# nmap

## NAME



           nmap - Network exploration tool and security / port scanner
    


## SYNOPSIS



    
           **nmap**[_Scan Type_...] [_Options_] {_target specification_}
    


## DESCRIPTION



           Nmap (“Network Mapper”) is an open source tool for network
           exploration and security auditing. It was designed to rapidly scan
           large networks, although it works fine against single hosts. Nmap
           uses raw IP packets in novel ways to determine what hosts are
           available on the network, what services (application name and
           version) those hosts are offering, what operating systems (and OS
           versions) they are running, what type of packet filters/firewalls
           are in use, and dozens of other characteristics. While Nmap is
           commonly used for security audits, many systems and network
           administrators find it useful for routine tasks such as network
           inventory, managing service upgrade schedules, and monitoring host
           or service uptime.
    
           The output from Nmap is a list of scanned targets, with
           supplemental information on each depending on the options used.
           Key among that information is the “interesting ports table”.  That
           table lists the port number and protocol, service name, and state.
           The state is either open, filtered, closed, or unfiltered.  Open
           means that an application on the target machine is listening for
           connections/packets on that port.  Filtered means that a firewall,
           filter, or other network obstacle is blocking the port so that
           Nmap cannot tell whether it is open or closed.  Closed ports have
           no application listening on them, though they could open up at any
           time. Ports are classified as unfiltered when they are responsive
           to Nmap's probes, but Nmap cannot determine whether they are open
           or closed. Nmap reports the state combinations open|filtered and
           closed|filtered when it cannot determine which of the two states
           describe a port. The port table may also include software version
           details when version detection has been requested. When an IP
           protocol scan is requested (**-sO**), Nmap provides information on
           supported IP protocols rather than listening ports.
    
           In addition to the interesting ports table, Nmap can provide
           further information on targets, including reverse DNS names,
           operating system guesses, device types, and MAC addresses.
    
           A typical Nmap scan is shown in Example 1. The only Nmap arguments
           used in this example are **-A** , to enable OS and version detection,
           script scanning, and traceroute; **-T4** for faster execution; and
           then the hostname.
    
           **Example 1. A representative Nmap scan**
    
               # **nmap -A -T4 scanme.nmap.org**
    
               Nmap scan report for scanme.nmap.org (74.207.244.221)
               Host is up (0.029s latency).
               rDNS record for 74.207.244.221: li86-221.members.linode.com
               Not shown: 995 closed ports
               PORT     STATE    SERVICE     VERSION
               22/tcp   open     ssh         OpenSSH 5.3p1 Debian 3ubuntu7 (protocol 2.0)
               | ssh-hostkey: 1024 8d:60:f1:7c:ca:b7:3d:0a:d6:67:54:9d:69:d9:b9:dd (DSA)
               |_2048 79:f8:09:ac:d4:e2:32:42:10:49:d3:bd:20:82:85:ec (RSA)
               80/tcp   open     http        Apache httpd 2.2.14 ((Ubuntu))
               |_http-title: Go ahead and ScanMe!
               646/tcp  filtered ldp
               1720/tcp filtered H.323/Q.931
               9929/tcp open     nping-echo  Nping echo
               Device type: general purpose
               Running: Linux 2.6.X
               OS CPE: cpe:/o:linux:linux_kernel:2.6.39
               OS details: Linux 2.6.39
               Network Distance: 11 hops
               Service Info: OS: Linux; CPE: cpe:/o:linux:kernel
    
               TRACEROUTE (using port 53/tcp)
               HOP RTT      ADDRESS
               [Cut first 10 hops for brevity]
               11  17.65 ms li86-221.members.linode.com (74.207.244.221)
    
               Nmap done: 1 IP address (1 host up) scanned in 14.40 seconds
    
           The newest version of Nmap can be obtained from **https://nmap.org ******.
           The newest version of this man page is available at**https://nmap.org/book/man.html ******.  It is also included as a chapter
           of Nmap Network Scanning: The Official Nmap Project Guide to
           Network Discovery and Security Scanning (see**https://nmap.org/book/ ******).


## OPTIONS SUMMARY



           This options summary is printed when Nmap is run with no
           arguments, and the latest version is always available at
           **https://svn.nmap.org/nmap/docs/nmap.usage.txt ******. It helps people
           remember the most common options, but is no substitute for the
           in-depth documentation in the rest of this manual. Some obscure
           options aren't even included here.
    
               Nmap 7.98SVN (https://nmap.org )
               Usage: nmap [Scan Type(s)] [Options] {target specification}
               TARGET SPECIFICATION:
                 Can pass hostnames, IP addresses, networks, etc.
                 Ex: scanme.nmap.org, microsoft.com/24, 192.168.0.1; 10.0.0-255.1-254
                 -iL <inputfilename>: Input from list of hosts/networks
                 -iR <num hosts>: Choose random targets
                 --exclude <host1[,host2][,host3],...>: Exclude hosts/networks
                 --excludefile <exclude_file>: Exclude list from file
               HOST DISCOVERY:
                 -sL: List Scan - simply list targets to scan
                 -sn: Ping Scan - disable port scan
                 -Pn: Treat all hosts as online -- skip host discovery
                 -PS/PA/PU/PY[portlist]: TCP SYN, TCP ACK, UDP or SCTP discovery to given ports
                 -PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes
                 -PO[protocol list]: IP Protocol Ping
                 -n/-R: Never do DNS resolution/Always resolve [default: sometimes]
                 --dns-servers <serv1[,serv2],...>: Specify custom DNS servers
                 --system-dns: Use OS's DNS resolver
                 --traceroute: Trace hop path to each host
               SCAN TECHNIQUES:
                 -sS/sT/sA/sW/sM: TCP SYN/Connect()/ACK/Window/Maimon scans
                 -sU: UDP Scan
                 -sN/sF/sX: TCP Null, FIN, and Xmas scans
                 --scanflags <flags>: Customize TCP scan flags
                 -sI <zombie host[:probeport]>: Idle scan
                 -sY/sZ: SCTP INIT/COOKIE-ECHO scans
                 -sO: IP protocol scan
                 -b <FTP relay host>: FTP bounce scan
               PORT SPECIFICATION AND SCAN ORDER:
                 -p <port ranges>: Only scan specified ports
                   Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080,S:9
                 --exclude-ports <port ranges>: Exclude the specified ports from scanning
                 -F: Fast mode - Scan fewer ports than the default scan
                 -r: Scan ports sequentially - don't randomize
                 --top-ports <number>: Scan <number> most common ports
                 --port-ratio <ratio>: Scan ports more common than <ratio>
               SERVICE/VERSION DETECTION:
                 -sV: Probe open ports to determine service/version info
                 --version-intensity <level>: Set from 0 (light) to 9 (try all probes)
                 --version-light: Limit to most likely probes (intensity 2)
                 --version-all: Try every single probe (intensity 9)
                 --version-trace: Show detailed version scan activity (for debugging)
               SCRIPT SCAN:
                 -sC: equivalent to --script=default
                 --script=<Lua scripts>: <Lua scripts> is a comma separated list of
                          directories, script-files or script-categories
                 --script-args=<n1=v1,[n2=v2,...]>: provide arguments to scripts
                 --script-args-file=filename: provide NSE script args in a file
                 --script-trace: Show all data sent and received
                 --script-updatedb: Update the script database.
                 --script-help=<Lua scripts>: Show help about scripts.
                          <Lua scripts> is a comma-separated list of script-files or
                          script-categories.
               OS DETECTION:
                 -O: Enable OS detection
                 --osscan-limit: Limit OS detection to promising targets
                 --osscan-guess: Guess OS more aggressively
               TIMING AND PERFORMANCE:
                 Options which take <time> are in seconds, or append 'ms' (milliseconds),
                 's' (seconds), 'm' (minutes), or 'h' (hours) to the value (e.g. 30m).
                 -T<0-5>: Set timing template (higher is faster)
                 --min-hostgroup/max-hostgroup <size>: Parallel host scan group sizes
                 --min-parallelism/max-parallelism <numprobes>: Probe parallelization
                 --min-rtt-timeout/max-rtt-timeout/initial-rtt-timeout <time>: Specifies
                     probe round trip time.
                 --max-retries <tries>: Caps number of port scan probe retransmissions.
                 --host-timeout <time>: Give up on target after this long
                 --scan-delay/--max-scan-delay <time>: Adjust delay between probes
                 --min-rate <number>: Send packets no slower than <number> per second
                 --max-rate <number>: Send packets no faster than <number> per second
               FIREWALL/IDS EVASION AND SPOOFING:
                 -f; --mtu <val>: fragment packets (optionally w/given MTU)
                 -D <decoy1,decoy2[,ME],...>: Cloak a scan with decoys
                 -S <IP_Address>: Spoof source address
                 -e <iface>: Use specified interface
                 -g/--source-port <portnum>: Use given port number
                 --proxies <url1,[url2],...>: Relay connections through HTTP/SOCKS4 proxies
                 --data <hex string>: Append a custom payload to sent packets
                 --data-string <string>: Append a custom ASCII string to sent packets
                 --data-length <num>: Append random data to sent packets
                 --ip-options <options>: Send packets with specified ip options
                 --ttl <val>: Set IP time-to-live field
                 --spoof-mac <mac address/prefix/vendor name>: Spoof your MAC address
                 --badsum: Send packets with a bogus TCP/UDP/SCTP checksum
               OUTPUT:
                 -oN/-oX/-oS/-oG <file>: Output scan in normal, XML, s|<rIpt kIddi3,
                    and Grepable format, respectively, to the given filename.
                 -oA <basename>: Output in the three major formats at once
                 -v: Increase verbosity level (use -vv or more for greater effect)
                 -d: Increase debugging level (use -dd or more for greater effect)
                 --reason: Display the reason a port is in a particular state
                 --open: Only show open (or possibly open) ports
                 --packet-trace: Show all packets sent and received
                 --iflist: Print host interfaces and routes (for debugging)
                 --append-output: Append to rather than clobber specified output files
                 --resume <filename>: Resume an aborted scan
                 --noninteractive: Disable runtime interactions via keyboard
                 --stylesheet <path/URL>: XSL stylesheet to transform XML output to HTML
                 --webxml: Reference stylesheet from Nmap.Org for more portable XML
                 --no-stylesheet: Prevent associating of XSL stylesheet w/XML output
               MISC:
                 -6: Enable IPv6 scanning
                 -A: Enable OS detection, version detection, script scanning, and traceroute
                 --datadir <dirname>: Specify custom Nmap data file location
                 --send-eth/--send-ip: Send using raw ethernet frames or IP packets
                 --privileged: Assume that the user is fully privileged
                 --unprivileged: Assume the user lacks raw socket privileges
                 -V: Print version number
                 -h: Print this help summary page.
               EXAMPLES:
                 nmap -v -A scanme.nmap.org
                 nmap -v -sn 192.168.0.0/16 10.0.0.0/8
                 nmap -v -iR 10000 -Pn -p 80
               SEE THE MAN PAGE (https://nmap.org/book/man.html) FOR MORE OPTIONS AND EXAMPLES
    


## TARGET SPECIFICATION



           Everything on the Nmap command-line that isn't an option (or
           option argument) is treated as a target host specification. The
           simplest case is to specify a target IP address or hostname for
           scanning.
    
           When a hostname is given as a target, it is resolved via the
           Domain Name System (DNS) to determine the IP address to scan. If
           the name resolves to more than one IP address, only the first one
           will be scanned. To make Nmap scan all the resolved addresses
           instead of only the first one, use the **--resolve-all** option.
    
           Sometimes you wish to scan a whole network of adjacent hosts. For
           this, Nmap supports CIDR-style addressing. You can append /_numbits_
           to an IP address or hostname and Nmap will scan every IP address
           for which the first _numbits_ are the same as for the reference IP
           or hostname given. For example, 192.168.10.0/24 would scan the 256
           hosts between 192.168.10.0 (binary: 11000000 10101000 00001010
           00000000) and 192.168.10.255 (binary: 11000000 10101000 00001010
           11111111), inclusive.  192.168.10.40/24 would scan exactly the
           same targets. Given that the host scanme.nmap.org is at the IP
           address 64.13.134.52, the specification scanme.nmap.org/16 would
           scan the 65,536 IP addresses between 64.13.0.0 and 64.13.255.255.
           The smallest allowed value is /0, which targets the whole
           Internet. The largest value for IPv4 is /32, which scans just the
           named host or IP address because all address bits are fixed. The
           largest value for IPv6 is /128, which does the same thing.
    
           CIDR notation is short but not always flexible enough. For
           example, you might want to scan 192.168.0.0/16 but skip any IPs
           ending with .0 or .255 because they may be used as subnet network
           and broadcast addresses. Nmap supports this through octet range
           addressing. Rather than specify a normal IP address, you can
           specify a comma-separated list of numbers or ranges for each
           octet. For example, 192.168.0-255.1-254 will skip all addresses in
           the range that end in .0 or .255, and 192.168.3-5,7.1 will scan
           the four addresses 192.168.3.1, 192.168.4.1, 192.168.5.1, and
           192.168.7.1. Either side of a range may be omitted; the default
           values are 0 on the left and 255 on the right. Using - by itself
           is the same as 0-255, but remember to use 0- in the first octet so
           the target specification doesn't look like a command-line option.
           Ranges need not be limited to the final octets: the specifier
           0-255.0-255.13.37 will perform an Internet-wide scan for all IP
           addresses ending in 13.37. This sort of broad sampling can be
           useful for Internet surveys and research.
    
           IPv6 addresses can be specified by their fully qualified IPv6
           address or hostname or with CIDR notation for subnets. Octet
           ranges aren't yet supported for IPv6.
    
           IPv6 addresses with non-global scope need to have a zone ID
           suffix. On Unix systems, this is a percent sign followed by an
           interface name; a complete address might be
           fe80::a8bb:ccff:fedd:eeff%eth0. On Windows, use an interface index
           number in place of an interface name: fe80::a8bb:ccff:fedd:eeff%1.
           You can see a list of interface indexes by running the command
           **netsh.exe interface ipv6 show interface**.
    
           Nmap accepts multiple host specifications on the command line, and
           they don't need to be the same type. The command **nmap**
           **scanme.nmap.org 192.168.0.0/8 10.0.0,1,3-7.-** does what you would
           expect.
    
           While targets are usually specified on the command lines, the
           following options are also available to control target selection:
    
           **-iL** _inputfilename_ (Input from list)
               Reads target specifications from _inputfilename_. Passing a huge
               list of hosts is often awkward on the command line, yet it is
               a common desire. For example, your DHCP server might export a
               list of 10,000 current leases that you wish to scan. Or maybe
               you want to scan all IP addresses _except_ for those to locate
               hosts using unauthorized static IP addresses. Simply generate
               the list of hosts to scan and pass that filename to Nmap as an
               argument to the **-iL** option. Entries can be in any of the
               formats accepted by Nmap on the command line (IP address,
               hostname, CIDR, IPv6, or octet ranges). Each entry must be
               separated by one or more spaces, tabs, or newlines. You can
               specify a hyphen (-) as the filename if you want Nmap to read
               hosts from standard input rather than an actual file.
    
               The input file may contain comments that start with # and
               extend to the end of the line.
    
           **-iR** _num hosts_ (Choose random targets)
               For Internet-wide surveys and other research, you may want to
               choose targets at random. The _num hosts_ argument tells Nmap
               how many IPs to generate. Undesirable IPs such as those in
               certain private, multicast, or unallocated address ranges are
               automatically skipped. The argument 0 can be specified for a
               never-ending scan. Keep in mind that some network
               administrators bristle at unauthorized scans of their networks
               and may complain. Use this option at your own risk! If you
               find yourself really bored one rainy afternoon, try the
               command **nmap -Pn -sS -p 80 -iR 0 --open** to locate random web
               servers for browsing.
    
           **--exclude** _host1_**[,**_host2_[,...]] (Exclude hosts/networks)
               Specifies a comma-separated list of targets to be excluded
               from the scan even if they are part of the overall network
               range you specify. The list you pass in uses normal Nmap
               syntax, so it can include hostnames, CIDR netblocks, octet
               ranges, etc. This can be useful when the network you wish to
               scan includes untouchable mission-critical servers, systems
               that are known to react adversely to port scans, or subnets
               administered by other people.
    
           **--excludefile** _exclude_file_ (Exclude list from file)
               This offers the same functionality as the **--exclude** option,
               except that the excluded targets are provided in a newline-,
               space-, or tab-delimited _exclude_file_ rather than on the
               command line.
    
               The exclude file may contain comments that start with # and
               extend to the end of the line.
    
           **-n**(No reverse DNS resolution)
    
               Tells Nmap to _never_ do reverse DNS resolution on the active IP
               addresses it finds. Since DNS can be slow even with Nmap's
               built-in parallel stub resolver, this option can slash
               scanning times.
    
           **-R**(Reverse DNS resolution for all targets)
               Tells Nmap to _always_ do reverse DNS resolution on the target
               IP addresses. Normally reverse DNS is only performed against
               responsive (online) hosts.
    
           **--resolve-all**(Scan each resolved address)
               If a hostname target resolves to more than one address, scan
               all of them. The default behavior is to only scan the first
               resolved address. Regardless, only addresses in the
               appropriate address family will be scanned: IPv4 by default,
               IPv6 with **-6**.
    
           **--unique**(Scan each address only once)
               Scan each IP address only once. The default behavior is to
               scan each address as many times as it is specified in the
               target list, such as when network ranges overlap or different
               hostnames resolve to the same address.
    
           **--system-dns**(Use system DNS resolver)
               By default, Nmap resolves names to IP addresses (and IP
               addresses to names) by sending queries directly to the name
               servers configured on your host and then listening for
               responses. Many requests (often dozens) are performed in
               parallel to improve performance. Specify this option to use
               your system resolver instead (one IP at a time via the
               **getnameinfo** call). This is slower and rarely useful unless you
               find a bug in the Nmap parallel resolver (please let us know
               if you do).
    
           **--dns-servers** _server1_**[,**_server2_[,...]]  (Servers to use for DNS
           queries)
               By default, Nmap determines your DNS servers from your
               resolv.conf file (Unix) or the Registry (Win32).
               Alternatively, you may use this option to specify alternate
               servers. This option is not honored if you are using
               **--system-dns**. Using multiple DNS servers is often faster,
               especially if you choose authoritative servers for your target
               IP space. This option can also improve stealth, as your
               requests can be bounced off just about any recursive DNS
               server on the Internet.
    
               This option also comes in handy when scanning private
               networks. Sometimes only a few name servers provide proper DNS
               information, and you may not even know where they are. You can
               scan the network for port 53 (perhaps with version detection),
               then try Nmap list scans (**-sL**) specifying each name server one
               at a time with **--dns-servers** until you find one which works.
    
               This option might not be honored if the DNS response exceeds
               the size of a UDP packet. In such a situation our DNS resolver
               will make the best effort to extract a response from the
               truncated packet, and if not successful it will fall back to
               using the system resolver.
    


## HOST DISCOVERY



           One of the very first steps in any network reconnaissance mission
           is to reduce a (sometimes huge) set of IP ranges into a list of
           active or interesting hosts. Scanning every port of every single
           IP address is slow and usually unnecessary. Of course what makes a
           host interesting depends greatly on the scan purposes. Network
           administrators may only be interested in hosts running a certain
           service, while security auditors may care about every single
           device with an IP address. An administrator may be comfortable
           using just an ICMP ping to locate hosts on his internal network,
           while an external penetration tester may use a diverse set of
           dozens of probes in an attempt to evade firewall restrictions.
    
           Because host discovery needs are so diverse, Nmap offers a wide
           variety of options for customizing the techniques used. Host
           discovery is sometimes called ping scan, but it goes well beyond
           the simple ICMP echo request packets associated with the
           ubiquitous ping tool. Users can skip the discovery step entirely
           with a list scan (**-sL**) or by disabling host discovery (**-Pn**), or
           engage the network with arbitrary combinations of multi-port TCP
           SYN/ACK, UDP, SCTP INIT and ICMP probes. The goal of these probes
           is to solicit responses which demonstrate that an IP address is
           actually active (is being used by a host or network device). On
           many networks, only a small percentage of IP addresses are active
           at any given time. This is particularly common with private
           address space such as 10.0.0.0/8. That network has 16 million IPs,
           but I have seen it used by companies with less than a thousand
           machines. Host discovery can find those machines in a sparsely
           allocated sea of IP addresses.
    
           If no host discovery options are given, Nmap sends an ICMP echo
           request, a TCP SYN packet to port 443, a TCP ACK packet to port
           80, and an ICMP timestamp request. (For IPv6, the ICMP timestamp
           request is omitted because it is not part of ICMPv6.) These
           defaults are equivalent to the **-PE -PS443 -PA80 -PP** options. The
           exceptions to this are the ARP (for IPv4) and Neighbor Discovery
           (for IPv6) scans which are used for any targets on a local
           ethernet network. For unprivileged Unix shell users, the default
           probes are a SYN packet to ports 80 and 443 using the **connect**
           system call.  This host discovery is often sufficient when
           scanning local networks, but a more comprehensive set of discovery
           probes is recommended for security auditing.
    
           The **-P*** options (which select ping types) can be combined. You can
           increase your odds of penetrating strict firewalls by sending many
           probe types using different TCP ports/flags and ICMP codes. Also
           note that ARP/Neighbor Discovery is done by default against
           targets on a local Ethernet network even if you specify other **-P***
           options, because it is almost always faster and more effective.
    
           By default, Nmap does host discovery and then performs a port scan
           against each host it determines is online. This is true even if
           you specify non-default host discovery types such as UDP probes
           (**-PU**). Read about the **-sn** option to learn how to perform only host
           discovery, or use **-Pn** to skip host discovery and port scan all
           target addresses. The following options control host discovery:
    
           **-sL**(List Scan)
               The list scan is a degenerate form of host discovery that
               simply lists each host of the network(s) specified, without
               sending any packets to the target hosts. By default, Nmap
               still does reverse-DNS resolution on the hosts to learn their
               names. It is often surprising how much useful information
               simple hostnames give out. For example, fw.chi is the name of
               one company's Chicago firewall.
    
               Nmap also reports the total number of IP addresses at the end.
               The list scan is a good sanity check to ensure that you have
               proper IP addresses for your targets. If the hosts sport
               domain names you do not recognize, it is worth investigating
               further to prevent scanning the wrong company's network.
    
               Since the idea is to simply print a list of target hosts,
               options for higher level functionality such as port scanning,
               OS detection, or host discovery cannot be combined with this.
               If you wish to disable host discovery while still performing
               such higher level functionality, read up on the **-Pn**(skip host
               discovery) option.
    
           **-sn**(No port scan)
               This option tells Nmap not to do a port scan after host
               discovery, and only print out the available hosts that
               responded to the host discovery probes. This is often known as
               a “ping scan”, but you can also request that traceroute and
               NSE host scripts be run. This is by default one step more
               intrusive than the list scan, and can often be used for the
               same purposes. It allows light reconnaissance of a target
               network without attracting much attention. Knowing how many
               hosts are up is more valuable to attackers than the list
               provided by list scan of every single IP and host name.
    
               Systems administrators often find this option valuable as
               well. It can easily be used to count available machines on a
               network or monitor server availability. This is often called a
               ping sweep, and is more reliable than pinging the broadcast
               address because many hosts do not reply to broadcast queries.
    
               The default host discovery done with **-sn** consists of an ICMP
               echo request, TCP SYN to port 443, TCP ACK to port 80, and an
               ICMP timestamp request by default. When executed by an
               unprivileged user, only SYN packets are sent (using a **connect**
               call) to ports 80 and 443 on the target. When a privileged
               user tries to scan targets on a local ethernet network, ARP
               requests are used unless **--send-ip** was specified. The **-sn**
               option can be combined with any of the discovery probe types
               (the **-P*** options) for greater flexibility. If any of those
               probe type and port number options are used, the default
               probes are overridden. When strict firewalls are in place
               between the source host running Nmap and the target network,
               using those advanced techniques is recommended. Otherwise
               hosts could be missed when the firewall drops probes or their
               responses.
    
               In previous releases of Nmap, **-sn** was known as **-sP**.
    
           **-Pn**(No ping)
               This option skips the host discovery stage altogether.
               Normally, Nmap uses this stage to determine active machines
               for heavier scanning and to gauge the speed of the network. By
               default, Nmap only performs heavy probing such as port scans,
               version detection, or OS detection against hosts that are
               found to be up. Disabling host discovery with **-Pn** causes Nmap
               to attempt the requested scanning functions against _every_
               target IP address specified. So if a /16 sized network is
               specified on the command line, all 65,536 IP addresses are
               scanned. Proper host discovery is skipped as with the list
               scan, but instead of stopping and printing the target list,
               Nmap continues to perform requested functions as if each
               target IP is active. Default timing parameters are used, which
               may result in slower scans. To skip host discovery _and_ port
               scan, while still allowing NSE to run, use the two options **-Pn**
               **-sn** together.
    
               For machines on a local ethernet network, ARP scanning will
               still be performed (unless **--disable-arp-ping** or **--send-ip** is
               specified) because Nmap needs MAC addresses to further scan
               target hosts. In previous versions of Nmap, **-Pn** was **-P0** and
               **-PN**.
    
           **-PS** _port list_ (TCP SYN Ping)
               This option sends an empty TCP packet with the SYN flag set.
               The default destination port is 80 (configurable at compile
               time by changing _DEFAULT_TCP_PROBE_PORT_SPEC_ in nmap.h).
               Alternate ports can be specified as a parameter. The syntax is
               the same as for the **-p** except that port type specifiers like
               T: are not allowed. Examples are **-PS22** and
               **-PS22-25,80,113,1050,35000**. Note that there can be no space
               between **-PS** and the port list. If multiple probes are
               specified they will be sent in parallel.
    
               The SYN flag suggests to the remote system that you are
               attempting to establish a connection. Normally the destination
               port will be closed, and a RST (reset) packet sent back. If
               the port happens to be open, the target will take the second
               step of a TCP three-way-handshake by responding with a SYN/ACK
               TCP packet. The machine running Nmap then tears down the
               nascent connection by responding with a RST rather than
               sending an ACK packet which would complete the
               three-way-handshake and establish a full connection. The RST
               packet is sent by the kernel of the machine running Nmap in
               response to the unexpected SYN/ACK, not by Nmap itself.
    
               Nmap does not care whether the port is open or closed. Either
               the RST or SYN/ACK response discussed previously tell Nmap
               that the host is available and responsive.
    
               On Unix boxes, only the privileged user root is generally able
               to send and receive raw TCP packets.  For unprivileged users,
               a workaround is automatically employed whereby the **connect**
               system call is initiated against each target port. This has
               the effect of sending a SYN packet to the target host, in an
               attempt to establish a connection. If **connect** returns with a
               quick success or an ECONNREFUSED failure, the underlying TCP
               stack must have received a SYN/ACK or RST and the host is
               marked available. If the connection attempt is left hanging
               until a timeout is reached, the host is marked as down.
    
           **-PA** _port list_ (TCP ACK Ping)
               The TCP ACK ping is quite similar to the just-discussed SYN
               ping. The difference, as you could likely guess, is that the
               TCP ACK flag is set instead of the SYN flag. Such an ACK
               packet purports to be acknowledging data over an established
               TCP connection, but no such connection exists. So remote hosts
               should always respond with a RST packet, disclosing their
               existence in the process.
    
               The **-PA** option uses the same default port as the SYN probe
               (80) and can also take a list of destination ports in the same
               format. If an unprivileged user tries this, the **connect**
               workaround discussed previously is used. This workaround is
               imperfect because **connect** is actually sending a SYN packet
               rather than an ACK.
    
               The reason for offering both SYN and ACK ping probes is to
               maximize the chances of bypassing firewalls. Many
               administrators configure routers and other simple firewalls to
               block incoming SYN packets except for those destined for
               public services like the company web site or mail server. This
               prevents other incoming connections to the organization, while
               allowing users to make unobstructed outgoing connections to
               the Internet. This non-stateful approach takes up few
               resources on the firewall/router and is widely supported by
               hardware and software filters. The Linux Netfilter/iptables
               firewall software offers the **--syn** convenience option to
               implement this stateless approach. When stateless firewall
               rules such as this are in place, SYN ping probes (**-PS**) are
               likely to be blocked when sent to closed target ports. In such
               cases, the ACK probe shines as it cuts right through these
               rules.
    
               Another common type of firewall uses stateful rules that drop
               unexpected packets. This feature was initially found mostly on
               high-end firewalls, though it has become much more common over
               the years. The Linux Netfilter/iptables system supports this
               through the **--state** option, which categorizes packets based on
               connection state. A SYN probe is more likely to work against
               such a system, as unexpected ACK packets are generally
               recognized as bogus and dropped. A solution to this quandary
               is to send both SYN and ACK probes by specifying **-PS** and **-PA**.
    
           **-PU** _port list_ (UDP Ping)
               Another host discovery option is the UDP ping, which sends a
               UDP packet to the given ports. For most ports, the packet will
               be empty, though some use a protocol-specific payload that is
               more likely to elicit a response.
    
               The payloads are the same probes used in service and version
               detection and are defined in the nmap-service-probes
    
               file. Packet content can also be affected with the **--data** ,
               **--data-string** , and **--data-length** options.
    
               The port list takes the same format as with the previously
               discussed **-PS** and **-PA** options. If no ports are specified, the
               default is 40125.  This default can be configured at
               compile-time by changing _DEFAULT_UDP_PROBE_PORT_SPEC_ in
               nmap.h.  A highly uncommon port is used by default because
               sending to open ports is often undesirable for this particular
               scan type.
    
               Upon hitting a closed port on the target machine, the UDP
               probe should elicit an ICMP port unreachable packet in return.
               This signifies to Nmap that the machine is up and available.
               Many other types of ICMP errors, such as host/network
               unreachables or TTL exceeded are indicative of a down or
               unreachable host. A lack of response is also interpreted this
               way. If an open port is reached, most services simply ignore
               the empty packet and fail to return any response. This is why
               the default probe port is 40125, which is highly unlikely to
               be in use. A few services, such as the Character Generator
               (chargen) protocol, will respond to an empty UDP packet, and
               thus disclose to Nmap that the machine is available.
    
               The primary advantage of this scan type is that it bypasses
               firewalls and filters that only screen TCP. For example, I
               once owned a Linksys BEFW11S4 wireless broadband router. The
               external interface of this device filtered all TCP ports by
               default, but UDP probes would still elicit port unreachable
               messages and thus give away the device.
    
           **-PY** _port list_ (SCTP INIT Ping)
               This option sends an SCTP packet containing a minimal INIT
               chunk. The default destination port is 80 (configurable at
               compile time by changing _DEFAULT_SCTP_PROBE_PORT_SPEC_ in
               nmap.h). Alternate ports can be specified as a parameter. The
               syntax is the same as for the **-p** except that port type
               specifiers like S: are not allowed. Examples are **-PY22** and
               **-PY22,80,179,5060**. Note that there can be no space between **-PY**
               and the port list. If multiple probes are specified they will
               be sent in parallel.
    
               The INIT chunk suggests to the remote system that you are
               attempting to establish an association. Normally the
               destination port will be closed, and an ABORT chunk will be
               sent back. If the port happens to be open, the target will
               take the second step of an SCTP four-way-handshake by
               responding with an INIT-ACK chunk. If the machine running Nmap
               has a functional SCTP stack, then it tears down the nascent
               association by responding with an ABORT chunk rather than
               sending a COOKIE-ECHO chunk which would be the next step in
               the four-way-handshake. The ABORT packet is sent by the kernel
               of the machine running Nmap in response to the unexpected
               INIT-ACK, not by Nmap itself.
    
               Nmap does not care whether the port is open or closed. Either
               the ABORT or INIT-ACK response discussed previously tell Nmap
               that the host is available and responsive.
    
               On Unix boxes, only the privileged user root is generally able
               to send and receive raw SCTP packets.  Using SCTP INIT Pings
               is currently not possible for unprivileged users.
    
           **-PE** ; **-PP** ; **-PM**(ICMP Ping Types)
               In addition to the unusual TCP, UDP and SCTP host discovery
               types discussed previously, Nmap can send the standard packets
               sent by the ubiquitous ping program. Nmap sends an ICMP type 8
               (echo request) packet to the target IP addresses, expecting a
               type 0 (echo reply) in return from available hosts.
               Unfortunately for network explorers, many hosts and firewalls
               now block these packets, rather than responding as required by
               **RFC 1122******[2].  For this reason, ICMP-only scans are rarely
               reliable enough against unknown targets over the Internet. But
               for system administrators monitoring an internal network, they
               can be a practical and efficient approach. Use the**-PE** option
               to enable this echo request behavior.
    
               While echo request is the standard ICMP ping query, Nmap does
               not stop there. The ICMP standards (**RFC 792******[3] and**RFC 950******[4]
               ) also specify timestamp request, information request, and
               address mask request packets as codes 13, 15, and 17,
               respectively. While the ostensible purpose for these queries
               is to learn information such as address masks and current
               times, they can easily be used for host discovery. A system
               that replies is up and available. Nmap does not currently
               implement information request packets, as they are not widely
               supported. RFC 1122 insists that “a host SHOULD NOT implement
               these messages”. Timestamp and address mask queries can be
               sent with the**-PP** and **-PM** options, respectively. A timestamp
               reply (ICMP code 14) or address mask reply (code 18) discloses
               that the host is available. These two queries can be valuable
               when administrators specifically block echo request packets
               while forgetting that other ICMP queries can be used for the
               same purpose.
    
           **-PO** _protocol list_ (IP Protocol Ping)
               One of the newer host discovery options is the IP protocol
               ping, which sends IP packets with the specified protocol
               number set in their IP header. The protocol list takes the
               same format as do port lists in the previously discussed TCP,
               UDP and SCTP host discovery options. If no protocols are
               specified, the default is to send multiple IP packets for ICMP
               (protocol 1), IGMP (protocol 2), and IP-in-IP (protocol 4).
               The default protocols can be configured at compile-time by
               changing _DEFAULT_PROTO_PROBE_PORT_SPEC_ in nmap.h. Note that
               for the ICMP, IGMP, TCP (protocol 6), UDP (protocol 17) and
               SCTP (protocol 132), the packets are sent with the proper
               protocol headers while other protocols are sent with no
               additional data beyond the IP header (unless any of **--data** ,
               **--data-string** , or **--data-length** options are specified).
    
               This host discovery method looks for either responses using
               the same protocol as a probe, or ICMP protocol unreachable
               messages which signify that the given protocol isn't supported
               on the destination host. Either type of response signifies
               that the target host is alive.
    
           **--disable-arp-ping**(No ARP or ND Ping)
               Nmap normally does ARP or IPv6 Neighbor Discovery (ND)
               discovery of locally connected ethernet hosts, even if other
               host discovery options such as **-Pn** or **-PE** are used. To disable
               this implicit behavior, use the **--disable-arp-ping** option.
    
               The default behavior is normally faster, but this option is
               useful on networks using proxy ARP, in which a router
               speculatively replies to all ARP requests, making every target
               appear to be up according to ARP scan.
    
           **--discovery-ignore-rst**
               In some cases, firewalls may spoof TCP reset (RST) replies in
               response to probes to unoccupied or disallowed addresses.
               Since Nmap ordinarily considers RST replies to be proof that
               the target is up, this can lead to wasted time scanning
               targets that aren't there. Using the **--discovery-ignore-rst**
               will prevent Nmap from considering these replies during host
               discovery. You may need to select extra host discovery options
               to ensure you don't miss targets in this case.
    
           **--traceroute**(Trace path to host)
               Traceroutes are performed post-scan using information from the
               scan results to determine the port and protocol most likely to
               reach the target. It works with all scan types except connect
               scans (**-sT**) and idle scans (**-sI**). All traces use Nmap's
               dynamic timing model and are performed in parallel.
    
               Traceroute works by sending packets with a low TTL
               (time-to-live) in an attempt to elicit ICMP Time Exceeded
               messages from intermediate hops between the scanner and the
               target host. Standard traceroute implementations start with a
               TTL of 1 and increment the TTL until the destination host is
               reached. Nmap's traceroute starts with a high TTL and then
               decrements the TTL until it reaches zero. Doing it backwards
               lets Nmap employ clever caching algorithms to speed up traces
               over multiple hosts. On average Nmap sends 5–10 fewer packets
               per host, depending on network conditions. If a single subnet
               is being scanned (i.e. 192.168.0.0/24) Nmap may only have to
               send two packets to most hosts.
    


## PORT SCANNING BASICS



           While Nmap has grown in functionality over the years, it began as
           an efficient port scanner, and that remains its core function. The
           simple command **nmap** _target_ scans 1,000 TCP ports on the host
           _target_. While many port scanners have traditionally lumped all
           ports into the open or closed states, Nmap is much more granular.
           It divides ports into six states: open, closed, filtered,
           unfiltered, open|filtered, or closed|filtered.
    
           These states are not intrinsic properties of the port itself, but
           describe how Nmap sees them. For example, an Nmap scan from the
           same network as the target may show port 135/tcp as open, while a
           scan at the same time with the same options from across the
           Internet might show that port as filtered.
    
           **The six port states recognized by Nmap**
    
           open
               An application is actively accepting TCP connections, UDP
               datagrams or SCTP associations on this port. Finding these is
               often the primary goal of port scanning. Security-minded
               people know that each open port is an avenue for attack.
               Attackers and pen-testers want to exploit the open ports,
               while administrators try to close or protect them with
               firewalls without thwarting legitimate users. Open ports are
               also interesting for non-security scans because they show
               services available for use on the network.
    
           closed
               A closed port is accessible (it receives and responds to Nmap
               probe packets), but there is no application listening on it.
               They can be helpful in showing that a host is up on an IP
               address (host discovery, or ping scanning), and as part of OS
               detection. Because closed ports are reachable, it may be worth
               scanning later in case some open up. Administrators may want
               to consider blocking such ports with a firewall. Then they
               would appear in the filtered state, discussed next.
    
           filtered
               Nmap cannot determine whether the port is open because packet
               filtering prevents its probes from reaching the port. The
               filtering could be from a dedicated firewall device, router
               rules, or host-based firewall software. These ports frustrate
               attackers because they provide so little information.
               Sometimes they respond with ICMP error messages such as type 3
               code 13 (destination unreachable: communication
               administratively prohibited), but filters that simply drop
               probes without responding are far more common. This forces
               Nmap to retry several times just in case the probe was dropped
               due to network congestion rather than filtering. This slows
               down the scan dramatically.
    
           unfiltered
               The unfiltered state means that a port is accessible, but Nmap
               is unable to determine whether it is open or closed. Only the
               ACK scan, which is used to map firewall rulesets, classifies
               ports into this state. Scanning unfiltered ports with other
               scan types such as Window scan, SYN scan, or FIN scan, may
               help resolve whether the port is open.
    
           open|filtered
               Nmap places ports in this state when it is unable to determine
               whether a port is open or filtered. This occurs for scan types
               in which open ports give no response. The lack of response
               could also mean that a packet filter dropped the probe or any
               response it elicited. So Nmap does not know for sure whether
               the port is open or being filtered. The UDP, IP protocol, FIN,
               NULL, and Xmas scans classify ports this way.
    
           closed|filtered
               This state is used when Nmap is unable to determine whether a
               port is closed or filtered. It is only used for the IP ID idle
               scan.
    


## 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 Npcap 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 **-s** _C_ , 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 0, 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
               **https://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******[5] 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 to increase response rate, but for most ports
               the packet is empty unless the **--data** , **--data-string** , or
               **--data-length** options are specified. If an ICMP port
               unreachable error (type 3, code 3) is returned, the port is
               closed. Other ICMP unreachable errors (type 3, codes 0, 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******[6] 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 0, 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******[7] 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 0, 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 0, 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******[7] (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
               **https://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 while port
               unreachable (type 3, code 3) marks the protocol open. Other
               ICMP unreachable errors (type 3, code 0, 1, 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******[8]) 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.
    
           **--exclude-ports** _port ranges_ (Exclude the specified ports from
           scanning)
               This option specifies which ports you do want Nmap to exclude
               from scanning. The _port ranges_ are specified similar to **-p**.
               For IP protocol scanning (**-sO**), this option specifies the
               protocol numbers you wish to exclude (0–255).
    
               When ports are asked to be excluded, they are excluded from
               all types of scans (i.e. they will not be scanned under any
               circumstances). This also includes the discovery phase.
    
           **-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 1.0.
    
           **--top-ports** _n_
               Scans the _n_ highest-ratio ports found in nmap-services file
               after excluding all ports specified by **--exclude-ports**.  _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
           **https://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 it 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-probes
               ports 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******[9]) 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**https://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******[10]
    
           ) to automate a wide variety of networking tasks. Those scripts
           are executed in parallel with the speed and efficiency you expect
           from Nmap. Users can rely on the growing and diverse set of
           scripts distributed with Nmap, or write their own to meet custom
           needs.
    
           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**https://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**https://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.
    
               Note that this shorthand option is ignored whenever at least
               one **--script** is also specified.
    
           **--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)
                   _APPDATA_ \nmap (only on Windows)
                   the directory containing the nmap executable
                   the directory containing the nmap executable, followed by
                   ../share/nmap (not searched on Windows)
                   _NMAPDATADIR_ (not searched on Windows)
                   the current directory.
    
               When a directory name ending in / 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
               **https://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******[11] 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
               **https://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 /24 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 lengthens 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.
    
               The special value 0 can be used to mean “no timeout”, which
               can be used to override the **T5** timing template, which sets the
               host timeout to 15 minutes.
    
           **--script-timeout** _time_
               While some scripts complete in fractions of a second, others
               can take hours or more depending on the nature of the script,
               arguments passed in, network and application conditions, and
               more. The **--script-timeout** option sets a ceiling on script
               execution time. Any script instance which exceeds that time
               will be terminated and no output will be shown. If debugging
               (**-d**) is enabled, Nmap will report on each timeout. For host
               and service scripts, a script instance only scans a single
               target host or port and the timeout period will be reset for
               the next instance.
    
               The special value 0 can be used to mean “no timeout”, which
               can be used to override the **T5** timing template, which sets the
               script timeout to 10 minutes.
    
           **--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.
    
           **--defeat-icmp-ratelimit**
               Similar to **--defeat-rst-ratelimit** , the **--defeat-icmp-ratelimit**
               option trades accuracy for speed, increasing UDP scanning
               speed against hosts that rate-limit ICMP error messages.
               Because this option causes Nmap to not delay in order to
               receive the port unreachable messages, a non-responsive port
               will be labeled closed|filtered instead of the default
               open|filtered. This has the effect of only treating ports
               which actually respond via UDP as open. Since many UDP
               services do not respond in this way, the chance for inaccuracy
               is greater with this option than with **--defeat-rst-ratelimit**.
    
           **--nsock-engine iocp|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 currently
               implemented are epoll, kqueue, poll, and select, but not all
               will be present on any platform. By default, Nmap will use the
               "best" engine, i.e. the first one in this list that is
               supported. Use **nmap -V** to see which engines are supported on
               your platform.
    
           **-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. Fortunately, 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 that 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.
               **-T4** does the equivalent of
                **--max-rtt-timeout 1250ms --min-rtt-timeout 100ms**
               **--initial-rtt-timeout 500ms --max-retries 6** and sets the
               maximum TCP and SCTP scan delay to 10ms.  **T5** does the
               equivalent of
                **--max-rtt-timeout 300ms --min-rtt-timeout 50ms**
               **--initial-rtt-timeout 250ms --max-retries 2 --host-timeout 15m**
               **--script-timeout 10m** as well as setting the maximum TCP and
               SCTP scan delay to 5ms. Maximum UDP scan delay is not set by
               **T4** or **T5** , but it can be set with the **--max-scan-delay** option.
    


## 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 host
               discovery 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). Right now random IP address generation is
               only supported with IPv4
    
               Decoys are used both in the initial host discovery 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** _hex string_ (Append custom binary data to sent packets)
               This option lets you include binary data as payload in sent
               packets.  _hex string_ may be specified in any of the following
               formats: 0xAABBCCDDEEFF _..._ , AABBCCDDEEFF _..._  or
               \xAA\xBB\xCC\xDD\xEE\xFF _..._. Examples of use are **--data**
               **0xdeadbeef** and **--data \xCA\xFE\x09**. Note that if you specify a
               number like 0x00ff no byte-order conversion is performed. Make
               sure you specify the information in the byte order expected by
               the receiver.
    
           **--data-string** _string_ (Append custom string to sent packets)
               This option lets you include a regular string as payload in
               sent packets.  _string_ can contain any string. However, note
               that some characters may depend on your system's locale and
               the receiver may not see the same information. Also, make sure
               you enclose the string in double quotes and escape any special
               characters from the shell. Examples: **--data-string "Scan**
               **conducted by Security Ops, extension 7192"** or **--data-string**
               **"Ph34r my l33t skills"**. Keep in mind that nobody is likely to
               actually see any comments left by this option unless they are
               carefully monitoring the network with a sniffer or custom IDS
               rules.
    
           **--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** _R|S [route]|L [route]|T|U ..._ **; --ip-options** _hex_
           _string_ (Send packets with specified ip options)
               The **IP protocol******[12] 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
               **https://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.
    
           **--proxies** _Comma-separated list of proxy URLs_ (Relay TCP
           connections through a chain of proxies)
               Asks Nmap to establish TCP connections with a final target
               through supplied chain of one or more HTTP or SOCKS4 proxies.
               Proxies can help hide the true source of a scan or evade
               certain firewall restrictions, but they can hamper scan
               performance by increasing latency. Users may need to adjust
               Nmap timeouts and other scan parameters accordingly. In
               particular, a lower **--max-parallelism** may help because some
               proxies refuse to handle as many concurrent connections as
               Nmap opens by default.
    
               This option takes a list of proxies as argument, expressed as
               URLs in the format proto://host:port. Use commas to separate
               node URLs in a chain. No authentication is supported yet.
               Valid protocols are HTTP and SOCKS4.
    
               Warning: this feature is still under development and has
               limitations. It is implemented within the nsock library and
               thus has no effect on the ping, port scanning and OS discovery
               phases of a scan. Only NSE and version scan benefit from this
               option so far—other features may disclose your true address.
               SSL connections are not yet supported, nor is proxy-side DNS
               resolution (hostnames are always resolved by Nmap).
    
           **--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
               **https://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******[13] originally defined
               Adler32 as checksum algorithm for SCTP;**RFC 4960******[6] 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******[14] and**Nmap::Parser******[15] 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
               **https://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), **-v** _level_ (Set 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), **-d** _level_ (Set 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.
    
               Beginning with Nmap 7.40, the **--open** option implies
    
               **--defeat-rst-ratelimit** , because that option only affects
               closed and filtered ports, which are hidden by **--open**.
    
           **--iflist**(List interfaces and routes)
               Prints the interface list and system routes as detected by
               Nmap and quits. 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
               scan output files 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 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. Scans can be resumed from any of the 3
               major output formats: Normal, Grepable, or XML
    
           **--noninteractive**(Disable runtime interactions)
               At times, such as when running Nmap in a shell background, it
               might be undesirable for Nmap to monitor and respond to user
               keyboard input when running. (See the section called “RUNTIME
               INTERACTION” about how to control Nmap during a scan.) Use
               option **--noninteractive** to prevent Nmap taking control of the
               terminal.
    
           **--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******[16] 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**
               **https://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
               **--stylesheethttps://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******[17]. 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. 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. Options which require privileges (e.g.
               root access) such as OS detection and traceroute will only be
               enabled if those privileges are available.
    
           **--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.
    
           **nmap -v scanme.nmap.org**
    
           This option scans all reserved TCP ports on the machine
           scanme.nmap.org . The **-v** option enables verbose mode.
    
           **nmap -sS -O scanme.nmap.org/24**
    
           Launches a stealth SYN scan against each machine that is up out of
           the 256 IPs on the /24 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.
    
           **nmap -sV -p 22,53,110,143,4564 198.116.0-255.1-127**
    
           Launches host enumeration and a TCP scan at the first half of each
           of the 255 possible eight-bit subnets in the 198.116.0.0/16
           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.
    
           **nmap -v -iR 100000 -Pn -p 80**
    
           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.
    
           **nmap -Pn -p80 -oX logs/pb-port80scan.xml -oG**
           **logs/pb-port80scan.gnmap 216.163.128.20/20**
    
           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
           **https://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 **https://nmap.org ******. If the problem persists,
           do some research to determine whether it has already been
           discovered and addressed. Try searching for the problem or error
           message on Google since that aggregates so many forums. If nothing
           comes of this, create an Issue on our tracker (‐**http://issues.nmap.org ******) and/or mail a bug report to <dev@nmap.org>. If you subscribe to the nmap-dev list before
           posting, your message will bypass moderation and get through more
           quickly. Subscribe at **https://nmap.org/mailman/listinfo/dev ******.
           Please include everything you have learned about the problem, as
           well as what version of Nmap you are using and what operating
           system version it is running on. Other suggestions for improving
           Nmap may be sent to the Nmap dev mailing list as well.
    
           If you are able to write a patch improving Nmap or fixing a bug,
           that is even better! Instructions for submitting patches or git
           pull requests are available from**https://github.com/nmap/nmap/blob/master/CONTRIBUTING.md **
    
           Particularly sensitive issues such as a security reports may be
           sent directly to Nmap's author Fyodor directly at
           <fyodor@nmap.org>. All other reports and comments should use the
           dev list or issue tracker instead because more people read,
           follow, and respond to those.
    


## LEGAL NOTICES



       **Nmap Copyright and Licensing**
           The Nmap Security Scanner is (C) 1996–2022 Nmap Software LLC ("The
           Nmap Project"). Nmap is also a registered trademark of the Nmap
           Project. It is published under the **Nmap Public Source License******[18].
           This generally allows end users to download and use Nmap for free.
           It doesn't allow Nmap to be used and redistributed within
           commercial software or hardware products (including appliances,
           virtual machines, and traditional applications). We fund the
           project by selling a special Nmap OEM Edition for this purpose, as
           described at**https://nmap.org/oem ******. Hundreds of large and small
           software vendors have already purchased OEM licenses to embed Nmap
           technology such as host discovery, port scanning, OS detection,
           version detection, and the Nmap Scripting Engine within their
           products.
    
           The Nmap Project has permission to redistribute Npcap, a packet
           capturing driver and library for the Microsoft Windows platform.
           Npcap is a separate work with it's own license rather than this
           Nmap license. Since the Npcap license does not permit
           redistribution without special permission, our Nmap Windows binary
           packages which contain Npcap may not be redistributed without
           special permission.
    
           Even though the NPSL is based on GPLv2, it contains different
           provisions and is not directly compatible. It is incompatible with
           some other open source licenses as well. In some cases we can
           relicense portions of Nmap or grant special permissions to use it
           in other open source software. Please contact fyodor@nmap.org with
           any such requests. Similarly, we don't incorporate incompatible
           open source software into Nmap without special permission from the
           copyright holders.
    
           If you have received a written license agreement or contract for
           Nmap (such as an**Nmap OEM license******[19]) stating terms other than
           these, you may choose to use and redistribute Nmap under those
           terms instead.**Creative Commons License for this Nmap Guide**
           This Nmap Reference Guide is (C) 2005–2022 Nmap Software LLC. It
           is hereby placed under version 3.0 of the **Creative Commons**
           **Attribution License******[20]. 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.
    
           Source code also allows you to port Nmap to new platforms, fix
           bugs, and add new features. You are highly encouraged to submit
           your changes as Github Pull Requests (PR) or send them to
           <dev@nmap.org> for possible incorporation into the main
           distribution. By submitting such changes, it is assumed that you
           are offering the Nmap Project the unlimited, non-exclusive right
           to reuse, modify, and relicense the code. 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 sell commercial licenses to **Nmap OEM******[21]. 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.
    
           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.
    
           Nmap is not designed, manufactured, or intended for use in
           hazardous environments requiring fail- safe performance where the
           failure of the software could lead directly to death, personal
           injury, or significant physical or environmental damage.
    
       **Third-Party Software and Funding Notices**
           This product includes software developed by the **Apache Software**
           **Foundation******[22]. A modified version of the**Libpcap portable packet**
           **capture library******[23] is distributed along with Nmap. The Windows
           version of Nmap utilizes the Libpcap-derived**Ncap library******[24]
           instead. Regular expression support is provided by the**PCRE**
           **library******[25], which is open-source software, written by Philip
           Hazel.  Certain raw networking functions use the**Libdnet******[26]
           networking library, which was written by Dug Song.  A modified
           version is distributed with Nmap. Nmap can optionally link with
           the**OpenSSL cryptography toolkit******[27] for SSL version detection
           support. The Nmap Scripting Engine uses an embedded version of the**Lua programming language******[10].  The**Liblinear linear classification**
           **library******[28] is used for our**IPv6 OS detection machine learning**
           **techniques******[29].
    
           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******[30] and the**DARPA CINDER program******[31] (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, the Nmap Project believes that Nmap is not subject to
           U.S.  **Export Administration Regulations (EAR)******[32] 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,
           the Nmap Project believes that Nmap falls under U.S. ECCN**5D002******[33] (“Information Security Software”). We distribute Nmap
           under the TSU exception for publicly available encryption software
           defined in**EAR 740.13(e)******[34].


## NOTES



            1. Nmap Network Scanning: The Official Nmap Project Guide to
               Network Discovery and Security Scanning
               https://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. UDP
               http://www.rfc-editor.org/rfc/rfc768.txt
    
            6. SCTP
               http://www.rfc-editor.org/rfc/rfc4960.txt
    
            7. TCP RFC
               http://www.rfc-editor.org/rfc/rfc793.txt
    
            8. RFC 959
               http://www.rfc-editor.org/rfc/rfc959.txt
    
            9. RFC 1323
               http://www.rfc-editor.org/rfc/rfc1323.txt
    
           10. Lua programming language
               https://lua.org
    
           11. precedence
               http://www.lua.org/manual/5.4/manual.html#3.4.8
    
           12. IP protocol
               http://www.rfc-editor.org/rfc/rfc791.txt
    
           13. RFC 2960
               http://www.rfc-editor.org/rfc/rfc2960.txt
    
           14. Nmap::Scanner
               http://sourceforge.net/projects/nmap-scanner/
    
           15. Nmap::Parser
               http://nmapparser.wordpress.com/
    
           16. xsltproc
               http://xmlsoft.org/XSLT/
    
           17. listed at Wikipedia
               http://en.wikipedia.org/wiki/List_of_IPv6_tunnel_brokers
    
           18. Nmap Public Source License
               https://nmap.org/npsl
    
           19. Nmap OEM license
               https://nmap.org/oem/
    
           20. Creative Commons Attribution License
               http://creativecommons.org/licenses/by/3.0/
    
           21. Nmap OEM
               https://nmap.org/oem
    
           22. Apache Software Foundation
               https://www.apache.org
    
           23. Libpcap portable packet capture library
               https://www.tcpdump.org
    
           24. Ncap library
               https://npcap.com
    
           25. PCRE library
               https://pcre.org
    
           26. Libdnet
               http://libdnet.sourceforge.net
    
           27. OpenSSL cryptography toolkit
               https://openssl.org
    
           28. Liblinear linear classification library
               https://www.csie.ntu.edu.tw/~cjlin/liblinear/
    
           29. IPv6 OS detection machine learning techniques
               https://nmap.org/book/osdetect-guess.html#osdetect-guess-ipv6
    
           30. Google Summer of Code
               https://nmap.org/soc/
    
           31. DARPA CINDER program
               https://www.fbo.gov/index?s=opportunity&mode=form&id=585e02a51f77af5cb3c9e06b9cc82c48&tab=core&_cview=1
    
           32. Export Administration Regulations (EAR)
               https://www.bis.doc.gov/index.php/regulations/export-administration-regulations-ear
    
           33. 5D002
               https://www.bis.doc.gov/index.php/documents/regulations-docs/federal-register-notices/federal-register-2014/951-ccl5-pt2/file
    
           34. EAR 740.13(e)
               https://www.bis.doc.gov/index.php/documents/regulations-docs/2341-740-2/file
    


* * *