NMAP(1)                     Nmap Reference Guide                     NMAP(1)

NAME         top

       nmap - Network exploration tool and security / port scanner

SYNOPSIS         top

       nmap [Scan Type...] [Options] {target specification}

DESCRIPTION         top

       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

           Nmap scan report for (
           Host is up (0.029s latency).
           rDNS record for
           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 (

           Nmap done: 1 IP address (1 host up) scanned in 14.40 seconds

       The newest version of Nmap can be obtained from . The
       newest version of this man page is available at .  It is also included as a chapter of
       Nmap Network Scanning: The Official Nmap Project Guide to Network
       Discovery and Security Scanning (see ).


       This options summary is printed when Nmap is run with no arguments,
       and the latest version is always available at . 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 7.70SVN ( )
           Usage: nmap [Scan Type(s)] [Options] {target specification}
             Can pass hostnames, IP addresses, networks, etc.
             Ex:,,; 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
             -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
             -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>
             -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
           OS DETECTION:
             -O: Enable OS detection
             --osscan-limit: Limit OS detection to promising targets
             --osscan-guess: Guess OS more aggressively
             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
             -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
             -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
             -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.
             nmap -v -A
             nmap -v -sn
             nmap -v -iR 10000 -Pn -p 80


       Everything on the Nmap command-line that isn't an option (or option
       argument) is treated as a target host specification. The simplest
       case is to specify a target IP address or hostname for scanning.

       When a hostname is given as a target, it is resolved via the Domain
       Name System (DNS) to determine the IP address to scan. If the name
       resolves to more than one IP address, only the first one will be
       scanned. To make Nmap scan all the resolved addresses instead of only
       the first one, use the --resolve-all option.

       Sometimes you wish to scan a whole network of adjacent hosts. For
       this, Nmap supports CIDR-style addressing. You can append /numbits to
       an IP address or hostname and Nmap will scan every IP address for
       which the first numbits are the same as for the reference IP or
       hostname given. For example, would scan the 256 hosts
       between (binary: 11000000 10101000 00001010 00000000)
       and (binary: 11000000 10101000 00001010 11111111),
       inclusive. would scan exactly the same targets.
       Given that the host is at the IP address, the specification would scan the
       65,536 IP addresses between and The smallest
       allowed value is /0, which targets the whole Internet. The largest
       value for IPv4 is /32, which scans just the named host or IP address
       because all address bits are fixed. The largest value for IPv6 is
       /128, which does the same thing.

       CIDR notation is short but not always flexible enough. For example,
       you might want to scan 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,,, and Either side
       of a range may be omitted; the default values are 0 on the left and
       255 on the right. Using - by itself is the same as 0-255, but
       remember to use 0- in the first octet so the target specification
       doesn't look like a command-line option. Ranges need not be limited
       to the final octets: the specifier 0-255.0-255.13.37 will perform an
       Internet-wide scan for all IP addresses ending in 13.37. This sort of
       broad sampling can be useful for Internet surveys and research.

       IPv6 addresses can be specified by their fully qualified IPv6 address
       or hostname or with CIDR notation for subnets. Octet ranges aren't
       yet supported for IPv6.

       IPv6 addresses with non-global scope need to have a zone ID suffix.
       On Unix systems, this is a percent sign followed by an interface
       name; a complete address might be fe80::a8bb:ccff:fedd:eeff%eth0. On
       Windows, use an interface index number in place of an interface name:
       fe80::a8bb:ccff:fedd:eeff%1. You can see a list of interface indexes
       by running the command netsh.exe interface ipv6 show interface.

       Nmap accepts multiple host specifications on the command line, and
       they don't need to be the same type. The command nmap 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

           The exclude file may contain comments that start with # and
           extend to the end of the line.

HOST DISCOVERY         top

       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 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

       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

           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 .

           . Packet content can also be affected with the --data,
           --data-string, and --data-length options.

           The port list takes the same format as with the previously
           discussed -PS and -PA options. If no ports are specified, the
           default is 40125.  This default can be configured at compile-time
           by changing DEFAULT_UDP_PROBE_PORT_SPEC in nmap.h.  A highly
           uncommon port is used by default because sending to open ports is
           often undesirable for this particular scan type.

           Upon hitting a closed port on the target machine, the UDP probe
           should elicit an ICMP port unreachable packet in return. This
           signifies to Nmap that the machine is up and available. Many
           other types of ICMP errors, such as host/network unreachables or
           TTL exceeded are indicative of a down or unreachable host. A lack
           of response is also interpreted this way. If an open port is
           reached, most services simply ignore the empty packet and fail to
           return any response. This is why the default probe port is 40125,
           which is highly unlikely to be in use. A few services, such as
           the Character Generator (chargen) protocol, will respond to an
           empty UDP packet, and thus disclose to Nmap that the machine is

           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

           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.
  Nmap may only have to send two packets to most

       -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.

       --resolve-all (Scan each resolved address)
           If a hostname target resolves to more than one address, scan all
           of them. The default behavior is to only scan the first resolved
           address. Regardless, only addresses in the appropriate address
           family will be scanned: IPv4 by default, IPv6 with -6.

       --system-dns (Use system DNS resolver)
           By default, Nmap reverse-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 forward lookups
           (getting an IP address from a hostname).

       --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. 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

           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.

           This option might not be honored if the DNS response exceeds the
           size of a UDP packet. In such a situation our DNS resolver will
           make the best effort to extract a response from the truncated
           packet, and if not successful it will fall back to using the
           system resolver. Also, responses that contain CNAME aliases will
           fall back to the system resolver.


       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

           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


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

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

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

       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

       -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

           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

           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

       -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

       -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

           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.


       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
           This option specifies which ports you do want Nmap to exclude
           from scanning. The port ranges are specified similar to -p. For
           IP protocol scanning (-sO), this option specifies the protocol
           numbers you wish to exclude (0–255).

           When ports are asked to be excluded, they are excluded from all
           types of scans (i.e. they will not be scanned under any
           circumstances). This also includes the discovery phase.

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

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

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

       --port-ratio ratio<decimal number between 0 and 1>
           Scans all ports in nmap-services file with a ratio greater than
           the one given.  ratio must be between 0.0 and 1.0.

       --top-ports n
           Scans the n highest-ratio ports found in nmap-services file after
           excluding all ports specified by --exclude-ports.  n must be 1 or


       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 .

       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

       -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

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

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

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

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

OS DETECTION         top

       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

       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 .

       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.


       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 .

       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 

       and is controlled by the following options:

           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:
               ~/.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
               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

           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

           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

           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
           The online NSE Documentation Portal at 
           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.

           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

           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.


       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

       --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

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

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

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

       --script-timeout time
           While some scripts complete in fractions of a second, others can
           take hours or more depending on the nature of the script,
           arguments passed in, network and application conditions, and
           more. The --script-timeout option sets a ceiling on script
           execution time. Any script instance which exceeds that time will
           be terminated and no output will be shown. If debugging (-d) is
           enabled, Nmap will report on each timeout. For host and service
           scripts, a script instance only scans a single target host or
           port and the timeout period will be reset for the next instance.

       --scan-delay time; --max-scan-delay time (Adjust delay between
           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

           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
           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

           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

           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

           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.

           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

           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.

           Similar to --defeat-rst-ratelimit, the --defeat-icmp-ratelimit
           option trades accuracy for speed, increasing UDP scanning speed
           against hosts that rate-limit ICMP error messages. Because this
           option causes Nmap to not delay in order to receive the port
           unreachable messages, a non-responsive port will be labeled
           closed|filtered instead of the default open|filtered. This has
           the effect of only treating ports which actually respond via UDP
           as open. Since many UDP services do not respond in this way, the
           chance for inaccuracy is greater with this option than with

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

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

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

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

           The main effects of T0 are serializing the scan so only one port
           is scanned at a time, and waiting five minutes between sending
           each probe.  T1 and T2 are similar but they only wait 15 seconds
           and 0.4 seconds, respectively, between probes.  T3 is Nmap's
           default behavior, which includes parallelization.  -T4 does the
           equivalent of --max-rtt-timeout 1250ms --min-rtt-timeout 100ms
           --initial-rtt-timeout 500ms --max-retries 6 and sets the maximum
           TCP 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
           --script-timeout 10m as well as setting the maximum TCP scan
           delay to 5 ms.


       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

       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).
           Right now random IP address generation is only supported with

           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

       --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

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

       --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 

       --adler32 (Use deprecated Adler32 instead of CRC32C for SCTP
           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         top

       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,

       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

       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

           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

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

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

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

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

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

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

       --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

       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
  . 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

       --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


       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

           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
  . 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

       --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

       --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.


       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         top

       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

       For testing purposes, you have permission to scan the host  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: These permissions also apply to the
       hosts,, and so on, though those
       hosts do not currently exist.

       nmap -v

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

       nmap -sS -O

       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

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

NMAP BOOK         top

       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 for more

BUGS         top

       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 . If the problem persists, do some
       research to determine whether it has already been discovered and
       addressed. Try searching for the problem or error message on Google
       since that aggregates so many forums. If nothing comes of this,
       create an Issue on our tracker ( ) and/or mail a
       bug report to <>. If you subscribe to the nmap-dev list
       before posting, your message will bypass moderation and get through
       more quickly. Subscribe at .
       Please include everything you have learned about the problem, as well
       as what version of Nmap you are using and what operating system
       version it is running on. Other suggestions for improving Nmap may be
       sent to the Nmap dev mailing list as well.

       If you are able to write a patch improving Nmap or fixing a bug, that
       is even better! Instructions for submitting patches or git pull
       requests are available from 

       Particularly sensitive issues such as a security reports may be sent
       directly to Nmap's author Fyodor directly at <>. All
       other reports and comments should use the dev list or issue tracker
       instead because more people read, follow, and respond to those.

AUTHORS         top

       Gordon “Fyodor” Lyon <> wrote and released Nmap in
       1997. Since then, hundreds of people have made valuable
       contributions, as detailed in the CHANGELOG file distributed with
       Nmap and also available from . David
       Fifield and Daniel Miller deserve special recognition for their
       enormous multi-year contributions!

LEGAL NOTICES         top

   Nmap Copyright and Licensing
       The Nmap Security Scanner is (C) 1996–2018 Insecure.Com LLC ("The
       Nmap Project"). Nmap is also a registered trademark of the Nmap
       Project. This program 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
       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 <>). 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

       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, the Nmap Project
       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.

       The Nmap Project has permission to redistribute Npcap, a packet
       capturing driver and library for the Microsoft Windows platform.
       Npcap is a separate work with it's own license rather than this Nmap
       license. Since the Npcap license does not permit redistribution
       without special permission, our Nmap Windows binary packages which
       contain Npcap may not be redistributed without special permission.

       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 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, we are happy to help. As mentioned above, we
       also offer an 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 support and updates. They also fund the continued
       development of Nmap. Please email <> for further

       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

   Creative Commons License for this Nmap Guide
       This Nmap Reference Guide is (C) 2005–2018 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 <> 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 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

   No Warranty
       This program is distributed in the hope that it will be useful, but
       WITHOUT ANY WARRANTY; without even the implied warranty of
       General Public License v2.0 for more details at , 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

   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 utilizes the Libpcap-derived Ncap 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, the Nmap Project 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, the
       Nmap Project 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

NOTES         top

        1. Nmap Network Scanning: The Official Nmap Project Guide to Network
           Discovery and Security Scanning

        2. RFC 1122

        3. RFC 792

        4. RFC 950

        5. RFC 1918

        6. UDP

        7. SCTP

        8. TCP RFC

        9. RFC 959

       10. RFC 1323

       11. Lua programming language

       12. precedence

       13. IP protocol

       14. RFC 2960

       15. Nmap::Scanner

       16. Nmap::Parser

       17. xsltproc

       18. listed at Wikipedia

       19. Creative Commons Attribution License

       20. Apache Software Foundation

       21. Libpcap portable packet capture library

       22. Ncap library

       23. PCRE library

       24. Libdnet

       25. OpenSSL cryptography toolkit

       26. Lua programming language

       27. Liblinear linear classification library

       28. IPv6 OS detection machine learning techniques

       29. Google Summer of Code

       30. DARPA CINDER program

       31. Export Administration Regulations (EAR)

       32. 5D002

       33. EAR 740.13(e)

COLOPHON         top

       This page is part of the nmap (a network scanner) project.
       Information about the project can be found at ⟨⟩.  If
       you have a bug report for this manual page, send it to
       This page was obtained from the project's upstream Git mirror of the
       Subversion repository ⟨⟩ on 2018-10-29.
       (At that time, the date of the most recent commit that was found in
       the repository was 2018-10-26.)  If you discover any rendering prob‐
       lems in this HTML version of the page, or you believe there is a bet‐
       ter or more up-to-date source for the page, or you have corrections
       or improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to

Nmap                             09/28/2018                          NMAP(1)