.

       Another bit of extra information enabled by OS detection is a guess at a target's uptime. This uses the TCP timestamp option (RFC 1323[10]) to guess when a machine was last rebooted. The guess can be inaccurate due to the
       timestamp counter not being initialized to zero or the counter overflowing and wrapping around, so it is printed only in verbose mode.

       A paper documenting the workings, usage, and customization of OS detection is available at http://nmap.org/book/osdetect.html.

       OS detection is enabled and controlled with the following options:

       -O (Enable OS detection) .
           Enables OS detection, as discussed above. Alternatively, you can use -A to enable OS detection along with other things.

       --osscan-limit (Limit OS detection to promising targets) .
           OS detection is far more effective if at least one open and one closed TCP port are found. Set this option and Nmap will not even try OS detection against hosts that do not meet this criteria. This can save substantial
           time, particularly on -Pn scans against many hosts. It only matters when OS detection is requested with -O or -A.

       --osscan-guess; --fuzzy (Guess OS detection results) .
           When Nmap is unable to detect a perfect OS match, it sometimes offers up near-matches as possibilities. The match has to be very close for Nmap to do this by default. Either of these (equivalent) options make Nmap guess
           more aggressively. Nmap will still tell you when an imperfect match is printed and display its confidence level (percentage) for each guess.

       --max-os-tries (Set the maximum number of OS detection tries against a target) .
           When Nmap performs OS detection against a target and fails to find a perfect match, it usually repeats the attempt. By default, Nmap tries five times if conditions are favorable for OS fingerprint submission, and twice when
           conditions aren't so good. Specifying a lower --max-os-tries value (such as 1) speeds Nmap up, though you miss out on retries which could potentially identify the OS. Alternatively, a high value may be set to allow even
           more retries when conditions are favorable. This is rarely done, except to generate better fingerprints for submission and integration into the Nmap OS database.

NMAP SCRIPTING ENGINE (NSE)
       The Nmap Scripting Engine (NSE) is one of Nmap's most powerful and flexible features. It allows users to write (and share) simple scripts (using the Lua programming language[11],

       Tasks we had in mind when creating the system include network discovery, more sophisticated version detection, vulnerability detection. NSE can even be used for vulnerability exploitation.

       To reflect those different uses and to simplify the choice of which scripts to run, each script contains a field associating it with one or more categories. Currently defined categories are auth, broadcast, default.  discovery,
       dos, exploit, external, fuzzer, intrusive, malware, safe, version, and vuln. These are all described at http://nmap.org/book/nse-usage.html#nse-categories.

       Scripts are not run in a sandbox and thus could accidentally or maliciously damage your system or invade your privacy. Never run scripts from third parties unless you trust the authors or have carefully audited the scripts
       yourself.

       The Nmap Scripting Engine is described in detail at http://nmap.org/book/nse.html and is controlled by the following options:

       -sC .
           Performs a script scan using the default set of scripts. It is equivalent to --script=default. Some of the scripts in this category are considered intrusive and should not be run against a target network without permission.

       --script filename|category|directory|expression[,...] .
           Runs a script scan using the comma-separated list of filenames, script categories, and directories. Each element in the list may also be a Boolean expression describing a more complex set of scripts. Each element is
           interpreted first as an expression, then as a category, and finally as a file or directory name.

           There are two special features for advanced users only. One is to prefix script names and expressions with + to force them to run even if they normally wouldn't (e.g. the relevant service wasn't detected on the target
           port). The other is that the argument all may be used to specify every script in Nmap's database. Be cautious with this because NSE contains dangerous scripts such as exploits, brute force authentication crackers, and
           denial of service attacks.

           File and directory names may be relative or absolute. Absolute names are used directly. Relative paths are looked for in the scripts of each of the following places until found: --datadir
           $NMAPDIR.
           ~/.nmap (not searched on Windows).
           HOME\AppData\Roaming\nmap (only on Windows).
           the directory containing the nmap executable
           the directory containing the nmap executable, followed by ../share/nmap
           NMAPDATADIR.
           the current directory.

       When a directory name is given, Nmap loads every file in the directory whose name ends with .nse. All other files are ignored and directories are not searched recursively. When a filename is given, it does not have to have the
       .nse extension; it will be added automatically if necessary.  Nmap scripts are stored in a scripts subdirectory of the Nmap data directory by default (see http://nmap.org/book/data-files.html).  For efficiency, scripts are
       indexed in a database stored in scripts/script.db,.  which lists the category or categories in which each script belongs.  When referring to scripts from script.db by name, you can use a shell-style `*' wildcard.

       nmap --script "http-*"
           Loads all scripts whose name starts with http-, such as http-auth and http-open-proxy. The argument to --script had to be in quotes to protect the wildcard from the shell.

       More complicated script selection can be done using the and, or, and not operators to build Boolean expressions. The operators have the same precedence[12] as in Lua: not is the highest, followed by and and then or. You can
       alter precedence by using parentheses. Because expressions contain space characters it is necessary to quote them.

       nmap --script "not intrusive"
           Loads every script except for those in the intrusive category.

       nmap --script "default or safe"
           This is functionally equivalent to nmap --script "default,safe". It loads all scripts that are in the default category or the safe category or both.

       nmap --script "default and safe"
           Loads those scripts that are in both the default and safe categories.

       nmap --script "(default or safe or intrusive) and not http-*"
           Loads scripts in the default, safe, or intrusive categories, except for those whose names start with http-.

       --script-args n1=v1,n2={n3=v3},n4={v4,v5} .
           Lets you provide arguments to NSE scripts. Arguments are a comma-separated list of name=value pairs. Names and values may be strings not containing whitespace or the characters `{', `}', `=', or `,'. To include one of these
           characters in a string, enclose the string in single or double quotes. Within a quoted string, `\' escapes a quote. A backslash is only used to escape quotation marks in this special case; in all other cases a backslash is
           interpreted literally. Values may also be tables enclosed in {}, just as in Lua. A table may contain simple string values or more name-value pairs, including nested tables. Many scripts qualify their arguments with the
           script name, as in xmpp-info.server_name. You may use that full qualified version to affect just the specified script, or you may pass the unqualified version (server_name in this case) to affect all scripts using that
           argument name. A script will first check for its fully qualified argument name (the name specified in its documentation) before it accepts an unqualified argument name. A complex example of script arguments is --script-args
           'user=foo,pass=",{}=bar",whois={whodb=nofollow+ripe},xmpp-info.server_name=localhost'. The online NSE Documentation Portal at http://nmap.org/nsedoc/ lists the arguments that each script accepts.

       --script-args-file filename .
           Lets you load arguments to NSE scripts from a file. Any arguments on the command line supersede ones in the file. The file can be an absolute path, or a path relative to Nmap's usual search path (NMAPDIR, etc.) Arguments
           can be comma-separated or newline-separated, but otherwise follow the same rules as for --script-args, without requiring special quoting and escaping, since they are not parsed by the shell.

       --script-help filename|category|directory|expression|all[,...] .
           Shows help about scripts. For each script matching the given specification, Nmap prints the script name, its categories, and its description. The specifications are the same as those accepted by --script; so for example if
           you want help about the ftp-anon script, you would run nmap --script-help ftp-anon. In addition to getting help for individual scripts, you can use this as a preview of what scripts will be run for a specification, for
           example with nmap --script-help default.

       --script-trace .
           This option does what --packet-trace does, just one ISO layer higher. If this option is specified all incoming and outgoing communication performed by a script is printed. The displayed information includes the
           communication protocol, the source, the target and the transmitted data. If more than 5% of all transmitted data is not printable, then the trace output is in a hex dump format. Specifying --packet-trace enables script
           tracing too.

       --script-updatedb .
           This option updates the script database found in scripts/script.db which is used by Nmap to determine the available default scripts and categories. It is only necessary to update the database if you have added or removed
           NSE scripts from the default scripts directory or if you have changed the categories of any script. This option is generally used by itself: nmap --script-updatedb.

TIMING AND PERFORMANCE
       One of my highest Nmap development priorities has always been performance. A default scan (nmap hostname) of a host on my local network takes a fifth of a second. That is barely enough time to blink, but adds up when you are
       scanning hundreds or thousands of hosts. Moreover, certain scan options such as UDP scanning and version detection can increase scan times substantially. So can certain firewall configurations, particularly response rate
       limiting. While Nmap utilizes parallelism and many advanced algorithms to accelerate these scans, the user has ultimate control over how Nmap runs. Expert users carefully craft Nmap commands to obtain only the information they
       care about while meeting their time constraints.

       Techniques for improving scan times include omitting non-critical tests, and upgrading to the latest version of Nmap (performance enhancements are made frequently). Optimizing timing parameters can also make a substantial
       difference. Those options are listed below.

       Some options accept a time parameter. This is specified in seconds by default, though you can append `ms', `s', `m', or `h' to the value to specify milliseconds, seconds, minutes, or hours. So the --host-timeout arguments
       900000ms, 900, 900s, and 15m all do the same thing.

       --min-hostgroup numhosts; --max-hostgroup numhosts (Adjust parallel scan group sizes) .
           Nmap has the ability to port scan or version scan multiple hosts in parallel. Nmap does this by dividing the target IP space into groups and then scanning one group at a time. In general, larger groups are more efficient.
           The downside is that host results can't be provided until the whole group is finished. So if Nmap started out with a group size of 50, the user would not receive any reports (except for the updates offered in verbose mode)
           until the first 50 hosts are completed.

           By default, Nmap takes a compromise approach to this conflict. It starts out with a group size as low as five so the first results come quickly and then increases the groupsize to as high as 1024. The exact default numbers
           depend on the options given. For efficiency reasons, Nmap uses larger group sizes for UDP or few-port TCP scans.

           When a maximum group size is specified with --max-hostgroup, Nmap will never exceed that size. Specify a minimum size with --min-hostgroup and Nmap will try to keep group sizes above that level. Nmap may have to use smaller
           groups than you specify if there are not enough target hosts left on a given interface to fulfill the specified minimum. Both may be set to keep the group size within a specific range, though this is rarely desired.

           These options do not have an effect during the host discovery phase of a scan. This includes plain ping scans (-sn). Host discovery always works in large groups of hosts to improve speed and accuracy.

           The primary use of these options is to specify a large minimum group size so that the full scan runs more quickly. A common choice is 256 to scan a network in Class C sized chunks. For a scan with many ports, exceeding that
           number is unlikely to help much. For scans of just a few port numbers, host group sizes of 2048 or more may be helpful.

       --min-parallelism numprobes; --max-parallelism numprobes (Adjust probe parallelization) .
           These options control the total number of probes that may be outstanding for a host group. They are used for port scanning and host discovery. By default, Nmap calculates an ever-changing ideal parallelism based on network
           performance. If packets are being dropped, Nmap slows down and allows fewer outstanding probes. The ideal probe number slowly rises as the network proves itself worthy. These options place minimum or maximum bounds on that
           variable. By default, the ideal parallelism can drop to one if the network proves unreliable and rise to several hundred in perfect conditions.

           The most common usage is to set --min-parallelism to a number higher than one to speed up scans of poorly performing hosts or networks. This is a risky option to play with, as setting it too high may affect accuracy.
           Setting this also reduces Nmap's ability to control parallelism dynamically based on network conditions. A value of 10 might be reasonable, though I only adjust this value as a last resort.

           The --max-parallelism option is sometimes set to one to prevent Nmap from sending more than one probe at a time to hosts. The --scan-delay option, discussed later, is another way to do this.

       --min-rtt-timeout time, --max-rtt-timeout time, --initial-rtt-timeout time (Adjust probe timeouts) .
           Nmap maintains a running timeout value for determining how long it will wait for a probe response before giving up or retransmitting the probe. This is calculated based on the response times of previous probes.

           If the network latency shows itself to be significant and variable, this timeout can grow to several seconds. It also starts at a conservative (high) level and may stay that way for a while when Nmap scans unresponsive
           hosts.

           Specifying a lower --max-rtt-timeout and --initial-rtt-timeout than the defaults can cut scan times significantly. This is particularly true for pingless (-Pn) scans, and those against heavily filtered networks. Don't get
           too aggressive though. The scan can end up taking longer if you specify such a low value that many probes are timing out and retransmitting while the response is in transit.

           If all the hosts are on a local network, 100 milliseconds (--max-rtt-timeout 100ms) is a reasonable aggressive value. If routing is involved, ping a host on the network first with the ICMP ping utility, or with a custom
           packet crafter such as Nping.  that is more likely to get through a firewall. Look at the maximum round trip time out of ten packets or so. You might want to double that for the --initial-rtt-timeout and triple or quadruple
           it for the --max-rtt-timeout. I generally do not set the maximum RTT below 100 ms, no matter what the ping times are. Nor do I exceed 1000 ms.

           --min-rtt-timeout is a rarely used option that could be useful when a network is so unreliable that even Nmap's default is too aggressive. Since Nmap only reduces the timeout down to the minimum when the network seems to be
           reliable, this need is unusual and should be reported as a bug to the nmap-dev mailing list..

       --max-retries numtries (Specify the maximum number of port scan probe retransmissions) .
           When Nmap receives no response to a port scan probe, it could mean the port is filtered. Or maybe the probe or response was simply lost on the network. It is also possible that the target host has rate limiting enabled that
           temporarily blocked the response. So Nmap tries again by retransmitting the initial probe. If Nmap detects poor network reliability, it may try many more times before giving up on a port. While this benefits accuracy, it
           also lengthen scan times. When performance is critical, scans may be sped up by limiting the number of retransmissions allowed. You can even specify --max-retries 0 to prevent any retransmissions, though that is only
           recommended for situations such as informal surveys where occasional missed ports and hosts are acceptable.

           The default (with no -T template) is to allow ten retransmissions. If a network seems reliable and the target hosts aren't rate limiting, Nmap usually only does one retransmission. So most target scans aren't even affected
           by dropping --max-retries to a low value such as three. Such values can substantially speed scans of slow (rate limited) hosts. You usually lose some information when Nmap gives up on ports early, though that may be
           preferable to letting the --host-timeout expire and losing all information about the target.

       --host-timeout time (Give up on slow target hosts) .
           Some hosts simply take a long time to scan. This may be due to poorly performing or unreliable networking hardware or software, packet rate limiting, or a restrictive firewall. The slowest few percent of the scanned hosts
           can eat up a majority of the scan time. Sometimes it is best to cut your losses and skip those hosts initially. Specify --host-timeout with the maximum amount of time you are willing to wait. For example, specify 30m to
           ensure that Nmap doesn't waste more than half an hour on a single host. Note that Nmap may be scanning other hosts at the same time during that half an hour, so it isn't a complete loss. A host that times out is skipped. No
           port table, OS detection, or version detection results are printed for that host.

       --scan-delay time; --max-scan-delay time (Adjust delay between probes) .
           This option causes Nmap to wait at least the given amount of time between each probe it sends to a given host. This is particularly useful in the case of rate limiting..  Solaris machines (among many others) will usually
           respond to UDP scan probe packets with only one ICMP message per second. Any more than that sent by Nmap will be wasteful. A --scan-delay of 1s will keep Nmap at that slow rate. Nmap tries to detect rate limiting and adjust
           the scan delay accordingly, but it doesn't hurt to specify it explicitly if you already know what rate works best.

           When Nmap adjusts the scan delay upward to cope with rate limiting, the scan slows down dramatically. The --max-scan-delay option specifies the largest delay that Nmap will allow. A low --max-scan-delay can speed up Nmap,
           but it is risky. Setting this value too low can lead to wasteful packet retransmissions and possible missed ports when the target implements strict rate limiting.

           Another use of --scan-delay is to evade threshold based intrusion detection and prevention systems (IDS/IPS)..

       --min-rate number; --max-rate number (Directly control the scanning rate) .
           Nmap's dynamic timing does a good job of finding an appropriate speed at which to scan. Sometimes, however, you may happen to know an appropriate scanning rate for a network, or you may have to guarantee that a scan will be
           finished by a certain time. Or perhaps you must keep Nmap from scanning too quickly. The --min-rate and --max-rate options are designed for these situations.

           When the --min-rate option is given Nmap will do its best to send packets as fast as or faster than the given rate. The argument is a positive real number representing a packet rate in packets per second. For example,
           specifying --min-rate 300 means that Nmap will try to keep the sending rate at or above 300 packets per second. Specifying a minimum rate does not keep Nmap from going faster if conditions warrant.

           Likewise, --max-rate limits a scan's sending rate to a given maximum. Use --max-rate 100, for example, to limit sending to 100 packets per second on a fast network. Use --max-rate 0.1 for a slow scan of one packet every ten
           seconds. Use --min-rate and --max-rate together to keep the rate inside a certain range.

           These two options are global, affecting an entire scan, not individual hosts. They only affect port scans and host discovery scans. Other features like OS detection implement their own timing.

           There are two conditions when the actual scanning rate may fall below the requested minimum. The first is if the minimum is faster than the fastest rate at which Nmap can send, which is dependent on hardware. In this case
           Nmap will simply send packets as fast as possible, but be aware that such high rates are likely to cause a loss of accuracy. The second case is when Nmap has nothing to send, for example at the end of a scan when the last
           probes have been sent and Nmap is waiting for them to time out or be responded to. It's normal to see the scanning rate drop at the end of a scan or in between hostgroups. The sending rate may temporarily exceed the maximum
           to make up for unpredictable delays, but on average the rate will stay at or below the maximum.

           Specifying a minimum rate should be done with care. Scanning faster than a network can support may lead to a loss of accuracy. In some cases, using a faster rate can make a scan take longer than it would with a slower rate.
           This is because Nmap's adaptive retransmission algorithms will detect the network congestion caused by an excessive scanning rate and increase the number of retransmissions in order to improve accuracy. So even though
           packets are sent at a higher rate, more packets are sent overall. Cap the number of retransmissions with the --max-retries option if you need to set an upper limit on total scan time.

       --defeat-rst-ratelimit .
           Many hosts have long used rate limiting.  to reduce the number of ICMP error messages (such as port-unreachable errors) they send. Some systems now apply similar rate limits to the RST (reset) packets they generate. This
           can slow Nmap down dramatically as it adjusts its timing to reflect those rate limits. You can tell Nmap to ignore those rate limits (for port scans such as SYN scan which don't treat non-responsive ports as open) by
           specifying --defeat-rst-ratelimit.

           Using this option can reduce accuracy, as some ports will appear non-responsive because Nmap didn't wait long enough for a rate-limited RST response. With a SYN scan, the non-response results in the port being labeled
           filtered rather than the closed state we see when RST packets are received. This option is useful when you only care about open ports, and distinguishing between closed and filtered ports isn't worth the extra time.

       --nsock-engine epoll|kqueue|poll|select .
           Enforce use of a given nsock IO multiplexing engine. Only the select(2)-based fallback engine is guaranteed to be available on your system. Engines are named after the name of the IO management facility they leverage.
           Engines currenty implemented are epoll, kqueue, poll, and select, but not all will be present on any platform. Use nmap -V to see which engines are supported.

       -T paranoid|sneaky|polite|normal|aggressive|insane (Set a timing template) .
           While the fine-grained timing controls discussed in the previous section are powerful and effective, some people find them confusing. Moreover, choosing the appropriate values can sometimes take more time than the scan you
           are trying to optimize. So Nmap offers a simpler approach, with six timing templates. You can specify them with the -T option and their number (0-5) or their name. The template names are paranoid (0), sneaky (1),
           polite (2), normal (3), aggressive (4), and insane (5). The first two are for IDS evasion. Polite mode slows down the scan to use less bandwidth and target machine resources. Normal mode is the default and so -T3 does
           nothing. Aggressive mode speeds scans up by making the assumption that you are on a reasonably fast and reliable network. Finally insane mode.  assumes that you are on an extraordinarily fast network or are willing to
           sacrifice some accuracy for speed.

           These templates allow the user to specify how aggressive they wish to be, while leaving Nmap to pick the exact timing values. The templates also make some minor speed adjustments for which fine-grained control options do
           not currently exist. For example, -T4.  prohibits the dynamic scan delay from exceeding 10 ms for TCP ports and -T5 caps that value at 5 ms. Templates can be used in combination with fine-grained controls, and the
           fine-grained controls will you specify will take precedence over the timing template default for that parameter. I recommend using -T4 when scanning reasonably modern and reliable networks. Keep that option even when you
           add fine-grained controls so that you benefit from those extra minor optimizations that it enables.

           If you are on a decent broadband or ethernet connection, I would recommend always using -T4. Some people love -T5 though it is too aggressive for my taste. People sometimes specify -T2 because they think it is less likely
           to crash hosts or because they consider themselves to be polite in general. They often don't realize just how slow -T polite.  really is. Their scan may take ten times longer than a default scan. Machine crashes and
           bandwidth problems are rare with the default timing options (-T3) and so I normally recommend that for cautious scanners. Omitting version detection is far more effective than playing with timing values at reducing these
           problems.

           While -T0.  and -T1.  may be useful for avoiding IDS alerts, they will take an extraordinarily long time to scan thousands of machines or ports. For such a long scan, you may prefer to set the exact timing values you need
           rather than rely on the canned -T0 and -T1 values.

           The main effects of T0 are serializing the scan so only one port is scanned at a time, and waiting five minutes between sending each probe.  T1 and T2 are similar but they only wait 15 seconds and 0.4 seconds, respectively,
           between probes.  T3 is Nmap's default behavior, which includes parallelization..  does the equivalent of --max-rtt-timeout 1250ms --initial-rtt-timeout 500ms --max-retries 6 and sets the maximum TCP scan delay to 10
           milliseconds.  T5 does the equivalent of --max-rtt-timeout 300ms --min-rtt-timeout 50ms --initial-rtt-timeout 250ms --max-retries 2 --host-timeout 15m as well as setting the maximum TCP scan delay to 5 ms.

FIREWALL/IDS EVASION AND SPOOFING
       Many Internet pioneers envisioned a global open network with a universal IP address space allowing virtual connections between any two nodes. This allows hosts to act as true peers, serving and retrieving information from each
       other. People could access all of their home systems from work, changing the climate control settings or unlocking the doors for early guests. This vision of universal connectivity has been stifled by address space shortages
       and security concerns. In the early 1990s, organizations began deploying firewalls for the express purpose of reducing connectivity. Huge networks were cordoned off from the unfiltered Internet by application proxies, network
       address translation, and packet filters. The unrestricted flow of information gave way to tight regulation of approved communication channels and the content that passes over them.

       Network obstructions such as firewalls can make mapping a network exceedingly difficult. It will not get any easier, as stifling casual reconnaissance is often a key goal of implementing the devices. Nevertheless, Nmap offers
       many features to help understand these complex networks, and to verify that filters are working as intended. It even supports mechanisms for bypassing poorly implemented defenses. One of the best methods of understanding your
       network security posture is to try to defeat it. Place yourself in the mind-set of an attacker, and deploy techniques from this section against your networks. Launch an FTP bounce scan, idle scan, fragmentation attack, or try
       to tunnel through one of your own proxies.

       In addition to restricting network activity, companies are increasingly monitoring traffic with intrusion detection systems (IDS). All of the major IDSs ship with rules designed to detect Nmap scans because scans are sometimes
       a precursor to attacks. Many of these products have recently morphed into intrusion prevention systems (IPS).  that actively block traffic deemed malicious. Unfortunately for network administrators and IDS vendors, reliably
       detecting bad intentions by analyzing packet data is a tough problem. Attackers with patience, skill, and the help of certain Nmap options can usually pass by IDSs undetected. Meanwhile, administrators must cope with large
       numbers of false positive results where innocent activity is misdiagnosed and alerted on or blocked.

       Occasionally people suggest that Nmap should not offer features for evading firewall rules or sneaking past IDSs. They argue that these features are just as likely to be misused by attackers as used by administrators to enhance
       security. The problem with this logic is that these methods would still be used by attackers, who would just find other tools or patch the functionality into Nmap. Meanwhile, administrators would find it that much harder to do
       their jobs. Deploying only modern, patched FTP servers is a far more powerful defense than trying to prevent the distribution of tools implementing the FTP bounce attack.

       There is no magic bullet (or Nmap option) for detecting and subverting firewalls and IDS systems. It takes skill and experience. A tutorial is beyond the scope of this reference guide, which only lists the relevant options and
       describes what they do.

       -f (fragment packets); --mtu (using the specified MTU) .
           The -f option causes the requested scan (including ping scans) to use tiny fragmented IP packets. The idea is to split up the TCP header over several packets to make it harder for packet filters, intrusion detection
           systems, and other annoyances to detect what you are doing. Be careful with this! Some programs have trouble handling these tiny packets. The old-school sniffer named Sniffit segmentation faulted immediately upon receiving
           the first fragment. Specify this option once, and Nmap splits the packets into eight bytes or less after the IP header. So a 20-byte TCP header would be split into three packets. Two with eight bytes of the TCP header, and
           one with the final four. Of course each fragment also has an IP header. Specify -f again to use 16 bytes per fragment (reducing the number of fragments)..  Or you can specify your own offset size with the --mtu option.
           Don't also specify -f if you use --mtu. The offset must be a multiple of eight. While fragmented packets won't get by packet filters and firewalls that queue all IP fragments, such as the CONFIG_IP_ALWAYS_DEFRAG option in
           the Linux kernel, some networks can't afford the performance hit this causes and thus leave it disabled. Others can't enable this because fragments may take different routes into their networks. Some source systems
           defragment outgoing packets in the kernel. Linux with the iptables.  connection tracking module is one such example. Do a scan while a sniffer such as Wireshark.  is running to ensure that sent packets are fragmented. If
           your host OS is causing problems, try the --send-eth.  option to bypass the IP layer and send raw ethernet frames.

           Fragmentation is only supported for Nmap's raw packet features, which includes TCP and UDP port scans (except connect scan and FTP bounce scan) and OS detection. Features such as version detection and the Nmap Scripting
           Engine generally don't support fragmentation because they rely on your host's TCP stack to communicate with target services.

       -D decoy1[,decoy2][,ME][,...] (Cloak a scan with decoys) .
           Causes a decoy scan to be performed, which makes it appear to the remote host that the host(s) you specify as decoys are scanning the target network too. Thus their IDS might report 5-10 port scans from unique IP addresses,
           but they won't know which IP was scanning them and which were innocent decoys. While this can be defeated through router path tracing, response-dropping, and other active mechanisms, it is generally an effective technique
           for hiding your IP address.

           Separate each decoy host with commas, and you can optionally use ME.  as one of the decoys to represent the position for your real IP address. If you put ME in the sixth position or later, some common port scan detectors
           (such as Solar Designer's.  excellent Scanlogd).  are unlikely to show your IP address at all. If you don't use ME, Nmap will put you in a random position. You can also use RND.  to generate a random, non-reserved IP
           address, or RND:number to generate number addresses.

           Note that the hosts you use as decoys should be up or you might accidentally SYN flood your targets. Also it will be pretty easy to determine which host is scanning if only one is actually up on the network. You might want
           to use IP addresses instead of names (so the decoy networks don't see you in their nameserver logs).

           Decoys are used both in the initial ping scan (using ICMP, SYN, ACK, or whatever) and during the actual port scanning phase. Decoys are also used during remote OS detection (-O). Decoys do not work with version detection or
           TCP connect scan. When a scan delay is in effect, the delay is enforced between each batch of spoofed probes, not between each individual probe. Because decoys are sent as a batch all at once, they may temporarily violate
           congestion control limits.

           It is worth noting that using too many decoys may slow your scan and potentially even make it less accurate. Also, some ISPs will filter out your spoofed packets, but many do not restrict spoofed IP packets at all.

       -S IP_Address (Spoof source address) .
           In some circumstances, Nmap may not be able to determine your source address (Nmap will tell you if this is the case). In this situation, use -S with the IP address of the interface you wish to send packets through.

           Another possible use of this flag is to spoof the scan to make the targets think that someone else is scanning them. Imagine a company being repeatedly port scanned by a competitor! The -e option and -Pn are generally
           required for this sort of usage. Note that you usually won't receive reply packets back (they will be addressed to the IP you are spoofing), so Nmap won't produce useful reports.

       -e interface (Use specified interface) .
           Tells Nmap what interface to send and receive packets on. Nmap should be able to detect this automatically, but it will tell you if it cannot.

       --source-port portnumber; -g portnumber (Spoof source port number) .
           One surprisingly common misconfiguration is to trust traffic based only on the source port number. It is easy to understand how this comes about. An administrator will set up a shiny new firewall, only to be flooded with
           complaints from ungrateful users whose applications stopped working. In particular, DNS may be broken because the UDP DNS replies from external servers can no longer enter the network. FTP is another common example. In
           active FTP transfers, the remote server tries to establish a connection back to the client to transfer the requested file.

           Secure solutions to these problems exist, often in the form of application-level proxies or protocol-parsing firewall modules. Unfortunately there are also easier, insecure solutions. Noting that DNS replies come from port
           53 and active FTP from port 20, many administrators have fallen into the trap of simply allowing incoming traffic from those ports. They often assume that no attacker would notice and exploit such firewall holes. In other
           cases, administrators consider this a short-term stop-gap measure until they can implement a more secure solution. Then they forget the security upgrade.

           Overworked network administrators are not the only ones to fall into this trap. Numerous products have shipped with these insecure rules. Even Microsoft has been guilty. The IPsec filters that shipped with Windows 2000 and
           Windows XP contain an implicit rule that allows all TCP or UDP traffic from port 88 (Kerberos). In another well-known case, versions of the Zone Alarm personal firewall up to 2.1.25 allowed any incoming UDP packets with the
           source port 53 (DNS) or 67 (DHCP).

           Nmap offers the -g and --source-port options (they are equivalent) to exploit these weaknesses. Simply provide a port number and Nmap will send packets from that port where possible. Most scanning operations that use raw
           sockets, including SYN and UDP scans, support the option completely. The option notably doesn't have an effect for any operations that use normal operating system sockets, including DNS requests, TCP connect scan,.  version
           detection, and script scanning. Setting the source port also doesn't work for OS detection, because Nmap must use different port numbers for certain OS detection tests to work properly.

       --data-length number (Append random data to sent packets) .
           Normally Nmap sends minimalist packets containing only a header. So its TCP packets are generally 40 bytes and ICMP echo requests are just 28. Some UDP ports.  and IP protocols.  get a custom payload by default. This option
           tells Nmap to append the given number of random bytes to most of the packets it sends, and not to use any protocol-specific payloads. (Use --data-length 0 for no random or protocol-specific payloads..  OS detection (-O)
           packets are not affected.  because accuracy there requires probe consistency, but most pinging and portscan packets support this. It slows things down a little, but can make a scan slightly less conspicuous.

       --ip-options S|R [route]|L [route]|T|U ... ; --ip-options hex string (Send packets with specified ip options) .
           The IP protocol[13] offers several options which may be placed in packet headers. Unlike the ubiquitous TCP options, IP options are rarely seen due to practicality and security concerns. In fact, many Internet routers block
           the most dangerous options such as source routing. Yet options can still be useful in some cases for determining and manipulating the network route to target machines. For example, you may be able to use the record route
           option to determine a path to a target even when more traditional traceroute-style approaches fail. Or if your packets are being dropped by a certain firewall, you may be able to specify a different route with the strict or
           loose source routing options.

           The most powerful way to specify IP options is to simply pass in values as the argument to --ip-options. Precede each hex number with \x then the two digits. You may repeat certain characters by following them with an
           asterisk and then the number of times you wish them to repeat. For example, \x01\x07\x04\x00*36\x01 is a hex string containing 36 NUL bytes.

           Nmap also offers a shortcut mechanism for specifying options. Simply pass the letter R, T, or U to request record-route,.  record-timestamp,.  or both options together, respectively. Loose or strict source routing.  may be
           specified with an L or S followed by a space and then a space-separated list of IP addresses.

           If you wish to see the options in packets sent and received, specify --packet-trace. For more information and examples of using IP options with Nmap, see http://seclists.org/nmap-dev/2006/q3/52.

       --ttl value (Set IP time-to-live field) .
           Sets the IPv4 time-to-live field in sent packets to the given value.

       --randomize-hosts (Randomize target host order) .
           Tells Nmap to shuffle each group of up to 16384 hosts before it scans them. This can make the scans less obvious to various network monitoring systems, especially when you combine it with slow timing options. If you want to
           randomize over larger group sizes, increase PING_GROUP_SZ.  in nmap.h.  and recompile. An alternative solution is to generate the target IP list with a list scan (-sL -n -oN filename), randomize it with a Perl script, then
           provide the whole list to Nmap with -iL..

       --spoof-mac MAC address, prefix, or vendor name (Spoof MAC address) .
           Asks Nmap to use the given MAC address for all of the raw ethernet frames it sends. This option implies --send-eth.  to ensure that Nmap actually sends ethernet-level packets. The MAC given can take several formats. If it
           is simply the number 0, Nmap chooses a completely random MAC address for the session. If the given string is an even number of hex digits (with the pairs optionally separated by a colon), Nmap will use those as the MAC. If
           fewer than 12 hex digits are provided, Nmap fills in the remainder of the six bytes with random values. If the argument isn't a zero or hex string, Nmap looks through nmap-mac-prefixes to find a vendor name containing the
           given string (it is case insensitive). If a match is found, Nmap uses the vendor's OUI (three-byte prefix).  and fills out the remaining three bytes randomly. Valid --spoof-mac argument examples are Apple, 0,
           01:02:03:04:05:06, deadbeefcafe, 0020F2, and Cisco. This option only affects raw packet scans such as SYN scan or OS detection, not connection-oriented features such as version detection or the Nmap Scripting Engine.

       --badsum (Send packets with bogus TCP/UDP checksums) .
           Asks Nmap to use an invalid TCP, UDP or SCTP checksum for packets sent to target hosts. Since virtually all host IP stacks properly drop these packets, any responses received are likely coming from a firewall or IDS that
           didn't bother to verify the checksum. For more details on this technique, see http://nmap.org/p60-12.html

       --adler32 (Use deprecated Adler32 instead of CRC32C for SCTP checksums) .
           Asks Nmap to use the deprecated Adler32 algorithm for calculating the SCTP checksum. If --adler32 is not given, CRC-32C (Castagnoli) is used.  RFC 2960[14] originally defined Adler32 as checksum algorithm for SCTP; RFC
           4960[7] later redefined the SCTP checksums to use CRC-32C. Current SCTP implementations should be using CRC-32C, but in order to elicit responses from old, legacy SCTP implementations, it may be preferable to use Adler32.

OUTPUT
       Any security tool is only as useful as the output it generates. Complex tests and algorithms are of little value if they aren't presented in an organized and comprehensible fashion. Given the number of ways Nmap is used by
       people and other software, no single format can please everyone. So Nmap offers several formats, including the interactive mode for humans to read directly and XML for easy parsing by software.

       In addition to offering different output formats, Nmap provides options for controlling the verbosity of output as well as debugging messages. Output types may be sent to standard output or to named files, which Nmap can append
       to or clobber. Output files may also be used to resume aborted scans.

       Nmap makes output available in five different formats. The default is called interactive output,.  and it is sent to standard output (stdout)..  There is also normal output,.  which is similar to interactive except that it
       displays less runtime information and warnings since it is expected to be analyzed after the scan completes rather than interactively.

       XML output.  is one of the most important output types, as it can be converted to HTML, easily parsed by programs such as Nmap graphical user interfaces, or imported into databases.

       The two remaining output types are the simple grepable output.  which includes most information for a target host on a single line, and sCRiPt KiDDi3 0utPUt.  for users who consider themselves |<-r4d.

       While interactive output is the default and has no associated command-line options, the other four format options use the same syntax. They take one argument, which is the filename that results should be stored in. Multiple
       formats may be specified, but each format may only be specified once. For example, you may wish to save normal output for your own review while saving XML of the same scan for programmatic analysis. You might do this with the
       options -oX myscan.xml -oN myscan.nmap. While this chapter uses the simple names like myscan.xml for brevity, more descriptive names are generally recommended. The names chosen are a matter of personal preference, though I use
       long ones that incorporate the scan date and a word or two describing the scan, placed in a directory named after the company I'm scanning.

       While these options save results to files, Nmap still prints interactive output to stdout as usual. For example, the command nmap -oX myscan.xml target prints XML to myscan.xml and fills standard output with the same
       interactive results it would have printed if -oX wasn't specified at all. You can change this by passing a hyphen character as the argument to one of the format types. This causes Nmap to deactivate interactive output, and
       instead print results in the format you specified to the standard output stream. So the command nmap -oX - target will send only XML output to stdout..  Serious errors may still be printed to the normal error stream, stderr..

       Unlike some Nmap arguments, the space between the logfile option flag (such as -oX) and the filename or hyphen is mandatory. If you omit the flags and give arguments such as -oG- or -oXscan.xml, a backwards compatibility
       feature of Nmap will cause the creation of normal format output files named G- and Xscan.xml respectively.

       All of these arguments support strftime-like.  conversions in the filename.  %H, %M, %S, %m, %d, %y, and %Y are all exactly the same as in strftime.  %T is the same as %H%M%S, %R is the same as %H%M, and %D is the same as
       %m%d%y. A % followed by any other character just yields that character (%% gives you a percent symbol). So -oX 'scan-%T-%D.xml' will use an XML file with a name in the form of scan-144840-121307.xml.

       Nmap also offers options to control scan verbosity and to append to output files rather than clobbering them. All of these options are described below.

       Nmap Output Formats

       -oN filespec (normal output) .
           Requests that normal output be directed to the given filename. As discussed above, this differs slightly from interactive output.

       -oX filespec (XML output) .
           Requests that XML output be directed to the given filename. Nmap includes a document type definition (DTD) which allows XML parsers to validate Nmap XML output. While it is primarily intended for programmatic use, it can
           also help humans interpret Nmap XML output. The DTD defines the legal elements of the format, and often enumerates the attributes and values they can take on. The latest version is always available from
           https://svn.nmap.org/nmap/docs/nmap.dtd.

           XML offers a stable format that is easily parsed by software. Free XML parsers are available for all major computer languages, including C/C++, Perl, Python, and Java. People have even written bindings for most of these
           languages to handle Nmap output and execution specifically. Examples are Nmap::Scanner[15].  and Nmap::Parser[16].  in Perl CPAN. In almost all cases that a non-trivial application interfaces with Nmap, XML is the preferred
           format.

           The XML output references an XSL stylesheet which can be used to format the results as HTML. The easiest way to use this is simply to load the XML output in a web browser such as Firefox or IE. By default, this will only
           work on the machine you ran Nmap on (or a similarly configured one) due to the hard-coded nmap.xsl filesystem path. Use the --webxml or --stylesheet options to create portable XML files that render as HTML on any
           web-connected machine.

       -oS filespec (ScRipT KIdd|3 oUTpuT) .
           Script kiddie output is like interactive output, except that it is post-processed to better suit the l33t HaXXorZ who previously looked down on Nmap due to its consistent capitalization and spelling. Humor impaired people
           should note that this option is making fun of the script kiddies before flaming me for supposedly "helping them".

       -oG filespec (grepable output) .
           This output format is covered last because it is deprecated. The XML output format is far more powerful, and is nearly as convenient for experienced users. XML is a standard for which dozens of excellent parsers are
           available, while grepable output is my own simple hack. XML is extensible to support new Nmap features as they are released, while I often must omit those features from grepable output for lack of a place to put them.

           Nevertheless, grepable output is still quite popular. It is a simple format that lists each host on one line and can be trivially searched and parsed with standard Unix tools such as grep, awk, cut, sed, diff, and Perl.
           Even I usually use it for one-off tests done at the command line. Finding all the hosts with the SSH port open or that are running Solaris takes only a simple grep to identify the hosts, piped to an awk or cut command to
           print the desired fields.

           Grepable output consists of comments (lines starting with a pound (#)).  and target lines. A target line includes a combination of six labeled fields, separated by tabs and followed with a colon. The fields are Host, Ports,
           Protocols, Ignored State, OS, Seq Index, IP ID, and Status.

           The most important of these fields is generally Ports, which gives details on each interesting port. It is a comma separated list of port entries. Each port entry represents one interesting port, and takes the form of seven
           slash (/) separated subfields. Those subfields are: Port number, State, Protocol, Owner, Service, SunRPC info, and Version info.

           As with XML output, this man page does not allow for documenting the entire format. A more detailed look at the Nmap grepable output format is available from http://nmap.org/book/output-formats-grepable-output.html.

       -oA basename (Output to all formats) .
           As a convenience, you may specify -oA basename to store scan results in normal, XML, and grepable formats at once. They are stored in basename.nmap, basename.xml, and basename.gnmap, respectively. As with most programs, you
           can prefix the filenames with a directory path, such as ~/nmaplogs/foocorp/ on Unix or c:\hacking\sco on Windows.

       Verbosity and debugging options

       -v (Increase verbosity level) .
           Increases the verbosity level, causing Nmap to print more information about the scan in progress. Open ports are shown as they are found and completion time estimates are provided when Nmap thinks a scan will take more than
           a few minutes. Use it twice or more for even greater verbosity: -vv, or give a verbosity level directly, for example -v3..

           Most changes only affect interactive output, and some also affect normal and script kiddie output. The other output types are meant to be processed by machines, so Nmap can give substantial detail by default in those
           formats without fatiguing a human user. However, there are a few changes in other modes where output size can be reduced substantially by omitting some detail. For example, a comment line in the grepable output that
           provides a list of all ports scanned is only printed in verbose mode because it can be quite long.

       -d (Increase debugging level) .
           When even verbose mode doesn't provide sufficient data for you, debugging is available to flood you with much more! As with the verbosity option (-v), debugging is enabled with a command-line flag (-d) and the debug level
           can be increased by specifying it multiple times,.  as in -dd, or by setting a level directly. For example, -d9 sets level nine. That is the highest effective level and will produce thousands of lines unless you run a very
           simple scan with very few ports and targets.

           Debugging output is useful when a bug is suspected in Nmap, or if you are simply confused as to what Nmap is doing and why. As this feature is mostly intended for developers, debug lines aren't always self-explanatory. You
           may get something like: Timeout vals: srtt: -1 rttvar: -1 to: 1000000 delta 14987 ==> srtt: 14987 rttvar: 14987 to: 100000. If you don't understand a line, your only recourses are to ignore it, look it up in the source
           code, or request help from the development list (nmap-dev)..  Some lines are self explanatory, but the messages become more obscure as the debug level is increased.

       --reason (Host and port state reasons) .
           Shows the reason each port is set to a specific state and the reason each host is up or down. This option displays the type of the packet that determined a port or hosts state. For example, A RST packet from a closed port
           or an echo reply from an alive host. The information Nmap can provide is determined by the type of scan or ping. The SYN scan and SYN ping (-sS and -PS) are very detailed, but the TCP connect scan (-sT) is limited by the
           implementation of the connect system call. This feature is automatically enabled by the debug option (-d).  and the results are stored in XML log files even if this option is not specified.

       --stats-every time (Print periodic timing stats) .
           Periodically prints a timing status message after each interval of time. The time is a specification of the kind described in the section called "TIMING AND PERFORMANCE"; so for example, use --stats-every 10s to get a
           status update every 10 seconds. Updates are printed to interactive output (the screen) and XML output.

       --packet-trace (Trace packets and data sent and received) .
           Causes Nmap to print a summary of every packet sent or received. This is often used for debugging, but is also a valuable way for new users to understand exactly what Nmap is doing under the covers. To avoid printing
           thousands of lines, you may want to specify a limited number of ports to scan, such as -p20-30. If you only care about the goings on of the version detection subsystem, use --version-trace instead. If you only care about
           script tracing, specify --script-trace. With --packet-trace, you get all of the above.

       --open (Show only open (or possibly open) ports) .
           Sometimes you only care about ports you can actually connect to (open ones), and don't want results cluttered with closed, filtered, and closed|filtered ports. Output customization is normally done after the scan using
           tools such as grep, awk, and Perl, but this feature was added due to overwhelming requests. Specify --open to only see hosts with at least one open, open|filtered, or unfiltered port, and only see ports in those states.
           These three states are treated just as they normally are, which means that open|filtered and unfiltered may be condensed into counts if there are an overwhelming number of them.

       --iflist (List interfaces and routes) .
           Prints the interface list and system routes as detected by Nmap. This is useful for debugging routing problems or device mischaracterization (such as Nmap treating a PPP connection as ethernet).

       Miscellaneous output options

       --append-output (Append to rather than clobber output files) .
           When you specify a filename to an output format flag such as -oX or -oN, that file is overwritten by default. If you prefer to keep the existing content of the file and append the new results, specify the --append-output
           option. All output filenames specified in that Nmap execution will then be appended to rather than clobbered. This doesn't work well for XML (-oX) scan data as the resultant file generally won't parse properly until you fix
           it up by hand.

       --resume filename (Resume aborted scan) .
           Some extensive Nmap runs take a very long time--on the order of days. Such scans don't always run to completion. Restrictions may prevent Nmap from being run during working hours, the network could go down, the machine Nmap
           is running on might suffer a planned or unplanned reboot, or Nmap itself could crash. The administrator running Nmap could cancel it for any other reason as well, by pressing ctrl-C. Restarting the whole scan from the
           beginning may be undesirable. Fortunately, if normal (-oN) or grepable (-oG) logs were kept, the user can ask Nmap to resume scanning with the target it was working on when execution ceased. Simply specify the --resume
           option and pass the normal/grepable output file as its argument. No other arguments are permitted, as Nmap parses the output file to use the same ones specified previously. Simply call Nmap as nmap --resume logfilename.
           Nmap will append new results to the data files specified in the previous execution. Resumption does not support the XML output format because combining the two runs into one valid XML file would be difficult.

       --stylesheet path or URL (Set XSL stylesheet to transform XML output) .
           Nmap ships with an XSL.  stylesheet.  named nmap.xsl.  for viewing or translating XML output to HTML..  The XML output includes an xml-stylesheet directive which points to nmap.xml where it was initially installed by Nmap.
           Run the XML file through an XSLT processor such as xsltproc[17].  to produce an HTML file. Directly opening the XML file in a browser no longer works well because modern browsers limit the locations a stylesheet may be
           loaded from. If you wish to use a different stylesheet, specify it as the argument to --stylesheet. You must pass the full pathname or URL. One common invocation is --stylesheet http://nmap.org/svn/docs/nmap.xsl. This tells
           an XSLT processor to load the latest version of the stylesheet from Nmap.Org. The --webxml option does the same thing with less typing and memorization. Loading the XSL from Nmap.Org makes it easier to view results on a
           machine that doesn't have Nmap (and thus nmap.xsl) installed. So the URL is often more useful, but the local filesystem location of nmap.xsl is used by default for privacy reasons.

       --webxml (Load stylesheet from Nmap.Org) .
           This is a convenience option, nothing more than an alias for --stylesheet http://nmap.org/svn/docs/nmap.xsl.

       --no-stylesheet (Omit XSL stylesheet declaration from XML) .
           Specify this option to prevent Nmap from associating any XSL stylesheet with its XML output. The xml-stylesheet directive is omitted.

MISCELLANEOUS OPTIONS
       This section describes some important (and not-so-important) options that don't really fit anywhere else.

       -6 (Enable IPv6 scanning) .
           Nmap has IPv6 support for its most popular features. Ping scanning, port scanning, version detection, and the Nmap Scripting Engine all support IPv6. The command syntax is the same as usual except that you also add the -6
           option. Of course, you must use IPv6 syntax if you specify an address rather than a hostname. An address might look like 3ffe:7501:4819:2000:210:f3ff:fe03:14d0, so hostnames are recommended. The output looks the same as
           usual, with the IPv6 address on the "interesting ports" line being the only IPv6 giveaway.

           While IPv6 hasn't exactly taken the world by storm, it gets significant use in some (usually Asian) countries and most modern operating systems support it. To use Nmap with IPv6, both the source and target of your scan must
           be configured for IPv6. If your ISP (like most of them) does not allocate IPv6 addresses to you, free tunnel brokers are widely available and work fine with Nmap. I use the free IPv6 tunnel broker.  service at
           http://www.tunnelbroker.net. Other tunnel brokers are listed at Wikipedia[18]. 6to4 tunnels are another popular, free approach.

           On Windows, raw-socket IPv6 scans are supported only on ethernet devices (not tunnels), and only on Windows Vista.  and later. Use the --unprivileged.  option in other situations.

       -A (Aggressive scan options) .
           This option enables additional advanced and aggressive options. I haven't decided exactly which it stands for yet. Presently this enables OS detection (-O), version scanning (-sV), script scanning (-sC) and traceroute
           (--traceroute)..  More features may be added in the future. The point is to enable a comprehensive set of scan options without people having to remember a large set of flags. However, because script scanning with the
           default set is considered intrusive, you should not use -A against target networks without permission. This option only enables features, and not timing options (such as -T4) or verbosity options (-v) that you might want as
           well.

       --datadir directoryname (Specify custom Nmap data file location) .
           Nmap obtains some special data at runtime in files named nmap-service-probes, nmap-services, nmap-protocols, nmap-rpc, nmap-mac-prefixes, and nmap-os-db. If the location of any of these files has been specified (using the
           --servicedb or --versiondb options), that location is used for that file. After that, Nmap searches these files in the directory specified with the --datadir option (if any). Any files not found there, are searched for in
           the directory specified by the NMAPDIR.  environment variable. Next comes ~/.nmap.  for real and effective UIDs; or on Windows, HOME\AppData\Roaming\nmap (where HOME is the user's home directory, like C:\Users\user). This
           is followed by the location of the nmap executable and the same location with ../share/nmap appended. Then a compiled-in location such as /usr/local/share/nmap or /usr/share/nmap.

       --servicedb services file (Specify custom services file) .
           Asks Nmap to use the specified services file rather than the nmap-services data file that comes with Nmap. Using this option also causes a fast scan (-F) to be used. See the description for --datadir for more information on
           Nmap's data files.

       --versiondb service probes file (Specify custom service probes file) .
           Asks Nmap to use the specified service probes file rather than the nmap-service-probes data file that comes with Nmap. See the description for --datadir for more information on Nmap's data files.

       --send-eth (Use raw ethernet sending) .
           Asks Nmap to send packets at the raw ethernet (data link) layer rather than the higher IP (network) layer. By default, Nmap chooses the one which is generally best for the platform it is running on. Raw sockets (IP layer).
           are generally most efficient for Unix machines, while ethernet frames are required for Windows operation since Microsoft disabled raw socket support. Nmap still uses raw IP packets on Unix despite this option when there is
           no other choice (such as non-ethernet connections).

       --send-ip (Send at raw IP level) .
           Asks Nmap to send packets via raw IP sockets rather than sending lower level ethernet frames. It is the complement to the --send-eth option discussed previously.

       --privileged (Assume that the user is fully privileged) .
           Tells Nmap to simply assume that it is privileged enough to perform raw socket sends, packet sniffing, and similar operations that usually require root privileges.  on Unix systems. By default Nmap quits if such operations
           are requested but geteuid is not zero.  --privileged is useful with Linux kernel capabilities and similar systems that may be configured to allow unprivileged users to perform raw-packet scans. Be sure to provide this
           option flag before any flags for options that require privileges (SYN scan, OS detection, etc.). The NMAP_PRIVILEGED.  environment variable may be set as an equivalent alternative to --privileged.

       --unprivileged (Assume that the user lacks raw socket privileges) .
           This option is the opposite of --privileged. It tells Nmap to treat the user as lacking network raw socket and sniffing privileges. This is useful for testing, debugging, or when the raw network functionality of your
           operating system is somehow broken. The NMAP_UNPRIVILEGED.  environment variable may be set as an equivalent alternative to --unprivileged.

       --release-memory (Release memory before quitting) .
           This option is only useful for memory-leak debugging. It causes Nmap to release allocated memory just before it quits so that actual memory leaks are easier to spot. Normally Nmap skips this as the OS does this anyway upon
           process termination.

       -V; --version (Print version number) .
           Prints the Nmap version number and exits.

       -h; --help (Print help summary page) .
           Prints a short help screen with the most common command flags. Running Nmap without any arguments does the same thing.

RUNTIME INTERACTION
       During the execution of Nmap, all key presses are captured. This allows you to interact with the program without aborting and restarting it. Certain special keys will change options, while any other keys will print out a status
       message telling you about the scan. The convention is that lowercase letters increase the amount of printing, and uppercase letters decrease the printing. You may also press `?' for help.

       v / V
           Increase / decrease the verbosity level

       d / D
           Increase / decrease the debugging Level

       p / P
           Turn on / off packet tracing

       ?
           Print a runtime interaction help screen

       Anything else
           Print out a status message like this:

               Stats: 0:00:07 elapsed; 20 hosts completed (1 up), 1 undergoing Service Scan
               Service scan Timing: About 33.33% done; ETC: 20:57 (0:00:12 remaining)

EXAMPLES
       Here are some Nmap usage examples, from the simple and routine to a little more complex and esoteric. Some actual IP addresses and domain names are used to make things more concrete. In their place you should substitute
       addresses/names from your own network. While I don't think port scanning other networks is or should be illegal, some network administrators don't appreciate unsolicited scanning of their networks and may complain. Getting
       permission first is the best approach.

       For testing purposes, you have permission to scan the host scanme.nmap.org..  This permission only includes scanning via Nmap and not testing exploits or denial of service attacks. To conserve bandwidth, please do not initiate
       more than a dozen scans against that host per day. If this free scanning target service is abused, it will be taken down and Nmap will report Failed to resolve given hostname/IP: scanme.nmap.org. These permissions also apply to
       the hosts scanme2.nmap.org, scanme3.nmap.org, and so on, though those hosts do not currently exist.

       This option scans all reserved TCP ports on the machine scanme.nmap.org . The -v option enables verbose mode.

       Launches a stealth SYN scan against each machine that is up out of the 256 IPs on the class C sized network where Scanme resides. It also tries to determine what operating system is running on each host that is up and running.
       This requires root privileges because of the SYN scan and OS detection.

       Launches host enumeration and a TCP scan at the first half of each of the 255 possible eight-bit subnets in the 198.116 class B address space. This tests whether the systems run SSH, DNS, POP3, or IMAP on their standard ports,
       or anything on port 4564. For any of these ports found open, version detection is used to determine what application is running.

       Asks Nmap to choose 100,000 hosts at random and scan them for web servers (port 80). Host enumeration is disabled with -Pn since first sending a couple probes to determine whether a host is up is wasteful when you are only
       probing one port on each target host anyway.

       This scans 4096 IPs for any web servers (without pinging them) and saves the output in grepable and XML formats.

NMAP BOOK
       While this reference guide details all material Nmap options, it can't fully demonstrate how to apply those features to quickly solve real-world tasks. For that, we released Nmap Network Scanning: The Official Nmap Project
       Guide to Network Discovery and Security Scanning.  Topics include subverting firewalls and intrusion detection systems, optimizing Nmap performance, and automating common networking tasks with the Nmap Scripting Engine. Hints
       and instructions are provided for common Nmap tasks such as taking network inventory, penetration testing, detecting rogue wireless access points, and quashing network worm outbreaks. Examples and diagrams show actual
       communication on the wire. More than half of the book is available free online. See http://nmap.org/book for more information.

BUGS
       Like its author, Nmap isn't perfect. But you can help make it better by sending bug reports or even writing patches. If Nmap doesn't behave the way you expect, first upgrade to the latest version available from http://nmap.org.
       If the problem persists, do some research to determine whether it has already been discovered and addressed. Try searching for the error message on our search page at http://insecure.org/search.html or at Google. Also try
       browsing the nmap-dev archives at http://seclists.org/..  Read this full manual page as well. If nothing comes of this, mail a bug report to <dev@nmap.org>. Please include everything you have learned about the problem, as well
       as what version of Nmap you are running and what operating system version it is running on. Problem reports and Nmap usage questions sent to <dev@nmap.org> are far more likely to be answered than those sent to Fyodor directly.
       If you subscribe to the nmap-dev list before posting, your message will bypass moderation and get through more quickly. Subscribe at http://nmap.org/mailman/listinfo/dev.

       Code patches to fix bugs are even better than bug reports. Basic instructions for creating patch files with your changes are available at https://svn.nmap.org/nmap/HACKING. Patches may be sent to nmap-dev (recommended) or to
       Fyodor directly.

AUTHOR
       Gordon "Fyodor" Lyon <fyodor@nmap.org> (http://insecure.org)

       Hundreds of people have made valuable contributions to Nmap over the years. These are detailed in the CHANGELOG.  file which is distributed with Nmap and also available from http://nmap.org/changelog.html.

LEGAL NOTICES
   Nmap Copyright and Licensing
       The Nmap Security Scanner is (C) 1996-2012 Insecure.Com LLC. Nmap is also a registered trademark of Insecure.Com LLC. This program is free software; you may redistribute and/or modify it under the terms of the GNU General
       Public License as published by the Free Software Foundation; Version 2 with the clarifications and exceptions described below. This guarantees your right to use, modify, and redistribute this software under certain conditions.
       If you wish to embed Nmap technology into proprietary software, we sell alternative licenses (contact <sales@insecure.com>). Dozens of software vendors already license Nmap technology such as host discovery, port scanning, OS
       detection, and version detection.

       Note that the GPL places important restrictions on "derived works", yet it does not provide a detailed definition of that term. To avoid misunderstandings, we consider an application to constitute a "derivative work" for the
       purpose of this license if it does any of the following:

       o   Integrates source code from Nmap

       o   Reads or includes Nmap copyrighted data files, such as nmap-os-db or nmap-service-probes.

       o   Executes Nmap and parses the results (as opposed to typical shell or execution-menu apps, which simply display raw Nmap output and so are not derivative works.)

       o   Integrates/includes/aggregates Nmap into a proprietary executable installer, such as those produced by InstallShield.

       o   Links to a library or executes a program that does any of the above.

       The term "Nmap" should be taken to also include any portions or derived works of Nmap. This list is not exclusive, but is meant to clarify our interpretation of derived works with some common examples. Our interpretation
       applies only to Nmap--we don't speak for other people's GPL works.

       If you have any questions about the GPL licensing restrictions on using Nmap in non-GPL works, we would be happy to help. As mentioned above, we also offer alternative license to integrate Nmap into proprietary applications and
       appliances. These contracts have been sold to many security vendors, and generally include a perpetual license as well as providing for priority support and updates as well as helping to fund the continued development of Nmap
       technology. Please email <sales@insecure.com> for further information.

       As a special exception to the GPL terms, Insecure.Com LLC grants permission to link the code of this program with any version of the OpenSSL library which is distributed under a license identical to that listed in the included
       COPYING.OpenSSL file, and distribute linked combinations including the two..  You must obey the GNU GPL in all respects for all of the code used other than OpenSSL. If you modify this file, you may extend this exception to your
       version of the file, but you are not obligated to do so.

       If you received these files with a written license agreement or contract stating terms other than the terms above, then that alternative license agreement takes precedence over these comments.

   Creative Commons License for this Nmap Guide
       This Nmap Reference Guide is (C) 2005-2012 Insecure.Com LLC. It is hereby placed under version 3.0 of the Creative Commons Attribution License[19]. This allows you redistribute and modify the work as you desire, as long as you
       credit the original source. Alternatively, you may choose to treat this document as falling under the same license as Nmap itself (discussed previously).

   Source Code Availability and Community Contributions
       Source is provided to this software because we believe users have a right to know exactly what a program is going to do before they run it. This also allows you to audit the software for security holes (none have been found so
       far).

       Source code also allows you to port Nmap to new platforms, fix bugs, and add new features. You are highly encouraged to send your changes to <dev@nmap.org> for possible incorporation into the main distribution. By sending these
       changes to Fyodor or one of the Insecure.Org development mailing lists, it is assumed that you are offering the Nmap Project (Insecure.Com LLC) the unlimited, non-exclusive right to reuse, modify, and relicense the code. Nmap
       will always be available open source,.  but this is important because the inability to relicense code has caused devastating problems for other Free Software projects (such as KDE and NASM). We also occasionally relicense the
       code to third parties as discussed above. If you wish to specify special license conditions of your contributions, just say so when you send them.

   No Warranty.
       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License v2.0 for
       more details at http://www.gnu.org/licenses/gpl-2.0.html, or in the COPYING file included with Nmap.

       It should also be noted that Nmap has occasionally been known to crash poorly written applications, TCP/IP stacks, and even operating systems..  While this is extremely rare, it is important to keep in mind.  Nmap should never
       be run against mission critical systems unless you are prepared to suffer downtime. We acknowledge here that Nmap may crash your systems or networks and we disclaim all liability for any damage or problems Nmap could cause.

   Inappropriate Usage
       Because of the slight risk of crashes and because a few black hats like to use Nmap for reconnaissance prior to attacking systems, there are administrators who become upset and may complain when their system is scanned. Thus,
       it is often advisable to request permission before doing even a light scan of a network.

       Nmap should never be installed with special privileges (e.g. suid root)..  That would open up a major security vulnerability as other users on the system (or attackers) could use it for privilege escalation.

   Third-Party Software and Funding Notices
       This product includes software developed by the Apache Software Foundation[20]. A modified version of the Libpcap portable packet capture library[21].  is distributed along with Nmap. The Windows version of Nmap utilized the
       Libpcap-derived WinPcap library[22].  instead. Regular expression support is provided by the PCRE library[23],.  which is open-source software, written by Philip Hazel..  Certain raw networking functions use the Libdnet[24].
       networking library, which was written by Dug Song..  A modified version is distributed with Nma.p Nmap can optionally link with the OpenSSL cryptography toolkit[25].  for SSL version detection support. The Nmap Scripting Engine
       uses an embedded version of the Lua programming language[26]..  The Liblinear linear classification library[27] is used for our IPv6 OS detection machine learning techniques[28].  All of the third-party software described in
       this paragraph is freely redistributable under BSD-style software licenses.

       Binary packages for Windows and Mac OS X include support libraries necessary to run Zenmap and Ndiff with Python and PyGTK. (Unix platforms commonly make these libraries easy to install, so they are not part of the packages.) A
       listing of these support libraries and their licenses is included in the LICENSES files.

       This software was supported in part through the Google Summer of Code[29] and the DARPA CINDER program[30] (DARPA-BAA-10-84).

   United States Export Control.
       Nmap only uses encryption when compiled with the optional OpenSSL support and linked with OpenSSL. When compiled without OpenSSL support, Insecure.Com LLC believes that Nmap is not subject to U.S.  Export Administration
       Regulations (EAR)[31] export control. As such, there is no applicable ECCN (export control classification number) and exportation does not require any special license, permit, or other governmental authorization.

       When compiled with OpenSSL support or distributed as source code, Insecure.Com LLC believes that Nmap falls under U.S. ECCN 5D002[32] ("Information Security Software"). We distribute Nmap under the TSU exception for publicly
       available encryption software defined in EAR 740.13(e)[33].

NOTES
        1. Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning
           http://nmap.org/book/

        2. RFC 1122
           http://www.rfc-editor.org/rfc/rfc1122.txt

        3. RFC 792
           http://www.rfc-editor.org/rfc/rfc792.txt

        4. RFC 950
           http://www.rfc-editor.org/rfc/rfc950.txt

        5. RFC 1918
           http://www.rfc-editor.org/rfc/rfc1918.txt

        6. UDP
           http://www.rfc-editor.org/rfc/rfc768.txt

        7. SCTP
           http://www.rfc-editor.org/rfc/rfc4960.txt

        8. TCP RFC
           http://www.rfc-editor.org/rfc/rfc793.txt

        9. RFC 959
           http://www.rfc-editor.org/rfc/rfc959.txt

       10. RFC 1323
           http://www.rfc-editor.org/rfc/rfc1323.txt

       11. Lua programming language
           http://lua.org

       12. precedence
           http://www.lua.org/manual/5.1/manual.html#2.5.3

       13. IP protocol
           http://www.rfc-editor.org/rfc/rfc791.txt

       14. RFC 2960
           http://www.rfc-editor.org/rfc/rfc2960.txt

       15. Nmap::Scanner
           http://sourceforge.net/projects/nmap-scanner/

       16. Nmap::Parser
           http://nmapparser.wordpress.com/

       17. xsltproc
           http://xmlsoft.org/XSLT/

       18. listed at Wikipedia
           http://en.wikipedia.org/wiki/List_of_IPv6_tunnel_brokers

       19. Creative Commons Attribution License
           http://creativecommons.org/licenses/by/3.0/

       20. Apache Software Foundation
           http://www.apache.org

       21. Libpcap portable packet capture library
           http://www.tcpdump.org

       22. WinPcap library
           http://www.winpcap.org

       23. PCRE library
           http://www.pcre.org

       24. Libdnet
           http://libdnet.sourceforge.net

       25. OpenSSL cryptography toolkit
           http://www.openssl.org

       26. Lua programming language
           http://www.lua.org

       27. Liblinear linear classification library
           http://www.csie.ntu.edu.tw/~cjlin/liblinear/

       28. IPv6 OS detection machine learning techniques
           http://nmap.org/book/osdetect-guess.html#osdetect-guess-ipv6

       29. Google Summer of Code
           http://nmap.org/soc/

       30. DARPA CINDER program
           https://www.fbo.gov/index?s=opportunity&mode=form&id=585e02a51f77af5cb3c9e06b9cc82c48&tab=core&_cview=1

       31. Export Administration Regulations (EAR)
           http://www.access.gpo.gov/bis/ear/ear_data.html

       32. 5D002
           http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf

       33. EAR 740.13(e)
           http://www.access.gpo.gov/bis/ear/pdf/740.pdf

Nmap                                                                                                            07/28/2013                                                                                                         NMAP(1)
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