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TCPDUMP(1)		    General Commands Manual		    TCPDUMP(1)

       tcpdump - dump traffic on a network

       tcpdump [ -AbdDefhHIJKlLnNOpqStuUvxX# ] [ -B buffer_size	]
	       [ -c count ]
	       [ -C file_size ]	[ -G rotate_seconds ] [	-F file	]
	       [ -i interface ]	[ -j tstamp_type ] [ -m	module ] [ -M secret ]
	       [ --number ] [ -Q in|out|inout ]
	       [ -r file ] [ -V	file ] [ -s snaplen ] [	-T type	] [ -w file ]
	       [ -W filecount ]
	       [ -E spi@ipaddr algo:secret,...	]
	       [ -y datalinktype ] [ -z	postrotate-command ] [ -Z user ]
	       [ --time-stamp-precision=tstamp_precision ]
	       [ --immediate-mode ] [ --version	]
	       [ expression ]

       Tcpdump	prints	out a description of the contents of packets on	a net-
       work interface that match the boolean expression;  the  description  is
       preceded	 by a time stamp, printed, by default, as hours, minutes, sec-
       onds, and fractions of a	second since midnight.	It  can	 also  be  run
       with the	-w flag, which causes it to save the packet data to a file for
       later analysis, and/or with the -r flag,	which causes it	to read	from a
       saved packet file rather	than to	read packets from a network interface.
       It can also be run with the -V flag, which causes it to read a list  of
       saved  packet  files.  In all cases, only packets that match expression
       will be processed by tcpdump.

       Tcpdump will, if	not run	with the -c flag, continue  capturing  packets
       until  it is interrupted	by a SIGINT signal (generated, for example, by
       typing your interrupt character,	typically control-C) or	a SIGTERM sig-
       nal  (typically generated with the kill(1) command); if run with	the -c
       flag, it	will capture packets until it is interrupted by	 a  SIGINT  or
       SIGTERM signal or the specified number of packets have been processed.

       When tcpdump finishes capturing packets,	it will	report counts of:

	      packets ``captured'' (this is the	number of packets that tcpdump
	      has received and processed);

	      packets ``received by filter'' (the meaning of this  depends  on
	      the  OS on which you're running tcpdump, and possibly on the way
	      the OS was configured - if a filter was specified	on the command
	      line,  on	some OSes it counts packets regardless of whether they
	      were matched by the filter expression and,  even	if  they  were
	      matched  by the filter expression, regardless of whether tcpdump
	      has read and processed them yet, on other	OSes  it  counts  only
	      packets that were	matched	by the filter expression regardless of
	      whether tcpdump has read and processed them yet,	and  on	 other
	      OSes  it counts only packets that	were matched by	the filter ex-
	      pression and were	processed by tcpdump);

	      packets ``dropped	by kernel'' (this is  the  number  of  packets
	      that  were dropped, due to a lack	of buffer space, by the	packet
	      capture mechanism	in the OS on which tcpdump is running, if  the
	      OS  reports that information to applications; if not, it will be
	      reported as 0).

       On platforms that support the SIGINFO signal, such as  most  BSDs  (in-
       cluding	Mac  OS	X) and Digital/Tru64 UNIX, it will report those	counts
       when it receives	a SIGINFO signal (generated, for  example,  by	typing
       your  ``status''	character, typically control-T,	although on some plat-
       forms, such as Mac OS X,	the ``status'' character is  not  set  by  de-
       fault,  so  you	must  set it with stty(1) in order to use it) and will
       continue	capturing packets. On platforms	that do	not support  the  SIG-
       INFO signal, the	same can be achieved by	using the SIGUSR1 signal.

       Reading packets from a network interface	may require that you have spe-
       cial privileges;	see the	pcap (3PCAP) man page for details.  Reading  a
       saved packet file doesn't require special privileges.

       -A     Print each packet	(minus its link	level header) in ASCII.	 Handy
	      for capturing web	pages.

       -b     Print the	AS number in BGP packets in ASDOT notation rather than
	      ASPLAIN notation.

       -B buffer_size
	      Set  the operating system	capture	buffer size to buffer_size, in
	      units of KiB (1024 bytes).

       -c count
	      Exit after receiving count packets.

       -C file_size
	      Before writing a raw packet to a	savefile,  check  whether  the
	      file  is	currently  larger than file_size and, if so, close the
	      current savefile and open	a new one.  Savefiles after the	 first
	      savefile	will  have the name specified with the -w flag,	with a
	      number after it, starting	at 1 and continuing upward.  The units
	      of  file_size  are  millions  of	bytes  (1,000,000  bytes,  not
	      1,048,576	bytes).

       -d     Dump the compiled	packet-matching	code in	a human	readable  form
	      to standard output and stop.

       -dd    Dump packet-matching code	as a C program fragment.

       -ddd   Dump  packet-matching  code  as decimal numbers (preceded	with a

	      Print the	list of	the network interfaces available on the	system
	      and  on which tcpdump can	capture	packets.  For each network in-
	      terface, a number	and an interface name, possibly	followed by  a
	      text  description	 of  the interface, is printed.	 The interface
	      name or the number can be	supplied to the	-i flag	to specify  an
	      interface	on which to capture.

	      This  can	be useful on systems that don't	have a command to list
	      them (e.g., Windows systems, or UNIX  systems  lacking  ifconfig
	      -a); the number can be useful on Windows 2000 and	later systems,
	      where the	interface name is a somewhat complex string.

	      The -D flag will not be supported	if tcpdump was built  with  an
	      older version of libpcap that lacks the pcap_findalldevs() func-

       -e     Print the	link-level header on each  dump	 line.	 This  can  be
	      used,  for  example,  to print MAC layer addresses for protocols
	      such as Ethernet and IEEE	802.11.

       -E     Use spi@ipaddr algo:secret for decrypting	IPsec ESP packets that
	      are addressed to addr and	contain	Security Parameter Index value
	      spi. This	combination may	be repeated with comma or newline sep-

	      Note  that  setting the secret for IPv4 ESP packets is supported
	      at this time.

	      Algorithms may  be  des-cbc,  3des-cbc,  blowfish-cbc,  rc3-cbc,
	      cast128-cbc,  or	none.  The default is des-cbc.	The ability to
	      decrypt packets is only present if  tcpdump  was	compiled  with
	      cryptography enabled.

	      secret is	the ASCII text for ESP secret key.  If preceded	by 0x,
	      then a hex value will be read.

	      The option assumes RFC2406 ESP, not RFC1827 ESP.	The option  is
	      only  for	 debugging purposes, and the use of this option	with a
	      true `secret' key	is discouraged.	 By  presenting	 IPsec	secret
	      key  onto	 command line you make it visible to others, via ps(1)
	      and other	occasions.

	      In addition to the above syntax, the syntax  file	 name  may  be
	      used  to	have  tcpdump  read  the provided file in. The file is
	      opened upon receiving the	first ESP packet, so any special  per-
	      missions	that  tcpdump  may have	been given should already have
	      been given up.

       -f     Print `foreign' IPv4 addresses numerically rather	than  symboli-
	      cally  (this option is intended to get around serious brain dam-
	      age in Sun's NIS server -- usually it hangs forever  translating
	      non-local	internet numbers).

	      The test for `foreign' IPv4 addresses is done using the IPv4 ad-
	      dress and	netmask	of the interface on  which  capture  is	 being
	      done.   If that address or netmask are not available, available,
	      either because the interface on which capture is being done  has
	      no  address  or  netmask or because the capture is being done on
	      the Linux	"any" interface, which can capture on  more  than  one
	      interface, this option will not work correctly.

       -F file
	      Use  file	as input for the filter	expression.  An	additional ex-
	      pression given on	the command line is ignored.

       -G rotate_seconds
	      If specified, rotates the	dump file specified with the -w	option
	      every  rotate_seconds  seconds.	Savefiles  will	 have the name
	      specified	by -w which should include a time format as defined by
	      strftime(3).  If no time format is specified, each new file will
	      overwrite	the previous.

	      If used in conjunction with the -C option, filenames  will  take
	      the form of `file<count>'.

       --help Print  the  tcpdump  and	libpcap	version	strings, print a usage
	      message, and exit.

	      Print the	tcpdump	and libpcap version strings and	exit.

       -H     Attempt to detect	802.11s	draft mesh headers.

       -i interface
	      Listen on	interface.  If unspecified, tcpdump searches the  sys-
	      tem interface list for the lowest	numbered, configured up	inter-
	      face (excluding loopback), which may turn	out to be,  for	 exam-
	      ple, ``eth0''.

	      On  Linux	 systems with 2.2 or later kernels, an interface argu-
	      ment of ``any'' can be used to capture packets from  all	inter-
	      faces.   Note  that  captures  on	the ``any'' device will	not be
	      done in promiscuous mode.

	      If the -D	flag is	supported, an interface	number as  printed  by
	      that flag	can be used as the interface argument, if no interface
	      on the system has	that number as a name.

	      Put the interface	in "monitor mode"; this	is supported  only  on
	      IEEE 802.11 Wi-Fi	interfaces, and	supported only on some operat-
	      ing systems.

	      Note that	in monitor mode	the adapter  might  disassociate  from
	      the  network with	which it's associated, so that you will	not be
	      able to use any wireless networks	with that adapter.  This could
	      prevent  accessing  files	on a network server, or	resolving host
	      names or network addresses, if you are capturing in monitor mode
	      and are not connected to another network with another adapter.

	      This  flag  will	affect the output of the -L flag.  If -I isn't
	      specified, only those link-layer types  available	 when  not  in
	      monitor mode will	be shown; if -I	is specified, only those link-
	      layer types available when in monitor mode will be shown.

	      Capture in "immediate mode".  In this mode, packets  are	deliv-
	      ered  to	tcpdump	 as  soon  as  they  arrive, rather than being
	      buffered for efficiency.	This  is  the  default	when  printing
	      packets  rather  than  saving  packets  to a ``savefile''	if the
	      packets are being	printed	to a terminal rather than to a file or

       -j tstamp_type
	      Set  the	time  stamp  type for the capture to tstamp_type.  The
	      names  to	 use  for  the	time  stamp   types   are   given   in
	      pcap-tstamp(7);  not all the types listed	there will necessarily
	      be valid for any given interface.

	      List the supported time stamp types for the interface and	 exit.
	      If  the time stamp type cannot be	set for	the interface, no time
	      stamp types are listed.

	      When capturing, set the time stamp precision for the capture  to
	      tstamp_precision.	 Note that availability	of high	precision time
	      stamps (nanoseconds) and their actual accuracy is	 platform  and
	      hardware	dependent.   Also note that when writing captures made
	      with nanosecond accuracy to a  savefile,	the  time  stamps  are
	      written with nanosecond resolution, and the file is written with
	      a	different magic	number,	to indicate that the time  stamps  are
	      in  seconds  and	nanoseconds;  not  all programs	that read pcap
	      savefiles	will be	able to	read those captures.

       When reading a savefile,	convert	time stamps to the precision specified
       by  timestamp_precision,	and display them with that resolution.	If the
       precision specified is less than	the precision of time  stamps  in  the
       file, the conversion will lose precision.

       The  supported values for timestamp_precision are micro for microsecond
       resolution and nano for nanosecond  resolution.	 The  default  is  mi-
       crosecond resolution.

	      Don't attempt to verify IP, TCP, or UDP checksums.  This is use-
	      ful for interfaces that perform some or all  of  those  checksum
	      calculation  in  hardware; otherwise, all	outgoing TCP checksums
	      will be flagged as bad.

       -l     Make stdout line buffered.  Useful if you	want to	see  the  data
	      while capturing it.  E.g.,

		     tcpdump -l	| tee dat


		     tcpdump -l	> dat &	tail -f	dat

	      Note  that on Windows,``line buffered'' means ``unbuffered'', so
	      that WinDump will	write each character  individually  if	-l  is

	      -U is similar to -l in its behavior, but it will cause output to
	      be ``packet-buffered'', so that the output is written to	stdout
	      at  the  end of each packet rather than at the end of each line;
	      this is buffered on all platforms, including Windows.

	      List the known data link types for the interface,	in the	speci-
	      fied  mode,  and exit.  The list of known	data link types	may be
	      dependent	on the specified mode; for example, on some platforms,
	      a	 Wi-Fi interface might support one set of data link types when
	      not in monitor mode (for example,	it  might  support  only  fake
	      Ethernet	headers,  or might support 802.11 headers but not sup-
	      port 802.11 headers with radio information) and another  set  of
	      data link	types when in monitor mode (for	example, it might sup-
	      port 802.11 headers, or 802.11 headers with  radio  information,
	      only in monitor mode).

       -m module
	      Load  SMI	 MIB module definitions	from file module.  This	option
	      can be used several times	to load	several	MIB modules into  tcp-

       -M secret
	      Use  secret  as a	shared secret for validating the digests found
	      in TCP segments with the TCP-MD5 option (RFC 2385), if present.

       -n     Don't convert addresses (i.e.,  host  addresses,	port  numbers,
	      etc.) to names.

       -N     Don't  print  domain name	qualification of host names.  E.g., if
	      you give this flag then tcpdump will print  ``nic''  instead  of

	      Print an optional	packet number at the beginning of the line.

	      Do  not  run the packet-matching code optimizer.	This is	useful
	      only if you suspect a bug	in the optimizer.

	      Don't put	the interface into promiscuous mode.   Note  that  the
	      interface	 might	be  in promiscuous mode	for some other reason;
	      hence, `-p' cannot be used as an abbreviation  for  `ether  host
	      {local-hw-addr} or ether broadcast'.

       -Q direction
	      Choose send/receive direction direction for which	packets	should
	      be captured. Possible values are `in', `out'  and	 `inout'.  Not
	      available	on all platforms.

       -q     Quick  (quiet?) output.  Print less protocol information so out-
	      put lines	are shorter.

       -r file
	      Read packets from	file (which was	created	with the -w option  or
	      by  other	tools that write pcap or pcap-ng files).  Standard in-
	      put is used if file is ``-''.

	      Print absolute, rather than relative, TCP	sequence numbers.

       -s snaplen
	      Snarf snaplen bytes of data from each packet rather than the de-
	      fault  of	 262144	bytes.	Packets	truncated because of a limited
	      snapshot are indicated in	the output  with  ``[|proto]'',	 where
	      proto  is	the name of the	protocol level at which	the truncation
	      has occurred.  Note that taking larger snapshots both  increases
	      the amount of time it takes to process packets and, effectively,
	      decreases	the amount of packet buffering.	 This may cause	 pack-
	      ets to be	lost.  You should limit	snaplen	to the smallest	number
	      that will	capture	the protocol information you're	interested in.
	      Setting snaplen to 0 sets	it to the default of 262144, for back-
	      wards compatibility with recent older versions of	tcpdump.

       -T type
	      Force packets selected by	"expression"  to  be  interpreted  the
	      specified	 type.	 Currently known types are aodv	(Ad-hoc	On-de-
	      mand Distance Vector protocol), carp (Common Address  Redundancy
	      Protocol),  cnfp	(Cisco NetFlow protocol), lmp (Link Management
	      Protocol),  pgm	(Pragmatic   General   Multicast),   pgm_zmtp1
	      (ZMTP/1.0	inside PGM/EPGM), resp (REdis Serialization Protocol),
	      radius (RADIUS), rpc (Remote Procedure Call), rtp	(Real-Time Ap-
	      plications  protocol), rtcp (Real-Time Applications control pro-
	      tocol), snmp (Simple Network Management Protocol), tftp (Trivial
	      File  Transfer  Protocol), vat (Visual Audio Tool), wb (distrib-
	      uted White Board), zmtp1 (ZeroMQ Message Transport Protocol 1.0)
	      and vxlan	(Virtual eXtensible Local Area Network).

	      Note  that  the  pgm type	above affects UDP interpretation only,
	      the native PGM is	always recognised as IP	protocol  113  regard-
	      less. UDP-encapsulated PGM is often called "EPGM"	or "PGM/UDP".

	      Note  that  the  pgm_zmtp1  type above affects interpretation of
	      both native PGM and UDP at once. During the native PGM  decoding
	      the  application	data of	an ODATA/RDATA packet would be decoded
	      as a ZeroMQ datagram with	ZMTP/1.0 frames.  During the  UDP  de-
	      coding in	addition to that any UDP packet	would be treated as an
	      encapsulated PGM packet.

       -t     Don't print a timestamp on each dump line.

       -tt    Print the	timestamp, as seconds since January 1, 1970, 00:00:00,
	      UTC,  and	 fractions  of	a second since that time, on each dump

       -ttt   Print a delta (micro-second resolution) between current and pre-
	      vious line on each dump line.

       -tttt  Print  a timestamp, as hours, minutes, seconds, and fractions of
	      a	second since midnight, preceded	by  the	 date,	on  each  dump

       -ttttt Print  a	delta  (micro-second  resolution)  between current and
	      first line on each dump line.

       -u     Print undecoded NFS handles.

	      If the -w	option is not specified, make the printed packet  out-
	      put  ``packet-buffered'';	 i.e.,	as the description of the con-
	      tents of each packet is printed, it will be written to the stan-
	      dard  output, rather than, when not writing to a terminal, being
	      written only when	the output buffer fills.

	      If the -w	option is specified, make the saved raw	packet	output
	      ``packet-buffered'';  i.e.,  as each packet is saved, it will be
	      written to the output file, rather than being written only  when
	      the output buffer	fills.

	      The  -U  flag will not be	supported if tcpdump was built with an
	      older version of libpcap that lacks the pcap_dump_flush()	 func-

       -v     When  parsing and	printing, produce (slightly more) verbose out-
	      put.  For	example,  the  time  to	 live,	identification,	 total
	      length  and  options  in an IP packet are	printed.  Also enables
	      additional packet	integrity checks such as verifying the IP  and
	      ICMP header checksum.

	      When writing to a	file with the -w option, report, every 10 sec-
	      onds, the	number of packets captured.

       -vv    Even more	verbose	output.	 For example,  additional  fields  are
	      printed  from  NFS  reply	packets, and SMB packets are fully de-

       -vvv   Even more	verbose	output.	 For example, telnet SB	... SE options
	      are  printed in full.  With -X Telnet options are	printed	in hex
	      as well.

       -V file
	      Read a list of filenames from file. Standard input  is  used  if
	      file is ``-''.

       -w file
	      Write  the  raw packets to file rather than parsing and printing
	      them out.	 They can later	be printed with	the -r option.	 Stan-
	      dard output is used if file is ``-''.

	      This  output will	be buffered if written to a file or pipe, so a
	      program reading from the file or pipe may	not see	packets	for an
	      arbitrary	 amount	 of  time after	they are received.  Use	the -U
	      flag to cause packets to be written as  soon  as	they  are  re-

	      The  MIME	 type application/vnd.tcpdump.pcap has been registered
	      with IANA	for pcap files.	The filename extension	.pcap  appears
	      to  be  the most commonly	used along with	.cap and .dmp. Tcpdump
	      itself doesn't check the extension when  reading	capture	 files
	      and  doesn't  add	 an extension when writing them	(it uses magic
	      numbers in the file header  instead).  However,  many  operating
	      systems and applications will use	the extension if it is present
	      and adding one (e.g. .pcap) is recommended.

	      See pcap-savefile(5) for a description of	the file format.

       -W     Used in conjunction with the -C option, this will	limit the num-
	      ber  of  files  created to the specified number, and begin over-
	      writing files from the beginning,	 thus  creating	 a  'rotating'
	      buffer.  In addition, it will name the files with	enough leading
	      0s to support the	maximum	number of files, allowing them to sort

	      Used in conjunction with the -G option, this will	limit the num-
	      ber of rotated dump files	that get created, exiting with	status
	      0	when reaching the limit. If used with -C as well, the behavior
	      will result in cyclical files per	timeslice.

       -x     When parsing and printing, in addition to	printing  the  headers
	      of  each	packet,	 print the data	of each	packet (minus its link
	      level header) in hex.  The  smaller  of  the  entire  packet  or
	      snaplen  bytes  will  be	printed.  Note that this is the	entire
	      link-layer packet, so for	link layers that pad (e.g.  Ethernet),
	      the  padding  bytes  will	 also be printed when the higher layer
	      packet is	shorter	than the required padding.

       -xx    When parsing and printing, in addition to	printing  the  headers
	      of  each	packet,	 print	the data of each packet, including its
	      link level header, in hex.

       -X     When parsing and printing, in addition to	printing  the  headers
	      of  each	packet,	 print the data	of each	packet (minus its link
	      level header)  in	 hex  and  ASCII.   This  is  very  handy  for
	      analysing	new protocols.

       -XX    When  parsing  and printing, in addition to printing the headers
	      of each packet, print the	data of	 each  packet,	including  its
	      link level header, in hex	and ASCII.

       -y datalinktype
	      Set  the	data  link  type  to  use  while  capturing packets to

       -z postrotate-command
	      Used in conjunction with the -C or -G options,  this  will  make
	      tcpdump  run " postrotate-command	file " where file is the save-
	      file being closed	after each rotation. For  example,  specifying
	      -z  gzip	or  -z bzip2 will compress each	savefile using gzip or

	      Note that	tcpdump	will run the command in	parallel to  the  cap-
	      ture, using the lowest priority so that this doesn't disturb the
	      capture process.

	      And in case you would like to use	a command  that	 itself	 takes
	      flags  or	 different  arguments,	you  can  always write a shell
	      script that will take the	savefile name as  the  only  argument,
	      make  the	flags &	arguments arrangements and execute the command
	      that you want.

       -Z user
	      If tcpdump is running as root, after opening the capture	device
	      or  input	savefile, but before opening any savefiles for output,
	      change the user ID to user and the group ID to the primary group
	      of user.

	      This behavior can	also be	enabled	by default at compile time.

	      selects  which  packets  will  be	 dumped.   If no expression is
	      given, all packets on the	net will be dumped.   Otherwise,  only
	      packets for which	expression is `true' will be dumped.

	      For the expression syntax, see pcap-filter(7).

	      The  expression  argument	 can  be passed	to tcpdump as either a
	      single Shell argument, or	as multiple Shell arguments, whichever
	      is more convenient.  Generally, if the expression	contains Shell
	      metacharacters, such as  backslashes  used  to  escape  protocol
	      names,  it  is  easier  to  pass it as a single, quoted argument
	      rather than to escape the	Shell metacharacters.  Multiple	 argu-
	      ments are	concatenated with spaces before	being parsed.

       To print	all packets arriving at	or departing from sundown:
	      tcpdump host sundown

       To print	traffic	between	helios and either hot or ace:
	      tcpdump host helios and \( hot or	ace \)

       To print	all IP packets between ace and any host	except helios:
	      tcpdump ip host ace and not helios

       To print	all traffic between local hosts	and hosts at Berkeley:
	      tcpdump net ucb-ether

       To  print all ftp traffic through internet gateway snup:	(note that the
       expression is quoted to prevent the shell from  (mis-)interpreting  the
	      tcpdump 'gateway snup and	(port ftp or ftp-data)'

       To  print traffic neither sourced from nor destined for local hosts (if
       you gateway to one other	net, this stuff	should never make it onto your
       local net).
	      tcpdump ip and not net localnet

       To  print  the  start and end packets (the SYN and FIN packets) of each
       TCP conversation	that involves a	non-local host.
	      tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net localnet'

       To print	all IPv4 HTTP packets to and from port	80,  i.e.  print  only
       packets	that  contain  data, not, for example, SYN and FIN packets and
       ACK-only	packets.  (IPv6	is left	as an exercise for the reader.)
	      tcpdump 'tcp port	80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) -	((tcp[12]&0xf0)>>2)) !=	0)'

       To print	IP packets longer than 576 bytes sent through gateway snup:
	      tcpdump 'gateway snup and	ip[2:2]	> 576'

       To print	IP broadcast or	multicast packets that were not	sent via  Eth-
       ernet broadcast or multicast:
	      tcpdump 'ether[0]	& 1 = 0	and ip[16] >= 224'

       To print	all ICMP packets that are not echo requests/replies (i.e., not
       ping packets):
	      tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'

       The output of tcpdump is	protocol dependent.   The  following  gives  a
       brief description and examples of most of the formats.


       By  default,  all  output lines are preceded by a timestamp.  The time-
       stamp is	the current clock time in the form
       and is as accurate as the kernel's clock.  The timestamp	 reflects  the
       time the	kernel applied a time stamp to the packet.  No attempt is made
       to account for the time lag between when	the network interface finished
       receiving  the  packet  from  the network and when the kernel applied a
       time stamp to the packet; that time lag could include a	delay  between
       the  time  when	the network interface finished receiving a packet from
       the network and the time	when an	interrupt was delivered	to the	kernel
       to get it to read the packet and	a delay	between	the time when the ker-
       nel serviced the	`new packet' interrupt and the time when it applied  a
       time stamp to the packet.

       Link Level Headers

       If  the '-e' option is given, the link level header is printed out.  On
       Ethernets, the source and destination addresses,	protocol,  and	packet
       length are printed.

       On  FDDI	 networks, the	'-e' option causes tcpdump to print the	`frame
       control'	field,	the source and destination addresses, and  the	packet
       length.	 (The  `frame control' field governs the interpretation	of the
       rest of the packet.  Normal packets (such as those containing IP	 data-
       grams)  are `async' packets, with a priority value between 0 and	7; for
       example,	`async4'.  Such	packets	are assumed to contain an 802.2	 Logi-
       cal  Link  Control (LLC)	packet;	the LLC	header is printed if it	is not
       an ISO datagram or a so-called SNAP packet.

       On Token	Ring networks, the '-e'	option causes  tcpdump	to  print  the
       `access control'	and `frame control' fields, the	source and destination
       addresses, and the packet length.  As on	FDDI networks, packets are as-
       sumed  to contain an LLC	packet.	 Regardless of whether the '-e'	option
       is specified or not, the	source	routing	 information  is  printed  for
       source-routed packets.

       On  802.11 networks, the	'-e' option causes tcpdump to print the	`frame
       control'	fields,	all of the addresses in	the  802.11  header,  and  the
       packet  length.	As on FDDI networks, packets are assumed to contain an
       LLC packet.

       (N.B.: The following description	assumes	familiarity with the SLIP com-
       pression	algorithm described in RFC-1144.)

       On SLIP links, a	direction indicator (``I'' for inbound,	``O'' for out-
       bound), packet type, and	compression information	are printed out.   The
       packet  type is printed first.  The three types are ip, utcp, and ctcp.
       No further link information is printed for ip packets.  For  TCP	 pack-
       ets,  the  connection identifier	is printed following the type.	If the
       packet is compressed, its encoded header	is printed out.	  The  special
       cases are printed out as	*S+n and *SA+n,	where n	is the amount by which
       the sequence number (or sequence	number and ack)	has changed.  If it is
       not  a special case, zero or more changes are printed.  A change	is in-
       dicated by U (urgent pointer), W	(window), A (ack),  S  (sequence  num-
       ber), and I (packet ID),	followed by a delta (+n	or -n),	or a new value
       (=n).  Finally, the amount of data in the packet	and compressed	header
       length are printed.

       For  example,  the  following  line  shows  an  outbound	compressed TCP
       packet, with an implicit	connection identifier; the ack has changed  by
       6, the sequence number by 49, and the packet ID by 6; there are 3 bytes
       of data and 6 bytes of compressed header:
	      O	ctcp * A+6 S+49	I+6 3 (6)

       ARP/RARP	Packets

       Arp/rarp	output shows the type of request and its arguments.  The  for-
       mat  is	intended to be self explanatory.  Here is a short sample taken
       from the	start of an `rlogin' from host rtsg to host csam:
	      arp who-has csam tell rtsg
	      arp reply	csam is-at CSAM
       The first line says that	rtsg sent an arp packet	asking for the	Ether-
       net  address of internet	host csam.  Csam replies with its Ethernet ad-
       dress (in this example, Ethernet	addresses are in caps and internet ad-
       dresses in lower	case).

       This would look less redundant if we had	done tcpdump -n:
	      arp who-has tell
	      arp reply is-at 02:07:01:00:01:c4

       If  we had done tcpdump -e, the fact that the first packet is broadcast
       and the second is point-to-point	would be visible:
	      RTSG Broadcast 0806  64: arp who-has csam	tell rtsg
	      CSAM RTSG	0806  64: arp reply csam is-at CSAM
       For the first packet this says the Ethernet source address is RTSG, the
       destination is the Ethernet broadcast address, the type field contained
       hex 0806	(type ETHER_ARP) and the total length was 64 bytes.

       IPv4 Packets

       If the link-layer header	is not being printed, for IPv4 packets,	IP  is
       printed after the time stamp.

       If  the -v flag is specified, information from the IPv4 header is shown
       in parentheses after the	IP or the link-layer header.  The general for-
       mat of this information is:
	      tos tos, ttl ttl,	id id, offset offset, flags [flags], proto proto, length length, options (options)
       tos  is	the type of service field; if the ECN bits are non-zero, those
       are reported as ECT(1), ECT(0), or CE.  ttl is the time-to-live;	it  is
       not reported if it is zero.  id is the IP identification	field.	offset
       is the fragment offset field; it	is printed whether this	is part	 of  a
       fragmented  datagram  or	 not.  flags are the MF	and DF flags; +	is re-
       ported if MF is set, and	DFP is reported	if F is	set.  If  neither  are
       set, . is reported.  proto is the protocol ID field.  length is the to-
       tal length field.  options are the IP options, if any.

       Next, for TCP and UDP packets, the source and destination IP  addresses
       and TCP or UDP ports, with a dot	between	each IP	address	and its	corre-
       sponding	port, will be printed, with a >	separating the source and des-
       tination.  For other protocols, the addresses will be printed, with a >
       separating the source and destination.  Higher level protocol  informa-
       tion, if	any, will be printed after that.

       For  fragmented	IP  datagrams,	the first fragment contains the	higher
       level protocol header; fragments	after  the  first  contain  no	higher
       level  protocol header.	Fragmentation information will be printed only
       with the	-v flag, in the	IP header information, as described above.

       TCP Packets

       (N.B.:The following description assumes familiarity with	the TCP	proto-
       col  described  in RFC-793.  If you are not familiar with the protocol,
       this description	will not be of much use	to you.)

       The general format of a TCP protocol line is:
	      src > dst: Flags [tcpflags], seq data-seqno, ack ackno, win window, urg urgent, options [opts], length len
       Src and dst are the source and  destination  IP	addresses  and	ports.
       Tcpflags	are some combination of	S (SYN), F (FIN), P (PUSH), R (RST), U
       (URG), W	(ECN CWR), E (ECN-Echo)	or `.' (ACK), or `none'	 if  no	 flags
       are set.	 Data-seqno describes the portion of sequence space covered by
       the data	in this	packet (see example below).  Ackno is sequence	number
       of the next data	expected the other direction on	this connection.  Win-
       dow is the number of bytes of receive buffer space available the	 other
       direction  on this connection.  Urg indicates there is `urgent' data in
       the packet.  Opts are TCP options (e.g.,	mss 1024).  Len	is the	length
       of payload data.

       Iptype,	Src,  dst, and flags are always	present.  The other fields de-
       pend on the contents of the packet's TCP	protocol header	and are	output
       only if appropriate.

       Here is the opening portion of an rlogin	from host rtsg to host csam.
	      IP rtsg.1023 > csam.login: Flags [S], seq	768512:768512, win 4096, opts [mss 1024]
	      IP csam.login > rtsg.1023: Flags [S.], seq, 947648:947648, ack 768513, win 4096, opts [mss 1024]
	      IP rtsg.1023 > csam.login: Flags [.], ack	1, win 4096
	      IP rtsg.1023 > csam.login: Flags [P.], seq 1:2, ack 1, win 4096, length 1
	      IP csam.login > rtsg.1023: Flags [.], ack	2, win 4096
	      IP rtsg.1023 > csam.login: Flags [P.], seq 2:21, ack 1, win 4096,	length 19
	      IP csam.login > rtsg.1023: Flags [P.], seq 1:2, ack 21, win 4077,	length 1
	      IP csam.login > rtsg.1023: Flags [P.], seq 2:3, ack 21, win 4077,	urg 1, length 1
	      IP csam.login > rtsg.1023: Flags [P.], seq 3:4, ack 21, win 4077,	urg 1, length 1
       The  first  line	 says that TCP port 1023 on rtsg sent a	packet to port
       login on	csam.  The S indicates that the	SYN flag was set.  The	packet
       sequence	 number	was 768512 and it contained no data.  (The notation is
       `first:last' which means	`sequence numbers first	up to but not  includ-
       ing last.)  There was no	piggy-backed ack, the available	receive	window
       was 4096	bytes and there	was a max-segment-size	option	requesting  an
       mss of 1024 bytes.

       Csam  replies  with  a similar packet except it includes	a piggy-backed
       ack for rtsg's SYN.  Rtsg then acks csam's SYN.	The `.'	means the  ACK
       flag  was  set.	 The  packet contained no data so there	is no data se-
       quence number or	length.	 Note that the ack sequence number is a	 small
       integer	(1).   The  first  time	 tcpdump sees a	TCP `conversation', it
       prints the sequence number from the packet.  On subsequent  packets  of
       the  conversation, the difference between the current packet's sequence
       number and this initial sequence	number is printed.   This  means  that
       sequence	 numbers  after	 the first can be interpreted as relative byte
       positions in the	conversation's data stream (with the first  data  byte
       each  direction	being  `1').  `-S' will	override this feature, causing
       the original sequence numbers to	be output.

       On the 6th line,	rtsg sends csam	19 bytes of data (bytes	2  through  20
       in the rtsg -> csam side	of the conversation).  The PUSH	flag is	set in
       the packet.  On the 7th line, csam says it's received data sent by rtsg
       up  to but not including	byte 21.  Most of this data is apparently sit-
       ting in the socket buffer since csam's receive  window  has  gotten  19
       bytes  smaller.	 Csam  also  sends  one	 byte  of data to rtsg in this
       packet.	On the 8th and 9th lines, csam	sends  two  bytes  of  urgent,
       pushed data to rtsg.

       If  the	snapshot was small enough that tcpdump didn't capture the full
       TCP header, it interprets as much of the	header as it can and then  re-
       ports  ``[|tcp]''  to  indicate the remainder could not be interpreted.
       If the header contains a	bogus option (one with a length	that's	either
       too  small  or  beyond  the  end	 of the	header), tcpdump reports it as
       ``[bad opt]'' and does not interpret any	further	 options  (since  it's
       impossible  to  tell where they start).	If the header length indicates
       options are present but the IP datagram length is not long  enough  for
       the  options  to	 actually  be  there, tcpdump reports it as ``[bad hdr

       Capturing TCP packets with particular flag combinations (SYN-ACK,  URG-
       ACK, etc.)

       There are 8 bits	in the control bits section of the TCP header:

	      CWR | ECE	| URG |	ACK | PSH | RST	| SYN |	FIN

       Let's  assume  that we want to watch packets used in establishing a TCP
       connection.  Recall that	TCP uses a 3-way handshake  protocol  when  it
       initializes  a  new  connection;	the connection sequence	with regard to
       the TCP control bits is

	      1) Caller	sends SYN
	      2) Recipient responds with SYN, ACK
	      3) Caller	sends ACK

       Now we're interested in capturing packets that have only	 the  SYN  bit
       set  (Step  1).	Note that we don't want	packets	from step 2 (SYN-ACK),
       just a plain initial SYN.  What we need is a correct filter  expression
       for tcpdump.

       Recall the structure of a TCP header without options:

	0			     15				     31
       |	  source port	       |       destination port	       |
       |			sequence number			       |
       |		     acknowledgment number		       |
       |  HL   | rsvd  |C|E|U|A|P|R|S|F|	window size	       |
       |	 TCP checksum	       |       urgent pointer	       |

       A  TCP  header  usually	holds  20  octets  of data, unless options are
       present.	 The first line	of the graph contains octets 0 - 3, the	second
       line shows octets 4 - 7 etc.

       Starting	 to  count with	0, the relevant	TCP control bits are contained
       in octet	13:

	0	      7|	     15|	     23|	     31
       |  HL   | rsvd  |C|E|U|A|P|R|S|F|	window size	       |
       |	       |  13th octet   |	       |	       |

       Let's have a closer look	at octet no. 13:

		       |	       |
		       |7   5	3     0|

       These are the TCP control bits we are interested	in.  We	have  numbered
       the  bits  in  this octet from 0	to 7, right to left, so	the PSH	bit is
       bit number 3, while the URG bit is number 5.

       Recall that we want to capture packets with only	SYN  set.   Let's  see
       what happens to octet 13	if a TCP datagram arrives with the SYN bit set
       in its header:

		       |0 0 0 0	0 0 1 0|
		       |7 6 5 4	3 2 1 0|

       Looking at the control bits section we see that only bit	number 1 (SYN)
       is set.

       Assuming	 that  octet number 13 is an 8-bit unsigned integer in network
       byte order, the binary value of this octet is


       and its decimal representation is

	  7	6     5	    4	  3	2     1	    0
       0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 1*2 + 0*2  =	 2

       We're almost done, because now we know that if only  SYN	 is  set,  the
       value  of the 13th octet	in the TCP header, when	interpreted as a 8-bit
       unsigned	integer	in network byte	order, must be exactly 2.

       This relationship can be	expressed as
	      tcp[13] == 2

       We can use this expression as the filter	for tcpdump in order to	 watch
       packets which have only SYN set:
	      tcpdump -i xl0 tcp[13] ==	2

       The expression says "let	the 13th octet of a TCP	datagram have the dec-
       imal value 2", which is exactly what we want.

       Now, let's assume that we need to capture SYN  packets,	but  we	 don't
       care  if	 ACK  or  any  other  TCP control bit is set at	the same time.
       Let's see what happens to octet 13 when a TCP datagram with SYN-ACK set

	    |0 0 0 1 0 0 1 0|
	    |7 6 5 4 3 2 1 0|

       Now  bits 1 and 4 are set in the	13th octet.  The binary	value of octet
       13 is


       which translates	to decimal

	  7	6     5	    4	  3	2     1	    0
       0*2 + 0*2 + 0*2 + 1*2 + 0*2 + 0*2 + 1*2 + 0*2   = 18

       Now we can't just use 'tcp[13] == 18' in	the tcpdump filter expression,
       because that would select only those packets that have SYN-ACK set, but
       not those with only SYN set.  Remember that we don't care if ACK	or any
       other control bit is set	as long	as SYN is set.

       In order	to achieve our goal, we	need to	logically AND the binary value
       of octet	13 with	some other value to preserve the  SYN  bit.   We  know
       that  we	 want  SYN  to	be set in any case, so we'll logically AND the
       value in	the 13th octet with the	binary value of	a SYN:

		 00010010 SYN-ACK	       00000010	SYN
	    AND	 00000010 (we want SYN)	  AND  00000010	(we want SYN)
		 --------		       --------
	    =	 00000010		  =    00000010

       We see that this	AND operation  delivers	 the  same  result  regardless
       whether ACK or another TCP control bit is set.  The decimal representa-
       tion of the AND value as	well as	the result of this operation is	2 (bi-
       nary  00000010),	so we know that	for packets with SYN set the following
       relation	must hold true:

	      (	( value	of octet 13 ) AND ( 2 )	) == ( 2 )

       This points us to the tcpdump filter expression
		   tcpdump -i xl0 'tcp[13] & 2 == 2'

       Some offsets and	field values may be expressed as names rather than  as
       numeric values. For example tcp[13] may be replaced with	tcp[tcpflags].
       The following TCP flag field values are also available:	tcp-fin,  tcp-
       syn, tcp-rst, tcp-push, tcp-act,	tcp-urg.

       This can	be demonstrated	as:
		   tcpdump -i xl0 'tcp[tcpflags] & tcp-push != 0'

       Note that you should use	single quotes or a backslash in	the expression
       to hide the AND ('&') special character from the	shell.

       UDP Packets

       UDP format is illustrated by this rwho packet:
	      actinide.who > broadcast.who: udp	84
       This says that port who on host actinide	sent a udp  datagram  to  port
       who on host broadcast, the Internet broadcast address.  The packet con-
       tained 84 bytes of user data.

       Some UDP	services are recognized	(from the source or  destination  port
       number) and the higher level protocol information printed.  In particu-
       lar, Domain Name	service	requests (RFC-1034/1035)  and  Sun  RPC	 calls
       (RFC-1050) to NFS.

       UDP Name	Server Requests

       (N.B.:The  following  description  assumes  familiarity with the	Domain
       Service protocol	described in RFC-1035.	If you are not	familiar  with
       the  protocol,  the  following description will appear to be written in

       Name server requests are	formatted as
	      src _ dst: id op?	flags qtype qclass name	(len)
	      h2opolo.1538 > helios.domain: 3+ A? (37)
       Host h2opolo asked the domain server on helios for  an  address	record
       (qtype=A)  associated  with the name  The query id
       was `3'.	 The `+' indicates the recursion desired flag  was  set.   The
       query  length was 37 bytes, not including the UDP and IP	protocol head-
       ers.  The query operation was the normal	one, Query, so	the  op	 field
       was  omitted.   If  the	op  had	been anything else, it would have been
       printed between the `3' and the `+'.  Similarly,	 the  qclass  was  the
       normal  one,  C_IN,  and	 omitted.   Any	 other	qclass would have been
       printed immediately after the `A'.

       A few anomalies are checked and may result in extra fields enclosed  in
       square  brackets:   If a	query contains an answer, authority records or
       additional records section, ancount, nscount, or	arcount	are printed as
       `[na]', `[nn]' or  `[nau]' where	n is the appropriate count.  If	any of
       the response bits are set (AA, RA or rcode) or  any  of	the  `must  be
       zero' bits are set in bytes two and three, `[b2&3=x]' is	printed, where
       x is the	hex value of header bytes two and three.

       UDP Name	Server Responses

       Name server responses are formatted as
	      src _ dst:  id op	rcode flags a/n/au type	class data (len)
	      helios.domain > h2opolo.1538: 3 3/3/7 A (273)
	      helios.domain > h2opolo.1537: 2 NXDomain*	0/1/0 (97)
       In the first example, helios responds to	query id 3 from	h2opolo	with 3
       answer  records,	 3  name server	records	and 7 additional records.  The
       first answer record is type A (address) and its data  is	 internet  ad-
       dress  The total size of the response was	273 bytes, ex-
       cluding UDP and IP headers.  The	op (Query) and response	code (NoError)
       were omitted, as	was the	class (C_IN) of	the A record.

       In  the second example, helios responds to query	2 with a response code
       of non-existent domain (NXDomain) with no answers, one name server  and
       no  authority records.  The `*' indicates that the authoritative	answer
       bit was set.  Since there were no answers, no type, class or data  were

       Other  flag  characters that might appear are `-' (recursion available,
       RA, not set) and	`|' (truncated message,	TC, set).  If  the  `question'
       section doesn't contain exactly one entry, `[nq]' is printed.

       SMB/CIFS	decoding

       tcpdump now includes fairly extensive SMB/CIFS/NBT decoding for data on
       UDP/137,	UDP/138	and TCP/139.  Some primitive decoding of IPX and  Net-
       BEUI SMB	data is	also done.

       By  default  a fairly minimal decode is done, with a much more detailed
       decode done if -v is used.  Be warned that with -v a single SMB	packet
       may  take  up a page or more, so	only use -v if you really want all the
       gory details.

       For information on SMB packet formats and what all the fields mean  see   or  the  pub/samba/specs/	 directory  on	your  favorite mirror	site.  The SMB patches were written by Andrew Tridgell

       NFS Requests and	Replies

       Sun NFS (Network	File System) requests and replies are printed as:	_ dst.nfs: NFS request xid xid len op args
	      src.nfs _	dst.dport: NFS reply xid xid reply stat	len op results
	      sushi.1023 > wrl.nfs: NFS	request	xid 26377
		   112 readlink	fh 21,24/10.73165
	      wrl.nfs >	sushi.1023: NFS	reply xid 26377
		   reply ok 40 readlink	"../var"
	      sushi.1022 > wrl.nfs: NFS	request	xid 8219
		   144 lookup fh 9,74/4096.6878	"xcolors"
	      wrl.nfs >	sushi.1022: NFS	reply xid 8219
		   reply ok 128	lookup fh 9,74/4134.3150
       In the first line, host sushi sends a transaction with id 26377 to wrl.
       The request was 112 bytes, excluding the	UDP and	IP headers.  The oper-
       ation  was  a  readlink	(read  symbolic	 link)	on  file  handle  (fh)
       21,24/10.731657119.  (If	one is lucky, as in this case, the file	handle
       can be interpreted as a major,minor device number pair, followed	by the
       inode number and	generation number.) In the second  line,  wrl  replies
       `ok' with the same transaction id and the contents of the link.

       In  the	third  line,  sushi  asks  (using a new	transaction id)	wrl to
       lookup the name `xcolors' in  directory	file  9,74/4096.6878.  In  the
       fourth line, wrl	sends a	reply with the respective transaction id.

       Note  that  the data printed depends on the operation type.  The	format
       is intended to be self explanatory if read in conjunction with  an  NFS
       protocol	 spec.	 Also  note that older versions	of tcpdump printed NFS
       packets in a slightly different format: the transaction id (xid)	 would
       be printed instead of the non-NFS port number of	the packet.

       If  the	-v (verbose) flag is given, additional information is printed.
       For example:
	      sushi.1023 > wrl.nfs: NFS	request	xid 79658
		   148 read fh 21,11/12.195 8192 bytes @ 24576
	      wrl.nfs >	sushi.1023: NFS	reply xid 79658
		   reply ok 1472 read REG 100664 ids 417/0 sz 29388
       (-v also	prints the  IP	header	TTL,  ID,  length,  and	 fragmentation
       fields, which have been omitted from this example.)  In the first line,
       sushi asks wrl to read 8192 bytes from file 21,11/12.195, at byte  off-
       set  24576.   Wrl  replies `ok';	the packet shown on the	second line is
       the first fragment of the reply,	and hence is only 1472 bytes long (the
       other bytes will	follow in subsequent fragments,	but these fragments do
       not have	NFS or even UDP	headers	and so might not be printed, depending
       on  the filter expression used).	 Because the -v	flag is	given, some of
       the file	attributes (which are returned in addition to the  file	 data)
       are  printed:  the file type (``REG'', for regular file), the file mode
       (in octal), the uid and gid, and	the file size.

       If the -v flag is given more than once, even more details are printed.

       Note that NFS requests are very large and much of the detail  won't  be
       printed	unless	snaplen	is increased.  Try using `-s 192' to watch NFS

       NFS reply packets do not	explicitly identify the	 RPC  operation.   In-
       stead,  tcpdump keeps track of ``recent'' requests, and matches them to
       the replies using the transaction ID.  If a reply does not closely fol-
       low the corresponding request, it might not be parsable.

       AFS Requests and	Replies

       Transarc	AFS (Andrew File System) requests and replies are printed as:	_ dst.dport: rx	packet-type	_ dst.dport: rx	packet-type service call call-name args	_ dst.dport: rx	packet-type service reply call-name args
	      elvis.7001 > pike.afsfs:
		   rx data fs call rename old fid 536876964/1/1	""
		   new fid 536876964/1/1 ".newsrc"
	      pike.afsfs > elvis.7001: rx data fs reply	rename
       In the first line, host elvis sends a RX	packet to pike.	 This was a RX
       data packet to the fs (fileserver) service, and is the start of an  RPC
       call.   The  RPC	 call  was a rename, with the old directory file id of
       536876964/1/1 and an old	filename of `', and a new directory
       file  id	 of  536876964/1/1  and	a new filename of `.newsrc'.  The host
       pike responds with a RPC	reply to the rename call (which	 was  success-
       ful, because it was a data packet and not an abort packet).

       In  general,  all AFS RPCs are decoded at least by RPC call name.  Most
       AFS RPCs	have at	least some of the arguments  decoded  (generally  only
       the `interesting' arguments, for	some definition	of interesting).

       The  format is intended to be self-describing, but it will probably not
       be useful to people who are not familiar	with the workings of  AFS  and

       If  the	-v  (verbose) flag is given twice, acknowledgement packets and
       additional header information is	printed, such as the RX	call ID,  call
       number, sequence	number,	serial number, and the RX packet flags.

       If  the -v flag is given	twice, additional information is printed, such
       as the RX call ID, serial number, and the RX packet flags.  The MTU ne-
       gotiation information is	also printed from RX ack packets.

       If  the -v flag is given	three times, the security index	and service id
       are printed.

       Error codes are printed for abort packets, with the exception  of  Ubik
       beacon  packets	(because  abort	packets	are used to signify a yes vote
       for the Ubik protocol).

       Note that AFS requests are very large and many of the  arguments	 won't
       be  printed  unless  snaplen is increased.  Try using `-s 256' to watch
       AFS traffic.

       AFS reply packets do not	explicitly identify the	 RPC  operation.   In-
       stead,  tcpdump keeps track of ``recent'' requests, and matches them to
       the replies using the call number and service ID.  If a reply does  not
       closely follow the corresponding	request, it might not be parsable.

       KIP AppleTalk (DDP in UDP)

       AppleTalk DDP packets encapsulated in UDP datagrams are de-encapsulated
       and dumped as DDP packets (i.e.,	all the	UDP header information is dis-
       carded).	  The file /etc/atalk.names is used to translate AppleTalk net
       and node	numbers	to names.  Lines in this file have the form
	      number	name

	      1.254	     ether
	      16.1	icsd-net
	      1.254.110	ace
       The first two lines give	the names of AppleTalk	networks.   The	 third
       line  gives the name of a particular host (a host is distinguished from
       a net by	the 3rd	octet in the number -  a  net  number  must  have  two
       octets  and a host number must have three octets.)  The number and name
       should  be   separated	by   whitespace	  (blanks   or	 tabs).	   The
       /etc/atalk.names	 file  may contain blank lines or comment lines	(lines
       starting	with a `#').

       AppleTalk addresses are printed in the form > icsd-net.112.220
	      office.2 > icsd-net.112.220
	      jssmag.149.235 > icsd-net.2
       (If the /etc/atalk.names	doesn't	exist or doesn't contain an entry  for
       some AppleTalk host/net number, addresses are printed in	numeric	form.)
       In the first example, NBP (DDP port 2) on net 144.1 node	209 is sending
       to  whatever is listening on port 220 of	net icsd node 112.  The	second
       line is the same	except the full	name of	the source node	is known (`of-
       fice').	 The third line	is a send from port 235	on net jssmag node 149
       to broadcast on the icsd-net NBP	port (note that	the broadcast  address
       (255)  is indicated by a	net name with no host number - for this	reason
       it's a good  idea  to  keep  node  names	 and  net  names  distinct  in

       NBP  (name  binding  protocol) and ATP (AppleTalk transaction protocol)
       packets have their contents interpreted.	 Other protocols just dump the
       protocol	name (or number	if no name is registered for the protocol) and
       packet size.

       NBP packets are formatted like the following examples:
	      icsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
	      jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
	      techpit.2	> icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186
       The first line is a name	lookup request for laserwriters	 sent  by  net
       icsd  host  112 and broadcast on	net jssmag.  The nbp id	for the	lookup
       is 190.	The second line	shows a	reply for this request (note  that  it
       has  the	same id) from host jssmag.209 saying that it has a laserwriter
       resource	named "RM1140" registered on port 250.	The third line is  an-
       other  reply  to	 the  same request saying host techpit has laserwriter
       "techpit" registered on port 186.

       ATP packet formatting is	demonstrated by	the following example:
	      jssmag.209.165 > helios.132: atp-req  12266<0-7> 0xae030001
	      helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
	      helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
	      helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
	      helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
	      helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
	      helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
	      helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
	      helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
	      jssmag.209.165 > helios.132: atp-req  12266<3,5> 0xae030001
	      helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
	      helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
	      jssmag.209.165 > helios.132: atp-rel  12266<0-7> 0xae030001
	      jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002
       Jssmag.209 initiates transaction	id 12266 with host helios by  request-
       ing  up	to  8 packets (the `<0-7>').  The hex number at	the end	of the
       line is the value of the	`userdata' field in the	request.

       Helios responds with 8 512-byte packets.	 The  `:digit'	following  the
       transaction  id gives the packet	sequence number	in the transaction and
       the number in parens is the amount of data in the packet, excluding the
       atp header.  The	`*' on packet 7	indicates that the EOM bit was set.

       Jssmag.209  then	 requests that packets 3 & 5 be	retransmitted.	Helios
       resends them then jssmag.209 releases the transaction.	Finally,  jss-
       mag.209	initiates  the next request.  The `*' on the request indicates
       that XO (`exactly once')	was not	set.

       stty(1),	   pcap(3PCAP),	    bpf(4),	nit(4P),     pcap-savefile(5),
       pcap-filter(7), pcap-tstamp(7)

       The original authors are:

       Van Jacobson, Craig Leres and  Steven  McCanne,	all  of	 the  Lawrence
       Berkeley	National Laboratory, University	of California, Berkeley, CA.

       It is currently being maintained	by

       The current version is available	via http:

       The original distribution is available via anonymous ftp:

       IPv6/IPsec  support  is	added by WIDE/KAME project.  This program uses
       Eric Young's SSLeay library, under specific configurations.

       To   report   a	 security   issue   please   send   an	  e-mail    to

       To  report  bugs	and other problems, contribute patches,	request	a fea-
       ture, provide generic feedback etc please see the file CONTRIBUTING  in
       the tcpdump source tree root.

       NIT doesn't let you watch your own outbound traffic, BPF	will.  We rec-
       ommend that you use the latter.

       On Linux	systems	with 2.0[.x] kernels:

	      packets on the loopback device will be seen twice;

	      packet filtering cannot be done in the kernel, so	that all pack-
	      ets  must	 be  copied from the kernel in order to	be filtered in
	      user mode;

	      all of a packet, not just	the part that's	 within	 the  snapshot
	      length,  will be copied from the kernel (the 2.0[.x] packet cap-
	      ture mechanism, if asked to copy only part of a packet to	 user-
	      land,  will not report the true length of	the packet; this would
	      cause most IP packets to get an error from tcpdump);

	      capturing	on some	PPP devices won't work correctly.

       We recommend that you upgrade to	a 2.2 or later kernel.

       Some attempt should be made to reassemble IP fragments or, at least  to
       compute the right length	for the	higher level protocol.

       Name server inverse queries are not dumped correctly: the (empty) ques-
       tion section is printed rather than real	query in the  answer  section.
       Some  believe  that  inverse queries are	themselves a bug and prefer to
       fix the program generating them rather than tcpdump.

       A packet	trace that crosses a daylight savings time  change  will  give
       skewed time stamps (the time change is ignored).

       Filter  expressions  on	fields	other than those in Token Ring headers
       will not	correctly handle source-routed Token Ring packets.

       Filter expressions on fields other than those in	 802.11	 headers  will
       not  correctly  handle  802.11 data packets with	both To	DS and From DS

       ip6 proto should	chase header chain, but	at this	moment	it  does  not.
       ip6 protochain is supplied for this behavior.

       Arithmetic  expression  against	transport  layer headers, like tcp[0],
       does not	work against IPv6 packets.  It only looks at IPv4 packets.

				2 February 2017			    TCPDUMP(1)


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