# Nmap network security scanner man page

    NMAP(1)                                                   NMAP(1)

## NAME

           nmap - Network exploration tool and security scanner

## SYNOPSIS

           nmap [Scan Type(s)] [Options] <host or net #1 ... [#N]>

## DESCRIPTION

           Nmap  is designed to allow system administrators and curi-
           ous individuals to scan large networks to determine  which
           hosts  are  up  and what services they are offering.  nmap
           supports a large number of scanning  techniques  such  as:
           UDP, TCP connect(), TCP SYN (half open), ftp proxy (bounce
           attack), Reverse-ident, ICMP (ping sweep), FIN, ACK sweep,
           Xmas Tree, SYN sweep, IP Protocol, and Null scan.  See the
           Scan Types section for more details.  nmap also  offers  a
           number  of  advanced  features such as remote OS detection
           via TCP/IP fingerprinting, stealth scanning, dynamic delay
           and retransmission calculations, parallel scanning, detec-
           tion of down hosts via  parallel  pings,  decoy  scanning,
           port  filtering  detection,  direct  (non-portmapper)  RPC
           scanning, fragmentation scanning, and flexible target  and
           port specification.

           Significant  effort  has been put into decent nmap perfor-
           mance for non-root users.   Unfortunately,  many  critical
           kernel interfaces (such as raw sockets) require root priv-
           ileges.  nmap should be run as root whenever possible (not
           setuid root, of course).

           The  result of running nmap is usually a list of interest-
           ing ports on the machine(s) being scanned (if any).   Nmap
           always  gives  the  port's  "well  known" service name (if
           any), number, state, and protocol.  The  state  is  either
           'open',  'filtered', or 'unfiltered'.  Open means that the
           target machine will accept()  connections  on  that  port.
           Filtered  means  that a firewall, filter, or other network
           obstacle is covering the port  and  preventing  nmap  from
           determining  whether  the  port is open.  Unfiltered means
           that the port is known by nmap to be closed and  no  fire-
           wall/filter  seems  to be interfering with nmap's attempts
           to determine this.  Unfiltered ports are the  common  case
           and  are  only shown when most of the scanned ports are in
           the filtered state.

           Depending on options used, nmap may also report  the  fol-
           lowing  characteristics of the remote host: OS in use, TCP
           sequencability, usernames running the programs which  have
           bound  to  each  port, the DNS name, whether the host is a
           smurf address, and a few others.

## OPTIONS

           Options that make sense together  can  generally  be  com-
           bined.   Some  options are specific to certain scan modes.
           nmap tries to catch and warn the user about  psychotic  or

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    NMAP(1)                                                   NMAP(1)

           unsupported option combinations.

           If you are impatient, you can skip to the examples section
           at the end, which demonstrates common usage.  You can also
           run  nmap  -h  for  a quick reference page listing all the
           options.

           SCAN TYPES

           -sT    TCP connect() scan: This is the most basic form  of
                  TCP scanning. The connect() system call provided by
                  your operating system is used to open a  connection
                  to  every  interesting  port on the machine. If the
                  port is listening, connect() will  succeed,  other-
                  wise the port isn't reachable. One strong advantage
                  to this technique is that you don't need  any  spe-
                  cial  privileges.  Any  user  on most UNIX boxes is
                  free to use this call.

                  This sort of scan is easily  detectable  as  target
                  host logs will show a bunch of connection and error
                  messages for the services which accept()  the  con-
                  nection just to have it immediately shutdown.

           -sS    TCP  SYN  scan: 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  you
                  wait  for  a response. A SYN|ACK indicates the port
                  is listening. A RST is  indicative  of  a  non-lis-
                  tener.   If a SYN|ACK is received, a RST is immedi-
                  ately sent to tear down  the  connection  (actually
                  our OS kernel does this for us). The primary advan-
                  tage to this scanning technique is that fewer sites
                  will  log  it.   Unfortunately you need root privi-
                  leges to build these custom SYN packets.

           -sF -sX -sN
                  Stealth FIN, Xmas Tree, or Null scan  modes:  There
                  are  times when even SYN scanning isn't clandestine
                  enough. Some firewalls and packet filters watch for
                  SYNs to restricted ports, and programs like Synlog-
                  ger and Courtney  are  available  to  detect  these
                  scans. These advanced scans, on the other hand, may
                  be able to pass through unmolested.

                  The idea is that closed ports are required to reply
                  to  your probe packet with an RST, while open ports
                  must ignore the packets in question (see RFC 793 pp
                  64).   The  FIN  scan  uses  a  bare (surprise) FIN
                  packet as the probe, while the Xmas tree scan turns
                  on  the  FIN,  URG,  and PUSH flags.  The Null scan
                  turns off all flags.  Unfortunately Microsoft (like
                  usual)  decided  to  completely ignore the standard

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    NMAP(1)                                                   NMAP(1)

                  and do things their own way.  Thus this  scan  type
                  will not work against systems running Windows95/NT.
                  On the positive side, this is a good way to distin-
                  guish between the two platforms.  If the scan finds
                  open ports, you know the machine is not  a  Windows
                  box.   If  a  -sF,-sX,or  -sN  scan shows all ports
                  closed, yet a SYN  (-sS)  scan  shows  ports  being
                  opened,  you are probably looking at a Windows box.
                  This is less useful now that  nmap  has  proper  OS
                  detection  built  in.   There  are also a few other
                  systems that are broken in the same way Windows is.
                  They  include  Cisco,  BSDI,  HP/UX, MVS, and IRIX.
                  All of the above send resets from  the  open  ports
                  when they should just drop the packet.

           -sP    Ping  scanning:  Sometimes  you  only  want to know
                  which hosts on a network are up.  Nmap can do  this
                  by  sending  ICMP  echo request packets to every IP
                  address on the networks you  specify.   Hosts  that
                  respond  are up.  Unfortunately, some sites such as
                  microsoft.com block  echo  request  packets.   Thus
                  nmap can also send a TCP ack packet to (by default)
                  port 80.  If we get an RST back,  that  machine  is
                  up.   A  third  technique  involves  sending  a SYN
                  packet and waiting for a RST  or  a  SYN/ACK.   For
                  non-root users, a connect() method is used.

                  By  default  (for  root  users), nmap uses both the
                  ICMP and  ACK  techniques  in  parallel.   You  can
                  change the -P option described later.

                  Note  that  pinging  is done by default anyway, and
                  only hosts that respond are scanned.  Only use this
                  option  if you wish to ping sweep without doing any
                  actual port scans.

           -sU    UDP scans: This method is used to  determine  which
                  UDP  (User  Datagram  Protocol,  RFC 768) ports are
                  open on a host.  The technique is to  send  0  byte
                  udp packets to each port on the target machine.  If
                  we receive an ICMP port unreachable  message,  then
                  the  port  is  closed.   Otherwise  we assume it is
                  open.

                  Some people think UDP scanning is pointless. I usu-
                  ally  remind  them  of  the  recent Solaris rcpbind
                  hole. Rpcbind can be found  hiding  on  an  undocu-
                  mented  UDP  port  somewhere  above  32770.  So  it
                  doesn't matter that 111 is blocked by the firewall.
                  But can you find which of the more than 30,000 high
                  ports it is listening on? With a  UDP  scanner  you
                  can!   There  is also the cDc Back Orifice backdoor
                  program which hides on a configurable UDP  port  on
                  Windows machines.  Not to mention the many commonly

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    NMAP(1)                                                   NMAP(1)

                  vulnerable services that utilize UDP such as  snmp,
                  tftp, NFS, etc.

                  Unfortunately  UDP  scanning is sometimes painfully
                  slow since most hosts implement a suggestion in RFC
                  1812  (section  4.3.2.8) of limiting the ICMP error
                  message rate.  For example, the  Linux  kernel  (in
                  net/ipv4/icmp.h)   limits  destination  unreachable
                  message generation to 80 per 4 seconds, with a  1/4
                  second  penalty  if  that is exceeded.  Solaris has
                  much more strict limits (about 2 messages per  sec-
                  ond)  and  thus  takes  even  longer to scan.  nmap
                  detects this rate limiting and slows  down  accord-
                  ingly,  rather  than flood the network with useless
                  packets that will be ignored by the target machine.

                  As  is typical, Microsoft ignored the suggestion of
                  the RFC and does not seem to do any  rate  limiting
                  at  all on Win95 and NT machines.  Thus we can scan
                  all 65K ports of a Windows  machine  very  quickly.
                  Woop!

           -sO    IP protocol scans: This method is used to determine
                  which IP protocols are supported on  a  host.   The
                  technique  is  to  send  raw IP packets without any
                  further protocol header to each specified  protocol
                  on  the target machine.  If we receive an ICMP pro-
                  tocol unreachable message, then the protocol is not
                  in use.  Otherwise we assume it is open.  Note that
                  some hosts (AIX, HP-UX, Digital UNIX) and firewalls
                  may  not  send protocol unreachable messages.  This
                  causes all of the protocols to appear "open".

                  Because the implemented technique is  very  similar
                  to  UDP  port scanning, ICMP rate limit might apply
                  too. But the IP protocol field has only 8 bits,  so
                  at most 256 protocols can be probed which should be
                  possible in reasonable time anyway.

           -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 cer-
                  tain  criteria).   I  am  planning  to  put  a more
                  detailed   explanation   up   at   http://www.inse-
                  cure.org/nmap/nmap_documentation.html  in  the near
                  future.

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    NMAP(1)                                                   NMAP(1)

                  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 tar-
                  get  using  various zombies that you think might be
                  trusted (via router/packet  filter  rules).   Obvi-
                  ously this is crucial information when prioritizing
                  attack targets.  Otherwise, you penetration testers
                  might  have  to expend considerable resources "own-
                  ing" an intermediate system, only to find out  that
                  its  IP  isn't even trusted by the target host/net-
                  work you are ultimately after.

                  a particular port  on  the  zombie  host  for  IPID
                  changes.   Otherwise Nmap will use the port it uses
                  by default for "tcp pings".

           -sA    ACK scan: This advanced method is usually  used  to
                  map  out  firewall rulesets.  In particular, it can
                  help determine whether a firewall  is  stateful  or
                  just  a  simple  packet filter that blocks incoming
                  SYN packets.

                  This scan type sends an  ACK  packet  (with  random
                  looking  acknowledgement/sequence  numbers)  to the
                  ports specified.  If a RST comes back, the ports is
                  classified  as "unfiltered".  If nothing comes back
                  (or if an ICMP unreachable is returned),  the  port
                  is  classified  as "filtered".  Note that nmap usu-
                  ally doesn't print "unfiltered" ports,  so  getting
                  no ports shown in the output is usually a sign that
                  all the probes got  through  (and  returned  RSTs).
                  This  scan  will  obviously never show ports in the
                  "open" state.

           -sW    Window scan: This advanced scan is very similar  to
                  the  ACK  scan, except that it can sometimes detect
                  open ports as well as filtered/nonfiltered  due  to
                  an anomaly in the TCP window size reporting by some
                  operating  systems.   Systems  vulnerable  to  this
                  include at least some versions of AIX, Amiga, BeOS,
                  BSDI, Cray, Tru64  UNIX,  DG/UX,  OpenVMS,  Digital
                  UNIX,  FreeBSD,  HP-UX,  OS/2, IRIX, MacOS, NetBSD,
                  OpenBSD,  OpenStep,  QNX,  Rhapsody,   SunOS   4.X,
                  Ultrix,  VAX,  and  VxWorks.   See the nmap-hackers
                  mailing list archive for a full list.

           -sR    RPC scan.  This method works  in  combination  with
                  the  various  port  scan methods of Nmap.  It takes
                  all the TCP/UDP ports found open  and  then  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

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    NMAP(1)                                                   NMAP(1)

                  serve up.  Thus you can effectively obtain the same
                  info  as  firewall  (or protected by TCP wrappers).
                  Decoys do not currently work with RPC scan, at some
                  point I may add decoy support for UDP RPC scans.

           -sL    List scan.  This method simply generates and prints
                  a list of IPs/Names  without  actually  pinging  or
                  port  scanning  them.   DNS name resolution will be
                  performed unless you use -n.

           -b <ftp relay host>
                  FTP bounce attack: An interesting "feature" of  the
                  ftp  protocol  (RFC 959) is support for "proxy" ftp
                  connections. In other words, I should  be  able  to
                  connect  from  evil.com  to  the FTP server of tar-
                  get.com and request that the  server  send  a  file
                  ANYWHERE on the internet!  Now this may have worked
                  well in 1985 when  the  RFC  was  written.  But  in
                  today's  Internet,  we  can't have people hijacking
                  ftp servers and requesting that data be spit out to
                  arbitrary points on the internet. As *Hobbit* wrote
                  back in 1995, this protocol flaw "can  be  used  to
                  post virtually untraceable mail and news, hammer on
                  servers at various sites, fill up disks, try to hop
                  firewalls,  and  generally  be annoying and hard to
                  track down at the same time." What we will  exploit
                  this  for is to (surprise, surprise) scan TCP ports
                  from a "proxy" ftp server. Thus you  could  connect
                  to  an  ftp server behind a firewall, and then scan
                  ports that are more likely to be blocked (139 is  a
                  good  one).  If  the ftp server allows reading from
                  and writing to some directory (such as  /incoming),
                  you  can  send  arbitrary data to ports that you do
                  find open (nmap doesn't do this for you though).

                  The argument passed to the 'b' option is  the  host
                  you  want  to use as a proxy, in standard URL nota-
                  tion.     The     format     is:     username:pass-
                  word@server:port.    Everything   but   server   is
                  optional.  To determine what servers are vulnerable
                  to  this  attack,  you can see my article in Phrack
                  51.  And updated version is available at  the  nmap
                  URL (http://www.insecure.org/nmap).

           GENERAL OPTIONS
                  None  of  these  are required but some can be quite
                  useful.

           -P0    Do not try and ping hosts at  all  before  scanning
                  them.   This  allows  the scanning of networks that
                  don't  allow  ICMP  echo  requests  (or  responses)
                  through  their firewall.  microsoft.com is an exam-
                  ple of such a network, and thus you  should  always

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    NMAP(1)                                                   NMAP(1)

                  use -P0 or -PT80 when portscanning microsoft.com.

           -PT    Use  TCP  "ping"  to  determine  what hosts are up.
                  Instead of sending ICMP echo  request  packets  and
                  waiting for a response, we spew out TCP ACK packets
                  throughout the  target  network  (or  to  a  single
                  machine)  and  then  wait  for responses to trickle
                  back.  Hosts that are up should respond with a RST.
                  This  option preserves the efficiency of only scan-
                  ning hosts that are up while still allowing you  to
                  scan  networks/hosts  that block ping packets.  For
                  non root users, we use connect().  To set the  des-
                  tination  port  of  the  probe packets use -PT<port
                  number>.  The default port is 80, since  this  port
                  is often not filtered out.

           -PS    This  option  uses SYN (connection request) packets
                  instead of ACK packets for root users.  Hosts  that
                  are  up  should  respond  with a RST (or, rarely, a
                  SYN|ACK).  You can set the destination port in  the
                  same manner as -PT above.

           -PI    This  option  uses  a true ping (ICMP echo request)
                  packet.  It finds hosts that are up and also  looks
                  for  subnet-directed  broadcast  addresses  on your
                  network.  These are IP addresses which  are  exter-
                  nally  reachable  and  translate  to a broadcast of
                  incomming IP packets  to  a  subnet  of  computers.
                  These  should  be eliminated if found as they allow
                  for numerous denial of service  attacks  (Smurf  is
                  the most common).

           -PB    This  is  the  default ping type.  It uses both the
                  ACK ( -PT ) and ICMP ( -PI )  sweeps  in  parallel.
                  This  way  you can get firewalls that filter either
                  one (but not both).

           -O     This option activates  remote  host  identification
                  via TCP/IP fingerprinting.  In other words, it uses
                  a bunch of techniques to detect subtleties  in  the
                  underlying  operating  system  network stack of the
                  computers you are scanning.  It uses this  informa-
                  tion  to  create  a 'fingerprint' which it compares
                  with its database of  known  OS  fingerprints  (the
                  nmap-os-fingerprints  file)  to decide what type of
                  system you are scanning.

                  If Nmap is unable to guess the OS of a machine, and
                  conditions  are  good  (eg at least one open port),
                  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.   Note

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    NMAP(1)                                                   NMAP(1)

                  that  if  you  leave an IP address on the form, the
                  machine may be scanned when we add the  fingerprint
                  (to validate that it works).

                  The  -O  option  also  enables several other tests.
                  One is the "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  test  enabled  by  -O is TCP Sequence Pre-
                  dictability Classification.  This is a measure that
                  describes approximately how hard it is to establish
                  a forged TCP connection against  the  remote  host.
                  This is useful for exploiting source-IP based trust
                  relationships (rlogin, firewall  filters,  etc)  or
                  for  hiding  the  source  of an attack.  The actual
                  difficulty number is based on statistical  sampling
                  and  may  fluctuate.  It is generally better to use
                  the English classification such  as  "worthy  chal-
                  lenge" or "trivial joke".  This is only reported in
                  normal output with -v.

                  When verbose mode (-v) is on 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.

           -I     This turns on TCP reverse ident scanning. As  noted
                  by Dave Goldsmith in a 1996 Bugtraq post, the ident
                  protocol (rfc 1413) allows for  the  disclosure  of
                  the  username  that  owns any process connected via
                  TCP, even if that process didn't initiate the  con-
                  nection.  So  you  can, for example, connect to the
                  http port and then use identd to find  out  whether
                  the  server  is  running  as root. This can only be
                  done with a full TCP connection to the target  port
                  (i.e.  the  -sT scanning option).  When -I is used,
                  the remote host's identd is queried for  each  open
                  port  found.  Obviously this won't work if the host
                  is not running identd.

           -f     This option causes the requested SYN, FIN, XMAS, or
                  NULL  scan  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.  My  favorite sniffer segmentation faulted
                  immediately  upon  receiving  the   first   36-byte

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    NMAP(1)                                                   NMAP(1)

                  fragment.  After  that  comes  a 24 byte one! While
                  this method won't get by packet filters  and  fire-
                  walls  that  queue  all IP fragments (like the CON-
                  FIG_IP_ALWAYS_DEFRAG option in the  Linux  kernel),
                  some networks can't afford the performance hit this
                  causes and thus leave it disabled.

                  Note that I do not yet have this option working  on
                  all  systems.  It works fine for my Linux, FreeBSD,
                  and OpenBSD boxes and  some  people  have  reported
                  success with other *NIX variants.

           -v     Verbose  mode.  This is a highly recommended option
                  and it gives out more  information  about  what  is
                  going on.  You can use it twice for greater effect.
                  Use -d a couple of times if you really want to  get
                  crazy with scrolling the screen!

           -h     This  handy option display a quick reference screen
                  of nmap usage options.  As you  may  have  noticed,
                  this man page is not exactly a 'quick reference' :)

           -oN <logfilename>
                  This logs the results of your  scans  in  a  normal
                  human readable form into the file you specify as an
                  argument.

           -oX <logfilename>
                  This logs the results of your  scans  in  XML  form
                  into  the  file  you  specify as an argument.  This
                  allows programs to  easily  capture  and  interpret
                  Nmap results.  You can give the argument '-' (with-
                  out quotes) to shoot output into stdout (for  shell
                  pipelines,  etc).   In this case normal output will
                  be suppressed.  Watch out for error messages if you
                  use this (they will still go to stderr).  Also note
                  that '-v' may cause some extra  information  to  be
                  printed.

           -oG <logfilename>
                  This  logs  the results of your scans in a grepable
                  form into the file  you  specify  as  an  argument.
                  This  simple format provides all the information on
                  one line (so you can easily grep  for  port  or  OS
                  information  and  see all the IPs.  This used to be
                  the preferred mechanism for  programs  to  interact
                  with  Nmap,  but  now  we recommend XML output (-oX
                  instead).  This simple format may  not  contain  as
                  much  information  as  the  other formats.  You can
                  give the argument '-'  (without  quotes)  to  shoot
                  output  into stdout (for shell pipelines, etc).  In
                  this case normal output will be suppressed.   Watch
                  out  for  error messages if you use this (they will
                  still go to stderr).   Also  note  that  '-v'  will

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                  cause some extra information to be printed.

           -oS <logfilename>
                  thIs  l0gz  th3  r3suLtS  of YouR ScanZ iN a s|<ipT
                  kiDd|3 f0rM iNto THe fiL3 U sPecfy 4s an  arGuMEnT!
                  U  kAn  gIv3  the  4rgument '-' (wItHOUt qUOteZ) to
                  sh00t output iNT0 stDouT!@!!

           --resume <logfilename>
                  A network scan that is cancelled due to  control-C,
                  network  outage,  etc.  can  be  resumed using this
                  option.  The logfilename must be  either  a  normal
                  (-oN)  or  machine  parsable  (-oM)  log  from  the
                  aborted scan.  No other options can be given  (they
                  will  be  the same as the aborted scan).  Nmap will
                  start on the machine after the  last  one  success-
                  fully scanned in the log file.

           -iL <inputfilename>
                  Reads target specifications from the file specified
                  RATHER than from the command line.  The file should
                  contain  a  list  of  host  or  network expressions
                  seperated by spaces,  tabs,  or  newlines.   Use  a
                  hyphen  (-)  as  inputfilename  if you want nmap to
                  read host expressions from stdin (like at  the  end
                  of  a  pipe).  See the section target specification
                  for more information on the  expressions  you  fill
                  the file with.

           -iR    This option tells Nmap to generate its own hosts to
                  scan by simply picking random numbers :).  It  will
                  never end.  This can be useful for statistical sam-
                  pling of the Internet to estimate  various  things.
                  If  you  are ever really bored, try nmap -sS -iR -p
                  80 to find some web servers to look at.

           -p <port ranges>
                  This option specifies what ports you want to  spec-
                  ify.  For  example '-p 23' will only try port 23 of
                  the target host(s).   '-p  20-30,139,60000-'  scans
                  ports  between  20  and 30, port 139, and all ports
                  greater than 60000.  The default  is  to  scan  all
                  ports  between  1  and  1024  as  well as any ports
                  listed in the services file which comes with  nmap.
                  For  IP protocol scanning (-sO), this specifies the
                  protocol number you wish to scan for (0-255).

                  When scanning both TCP and UDP ports, you can spec-
                  ify  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  &

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    NMAP(1)                                                   NMAP(1)

                  TCP,  you  have to specify -sU and at least one TCP
                  scan type (such as -sS, -sF, or -sT).  If no proto-
                  col  qualifier is given, the port numbers are added
                  to all protocol lists.

           -F Fast scan mode.
                  Specifies that you only  wish  to  scan  for  ports
                  listed  in  the services file which comes with nmap
                  (or the protocols file for -sO).  This is obviously
                  much  faster  than  scanning  all  65535 ports on a
                  host.

           -D <decoy1 [,decoy2][,ME],...>
                  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 extremely  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  repre-
                  sent  the  position  you want your IP address to be
                  used.  If your put 'ME'  in  the  6th  position  or
                  later,  some  common  port  scan detectors (such as
                  Solar Designer's excellent scanlogd) are  unlikeley
                  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  accidently  SYN flood your targets.
                  Also it will be pretty easy to determine which host
                  is  scanning if only one is actually up on the net-
                  work.  You might want to use IP  addresses  instead
                  of  names  (so  the decoy networks don't see you in
                  their nameserver logs).

                  Also note that some (stupid) "port scan  detectors"
                  will  firewall/deny  routing  to hosts that attempt
                  port scans.  Thus you might inadvertantly cause the
                  machine  you  scan  to  lose  connectivity with the
                  decoy machines you are using.  This could cause the
                  target  machines  major  problems  if the decoy is,
                  say, its  internet  gateway  or  even  "localhost".
                  Thus  you  might want to be careful of this option.
                  The real moral of the story is  that  detectors  of
                  spoofable port scans should not take action against
                  the machine that seems like  it  is  port  scanning
                  them.  It could just be a decoy!

                                                                   11

    NMAP(1)                                                   NMAP(1)

                  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 ).

                  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, although many (currently most) do
                  not restrict spoofed IP packets at all.

           -S <IP_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  your 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!  This is not a sup-
                  ported usage (or the main purpose) of this flag.  I
                  just  think  it  raises  an interesting possibility
                  that people should  be  aware  of  before  they  go
                  accusing  others  of  port scanning them.  -e would
                  generally be required for this sort of usage.

           -e <interface>
                  Tells nmap what interface to send and receive pack-
                  ets  on.  Nmap should be able to detect this but it
                  will tell you if it cannot.

           -g <portnumber>
                  Sets the source port number used  in  scans.   Many
                  naive firewall and packet filter installations make
                  an exception in their ruleset to allow DNS (53)  or
                  FTP-DATA (20) packets to come through and establish
                  a connection.  Obviously this  completely  subverts
                  the  security  advantages  of  the  firewall  since
                  intruders can just masquerade as FTP or DNS by mod-
                  ifying their source port.  Obviously for a UDP scan
                  you should try 53 first and TCP scans should try 20
                  before  53.   Note  that  this is only a request --
                  nmap will honor it only if and when it is able  to.
                  For example, you can't do TCP ISN sampling all from
                  one host:port to one host:port, so nmap changes the
                  source port even if you used -g.

                  Be  aware that there is a small performance penalty
                  on some scans for  using  this  option,  because  I
                  sometimes  store  useful  information in the source
                  port number.

                                                                   12

    NMAP(1)                                                   NMAP(1)

           -n     Tells Nmap to NEVER do reverse  DNS  resolution  on
                  the  active  IP  addresses  it finds.  Since DNS is
                  often slow, this can help speed things up.

           -R     Tells Nmap to ALWAYS do reverse DNS  resolution  on
                  the  target  IP  addresses.   Normally this is only
                  done when a machine is found to be alive.

           -r     Tells Nmap NOT to  randomize  the  order  in  which
                  ports are scanned.

           --randomize_hosts
                  Tells  Nmap  to  shuffle  each  group of up to 2048
                  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 (see below).

           -M <max sockets>
                  Sets  the  maximum  number  of sockets that will be
                  used in parallel for  a  TCP  connect()  scan  (the
                  default).   This  is useful to slow down the scan a
                  little bit  and  avoid  crashing  remote  machines.
                  Another  approach is to use -sS, which is generally
                  easier for machines to handle.

           TIMING OPTIONS
                  Generally Nmap does a good  job  at  adjusting  for
                  Network  characteristics at runtime and scanning as
                  fast as possible while minimizing that  chances  of
                  hosts/ports  going  undetected.  However, there are
                  same cases where Nmap's default timing  policy  may
                  not  meet  your  objectives.  The following options
                  provide a fine level of control over the scan  tim-
                  ing:

           -T <Paranoid|Sneaky|Polite|Normal|Aggressive|Insane>
                  These  are  canned timing policies for conveniently
                  expressing your priorities to Nmap.  Paranoid  mode
                  scans  very  slowly in the hopes of avoiding detec-
                  tion by IDS systems.  It serializes all  scans  (no
                  parallel  scanning)  and generally waits at least 5
                  minutes between sending packets.  Sneaky  is  simi-
                  lar,  except it only waits 15 seconds between send-
                  ing packets.  Polite is meant to ease load  on  the
                  network   and   reduce   the  chances  of  crashing
                  machines.  It serializes the probes  and  waits  at
                  least  0.4  seconds  between  them.   Normal is the
                  default Nmap  behaviour,  which  tries  to  run  as
                  quickly as possible without overloading the network
                  or missing hosts/ports.  Aggressive mode adds  a  5
                  minute  timeout  per  host  and it never waits more
                  than 1.25 seconds for probe responses.   Insane  is
                  only  suitable  for very fast networks or where you

                                                                   13

    NMAP(1)                                                   NMAP(1)

                  don't mind losing some information.  It  times  out
                  hosts  in 75 seconds and only waits 0.3 seconds for
                  individual probes.  It does allow  for  very  quick
                  network  sweeps  though :).  You can also reference
                  these by number (0-5).  For example, '-T  0'  gives
                  you Paranoid mode and '-T 5' is Insane mode.

                  These  canned  timing  modes  should NOT be used in
                  combination with the  lower  level  controls  given
                  below.

           --host_timeout <milliseconds>
                  Specifies  the  amount  of  time Nmap is allowed to
                  spend scanning a single host before  giving  up  on
                  that IP.  The default timing mode has no host time-
                  out.

           --max_rtt_timeout <milliseconds>
                  Specifies  the  maximum  amount  of  time  Nmap  is
                  allowed   to  wait  for  a  probe  response  before
                  retransmitting or timing out that particular probe.
                  The default mode sets this to about 9000.

           --min_rtt_timeout <milliseconds>
                  When  the target hosts start to establish a pattern
                  of responding very quickly, Nmap  will  shrink  the
                  amount of time given per probe.  This speeds up the
                  scan,  but  can  lead  to  missed  packets  when  a
                  response takes longer than usual.  With this param-
                  eter you can guarantee that Nmap will wait at least
                  the  given  amount  of  time  before giving up on a
                  probe.

           --initial_rtt_timeout <milliseconds>
                  Specifies the initial probe timeout.  This is  gen-
                  erally  only  useful  when scanning firwalled hosts
                  with -P0.  Normally Nmap can obtain good RTT  esti-
                  mates  from the ping and the first few probes.  The
                  default mode uses 6000.

           --max_parallelism <number>
                  Specifies the  maximum  number  of  scans  Nmap  is
                  allowed  to  perform  in parallel.  Setting this to
                  one means Nmap will never try to scan more  than  1
                  port  at  a  time.   It also effects other parallel
                  scans such as ping sweep, RPC scan, etc.

           --scan_delay <milliseconds>
                  Specifies the minimum amount of time Nmap must wait
                  between  probes.   This  is mostly useful to reduce
                  network load or to slow the scan way down to  sneak
                  under IDS thresholds.

                                                                   14

    NMAP(1)                                                   NMAP(1)

## TARGET SPECIFICATION

           Everything  that  isn't  an option (or option argument) in
           nmap is treated as a target host specification.  The  sim-
           plest  case is listing single hostnames or IP addresses on
           the command line.  If you want to  scan  a  subnet  of  IP
           addresses,  you  can  append '/mask' to the hostname or IP
           address.  mask must be between 0 (scan the whole internet)
           and  32 (scan the single host specified).  Use /24 to scan
           a class 'C' address and /16 for a class 'B'.

           Nmap also has a more  powerful  notation  which  lets  you
           specify an IP address using lists/ranges for each element.
           Thus you can scan the whole class 'B' network  192.168.*.*
           by  specifying  '192.168.*.*'  or '192.168.0-255.0-255' or
           even '192.168.1-50,51-255.1,2,3,4,5-255'.  And  of  course
           you  can  use  the mask notation: '192.168.0.0/16'.  These
           are all equivalent.  If you use asterisks ('*'),  remember
           that  most  shells  require  you  to escape them with back
           slashes or protect them with quotes.

           Another interesting thing to do is slice the Internet  the
           other  way.   Instead of scanning all the hosts in a class
           specifying hosts to scan, see the examples section.

## EXAMPLES

           Here are some examples of using nmap, from simple and nor-
           mal  to  a little more complex/esoteric.  Note that actual
           numbers and some actual domain  names  are  used  to  make
           things  more  concrete.  In their place you should substi-
           tute addresses/names from your  own  network.   I  do  not
           think  portscanning  other networks is illegal; nor should
           portscans be construed by others as  an  attack.   I  have
           scanned   hundreds  of  thousands  of  machines  and  have
           received only one complaint.  But I am not  a  lawyer  and
           some  (anal)  people  may  be annoyed by nmap probes.  Get
           permission first or use at your own risk.

           nmap -v target.example.com

           This option scans all reserved TCP ports  on  the  machine
           target.example.com .  The -v means turn on verbose mode.

           nmap -sS -O target.example.com/24

           Launches  a  stealth SYN scan against each machine that is
           up out of the 255 machines on class 'C' where target.exam-
           ple.com  resides.  It also tries to determine what operat-
           ing system is running on each host that is up and running.
           This  requires root privileges because of the SYN scan and
           the OS detection.

           nmap -sX -p 22,53,110,143,4564 198.116.*.1-127

           Sends an Xmas tree scan to the first half of each  of  the

                                                                   15

    NMAP(1)                                                   NMAP(1)

           255  possible  8  bit  subnets  in  the  198.116 class 'B'
           address space.  We are testing  whether  the  systems  run
           sshd,  DNS,  pop3d,  imapd,  or port 4564.  Note that Xmas
           scan doesn't work on Microsoft boxes due  to  their  defi-
           cient  TCP  stack.  Same goes with CISCO, IRIX, HP/UX, and
           BSDI boxes.

           nmap -v --randomize_hosts -p 80 '*.*.2.3-5'

           Rather than focus on a specific IP range, it is  sometimes
           interesting  to  slice  up  the entire Internet and scan a
           small sample from each slice.  This command finds all  web
           servers  on  machines  with  IP  addresses ending in .2.3,
           .2.4, or .2.5 find more interesting machines  starting  at
           127.  so  you  might  want to use '127-222' instead of the
           first asterisks because that section has a greater density
           of interesting machines (IMHO).

           host -l company.com | cut '-d ' -f 4 | ./nmap -v -iL -

           Do  a  DNS  zone transfer to find the hosts in company.com
           and then feed the IP addresses to nmap.   The  above  com-
           mands  are  for  my GNU/Linux box.  You may need different
           commands/options on other operating systems.

## BUGS

           Bugs?  What bugs?  Send me any that you find.  Patches are
           nice  too  :) Remember to also send in new OS fingerprints
           so we can grow the database.  Nmap will give you a submis-
           sion URL when an appropriate fingerprint is found.

## AUTHOR

           Fyodor <fyodor@insecure.org>

## DISTRIBUTION

           The   newest   version   of  nmap  can  be  obtained  from
           http://www.insecure.org/nmap/

           nmap is (C) 1995-2001 by Insecure.Com LLC

           libpcap is also distributed along with nmap.  It is  copy-
           righted  by  Van Jacobson, Craig Leres and Steven McCanne,
           all of the Lawrence Berkeley National Laboratory,  Univer-
           sity of California, Berkeley, CA.  The version distributed
           with nmap may be modified, pristine sources are  available
           from ftp://ftp.ee.lbl.gov/libpcap.tar.Z .

           This  program  is  free  software; you can redistribute it
           and/or modify it under the terms of the GNU General Public
           License as published by the Free Software Foundation; Ver-
           sion 2.  This guarantees your right to  use,  modify,  and
           redistribute  Nmap  under  certain  conditions.   If  this
           license is unacceptable to you, Insecure.Org may be  will-
           ing     to     sell    alternative    licenses    (contact

                                                                   16

    NMAP(1)                                                   NMAP(1)

           fyodor@insecure.org).

           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 the  insecure.org  develop-
           ment  mailing  lists,  it is assumed that you are offering
           Fyodor the unlimited, non-exclusive right to  reuse,  mod-
           ify,  and  relicense  the code.  This is important because
           the inability to relicense  code  has  caused  devastating
           problems for other Free Software projects (such as KDE and
           NASM).  Nmap will always be available Open Source.  If you
           wish to specify special license conditions of your contri-
           butions, just say so when you send them.

           This program is distributed in the hope that  it  will  be
           useful, but WITHOUT ANY WARRANTY; without even the implied
           warranty of MERCHANTABILITY or FITNESS  FOR  A  PARTICULAR
           PURPOSE.   See  the  GNU  General  Public License for more
           details (it is in the COPYING file of the  nmap  distribu-
           tion).

           It  should also be noted that Nmap has been known to crash
           certain poorly written applications,  TCP/IP  stacks,  and
           even  operating systems.  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.

           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 run with privileges  (eg  suid  root)
           for security reasons.

           All  versions  of  Nmap  equal  to or greater than 2.0 are
           believed to be Year 2000 (Y2K) compliant in all  respects.
           There  is  no  reason to believe versions earlier than 2.0
           are susceptible to problems, but we have not tested  them.

                                                                   17