Provided by: nmap_7.01-2ubuntu2_amd64 bug

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 7.01 ( 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/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 consecutively - 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
             --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.

       Sometimes you wish to scan a whole network of adjacent hosts. For this, Nmap supports
       CIDR-style.  addressing. You can append /numbits to an IPv4 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 is /32, which scans just the named host or IP address because all address
       bits are fixed.

       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 only be specified by their fully qualified IPv6 address or hostname.
       CIDR and 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.

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 ping step entirely with a list scan (-sL) or by disabling ping (-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 (-PR).  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 hosts. 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 ping scanning cannot be combined
           with this. If you wish to disable ping scanning while still performing such higher
           level functionality, read up on the -Pn (skip ping) 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, excluding -Pn)
           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 Nmap discovery stage altogether. Normally, Nmap uses this stage
           to determine active machines for heavier scanning. 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 class
           B target address space (/16) 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. To skip ping scan 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 payload database is described
           at https://nmap.org/book/nmap-payloads.html..  --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.

       -PR (ARP Ping) .
           One of the most common Nmap usage scenarios is to scan an ethernet LAN. On most LANs,
           especially those using private address ranges specified by RFC 1918[5], the vast
           majority of IP addresses are unused at any given time. When Nmap tries to send a raw
           IP packet such as an ICMP echo request, the operating system must determine the
           destination hardware (ARP) address corresponding to the target IP so that it can
           properly address the ethernet frame. This is often slow and problematic, since
           operating systems weren't written with the expectation that they would need to do
           millions of ARP requests against unavailable hosts in a short time period.

           ARP scan puts Nmap and its optimized algorithms in charge of ARP requests. And if it
           gets a response back, Nmap doesn't even need to worry about the IP-based ping packets
           since it already knows the host is up. This makes ARP scan much faster and more
           reliable than IP-based scans. So it is done by default when scanning ethernet hosts
           that Nmap detects are on a local ethernet network. Even if different ping types (such
           as -PE or -PS) are specified, Nmap uses ARP instead for any of the targets which are
           on the same LAN. If you absolutely don't want to do an ARP scan, specify
           --disable-arp-ping.

           For IPv6 (-6 option), -PR uses ICMPv6 Neighbor Discovery instead of ARP. Neighbor
           Discovery, defined in RFC 4861, can be seen as the IPv6 equivalent of ARP.

       --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.

       --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.

       -n (No 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 (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.

       --system-dns (Use system DNS resolver) .
           By default, Nmap resolves IP addresses 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). The system resolver is always used for IPv6 scans.

       --dns-servers server1[,server2[,...]]  (Servers to use for reverse DNS queries) .
           By default, Nmap determines your DNS servers (for rDNS resolution) 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 or an IPv6 scan. 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 rDNS 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.

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

           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.

           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.

           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.

           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.

           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.

           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 WinPcap has already been loaded into the OS.
       Requiring root privileges was a serious limitation when Nmap was released in 1997, as many
       users only had access to shared shell accounts. Now, the world is different. Computers are
       cheaper, far more people have always-on direct Internet access, and desktop Unix systems
       (including Linux and Mac OS X) are prevalent. A Windows version of Nmap is now available,
       allowing it to run on even more desktops. For all these reasons, users have less need to
       run Nmap from limited shared shell accounts. This is fortunate, as the privileged options
       make Nmap far more powerful and flexible.

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

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

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

           This technique is often referred to as half-open scanning, because you don't open a
           full TCP connection. You send a SYN packet, as if you are going to open a real
           connection and then wait for a response. A SYN/ACK indicates the port is listening
           (open), while a RST (reset) is indicative of a non-listener. If no response is
           received after several retransmissions, the port is marked as filtered. The port is
           also marked filtered if an ICMP unreachable error (type 3, code 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[6] services
           are widely deployed. DNS, SNMP, and DHCP (registered ports 53, 161/162, and 67/68) are
           three of the most common. Because UDP scanning is generally slower and more difficult
           than TCP, some security auditors ignore these ports. This is a mistake, as exploitable
           UDP services are quite common and attackers certainly don't ignore the whole protocol.
           Fortunately, Nmap can help inventory UDP ports.

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

           UDP scan works by sending a UDP packet to every targeted port. For some common ports
           such as 53 and 161, a protocol-specific payload is sent 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[7] is a relatively new alternative to the TCP and UDP protocols, combining most
           characteristics of TCP and UDP, and also adding new features like multi-homing and
           multi-streaming. It is mostly being used for SS7/SIGTRAN related services but has the
           potential to be used for other applications as well. SCTP INIT scan is the SCTP
           equivalent of a TCP SYN scan. It can be performed quickly, scanning thousands of ports
           per second on a fast network not hampered by restrictive firewalls. Like SYN scan,
           INIT scan is relatively unobtrusive and stealthy, since it never completes SCTP
           associations. It also allows clear, reliable differentiation between the open, closed,
           and filtered states.

           This technique is often referred to as half-open scanning, because you don't open a
           full SCTP association. You send an INIT chunk, as if you are going to open a real
           association and then wait for a response. An INIT-ACK chunk indicates the port is
           listening (open), while an ABORT chunk is indicative of a non-listener. If no response
           is received after several retransmissions, the port is marked as filtered. The port is
           also marked filtered if an ICMP unreachable error (type 3, code 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[8] to differentiate
           between open and closed ports. Page 65 of RFC 793 says that “if the [destination] port
           state is CLOSED .... an incoming segment not containing a RST causes a RST to be sent
           in response.”  Then the next page discusses packets sent to open ports without the
           SYN, RST, or ACK bits set, stating that: “you are unlikely to get here, but if you do,
           drop the segment, and return.”

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

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

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

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

           These three scan types are exactly the same in behavior except for the TCP flags set
           in probe packets. If a RST packet is received, the port is considered closed, while no
           response means it is open|filtered. The port is marked filtered if an ICMP unreachable
           error (type 3, code 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[8] (TCP),
           a RST packet should be generated in response to such a probe whether the port is open
           or closed. However, Uriel noticed that many BSD-derived systems simply drop the packet
           if the port is open.

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

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

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

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

       -sI zombie host[:probeport] (idle scan) .
           This advanced scan method allows for a truly blind TCP port scan of the target
           (meaning no packets are sent to the target from your real IP address). Instead, a
           unique side-channel attack exploits predictable IP fragmentation ID sequence
           generation on the zombie host to glean information about the open ports on the target.
           IDS systems will display the scan as coming from the zombie machine you specify (which
           must be up and meet certain criteria).  This fascinating scan type is too complex to
           fully describe in this reference guide, so I wrote and posted an informal paper with
           full details at 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[9]) is support for so-called proxy
           FTP connections. This allows a user to connect to one FTP server, then ask that files
           be sent to a third-party server. Such a feature is ripe for abuse on many levels, so
           most servers have ceased supporting it. One of the abuses this feature allows is
           causing the FTP server to port scan other hosts. Simply ask the FTP server to send a
           file to each interesting port of a target host in turn. The error message will
           describe whether the port is open or not. This is a good way to bypass firewalls
           because organizational FTP servers are often placed where they have more access to
           other internal hosts than any old Internet host would. Nmap supports FTP bounce scan
           with the -b option. It takes an argument of the form username:password@server:port.
           Server is the name or IP address of a vulnerable FTP server. As with a normal URL, you
           may omit username:password, in which case anonymous login credentials (user: anonymous
           password:-wwwuser@) are used. The port number (and preceding colon) may be omitted as
           well, in which case the default FTP port (21) on server is used.

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

PORT SPECIFICATION AND SCAN ORDER

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

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

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

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

       --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 1.1.

       --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 if to if you know for sure
       what is running on the port. Please take a couple minutes to make the submission so that
       your find can benefit everyone. Thanks to these submissions, Nmap has about 6,500 pattern
       matches for more than 650 protocols such as SMTP, FTP, HTTP, etc..

       Version detection is enabled and controlled with the following options:

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

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

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

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

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

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

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

OS DETECTION

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

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

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

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

       A paper documenting the workings, usage, and customization of OS detection is available at
       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[11].
       ) 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.

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

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

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

       When a directory name is given, Nmap loads every file in the directory whose name ends
       with .nse. All other files are ignored and directories are not searched recursively. When
       a filename is given, it does not have to have the .nse extension; it will be added
       automatically if necessary.  Nmap scripts are stored in a scripts subdirectory of the Nmap
       data directory by default (see 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[12] as in Lua: not is
       the highest, followed by and and then or. You can alter precedence by using parentheses.
       Because expressions contain space characters it is necessary to quote them.

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

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

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

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

       --script-args n1=v1,n2={n3=v3},n4={v4,v5} .
           Lets you provide arguments to NSE scripts. Arguments are a comma-separated list of
           name=value pairs. Names and values may be strings not containing whitespace or the
           characters ‘{’, ‘}’, ‘=’, or ‘,’. To include one of these characters in a string,
           enclose the string in single or double quotes. Within a quoted string, ‘\’ escapes a
           quote. A backslash is only used to escape quotation marks in this special case; in all
           other cases a backslash is interpreted literally. Values may also be tables enclosed
           in {}, just as in Lua. A table may contain simple string values or more name-value
           pairs, including nested tables. Many scripts qualify their arguments with the script
           name, as in xmpp-info.server_name. You may use that full qualified version to affect
           just the specified script, or you may pass the unqualified version (server_name in
           this case) to affect all scripts using that argument name. A script will first check
           for its fully qualified argument name (the name specified in its documentation) before
           it accepts an unqualified argument name. A complex example of script arguments is
           --script-args
           'user=foo,pass=",{}=bar",whois={whodb=nofollow+ripe},xmpp-info.server_name=localhost'.
           The online NSE Documentation Portal at 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 Class C sized
           chunks. For a scan with many ports, exceeding that number is unlikely to help much.
           For scans of just a few port numbers, host group sizes of 2048 or more may be helpful.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

FIREWALL/IDS EVASION AND SPOOFING

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       --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[14] originally
           defined Adler32 as checksum algorithm for SCTP; RFC 4960[7] later redefined the SCTP
           checksums to use CRC-32C. Current SCTP implementations should be using CRC-32C, but in
           order to elicit responses from old, legacy SCTP implementations, it may be preferable
           to use Adler32.

OUTPUT

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

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

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

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

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

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

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

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

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

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

       Nmap Output Formats

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

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

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

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

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

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

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

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

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

           As with XML output, this man page does not allow for documenting the entire format. A
           more detailed look at the Nmap grepable output format is available from
           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) .
           Increases the verbosity level, causing Nmap to print more information about the scan
           in progress. Open ports are shown as they are found and completion time estimates are
           provided when Nmap thinks a scan will take more than a few minutes. Use it twice or
           more for even greater verbosity: -vv, or give a verbosity level directly, for example
           -v3..

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

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

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

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

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

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

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

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

       Miscellaneous output options

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

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

       --stylesheet path or URL (Set XSL stylesheet to transform XML output) .
           Nmap ships with an XSL.  stylesheet.  named nmap.xsl.  for viewing or translating XML
           output to HTML..  The XML output includes an xml-stylesheet directive which points to
           nmap.xml where it was initially installed by Nmap. Run the XML file through an XSLT
           processor such as xsltproc[17].  to produce an HTML file. Directly opening the XML
           file in a browser no longer works well because modern browsers limit the locations a
           stylesheet may be loaded from. If you wish to use a different stylesheet, specify it
           as the argument to --stylesheet. You must pass the full pathname or URL. One common
           invocation is --stylesheet 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 --stylesheet
           https://nmap.org/svn/docs/nmap.xsl.

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

MISCELLANEOUS OPTIONS

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

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

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

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

       -A (Aggressive scan options) .
           This option enables additional advanced and aggressive options. 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
       class C sized network where Scanme resides. It also tries to determine what operating
       system is running on each host that is up and running. This requires root privileges
       because of the SYN scan and OS detection.

       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 class B address space. This tests whether the systems run
       SSH, DNS, POP3, or IMAP on their standard ports, or anything on port 4564. For any of
       these ports found open, version detection is used to determine what application is
       running.

       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 error message on our search page at http://insecure.org/search.html or at Google.
       Also try browsing the nmap-dev archives at http://seclists.org/..  Read this full manual
       page as well. If nothing comes of this, mail a bug report to <dev@nmap.org>. Please
       include everything you have learned about the problem, as well as what version of Nmap you
       are running and what operating system version it is running on. Problem reports and Nmap
       usage questions sent to <dev@nmap.org> are far more likely to be answered than those sent
       to Fyodor directly. If you subscribe to the nmap-dev list before posting, your message
       will bypass moderation and get through more quickly. Subscribe at
       https://nmap.org/mailman/listinfo/dev.

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

AUTHOR

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

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

LEGAL NOTICES

   Nmap Copyright and Licensing
       The Nmap Security Scanner is (C) 1996–2015 Insecure.Com LLC. Nmap is also a registered
       trademark of Insecure.Com LLC. This program is free software; you may redistribute and/or
       modify it under the terms of the GNU General Public License as published by the Free
       Software Foundation; Version 2 (“GPL”), BUT ONLY WITH ALL OF THE CLARIFICATIONS AND
       EXCEPTIONS DESCRIBED HEREIN. This guarantees your right to use, modify, and redistribute
       this software under certain conditions. If you wish to embed Nmap technology into
       proprietary software, we sell alternative licenses (contact <sales@nmap.com>). Dozens of
       software vendors already license Nmap technology such as host discovery, port scanning, OS
       detection, version detection, and the Nmap Scripting Engine.

       Note that the GPL places important restrictions on “derivative works”, yet it does not
       provide a detailed definition of that term. To avoid misunderstandings, we interpret that
       term as broadly as copyright law allows. For example, we consider an application to
       constitute a derivative work for the purpose of this license if it does any of the
       following with any software or content covered by this license (“Covered Software”):

       ·   Integrates source code from Covered Software.

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

       ·   Is designed specifically to execute Covered Software and parse the results (as opposed
           to typical shell or execution-menu apps, which will execute anything you tell them
           to).

       ·   Includes Covered Software in a proprietary executable installer. The installers
           produced by InstallShield are an example of this. Including Nmap with other software
           in compressed or archival form does not trigger this provision, provided appropriate
           open source decompression or de-archiving software is widely available for no charge.
           For the purposes of this license, an installer is considered to include Covered
           Software even if it actually retrieves a copy of Covered Software from another source
           during runtime (such as by downloading it from the Internet).

       ·   Links (statically or dynamically) to a library which does any of the above.

       ·   Executes a helper program, module, or script to do any of the above.

       This list is not exclusive, but is meant to clarify our interpretation of derived works
       with some common examples. Other people may interpret the plain GPL differently, so we
       consider this a special exception to the GPL that we apply to Covered Software. Works
       which meet any of these conditions must conform to all of the terms of this license,
       particularly including the GPL Section 3 requirements of providing source code and
       allowing free redistribution of the work as a whole.

       As another special exception to the GPL terms, Insecure.Com LLC grants permission to link
       the code of this program with any version of the OpenSSL library which is distributed
       under a license identical to that listed in the included docs/licenses/OpenSSL.txt file,
       and distribute linked combinations including the two..

       Any redistribution of Covered Software, including any derived works, must obey and carry
       forward all of the terms of this license, including obeying all GPL rules and
       restrictions. For example, source code of the whole work must be provided and free
       redistribution must be allowed. All GPL references to "this License", are to be treated as
       including the terms and conditions of this license text as well.

       Because this license imposes special exceptions to the GPL, Covered Work may not be
       combined (even as part of a larger work) with plain GPL software. The terms, conditions,
       and exceptions of this license must be included as well. This license 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 Covered Software without special permission from the copyright
       holders.

       If you have any questions about the licensing restrictions on using Nmap in other works,
       are happy to help. As mentioned above, we also offer alternative license to integrate Nmap
       into proprietary applications and appliances. These contracts have been sold to dozens of
       software vendors, and generally include a perpetual license as well as providing for
       priority support and updates. They also fund the continued development of Nmap. Please
       email <sales@nmap.com> for further information.

       If you have received a written license agreement or contract for Covered Software stating
       terms other than these, you may choose to use and redistribute Covered Software under
       those terms instead of these.

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

   Source Code Availability and Community Contributions
       Source is provided to this software because we believe users have a right to know exactly
       what a program is going to do before they run it. This also allows you to audit the
       software for security holes.

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

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

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

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

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

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

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

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

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

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

NOTES

        1. Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and
           Security Scanning
           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. RFC 1918
           http://www.rfc-editor.org/rfc/rfc1918.txt

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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