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nmap (1)


nmap - Network exploration tool and security / port scanner


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


Nmap Reference Guide                                      NMAP(1)

     nmap - Network exploration tool and security / port scanner

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

     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

     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 two target hostnames.

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

     This options summary is printed when Nmap is run with no
     arguments, and the latest version is always available at
     blue]]. 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 6.25 ( )
         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

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           -iR <num hosts>: Choose random targets
           --exclude <host1[,host2][,host3],...>: Exclude hosts/networks
           --excludefile <exclude_file>: Exclude list from file
           -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
           -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 separted 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

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           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
           --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)
           --log-errors: Log errors/warnings to the normal-format output file
           --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

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

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

     CIDR notation is short but not always flexible enough. For
     example, you might want to scan 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 only be specified by their fully
     qualified IPv6 address or hostname. CIDR and octet ranges
     aren't yet supported for IPv6.

     IPv6 addresses with non-global scope need to have a zone ID
     suffix. On Unix systems, this is a percent sign followed by
     an interface name; a complete address might be

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     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

     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

     -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

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         overall network range you specify. The list you pass in
         uses normal Nmap syntax, so it can include hostnames,
         CIDR netblocks, octet ranges, etc. This can be useful
         when the network you wish to scan includes untouchable
         mission-critical servers, systems that are known to
         react adversely to port scans, or subnets administered
         by other people.

     --excludefile exclude_file (Exclude list from file) .
         This offers the same functionality as the --exclude
         option, except that the excluded targets are provided in
         a newline-, space-, or tab-delimited exclude_file rather
         than on the command line.

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

     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

     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

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     to port 80, and an ICMP timestamp request. (For IPv6, the
     ICMP timestamp request is omitted because it is not part of
     ICMPv6.) These defaults are equivalent to the -PE -PS443
     -PA80 -PP options. The exceptions to this are the ARP (for
     IPv4) and Neighbor Discovery.  (for IPv6) scans which are
     used for any targets on a local ethernet network. For
     unprivileged Unix shell users, the default probes are a SYN
     packet to ports 80 and 443 using the connect system call..
     This host discovery is often sufficient when scanning local
     networks, but a more comprehensive set of discovery probes
     is recommended for security auditing.

     The -P* options (which select ping types) can be combined.
     You can increase your odds of penetrating strict firewalls
     by sending many probe types using different TCP ports/flags
     and ICMP codes. Also note that ARP/Neighbor Discovery (-PR).
     is done by default against targets on a local ethernet
     network even if you specify other -P* options, because it is
     almost always faster and more effective.

     By default, Nmap does host discovery and then performs a
     port scan against each host it determines is online. This is
     true even if you specify non-default host discovery types
     such as UDP probes (-PU). Read about the -sn option to learn
     how to perform only host discovery, or use -Pn to skip host
     discovery and port scan all target hosts. The following
     options control host discovery:

     -sL (List Scan) .
         The list scan is a degenerate form of host discovery
         that simply lists each host of the network(s) specified,
         without sending any packets to the target hosts. By
         default, Nmap still does reverse-DNS resolution on the
         hosts to learn their names. It is often surprising how
         much useful information simple hostnames give out. For
         example, fw.chi is the name of one company's Chicago
         firewall.  Nmap also reports the total number of IP
         addresses at the end. The list scan is a good sanity
         check to ensure that you have proper IP addresses for
         your targets. If the hosts sport domain names you do not
         recognize, it is worth investigating further to prevent
         scanning the wrong company's network.

         Since the idea is to simply print a list of target
         hosts, options for higher level functionality such as
         port scanning, OS detection, or ping scanning cannot be
         combined with this. If you wish to disable ping scanning
         while still performing such higher level functionality,
         read up on the -Pn (skip ping) option.

     -sn (No port scan) .
         This option tells Nmap not to do a port scan after host

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         discovery, and only print out the available hosts that
         responded to the scan. 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

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         allowing NSE to run, use the two options -Pn -sn

         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

         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.

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     -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

         The -PA option uses the same default port as the SYN
         probe (80) and can also take a list of destination ports
         in the same format. If an unprivileged user tries this,
         the connect workaround discussed previously is used.
         This workaround is imperfect because connect is actually
         sending a SYN packet rather than an ACK.

         The reason for offering both SYN and ACK ping probes is
         to maximize the chances of bypassing firewalls. Many
         administrators configure routers and other simple
         firewalls to block incoming SYN packets except for those
         destined for public services like the company web site
         or mail server. This prevents other incoming connections
         to the organization, while allowing users to make
         unobstructed outgoing connections to the Internet. This
         non-stateful approach takes up few resources on the
         firewall/router and is widely supported by hardware and
         software filters. The Linux Netfilter/iptables.
         firewall software offers the --syn convenience option to
         implement this stateless approach. When stateless
         firewall rules such as this are in place, SYN ping
         probes (-PS) are likely to be blocked when sent to
         closed target ports. In such cases, the ACK probe shines
         as it cuts right through these rules.

         Another common type of firewall uses stateful rules that
         drop unexpected packets. This feature was initially
         found mostly on high-end firewalls, though it has become
         much more common over the years. The Linux
         Netfilter/iptables system supports this through the
         --state option, which categorizes packets based on
         connection state. A SYN probe is more likely to work
         against such a system, as unexpected ACK packets are
         generally recognized as bogus and dropped. A solution to
         this quandary is to send both SYN and ACK probes by
         specifying -PS and -PA.

     -PU port list (UDP Ping) .
         Another host discovery option is the UDP ping, which
         sends a UDP packet to the given ports. For most ports,
         the packet will be empty, though for a few a
         protocol-specific payload will be sent that is more

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         likely to get a response..  The payload database is
         described at blue]-].

         The --data-length.  option can be used to send a
         fixed-length random payload to every port or (if you
         specify a value of 0) to disable payloads. You can also
         disable payloads by specifying --data-length 0.

         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

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

         The primary advantage of this scan type is that it
         bypasses firewalls and filters that only screen TCP. For
         example, I once owned a Linksys BEFW11S4 wireless
         broadband router. The external interface of this device
         filtered all TCP ports by default, but UDP probes would
         still elicit port unreachable messages and thus give
         away the device.

     -PY port list (SCTP INIT Ping) .
         This option sends an SCTP packet containing a minimal
         INIT chunk. The default destination port is 80
         (configurable at compile time by changing
         DEFAULT_SCTP_PROBE_PORT_SPEC.  in nmap.h). Alternate
         ports can be specified as a parameter. The syntax is the
         same as for the -p except that port type specifiers like
         S: are not allowed. Examples are -PY22 and
         -PY22,80,179,5060. Note that there can be no space
         between -PY and the port list. If multiple probes are
         specified they will be sent in parallel.

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         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

         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 blue]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

         While echo request is the standard ICMP ping query, Nmap
         does not stop there. The ICMP standards (blue]RFC
         792][3].  and blue]RFC 950][4].  "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.

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     -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 the
         --data-length.  option is 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

     -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 blue]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

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         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 hosts.

     -n (No DNS resolution) .
         Tells Nmap to never do reverse DNS resolution on the
         active IP addresses it finds. Since DNS can be slow even
         with Nmap's built-in parallel stub resolver, this option
         can slash scanning times.

     -R (DNS resolution for all targets) .
         Tells Nmap to always do reverse DNS resolution on the
         target IP addresses. Normally reverse DNS is only
         performed against responsive (online) hosts.

     --system-dns (Use system DNS resolver) .
         By default, Nmap resolves IP addresses by sending
         queries directly to the name servers configured on your

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         host and then listening for responses. Many requests
         (often dozens) are performed in parallel to improve
         performance. Specify this option to use your system
         resolver instead (one IP at a time via the getnameinfo
         call). This is slower and rarely useful unless you find
         a bug in the Nmap parallel resolver (please let us know
         if you do). The system resolver is always used for IPv6

     --dns-servers server1[,server2[,...]]  (Servers to use for
     reverse DNS queries) .
         By default, Nmap determines your DNS servers (for rDNS
         resolution) from your resolv.conf file (Unix) or the
         Registry (Win32). Alternatively, you may use this option
         to specify alternate servers. This option is not honored
         if you are using --system-dns or an IPv6 scan. Using
         multiple DNS servers is often faster, especially if you
         choose authoritative servers for your target IP space.
         This option can also improve stealth, as your requests
         can be bounced off just about any recursive DNS server
         on the Internet.

         This option also comes in handy when scanning private
         networks. Sometimes only a few name servers provide
         proper rDNS information, and you may not even know where
         they are. You can scan the network for port 53 (perhaps
         with version detection), then try Nmap list scans (-sL)
         specifying each name server one at a time with
         --dns-servers until you find one which works.

     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

     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.

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         Security-minded people know that each open port is an
         avenue for attack. Attackers and pen-testers want to
         exploit the open ports, while administrators try to
         close or protect them with firewalls without thwarting
         legitimate users. Open ports are also interesting for
         non-security scans because they show services available
         for use on the network.

         A closed port is accessible (it receives and responds to
         Nmap probe packets), but there is no application
         listening on it. They can be helpful in showing that a
         host is up on an IP address (host discovery, or ping
         scanning), and as part of OS detection. Because closed
         ports are reachable, it may be worth scanning later in
         case some open up. Administrators may want to consider
         blocking such ports with a firewall. Then they would
         appear in the filtered state, discussed next.

         Nmap cannot determine whether the port is open because
         packet filtering prevents its probes from reaching the
         port. The filtering could be from a dedicated firewall
         device, router rules, or host-based firewall software.
         These ports frustrate attackers because they provide so
         little information. Sometimes they respond with ICMP
         error messages such as type 3 code 13 (destination
         unreachable: communication administratively prohibited),
         but filters that simply drop probes without responding
         are far more common. This forces Nmap to retry several
         times just in case the probe was dropped due to network
         congestion rather than filtering. This slows down the
         scan dramatically.

         The unfiltered state means that a port is accessible,
         but Nmap is unable to determine whether it is open or
         closed. Only the ACK scan, which is used to map firewall
         rulesets, classifies ports into this state. Scanning
         unfiltered ports with other scan types such as Window
         scan, SYN scan, or FIN scan, may help resolve whether
         the port is open.

         Nmap places ports in this state when it is unable to
         determine whether a port is open or filtered. This
         occurs for scan types in which open ports give no
         response. The lack of response could also mean that a
         packet filter dropped the probe or any response it
         elicited. So Nmap does not know for sure whether the
         port is open or being filtered. The UDP, IP protocol,
         FIN, NULL, and Xmas scans classify ports this way.

         This state is used when Nmap is unable to determine
         whether a port is closed or filtered. It is only used
         for the IP ID idle scan.

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

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

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

     This section documents the dozen or so port scan techniques
     supported by Nmap. Only one method may be used at a time,
     except that UDP scan (-sU) and any one of the SCTP scan
     types (-sY, -sZ) may be combined with any one of the TCP
     scan types. As a memory aid, port scan type options are of
     the form -sC, where C is a prominent character in the scan
     name, usually the first. The one exception to this is the

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     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

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

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

         When SYN scan is available, it is usually a better

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

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

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

         A big challenge with UDP scanning is doing it quickly.
         Open and filtered ports rarely send any response,

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         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

         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) .

         blue]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

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

     -sN; -sF; -sX (TCP NULL, FIN, and Xmas scans) .
         These three scan types (even more are possible with the

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         --scanflags option described in the next section)
         exploit a subtle loophole in the blue]TCP RFC][8] to
         differentiate between open and closed ports. Page 65 of
         RFC 793 says that "if the [destination] port state is
         CLOSED .... an incoming segment not containing a RST
         causes a RST to be sent in response."  Then the next
         page discusses packets sent to open ports without the
         SYN, RST, or ACK bits set, stating that: "you are
         unlikely to get here, but if you do, drop the segment,
         and return."

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

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

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

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

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

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

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

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

     -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 blue]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

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         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

         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 cases.

     -sI zombie host[:probeport] (idle scan) .
         This advanced scan method allows for a truly blind TCP
         port scan of the target (meaning no packets are sent to
         the target from your real IP address). Instead, a unique
         side-channel attack exploits predictable IP
         fragmentation ID sequence generation on the zombie host
         to glean information about the open ports on the target.
         IDS systems will display the scan as coming from the

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         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 nmap-hackers mailing
         list..  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

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         functions to create them. Instead of watching for ICMP
         port unreachable messages, protocol scan is on the
         lookout for ICMP protocol unreachable messages. If Nmap
         receives any response in any protocol from the target
         host, Nmap marks that protocol as open. An ICMP protocol
         unreachable error (type 3, code 2) causes the protocol
         to be marked as closed Other ICMP unreachable errors
         (type 3, code 1, 3, 9, 10, or 13) cause the protocol to
         be marked filtered (though they prove that ICMP is open
         at the same time). If no response is received after
         retransmissions, the protocol is marked open|filtered

     -b FTP relay host (FTP bounce scan) .
         An interesting feature of the FTP protocol (blue]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.

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     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

     -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

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

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

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

         Nmap needs an nmap-services file with frequency
         information in order to know which ports are the most

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

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

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

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

     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

     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

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     (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 blue]].

     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,

     Version detection is enabled and controlled with the
     following options:

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

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

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

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

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

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

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

     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

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     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

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

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

     Another bit of extra information enabled by OS detection is
     a guess at a target's uptime. This uses the TCP timestamp
     option (blue]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 blue]-].

     OS detection is enabled and controlled with the following

     -O (Enable OS detection) .
         Enables OS detection, as discussed above. Alternatively,

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         you can use -A to enable OS detection along with other

     --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

     --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 blue]Lua programming

     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 blue]-

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     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 blue]-]

     and is controlled by the following options:

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

     --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 ../share/nmap
             the current directory.

         When a directory name is given, Nmap loads every file in

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         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 blue]-]).

         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 blue]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 categories.

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

     --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

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         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 blue]-] 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.

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

     --script-trace .
         This option does what --packet-trace does, just one ISO
         layer higher. If this option is specified all incoming
         and outgoing communication performed by a script is
         printed. The displayed information includes the
         communication protocol, the source, the target and the
         transmitted data. If more than 5% of all transmitted

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         data is not printable, then the trace output is in a hex
         dump format. Specifying --packet-trace enables script
         tracing too.

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

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

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

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

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

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         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

         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

         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

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         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

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

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

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

     --max-retries numtries (Specify the maximum number of port
     scan probe retransmissions) .
         When Nmap receives no response to a port scan probe, it

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         could mean the port is filtered. Or maybe the probe or
         response was simply lost on the network. It is also
         possible that the target host has rate limiting enabled
         that temporarily blocked the response. So Nmap tries
         again by retransmitting the initial probe. If Nmap
         detects poor network reliability, it may try many more
         times before giving up on a port. While this benefits
         accuracy, it also lengthen scan times. When performance
         is critical, scans may be sped up by limiting the number
         of retransmissions allowed. You can even specify
         --max-retries 0 to prevent any retransmissions, though
         that is only recommended for situations such as informal
         surveys where occasional missed ports and hosts are

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

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

     --scan-delay time; --max-scan-delay time (Adjust delay
     between probes) .
         This option causes Nmap to wait at least the given
         amount of time between each probe it sends to a given
         host. This is particularly useful in the case of rate
         limiting..  Solaris machines (among many others) will
         usually respond to UDP scan probe packets with only one
         ICMP message per second. Any more than that sent by Nmap
         will be wasteful. A --scan-delay of 1s will keep Nmap at
         that slow rate. Nmap tries to detect rate limiting and

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

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

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

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

         There are two conditions when the actual scanning rate
         may fall below the requested minimum. The first is if
         the minimum is faster than the fastest rate at which
         Nmap can send, which is dependent on hardware. In this
         case Nmap will simply send packets as fast as possible,

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         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.

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

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

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

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         Use nmap -V to see which engines are supported.

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

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

         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.

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         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 --initial-rtt-timeout 500ms
         --max-retries 6 and sets the maximum TCP scan delay to
         10 milliseconds.  T5 does the equivalent of
         --max-rtt-timeout 300ms --min-rtt-timeout 50ms
         --initial-rtt-timeout 250ms --max-retries 2
         --host-timeout 15m as well as setting the maximum TCP
         scan delay to 5 ms.

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

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

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     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

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         packets won't get by packet filters and firewalls that
         queue all IP fragments, such as the
         CONFIG_IP_ALWAYS_DEFRAG option in the Linux kernel, some
         networks can't afford the performance hit this causes
         and thus leave it disabled. Others can't enable this
         because fragments may take different routes into their
         networks. Some source systems defragment outgoing
         packets in the kernel. Linux with the iptables.
         connection tracking module is one such example. Do a
         scan while a sniffer such as Wireshark.  is running to
         ensure that sent packets are fragmented. If your host OS
         is causing problems, try the --send-eth.  option to
         bypass the IP layer and send raw ethernet frames.

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

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

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

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

         Decoys are used both in the initial ping scan (using

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         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

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         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

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

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

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

     --ip-options S|R [route]|L [route]|T|U ... ; --ip-options
     hex string (Send packets with specified ip options) .
         The blue]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

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         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

         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 blue]-].

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

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

     --spoof-mac MAC address, prefix, or vendor name (Spoof MAC
     address) .
         Asks Nmap to use the given MAC address for all of the
         raw ethernet frames it sends. This option implies
         --send-eth.  to ensure that Nmap actually sends

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

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

     --adler32 (Use deprecated Adler32 instead of CRC32C for SCTP
     checksums) .
         Asks Nmap to use the deprecated Adler32 algorithm for
         calculating the SCTP checksum. If --adler32 is not
         given, CRC-32C (Castagnoli) is used.  blue]RFC 2960][14]
         originally defined Adler32 as checksum algorithm for
         SCTP; blue]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.

     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

     In addition to offering different output formats, Nmap
     provides options for controlling the verbosity of output as

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     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

     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

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

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

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

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     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 blue]-].

         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 blue]Nmap::Scanner][15].  and
         blue]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

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         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

     -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

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         the Nmap grepable output format is available from blue]-

     -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

     Verbosity and debugging options

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

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

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

         Debugging output is useful when a bug is suspected in
         Nmap, or if you are simply confused as to what Nmap is
         doing and why. As this feature is mostly intended for
         developers, debug lines aren't always self-explanatory.
         You may get something like: Timeout vals: srtt: -1
         rttvar: -1 to: 1000000 delta 14987 ==> srtt: 14987

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         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

     --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

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         are, which means that open|filtered and unfiltered may
         be condensed into counts if there are an overwhelming
         number of them.

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

     Miscellaneous output options

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

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

     --stylesheet path or URL (Set XSL stylesheet to transform
     XML output) .
         Nmap ships with an XSL.  stylesheet.  named nmap.xsl.
         for viewing or translating XML output to HTML..  The XML
         output includes an xml-stylesheet directive which points
         to nmap.xml where it was initially installed by Nmap.

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         Run the XML file through an XSLT processor such as
         blue]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

     --webxml (Load stylesheet from Nmap.Org) .
         This is a convenience option, nothing more than an alias
         for --stylesheet

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

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

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

         While IPv6 hasn't exactly taken the world by storm, it
         gets significant use in some (usually Asian) countries
         and most modern operating systems support it. To use
         Nmap with IPv6, both the source and target of your scan
         must be configured for IPv6. If your ISP (like most of
         them) does not allocate IPv6 addresses to you, free
         tunnel brokers are widely available and work fine with
         Nmap. I use the free IPv6 tunnel broker.  service at
         blue]]. Other tunnel brokers

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         are blue]listed at Wikipedia][18]. 6to4 tunnels are
         another popular, free approach.

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

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

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

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

     --versiondb service probes file (Specify custom service
     probes file) .
         Asks Nmap to use the specified service probes file

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         rather than the nmap-service-probes data file that comes
         with Nmap. See the description for --datadir for more
         information on Nmap's data files.

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

     --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

     --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.

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     -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

     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)

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

     For testing purposes, you have permission to scan the host  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

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     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

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

     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

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     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 blue]] for more information.

     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 blue]]. If the
     problem persists, do some research to determine whether it
     has already been discovered and addressed. Try searching for
     the error message on our search page at blue]-] or at Google. Also try
     browsing the nmap-dev archives at blue]-]..  Read this full manual page as well.
     If nothing comes of this, mail a bug report to Please include everything you have
     learned about the problem, as well as what version of Nmap
     you are running and what operating system version it is
     running on. Problem reports and Nmap usage questions sent to are far more likely to be answered
     than those sent to Fyodor directly. If you subscribe to the
     nmap-dev list before posting, your message will bypass
     moderation and get through more quickly. Subscribe at blue]-].

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

     Gordon "Fyodor" Lyon (blue]-])

     Hundreds of people have made valuable contributions to Nmap
     over the years. These are detailed in the CHANGELOG.  file
     which is distributed with Nmap and also available from

  Nmap Copyright and Licensing
     The Nmap Security Scanner is (C) 1996-2012 Insecure.Com LLC.
     Nmap is also a registered trademark of Insecure.Com LLC.
     This program is free software; you may redistribute and/or
     modify it under the terms of the GNU General Public License
     as published by the Free Software Foundation; Version 2 with
     the clarifications and exceptions described below. This
     guarantees your right to use, modify, and redistribute this

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     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, and version

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

     o   Integrates source code from Nmap

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

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

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

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

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

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

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

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     including the two..  You must obey the GNU GPL in all
     respects for all of the code used other than OpenSSL. If you
     modify this file, you may extend this exception to your
     version of the file, but you are not obligated to do so.

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

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

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

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

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

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     it is important to keep in mind.  Nmap should never be run
     against mission critical systems unless you are prepared to
     suffer downtime. We acknowledge here that Nmap may crash
     your systems or networks and we disclaim all liability for
     any damage or problems Nmap could cause.

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

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

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

     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 blue]Google
     Summer of Code][29] and the blue]DARPA CINDER program][30]

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

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

     See attributes(5) for descriptions of the following

     |Availability   | diagnostic/nmap  |
     |Stability      | Volatile         |
      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

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      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. WinPcap library

     23. PCRE library

     24. Libdnet

     25. OpenSSL cryptography toolkit

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     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)

     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

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