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NMAP(1)                 Nmap Network Scanning (PRE-REL                 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 ports.

       In addition to the interesting ports table, Nmap can provide further
       information on targets, including reverse DNS names, operating system
       guesses, device types, and MAC addresses.

       A typical Nmap scan is shown in Example 15.1, "A representative Nmap
       scan". 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.

       Example 15.1. A representative Nmap scan

           # nmap -A -T4 playground

           Starting nmap ( )
           Interesting ports on (
           (The 1663 ports scanned but not shown below are in state: filtered)
           22/tcp  open   ssh     OpenSSH 3.9p1 (protocol 1.99)
           53/tcp  open   domain
           70/tcp  closed gopher
           80/tcp  open   http    Apache httpd 2.0.52 ((Fedora))
           113/tcp closed auth
           Device type: general purpose
           Running: Linux 2.4.X|2.5.X|2.6.X
           OS details: Linux 2.4.7 - 2.6.11, Linux 2.6.0 - 2.6.11
           Uptime 33.908 days (since Thu Jul 21 03:38:03 2005)

           Interesting ports on (
           (The 1659 ports scanned but not shown below are in state: closed)
           PORT     STATE SERVICE       VERSION
           135/tcp  open  msrpc         Microsoft Windows RPC
           139/tcp  open  netbios-ssn
           389/tcp  open  ldap?
           445/tcp  open  microsoft-ds  Microsoft Windows XP microsoft-ds
           1002/tcp open  windows-icfw?
           1025/tcp open  msrpc         Microsoft Windows RPC
           1720/tcp open  H.323/Q.931   CompTek AquaGateKeeper
           5800/tcp open  vnc-http      RealVNC 4.0 (Resolution 400x250; VNC port: 5900)
           5900/tcp open  vnc           VNC (protocol 3.8)
           MAC Address: 00:A0:CC:63:85:4B (Lite-on Communications)
           Device type: general purpose
           Running: Microsoft Windows NT/2K/XP
           OS details: Microsoft Windows XP Pro RC1+ through final release
           Service Info: OSs: Windows, Windows XP

           Nmap finished: 2 IP addresses (2 hosts up) scanned in 88.392 seconds

       The newest version of Nmap can be obtained from The
       newest version of the man page is available from

       This options summary is printed when Nmap is run with no arguments, and
       the latest version is always available at It helps people remember the most
       common options, but is no substitute for the in-depth documentation in
       the rest of this manual. Some obscure options aren't even included

           Nmap 4.62 ( )
           Usage: nmap [Scan Type(s)] [Options] {target specification}
             Can pass hostnames, IP addresses, networks, etc.
             Ex:,,; 10.0.0-255.1-254
             -iL <inputfilename>: Input from list of hosts/networks
             -iR <num hosts>: Choose random targets
             --exclude <host1[,host2][,host3],...>: Exclude hosts/networks
             --excludefile <exclude_file>: Exclude list from file
           HOST DISCOVERY:
             -sL: List Scan - simply list targets to scan
             -sP: Ping Scan - go no further than determining if host is online
             -PN: Treat all hosts as online -- skip host discovery
             -PS/PA/PU [portlist]: TCP SYN/ACK or UDP 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
             -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
             -sO: IP protocol scan
             -b <FTP relay host>: FTP bounce scan
             --traceroute: Trace hop path to each host
             --reason: Display the reason a port is in a particular state
             -p <port ranges>: Only scan specified ports
               Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080
             -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=safe,intrusive
             --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-trace: Show all data sent and received
             --script-updatedb: Update the script database.
           OS DETECTION:
             -O: Enable OS detection
             --osscan-limit: Limit OS detection to promising targets
             --osscan-guess: Guess OS more aggressively
             Options which take <time> are in milliseconds, unless you append '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 <time>: 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
             -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 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 twice or more for greater effect)
             -d[level]: Set or increase debugging level (Up to 9 is meaningful)
             --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 Insecure.Org for more portable XML
             --no-stylesheet: Prevent associating of XSL stylesheet w/XML output
             -6: Enable IPv6 scanning
             -A: Enables OS detection and 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 -sP
             nmap -v -iR 10000 -PN -p 80

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

       Sometimes you wish to scan a whole network of adjacent hosts. For this,
       Nmap supports CIDR-style addressing. You can append /numbits to an IP
       address or hostname and Nmap will scan every IP address for which the
       first numbits are the same as for the reference IP or hostname given.
       For example, would scan the 256 hosts between (binary: 11000000 10101000 00001010 00000000) and (binary: 11000000 10101000 00001010 11111111),
       inclusive. would do exactly the same thing. 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
       /1, which scans half the 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 are commonly 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 and or .255. 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

       IPv6 addresses can only be specified by their fully qualified IPv6
       address or hostname. CIDR and octet ranges aren't supported for IPv6
       because they are rarely useful.

       Nmap accepts multiple host specifications on the command line, and they
       don't need to be the same type. The command nmap 10.0.0,1,3-7.0-255 does what you would expect.

       While targets are usually specified on the command lines, the following
       options are also available to control target selection:

       -iL <inputfilename> (Input from list)
           Reads target specifications from inputfilename. Passing a huge list
           of hosts is often awkward on the command line, yet it is a common
           desire. For example, your DHCP server might export a list of 10,000
           current leases that you wish to scan. Or maybe you want to scan all
           IP addresses except for those to locate hosts using unauthorized
           static IP addresses. Simply generate the list of hosts to scan and
           pass that filename to Nmap as an argument to the -iL option.
           Entries can be in any of the formats accepted by Nmap on the
           command line (IP address, hostname, CIDR, IPv6, or octet ranges).
           Each entry must be separated by one or more spaces, tabs, or
           newlines. You can specify a hyphen (-) as the filename if you want
           Nmap to read hosts from standard input rather than an actual file.

       -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 -sS -PS80 -iR 0 -p 80 to
           locate random web servers for browsing.

       --exclude <host1[,host2][,host3],...> (Exclude hosts/networks)
           Specifies a comma-separated list of targets to be excluded from the
           scan even if they are part of the overall network range you
           specify. The list you pass in uses normal Nmap syntax, so it can
           include hostnames, CIDR netblocks, octet ranges, etc. This can be
           useful when the network you wish to scan includes untouchable
           mission-critical servers, systems that are known to react adversely
           to port scans, or subnetworks 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.

       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, 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 a TCP ACK packet
       destined for port 80 and an ICMP echo request query to each target
       machine. An exception to this is that an ARP scan is used for any
       targets which are on a local ethernet network. For unprivileged Unix
       shell users, a SYN packet is sent instead of the ack using the
       connect() system call. These defaults are equivalent to the -PA -PE
       options. 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 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 -sP 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 option.

       -sP (Ping Scan)
           This option tells Nmap to only perform a ping scan (host
           discovery), then print out the available hosts that responded to
           the scan. No further testing (such as port scanning or OS
           detection) is performed. This is 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 -sP option sends an ICMP echo request and a TCP packet to port
           80 by default. When executed by an unprivileged user, only a SYN
           packet is sent (using a connect() call) to port 80 on the target.
           When a privileged user tries to scan targets on a local ethernet
           network, ARP requests (-PR) are used unless --send-ip was
           specified. The -sP 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 (ACK and echo request) 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.

       -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 sized 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. For machines on a local ethernet network, ARP scanning will
           still be performed (unless --send-ip is specified) because Nmap
           needs MAC addresses to further scan target hosts. This option flag
           for this used to be P0 (uses zero), but was renamed to avoid
           confusion with protocol ping's PO (uses the letter O) flag.

       -PS [portlist] (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
           3-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 3-way-handshake and establish a full connection. The
           RST packet is sent by the kernel of the machine running Nmap in
           response to the unexpected SYN/ACK, not by Nmap itself.

           Nmap does not care whether the port is open or closed. Either the
           RST or SYN/ACK response discussed previously tell Nmap that the
           host is available and responsive.

           On Unix boxes, only the privileged user root is generally able to
           send and receive raw TCP packets. For unprivileged users, a
           workaround is automatically employed whereby the connect() system
           call is initiated against each target port. This has the effect of
           sending a SYN packet to the target host, in an attempt to establish
           a connection. If connect() returns with a quick success or an
           ECONNREFUSED failure, the underlying TCP stack must have received a
           SYN/ACK or RST and the host is marked available. If the connection
           attempt is left hanging until a timeout is reached, the host is
           marked as down. This workaround is also used for IPv6 connections,
           as raw IPv6 packet building support is not yet available in Nmap.

       -PA [portlist] (TCP ACK Ping)
           The TCP ACK ping is quite similar to the just-discussed SYN ping.
           The difference, as you could likely guess, is that the TCP ACK flag
           is set instead of the SYN flag. Such an ACK packet purports to be
           acknowledging data over an established TCP connection, but no such
           connection exists. So remote hosts should always respond with a RST
           packet, disclosing their existence in the process.

           The -PA option uses the same default port as the SYN probe (80) and
           can also take a list of destination ports in the same format. If an
           unprivileged user tries this, or an IPv6 target is specified, 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 [portlist] (UDP Ping)
           Another host discovery option is the UDP ping, which sends an empty
           (unless --data-length is specified) UDP packet to the given ports.
           The portlist takes the same format as with the previously discussed
           -PS and -PA options. If no ports are specified, the default is
           31338. This default can be configured at compile-time by changing
           DEFAULT_UDP_PROBE_PORT_SPEC in nmap.h. A highly uncommon port is
           used by default because sending to open ports is often undesirable
           for this particular scan type.

           Upon hitting a closed port on the target machine, the UDP probe
           should elicit an ICMP port unreachable packet in return. This
           signifies to Nmap that the machine is up and available. Many other
           types of ICMP errors, such as host/network unreachables or TTL
           exceeded are indicative of a down or unreachable host. A lack of
           response is also interpreted this way. If an open port is reached,
           most services simply ignore the empty packet and fail to return any
           response. This is why the default probe port is 31338, which is
           highly unlikely to be in use. A few services, such as chargen, 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.

       -PE; -PP; -PM (ICMP Ping Types)
           In addition to the unusual TCP and UDP host discovery types
           discussed previously, Nmap can send the standard packets sent by
           the ubiquitous ping program. Nmap sends an ICMP type 8 (echo
           request) packet to the target IP addresses, expecting a type 0
           (echo reply) in return from available hosts. Unfortunately for
           network explorers, many hosts and firewalls now block these
           packets, rather than responding as required by RFC 1122[1]. 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 standard (RFC 792[2]) also specifies timestamp
           request, information request, and address mask request packets as
           codes 13, 15, and 17, respectively. While the ostensible purpose
           for these queries is to learn information such as address masks and
           current times, they can easily be used for host discovery. A system
           that replies is up and available. Nmap does not currently implement
           information request packets, as they are not widely supported. RFC
           1122 insists that "a host SHOULD NOT implement these messages".
           Timestamp and address mask queries can be sent with the -PP and -PM
           options, respectively. A timestamp reply (ICMP code 14) or address
           mask reply (code 18) discloses that the host is available. These
           two queries can be valuable when administrators specifically block
           echo request packets while forgetting that other ICMP queries can
           be used for the same purpose.

       -PO [protolist] (IP Protocol Ping)
           The newest host discovery option 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 and UDP 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), and UDP (protocol 17), 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 alive.

       -PR (ARP Ping)
           One of the most common Nmap usage scenarios is to scan an ethernet
           LAN. On most LANs, especially those using private address ranges
           specified by RFC 1918[3], 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 --send-ip.

       --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 implementation 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 0.
           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 a single packet to most hosts.

       --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 -PT) are very detailed,
           but the TCP connect scan and ping (-sT) are 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.

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

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

       --system-dns (Use system DNS resolver)
           By default, Nmap resolves IP addresses by sending queries directly
           to the name servers configured on your host and then listening for
           responses. Many requests (often dozens) are performed in parallel
           to improve performance. Specify this option to use your system
           resolver instead (one IP at a time via the getnameinfo() call).
           This is slower and rarely useful unless you find a bug in the Nmap
           parallel resolver (please let us know if you do). The system
           resolver is always used for IPv6 scans.

       --dns-servers <server1[,server2],...>  (Servers to use for reverse DNS
           By default Nmap will try to determine 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 more than 1660 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

       These states are not intrinsic properties of the port itself, but
       describe how Nmap sees them. For example, an Nmap scan from the same
       network as the target may show port 135/tcp as open, while a scan at
       the same time with the same options from across the Internet might show
       that port as filtered.

       The six port states recognized by Nmap

           An application is actively accepting TCP connections or UDP packets
           on this port. Finding these is often the primary goal of port
           scanning. Security-minded people know that each open port is an
           avenue for attack. Attackers and pen-testers want to exploit the
           open ports, while administrators try to close or protect them with
           firewalls without thwarting legitimate users. Open ports are also
           interesting for non-security scans because they show services
           available for use on the network.

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

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

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

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

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

       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) may be combined with any one of the TCP scan types. As a memory
       aid, port scan type options are of the form -sC, where C is a prominent
       character in the scan name, usually the first. The one exception to
       this is the deprecated FTP bounce scan (-b). By default, Nmap performs
       a SYN Scan, though it substitutes a connect scan if the user does not
       have proper privileges to send raw packets (requires root access on
       Unix) or if IPv6 targets were specified. Of the scans listed in this
       section, unprivileged users can only execute connect and FTP bounce

       -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 intrusive firewalls.
           SYN scan is relatively unobtrusive and stealthy, since it never
           completes TCP connections. It also works against any compliant TCP
           stack rather than depending on idiosyncrasies of specific platforms
           as Nmap's FIN/null/Xmas, Maimon and idle scans do. It also allows
           clear, reliable differentiation between the open, closed, and
           filtered states.

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

       -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 or is scanning IPv6 networks. Instead of writing raw
           packets as most other scan types do, Nmap asks the underlying
           operating system to establish a connection with the target machine
           and port by issuing the connect() system call. This is the same
           high-level system call that web browsers, P2P clients, and most
           other network-enabled applications use to establish a connection.
           It is part of a programming interface known as the Berkeley Sockets
           API. Rather than read raw packet responses off the wire, Nmap uses
           this API to obtain status information on each connection attempt.

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

       -sU (UDP scans)
           While most popular services on the Internet run over the TCP
           protocol, UDP[4] 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 an empty (no data) UDP header to every
           targeted port. 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. Versions scan (-sV) can be used to help
           differentiate the truly open ports from the filtered ones.

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

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

       -sN; -sF; -sX (TCP Null, FIN, and Xmas scans)
           These three scan types (even more are possible with the --scanflags
           option described in the next section) exploit a subtle loophole in
           the TCP RFC[5] to differentiate between open and closed ports. Page
           65 says that "if the [destination] port state is CLOSED .... an
           incoming segment not containing a RST causes a RST to be sent in
           response."  Then the next page discusses packets sent to open ports
           without the SYN, RST, or ACK bits set, stating that: "you are
           unlikely to get here, but if you do, drop the segment, and return."

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

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

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

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

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

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

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

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

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

           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 1000 open ports and 3 closed
           or filtered ports, then those three may very well be the truly open

       -sM (TCP Maimon scan)
           The Maimon scan is named after its discoverer, Uriel Maimon. He
           described the technique in Phrack Magazine issue #49 (November
           1996). Nmap, which included this technique, was released two issues
           later. This technique is exactly the same as null, FIN, and Xmas
           scans, except that the probe is FIN/ACK. According to RFC 793[5]
           (TCP), a RST packet should be generated in response to such a probe
           whether the port is open or closed. However, Uriel noticed that
           many BSD-derived systems simply drop the packet if the port is

       --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

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

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

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

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

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

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

           Besides being useful in its own right, protocol scan demonstrates
           the power of open source software. While the fundamental idea is
           pretty simple, I had not thought to add it nor received any
           requests for such functionality. Then in the summer of 2000,
           Gerhard Rieger conceived the idea, wrote an excellent patch
           implementing it, and sent it to the 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

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

       -b <FTP relay host> (FTP bounce scan)
           An interesting feature of the FTP protocol (RFC 959[6]) 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 open port 21 (or even for
           any FTP services if you scan all ports with version detection),
           then try a bounce scan using each. Nmap will tell you whether the
           host is vulnerable or not. If you are just trying to cover your
           tracks, you don't need to (and, in fact, shouldn't) limit yourself
           to hosts on the target network. Before you go scanning random
           Internet addresses for vulnerable FTP servers, consider that
           sysadmins may not appreciate you abusing their servers in this way.

       In addition to all of the scan methods discussed previously, Nmap
       offers options for specifying which ports are scanned and whether the
       scan order is randomized or sequential. By default, Nmap scans all
       ports up to and including 1024 as well as higher numbered ports listed
       in the nmap-services file for the protocol(s) being scanned.

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

           When scanning both TCP and UDP ports, you can specify a particular
           protocol by preceding the port numbers by T: or U:. 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 & 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 only wish to scan for ports listed in the
           nmap-services file which comes with nmap (or the protocols file for
           -sO). This is much faster than scanning all 65535 ports on a host.
           Because this list contains so many TCP ports (more than 1200), the
           speed difference from a default TCP scan (about 1650 ports) isn't
           dramatic. The difference can be enormous if you specify your own
           tiny nmap-services file using the --servicedb or --datadir options.

       -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 port scanning instead.

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

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

       After TCP and/or UDP ports are discovered using one of the other scan
       methods, version detection interrogates those ports to determine more
       about what is actually running. The nmap-service-probes database
       contains probes for querying various services and match expressions to
       recognize and parse responses. Nmap tries to determine the service
       protocol (e.g. FTP, SSH, telnet, http), the application name (e.g. ISC
       BIND, Apache httpd, Solaris telnetd), the version number, hostname,
       device type (e.g. printer, router), the OS family (e.g. Windows, Linux)
       and sometimes miscellaneous details like whether an X server is open to
       connections, the SSH protocol version, or the KaZaA user name). 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. When RPC
       services are discovered, the Nmap RPC grinder (-sR) is automatically
       used to determine the RPC program and version numbers. Some UDP ports
       are left in the open|filtered state after a UDP port scan is unable to
       determine whether the port is open or filtered. Version detection will
       try to elicit a response from these ports (just as it does with open
       ports), and change the state to open if it succeeds.  open|filtered TCP
       ports are treated the same way. Note that the Nmap -A option enables
       version detection among other things. A paper documenting the workings,
       usage, and customization of version detection is available at

       When 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 3,000
       pattern matches for more than 350 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.

       --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 1 and 9.
           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

       -sR (RPC scan)
           This method works in conjunction with the various port scan methods
           of Nmap. It takes all the TCP/UDP ports found open 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. This is automatically enabled as part of version scan
           (-sV) if you request that. As version detection includes this and
           is much more comprehensive, -sR is rarely needed.

       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 800 known OS fingerprints and prints out the OS details if there
       is a match. Each fingerprint includes a freeform textual description of
       the OS, and a classification which provides the vendor name (e.g. Sun),
       underlying OS (e.g. Solaris), OS generation (e.g. 10), and device type
       (general purpose, router, switch, game console, etc).

       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 several other tests which make use of information
       that is gathered during the process anyway. One of these is uptime
       measurement, which uses the TCP timestamp option (RFC 1323[7]) to guess
       when a machine was last rebooted. This is only reported for machines
       which provide this information. Another 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.

       A paper documenting the workings, usage, and customization of OS
       detection is available at

       OS detection is enabled and controlled with the following options:

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

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

       --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
           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) combines the efficiency of Nmap's
       network handling with the versatility of the lightweight scripting
       language Lua[8], thus providing innumerable opportunities. A more
       extensive documentation of the NSE (including its API) can be found at: The target of the NSE is to provide Nmap with a
       flexible infrastructure for extending its capabilities and offering its
       users a simple way of creating customized tests. Uses for the NSE
       include (but definitely are not limited to):

       Enhanced version detection (category version)--While Nmap already
       offers its Service and Version detection system, which is unmatched in
       terms of efficiency and scope, this power has its downside when it
       comes to services requiring more complex probes. The Skype-Protocol
       version 2 for instance can be identified by sending 2 independent
       probes to it, which the builtin system is not laid out for: a simple
       NSE-script can do the job and update the port's service information.

       Malware-detection (categories malware and backdoor)- Both attackers and
       worms often leave backdoors--be it in form of SMTP-servers listening on
       uncommon ports mostly used by spammers for mail relay, or in form of an
       FTP-server giving crackers access to critical data. A few lines of Lua
       code can help to identify those loopholes easily.

       Vulnerability Detection (category vulnerability)- NSE's capacity in
       detecting risks ranges from checking for default passwords on Apache
       distributions to testing whether a SMTP-server supports relaying mail
       from arbitrary domains.

       Network Discovery and Information Gathering (categories safe, intrusive
       and discovery)--By providing you with a scripting language and a really
       efficient asynchronous network API on the one hand and the information
       gathered during earlier stages of a scan on the other hand the NSE is
       suited to write client programs for the services listening on a target
       machine. These clients may collect information like: listings of
       available NFS/SMB/RPC shares, the number of channels of an irc-network
       or currently logged on users.

       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 of the above mentioned categories. To maintain the matching from
       scripts to categories a file called script.db is installed along with
       the distributed scripts. Therefore, if you, for example, want to see if
       a machine is infected by any worm Nmap provides a script for you can
       simply run nmap --script=malware target-ip and check the output
       afterwards. The version scripts are always run implicitly when a
       script-scan is requested. The script.db is a Lua-script itself and can
       be updated through the --script-updatedb option.

       A NSE-script basically is a chunk of Lua-code which has (among some
       informational fields, like name, id and categories) 2 functions: a test
       whether the particular script should be run against a certain host or
       port (called a hostrule or portrule respectively) and an action to be
       carried out if the test returns true. Scripts have access to most
       information gathered by Nmap during earlier stages. For each host this
       includes the IP address, hostname and (if available) operating system.
       If a script is targeted at a port it has access to the portnumber, the
       protocol (tcp, udp or ssl), the service running behind that port, and
       optionally information from a version-scan. NSE scripts by convention
       have an nse extension. Although you are not required to follow this for
       the moment, this may change in the future. Nmap will issue a warning if
       a file has any other extension. More extensive documentation on the
       NSE, including a description of its API can be found at

           performs a script scan using the default set of scripts. it is
           equivalent to --script=safe,intrusive

       --script <script-categories|directory|filename|all>
           Runs a script scan (like -sC) with the scripts you have chosen
           rather than the defaults. Arguments can be script categories,
           single scripts or directories with scripts which are to be run
           against the target hosts instead of the default set. Nmap will try
           to interpret the arguments at first as categories and afterwards as
           files or directories. Absolute paths are used as is, relative paths
           are searched in the following places until found: --datadir/;
           $(NMAPDIR)/; ~user/nmap/ (not searched on Windows); NMAPDATADIR/ or
           ./. A scripts/ subdirectory is also tried in each of these. Give
           the argument all to execute all scripts in the Nmap script

           If a directory is specified and found, Nmap loads all NSE scripts
           (any filenames with the nse extension) from that directory. They
           must have the filename extension nse. Nmap does not recurse into
           subdirectories to find scripts. When individual file names are
           specified, the file extension does not have to be nse.

           Nmap scripts are stored in a scripts subdirectory of the Nmap data
           directory by default. Scripts are indexed in a database stored in
           scripts/script.db. The database lists all of the scripts in each
           category. A single script may be in several categories.

           lets you provide arguments to NSE-scripts. Arguments are passed as
           name=value pairs. The provided argument is processed and stored
           inside a Lua table, to which all scripts have access. The names are
           taken as strings (which must be alphanumeric values) and used as
           keys inside the argument-table. Values are either strings or tables
           themselves (surrounded by '{' and '}'. Subtables make it possible
           to override arguments for specific scripts (e.g. when you want to
           provide different login/password pairs for different scripts). For
           example, you could pass the comma-separated arguments:
           user=bar,password=foo, and anonFTP={}. If
           you want to override an option to a script, you should index the
           subtable with the script's id, since this is the only way the
           script knows about its special argument.

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

           updates the script database which stores a mapping from category
           tags to filenames. The database is a Lua script which is
           interpreted once to choose a set of scripts from the categories
           provided to the --script argument. It should be run if you have
           changed the categories field of a script, if you have added new
           scripts or if you have removed scripts from the scripts/ directory.

       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 tens or hundreds of 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 milliseconds
       by default, though you can append 's', 'm', or 'h' to the value to
       specify seconds, minutes, or hours. So the --host-timeout arguments
       900000, 900s, and 15m all do the same thing.

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

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

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

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

           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 1 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
           value of ten 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. This can
           be useful in combination with --scan-delay (discussed later),
           although the latter usually serves the purpose well enough by

       --min-rtt-timeout <time>, --max-rtt-timeout <time>,
       --initial-rtt-timeout <time> (Adjust probe timeouts)
           Nmap maintains a running timeout value for determining how long it
           will wait for a probe response before giving up or retransmitting
           the probe. This is calculated based on the response times of
           previous probes. If the network latency shows itself to be
           significant and variable, this timeout can grow to several seconds.
           It also starts at a conservative (high) level and may stay that way
           for a while when Nmap scans unresponsive hosts.

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

           If all the hosts are on a local network, 100 milliseconds is a
           reasonable aggressive --max-rtt-timeout 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 hping2 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
           100ms, no matter what the ping times are. Nor do I exceed 1000ms.

           --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
           When Nmap receives no response to a port scan probe, it could mean
           the port is filtered. Or maybe the probe or response was simply
           lost on the network. It is also possible that the target host has
           rate limiting enabled that temporarily blocked the response. So
           Nmap tries again by retransmitting the initial probe. If Nmap
           detects poor network reliability, it may try many more times before
           giving up on a port. While this benefits accuracy, it also lengthen
           scan times. When performance is critical, scans may be sped up by
           limiting the number of retransmissions allowed. You can even
           specify --max-retries 0 to prevent any retransmissions, though that
           is rarely recommended.

           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

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

           When Nmap adjusts the scan delay upward to cope with rate limiting,
           the scan slows down dramatically. The --max-scan-delay option
           specifies the largest delay that Nmap will allow. 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> (Specify a minimum 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. When the
           --min-rate option is given Nmap will do its best to send packets as
           fast 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

           There are two conditions when the actual scanning rate may fall
           below the specified 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 send packets as fast as possible,
           but be aware that such high rates are likely to cause a loss of
           accuracy. The second case is when Nmap has nothing to send, for
           example at the end of a scan when the last probes have been sent
           and Nmap is waiting for them to time out or be responded to. It's
           normal to see the scanning rate drop at the end of a scan or in
           between groups of hosts.

           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 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.

           The --min-rate option is global, affecting an entire scan, not
           individual hosts. It only affects port and host discovery scans.
           Other features like OS detection implement their own timing.

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

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

       -T <paranoid|sneaky|polite|normal|aggressive|insane> (Set a timing
           While the fine-grained timing controls discussed in the previous
           section are powerful and effective, some people find them
           confusing. Moreover, choosing the appropriate values can sometimes
           take more time than the scan you are trying to optimize. 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 10ms for TCP
           ports and -T5 caps that value at 5 milliseconds. Templates can be
           used in combination with fine-grained controls, and the
           fine-grained controls will you specify will take precedence over
           the timing template default for that parameter. I recommend using
           -T4 when scanning reasonably modern and reliable networks. Keep
           that option even when you add fine-grained controls so that you
           benefit from those extra minor optimizations that it enables.

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

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

           The main effects of T0 are serializing the scan so only one port is
           scanned at a time, and waiting five minutes between sending each
           probe.  T1 and T2 are similar but they only wait 15 seconds and 0.4
           seconds, respectively, between probes.  T3 is Nmap's default
           behavior, which includes parallelization.  T4 does the equivalent
           of --max-rtt-timeout 1250 --initial-rtt-timeout 500 --max-retries 6
           and sets the maximum TCP scan delay to 10 milliseconds.  T5 does
           the equivalent of --max-rtt-timeout 300 --min-rtt-timeout 50
           --initial-rtt-timeout 250 --max-retries 2 --host-timeout 15m as
           well as setting the maximum TCP scan delay to 5ms.

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

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

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

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

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

       -f (fragment packets); --mtu (using the specified MTU)
           The -f option causes the requested scan (including ping scans) to
           use tiny fragmented IP packets. The idea is to split up the TCP
           header over several packets to make it harder for packet filters,
           intrusion detection systems, and other annoyances to detect what
           you are doing. Be careful with this! Some programs have trouble
           handling these tiny packets. The old-school sniffer named Sniffit
           segmentation faulted immediately upon receiving the first fragment.
           Specify this option once, and Nmap splits the packets into 8 bytes
           or less after the IP header. So a 20-byte TCP header would be split
           into 3 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 8. While fragmented packets won't get by
           packet filters and firewalls that queue all IP fragments, such as
           the CONFIG_IP_ALWAYS_DEFRAG option in the Linux kernel, some
           networks can't afford the performance hit this causes and thus
           leave it disabled. Others can't enable this because fragments may
           take different routes into their networks. Some source systems
           defragment outgoing packets in the kernel. Linux with the iptables
           connection tracking module is one such example. Do a scan while a
           sniffer such as Wireshark is running to ensure that sent packets
           are fragmented. If your host OS is causing problems, try the
           --send-eth option to bypass the IP layer and send raw ethernet

       -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 6th position or later, some common
           port scan detectors (such as Solar Designer's excellent Scanlogd)
           are unlikely to show your IP address at all. If you don't use ME,
           nmap will put you in a random position. You can also use RND to
           generate a random, non-reserved IP address, or RND:<number> to
           generate <number> addresses.

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

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

           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 complains from ungrateful users whose
           applications stopped working. In particular, DNS may be broken
           because the UDP DNS replies from external servers can no longer
           enter the network. FTP is another common example. In active FTP
           transfers, the remote server tries to establish a connection back
           to the client to transfer the requested file.

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

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

           Nmap offers the -g and --source-port options (they are equivalent)
           to exploit these weaknesses. Simply provide a port number and Nmap
           will send packets from that port where possible. Nmap must use
           different port numbers for certain OS detection tests to work
           properly, and DNS requests ignore the --source-port flag because
           Nmap relies on system libraries to handle those. Most TCP scans,
           including SYN scan, support the option completely, as does UDP

       --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. This option tells Nmap to append the given number of
           random bytes to most of the packets it sends. 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

       --ip-options <S|R [route]|L [route]|T|U ... >; --ip-options <hex
       string> (Send packets with specified ip options)
           The IP protocol[9] offers several options which may be placed in
           packet headers. Unlike the ubiquitous TCP options, IP options are
           rarely seen due to practicality and security concerns. In fact,
           many Internet routers block the most dangerous options such as
           source routing. Yet options can still be useful in some cases for
           determining and manipulating the network route to target machines.
           For example, you may be able to use the record route option to
           determine a path to a target even when more traditional
           traceroute-style approaches fail. Or if your packets are being
           dropped by a certain firewall, you may be able to specify a
           different route with the strict or loose source routing options.

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

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

           If you wish to see the options in packets sent and received,
           specify --packet-trace. For more information and examples of using
           IP options with Nmap, see

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

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

       --spoof-mac <MAC address, prefix, or vendor name> (Spoof MAC address)
           Asks Nmap to use the given MAC address for all of the raw ethernet
           frames it sends. This option implies --send-eth to ensure that Nmap
           actually sends ethernet-level packets. The MAC given can take
           several formats. If it is simply the string "0", Nmap chooses a
           completely random MAC 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 less than 12 hex digits
           are provided, Nmap fills in the remainder of the 6 bytes with
           random values. If the argument isn't a 0 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 (3-byte prefix) and fills out the remaining 3
           bytes randomly. Valid --spoof-mac argument examples are Apple, 0,
           01:02:03:04:05:06, deadbeefcafe, 0020F2, and Cisco.

       --badsum (Send packets with bogus TCP/UDP checksums)
           Asks Nmap to use an invalid TCP or UDP 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

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

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

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

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

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

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

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

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

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

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

       Nmap Output Formats

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

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

           XML offers a stable format that is easily parsed by software. Free
           XML parsers are available for all major computer languages,
           including C/C++, Perl, Python, and Java. People have even written
           bindings for most of these languages to handle Nmap output and
           execution specifically. Examples are Nmap::Scanner[10] and
           Nmap::Parser[11] in Perl CPAN. In almost all cases that a
           non-trivial application interfaces with Nmap, XML is the preferred

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

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

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

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

           Grepable output consists of comments (lines starting with a pound
           (#)) and target lines. A target line includes a combination of 6
           labeled fields, separated by tabs and followed with a colon. The
           fields are Host, Ports, Protocols, Ignored State, OS, Seq Index, IP
           ID, and Status.

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

           As with XML output, this man page does not allow for documenting
           the entire format. A more detailed look at the Nmap grepable output
           format is available from

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

       Verbosity and debugging options

       -v (Increase verbosity level)
           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.

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

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

       --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.

       --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 open, open|filtered, and unfiltered
           ports. These three ports are treated just as they normally are,
           which means that open|filtered and unfiltered may be condensed into
           counts if there are an overwhelming number of them.

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

       --log-errors (Log errors/warnings to normal mode output file)
           Warnings and errors printed by Nmap usually go only to the screen
           (interactive output), leaving any specified normal-format output
           files uncluttered. But when you do want to see those messages in
           the normal output file you specified, add this option. It is useful
           when you aren't watching the interactive output or are trying to
           debug a problem. The messages will also still appear in interactive
           mode. This will not work for most errors related to bad
           command-line arguments, as Nmap may not have initialized its output
           files yet. In addition, some Nmap error/warning messages use a
           different system that does not yet support this option. An
           alternative to using this option is redirecting interactive output
           (including the standard error stream) to a file. While most Unix
           shells make that approach easy, it can be difficult on Windows.

       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 (or in the current working directory on
           Windows). Simply load Nmap's XML output in a modern web browser and
           it should retrieve nmap.xsl from the filesystem and use it to
           render results. 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 a browser to load the
           latest version of the stylesheet from Insecure.Org. The --webxml
           option does the same thing with less typing and memorization.
           Loading the XSL from Insecure.Org makes it easier to view results
           on a machine that doesn't have Nmap (and thus nmap.xsl) installed.
           So the URL is often more useful, but the local filesystem location
           of nmap.xsl is used by default for privacy reasons.

       --webxml (Load stylesheet from Insecure.Org)
           This convenience option is simply 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

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

       -6 (Enable IPv6 scanning)
           Since 2002, Nmap has offered IPv6 support for its most popular
           features. In particular, ping scanning (TCP-only), connect
           scanning, and version detection 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 give

           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.
           One of the better ones is run by BT Exact at
  I have also used one that Hurricane
           Electric provides at 6to4 tunnels are
           another popular, free approach.

       -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.
           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 environmental variable. Next
           comes ~/.nmap for real and effective UIDs (POSIX systems only) or
           location of the Nmap executable (Win32 only), and then a
           compiled-in location such as /usr/local/share/nmap or

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

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

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

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

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

       --interactive (Start in interactive mode)
           Starts Nmap in interactive mode, which offers an interactive Nmap
           prompt allowing easy launching of multiple scans (either
           synchronously or in the background). This is useful for people who
           scan from multi-user systems as they often want to test their
           security without letting everyone else on the system know exactly
           which systems they are scanning. Use --interactive to activate this
           mode and then type h for help. This option is rarely used because
           proper shells are usually more familiar and feature-complete. This
           option includes a bang (!) operator for executing shell commands,
           which is one of many reasons not to install Nmap setuid root.

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

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

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

       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: 0:00:08 elapsed; 111 hosts completed (5 up), 5 undergoing
           Service Scan

           Service scan Timing: About 28.00% done; ETC: 16:18 (0:00:15

       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 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
       -v option enables verbose mode.

       nmap -sS -O

       Launches a stealth SYN scan against each machine that is up out of the
       255 machines on "class C" 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 8 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

       nmap -v -iR 100000 -PN -p 80

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

       nmap -PN -p80 -oX logs/pb-port80scan.xml -oG logs/pb-port80scan.gnmap

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

       Like its author, Nmap isn't perfect. But you can help make it better by
       sending bug reports or even writing patches. If Nmap doesn't behave the
       way you expect, first upgrade to the latest version available from If the problem persists, do some research to determine
       whether it has already been discovered and addressed. Try Googling the
       error message or browsing the nmap-dev archives at 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.

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

       Fyodor <> (

       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) 1996-2008 Insecure.Com LLC. Nmap is
       also a registered trademark of Insecure.Com LLC. This program is free
       software; you may redistribute and/or modify it under the terms of the
       GNU General Public License as published by the Free Software
       Foundation; Version 2 with the clarifications and exceptions described
       below. This guarantees your right to use, modify, and redistribute this
       software under certain conditions. If you wish to embed Nmap technology
       into proprietary software, we sell alternative licenses (contact
       <>). Dozens of software vendors already license Nmap
       technology such as host discovery, port scanning, OS detection, and
       version detection.

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

       o   Integrates source code from Nmap

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

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

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

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

       The term "Nmap" should be taken to also include any portions or derived
       works of Nmap. This list is not exclusive, but is just meant to clarify
       our interpretation of derived works with some common examples. These
       restrictions only apply when you actually redistribute Nmap. For
       example, nothing stops you from writing and selling a proprietary
       front-end to Nmap. Just distribute it by itself, and point people to to download Nmap.

       We don't consider these to be added restrictions on top of the GPL, but
       just a clarification of how we interpret "derived works" as it applies
       to our GPL-licensed Nmap product. This is similar to the way Linus
       Torvalds has announced his interpretation of how "derived works"
       applies to Linux kernel modules. Our interpretation refers only to
       Nmap--we don't speak for any other GPL products.

       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 information.

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

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

   Creative Commons License for this Nmap Guide
       This Nmap Reference Guide is (C) 2005 Insecure.Com LLC. It is hereby
       placed under version 2.5 of the Creative Commons Attribution
       License[12]. 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 Fyodor and 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

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

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

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

       Nmap should never be installed with special privileges (e.g. suid root)
       for security reasons.

   Third-Party Software
       This product includes software developed by the Apache Software
       Foundation[13]. A modified version of the Libpcap portable packet
       capture library[14] is distributed along with nmap. The Windows version
       of Nmap utilized the Libpcap-derived WinPcap library[15] instead.
       Regular expression support is provided by the PCRE library[16], which
       is open source software, written by Philip Hazel. Certain raw
       networking functions use the Libdnet[17] networking library, which was
       written by Dug Song. A modified version is distributed with Nmap. Nmap
       can optionally link with the OpenSSL cryptography toolkit[18] for SSL
       version detection support. The Nmap Scripting Engine uses an embedded
       version of the Lua programming language[19]. All of the third-party
       software described in this paragraph is freely redistributable under
       BSD-style software licenses.

   US Export Control Classification
       US Export Control: Insecure.Com LLC believes that Nmap falls under US
       ECCN (export control classification number) 5D992. This category is
       called "Information Security software not controlled by 5D002". The
       only restriction of this classification is AT (anti-terrorism), which
       applies to almost all goods and denies export to a handful of rogue
       nations such as Iran and North Korea. Thus exporting Nmap does not
       require any special license, permit, or other governmental

       Gordon "Fyodor" Lyon

        1. RFC 1122

        2. RFC 792

        3. RFC 1918

        4. UDP

        5. TCP RFC

        6. RFC 959

        7. RFC 1323

        8. Lua

        9. IP protocol

       10. Nmap::Scanner

       11. Nmap::Parser

       12. Creative Commons Attribution License

       13. Apache Software Foundation

       14. Libpcap portable packet capture library

       15. WinPcap library

       16. PCRE library

       17. Libdnet

       18. OpenSSL cryptography toolkit

       19. Lua programming language

Insecure.Org Zero Day  <pubdate>April 9, 2008</pubdate>                NMAP(1)

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