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NMAP(1)			     Nmap Reference Guide		       NMAP(1)

       nmap - Network exploration tool and security / port scanner

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

       Nmap ("Network Mapper") is an open source tool for network exploration
       and security auditing. It was designed to rapidly scan large networks,
       although it works fine against single hosts. Nmap uses raw IP packets
       in novel ways to determine what hosts are available on the network,
       what services (application name and version) those hosts are offering,
       what operating systems (and OS versions) they are running, what type of
       packet filters/firewalls are in use, and dozens of other
       characteristics. While Nmap is commonly used for security audits, many
       systems and network administrators find it useful for routine tasks
       such as network inventory, managing service upgrade schedules, and
       monitoring host or service uptime.

       The output from Nmap is a list of scanned targets, with supplemental
       information on each depending on the options used. Key among that
       information is the "interesting ports table". That table lists the port
       number and protocol, service name, and state. The state is either open,
       filtered, closed, or unfiltered. Open means that an application on the
       target machine is listening for connections/packets on that port.
       Filtered means that a firewall, filter, or other network obstacle is
       blocking the port so that Nmap cannot tell whether it is open or
       closed.	Closed ports have no application listening on them, though
       they could open up at any time. Ports are classified as unfiltered when
       they are responsive to Nmap's probes, but Nmap cannot determine whether
       they are open or closed. Nmap reports the state combinations
       open|filtered and closed|filtered when it cannot determine which of the
       two states describe a port. The port table may also include software
       version details when version detection has been requested. When an IP
       protocol scan is requested (-sO), Nmap provides information on
       supported IP protocols rather than listening 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 13.1, "A representative Nmap
       scan". The only Nmap arguments used in this example are -A, to enable
       OS and version detection, -T4 for faster execution, and then the two
       target hostnames.  Example 13.1. A representative Nmap scan.sp
       # nmap -A -T4 scanme.nmap.org playground

       Starting nmap ( http://www.insecure.org/nmap/ )
       Interesting ports on scanme.nmap.org (
       (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 playground.nmap.org (
       (The 1659 ports scanned but not shown below are in state: closed)
       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 TCP 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
       http://www.insecure.org/nmap/. The newest version of the man page is
       available from http://www.insecure.org/nmap/man/.

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

       Usage: nmap [Scan Type(s)] [Options] {target specification}
	 Can pass hostnames, IP addresses, networks, etc.
	 Ex: scanme.nmap.org,; 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
	 -sL: List Scan - simply list targets to scan
	 -sP: Ping Scan - go no further than determining if host is online
	 -P0: 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
	 -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
	 -sN/sF/sX: TCP Null, FIN, and Xmas scans
	 --scanflags <flags>: Customize TCP scan flags
	 -sI <zombie host[:probeport]>: Idlescan
	 -sO: IP protocol scan
	 -b <ftp relay host>: FTP bounce scan
	 -p <port ranges>: Only scan specified ports
	   Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080
	 -F: Fast - Scan only the ports listed in the nmap-services file)
	 -r: Scan ports consecutively - don't randomize
	 -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)
	 -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
	 -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
	 --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 for more effect)
	 -d[level]: Set or increase debugging level (Up to 9 is meaningful)
	 --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
	 --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
	 -V: Print version number
	 -h: Print this help summary page.
	 nmap -v -A scanme.nmap.org
	 nmap -v -sP
	 nmap -v -iR 10000 -P0 -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 scanme.nmap.org is at the IP address, the specification scanme.nmap.org/16 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 octects: 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 scanme.nmap.org 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

       --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

       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 (-P0), 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 RFC1918-blessed 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 -P0 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.playboy.com is the firewall for
	      the Chicago office of Playboy Enterprises. 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 -P0 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, 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 -P0) 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.

       -P0 (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 -P0
	      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. That second option character in -P0 is
	      a zero and not the letter O. 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.

       -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 in nmap.h), but an alternate
	      port can be specified as a parameter. A comma separated list of
	      ports can even be specified (e.g.
	      -PS22,23,25,80,113,1050,35000), in which case probes will be
	      attempted against each port 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

	      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 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 [1]RFC 1122. For
	      this reason, ICMP-only scans are rarely reliable enough against
	      unknown targets over the Internet. But for system administrators
	      monitoring an internal network, they can be a practical and
	      efficient approach. Use the -PE option to enable this echo
	      request behavior.

	      While echo request is the standard ICMP ping query, Nmap does
	      not stop there. The ICMP standard ([2]RFC 792) 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 admins specifically block echo request packets
	      while forgetting that other ICMP queries can be used for the
	      same purpose.

       -PR (ARP Ping)
	      One of the most common Nmap usage scenarios is to scan an
	      ethernet LAN. On most LANs, especially those using
	      RFC1918-blessed private address ranges, 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.

       -n (No DNS resolution)
	      Tells Nmap to never do reverse DNS resolution on the active IP
	      addresses it finds. Since DNS is often slow, this speeds things

       -R (DNS resolution for all targets)
	      Tells Nmap to always do reverse DNS resolution on the target IP
	      addresses. Normally this is only performed when a machine is
	      found to be alive.

       --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 for performance. Specify this option if
	      you wish to use your system resolver instead (one IP at a time
	      via the getnameinfo() call). This is slower and rarely useful
	      unless there is a bug in the Nmap DNS code -- please contact us
	      if that is the case. The system resolver is always used for IPv6

       --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 and more stealthy than querying just one. The best
	      performance is often obtained by specifying all of the
	      authoritative servers for the target IP space.

       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

       open   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.

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

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

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

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

	      This state is used when Nmap is unable to determine whether a
	      port is closed or filtered. It is only used for the IPID Idle

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

       Most of the scan types are only available to privileged users. This is
       because they send and receive raw packets, which requires root access
       on UNIX systems. Using an administrator account on Windows is
       recommended, though Nmap sometimes works for unprivileged users on that
       platform when 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

       -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, [3]UDP 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 [4]TCP RFC 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

	      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, respectively.

	      This scan relies on an implementation detail of a minority of
	      systems out on the Internet, so you can't always trust it.
	      Systems that don't support it will usually return all ports
	      closed. Of course, it is possible that the machine really has no
	      open ports. If most scanned ports are closed but a few common
	      port numbers (such as 22, 25, 53) are filtered, the system is
	      most likely susceptible. Occasionally, systems will even show
	      the exact opposite behavior. If your scan shows 1000 open ports
	      and 3 closed or filtered ports, then those three may very well
	      be the truly open ones.

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

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

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

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

       -sI <zombie host[:probeport]> (Idlescan)
	      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 IPID
	      changes. Otherwise Nmap will use the port it uses by default for
	      tcp pings (80).

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

	      Besides being useful in its own right, protocol scan
	      demonstrates the power of open source software. While the
	      fundamental idea is pretty simple, I had not thought to add it
	      nor received any requests for such functionality. Then in the
	      summer of 2000, Gerhard Rieger conceived the idea, wrote an
	      excellent patch implementing it, and sent it to the nmap-hackers
	      mailing list. I incorporated that patch into the Nmap tree and
	      released a new version the next day. Few pieces of commercial
	      software have users enthusiastic enough to design and contribute
	      their own improvements!

	      Protocol scan works in a similar fashion to UDP scan. Instead of
	      iterating through the port number field of a UDP packet, it
	      sends IP packet headers and iterates through the 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 ([5]RFC 959) 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.

       -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 --datadir

       -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

       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 to enable both OS detection and version

       --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-probesports directive, that probe is tried
	      regardless of intensity level. This ensures that the DNS probes
	      will always be attempted against any open port 53, the SSL probe
	      will be done against 443, etc.

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

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

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

       -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, IPID sampling, and the initial window size check,
       Nmap compares the results to its nmap-os-fingerprints database of more
       than 1500 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) 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, IPID 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 version
       detection is available in more than a dozen languages 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 both OS detection and version detection.

       --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 -P0
	      scans against many hosts. It only matters when OS detection is
	      requested with -O or -A.

       --osscan-guess; --fuzzy (Guess OS detection results)
	      When Nmap is unable to detect a perfect OS match, it sometimes
	      offers up near-matches as possibilities. The match has to be
	      very close for Nmap to do this by default. Either of these
	      (equivalent) options make Nmap guess more aggressively. Nmap
	      will still tell you when an imperfect match is printed and
	      display its confidence level (percentage) for each guess.

       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.

	      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 conditions.

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

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

	      Specifying a lower --max-rtt-timeout and --initial-rtt-timeout
	      than the defaults can cut scan times significantly. This is
	      particularly true for pingless (-P0) 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

       --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 target.

       --host-timeout <time> (Give up on slow target hosts)
	      Some hosts simply take a long time to scan. This may be due to
	      poorly performing or unreliable networking hardware or software,
	      packet rate limiting, or a restrictive firewall. The slowest few
	      percent of the scanned hosts can eat up a majority of the scan
	      time. Sometimes it is best to cut your losses and skip those
	      hosts initially. Specify --host-timeout with the maximum amoung
	      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).

	      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 nonresponsive ports as open) by
	      specifying --defeat-rst-ratelimit.

	      Using this option can reduce accuracy, as some ports will appear
	      nonresponse 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 mindset 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 Ethereal is running to ensure
	      that sent packets are fragmented. If your host OS is causing
	      problems, try the --send-eth option to bypass the IP layer and
	      send raw ethernet frames.

       -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.

	      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

	      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.

	      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 would generally be required for this sort of usage, and
	      -P0 would normally be advisable as well.

       -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 admins 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, admins 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 scan.

       --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 conspicuous.

       --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 8096 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.

       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

       -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 [6]Nmap::Scanner
	      and [7]Nmap::Parser in Perl CPAN. In almost all cases that a
	      non-trivial application interfaces with Nmap, XML is the
	      preferred format.

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

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

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

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

	      Grepable output consists of comments (lines starting with a
	      pound (#)) and target lines. A target line includes a
	      combination of 6 labeled fields, separated by tabs and followed
	      with a colon. The fields are Host, Ports, Protocols, Ignored
	      State, OS, Seq Index, IPID, 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 for even greater verbosity. Using it more than twice has
	      no effect.

	      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

	      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.

       --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-fomat
	      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 admin 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 http://www.insecure.org/nmap/data/nmap.xsl. 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
	      https://tb.ipv6.btexact.com/. I have also used one that
	      Hurricane Electric provides at http://ipv6tb.he.net/. 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) and version scanning (-sV). 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-fingerprints. Nmap first 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

       --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 variable may be set as an equivalent alternative
	      to --privileged.

       --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

       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
       scanme.nmap.org. This permission only includes scanning via Nmap and
       not testing exploits or denial of service attacks. To conserve
       bandwidth, please do not initiate more than a dozen scans against that
       host per day. If this free scanning target service is abused, it will
       be taken down and Nmap will report Failed to resolve given hostname/IP:
       scanme.nmap.org. These permissions also apply to the hosts
       scanme2.nmap.org, scanme3.nmap.org, and so on, though those hosts do
       not currently exist.

       nmap -v scanme.nmap.org

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

       nmap -sS -O scanme.nmap.org/24

       Launches a stealth SYN scan against each machine that is up out of the
       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 sshd, DNS, pop3d, imapd, or port
       4564. For any of these ports found open, version detection is used to
       determine what application is running.

       nmap -v -iR 100000 -P0 -p 80

       Asks Nmap to choose 100,000 hosts at random and scan them for web
       servers (port 80). Host enumeration is disabled with -P0 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 -P0 -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
       http://www.insecure.org/nmap/. 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 http://seclists.org/. Read this full munaual page as well.
       If nothing comes of this, mail a bug report to <nmap-dev@insecure.org>.
       Please include everything you have learned about the problem, as well
       as what version of Nmap you are running and what operating system
       version it is running on. Problem reports and Nmap usage questions sent
       to nmap-dev@insecure.org 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 http://www.insecure.org/nmap/data/HACKING. Patches may be sent to
       nmap-dev (recommended) or to Fyodor directly.

       Fyodor <fyodor@insecure.org> (http://www.insecure.org)

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

   Nmap Copyright and Licensing
       The Nmap Security Scanner is (C) 1996-2005 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. 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 may be willing to
       sell alternative licenses (contact <sales@insecure.com>). Many security
       scanner vendors already license Nmap technology such as host discovery,
       port scanning, OS detection, and service/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

       ?  Integrates source code from Nmap

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

       ?  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.)

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

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

       The term "Nmap" should be taken to also include any portions or derived
       works of Nmap. This list is not exclusive, but is 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
       http://www.insecure.org/nmap/ 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
       <sales@insecure.com> 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 [8]Creative Commons Attribution
       License. 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
       <fyodor@insecure.org> for possible incorporation into the main
       distribution. By sending these changes to Fyodor or one of the
       Insecure.Org development mailing lists, it is assumed that you are
       offering 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
       http://www.gnu.org/copyleft/gpl.html, or in the COPYING file included
       with Nmap.

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

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

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

   Third-Party Software
       This product includes software developed by the [9]Apache Software
       Foundation. A modified version of the [10]Libpcap portable packet
       capture library is distributed along with nmap. The Windows version of
       Nmap utilized the libpcap-derived [11]WinPcap library instead. Regular
       expression support is provided by the [12]PCRE library, which is open
       source software, written by Philip Hazel. Certain raw networking
       functions use the [13]Libdnet networking library, which was written by
       Dug Song. A modified version is distributed with Nmap. Nmap can
       optionally link with the [14]OpenSSL cryptography toolkit for SSL
       version detection support. All of the third-party software described in
       this paragraph is freely redistributable under BSD-style software

   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

	1. RFC 1122

	2. RFC 792

	3. UDP


	5. RFC 959

	6. Nmap::Scanner

	7. Nmap::Parser

	8. Creative Commons Attribution License

	9. Apache Software Foundation

       10. Libpcap portable packet capture library

       11. WinPcap library

       12. PCRE library

       13. Libdnet

       14. OpenSSL cryptography toolkit

				  06/23/2006			       NMAP(1)
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