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TCPDUMP(1)		    General Commands Manual		    TCPDUMP(1)

NAME
       tcpdump - dump traffic on a network

SYNOPSIS
       tcpdump [ -AdDeflLnNOpqRStuUvxX ] [ -c count ]
	       [ -C file_size ]	[ -F file ]
	       [ -i interface ]	[ -m module ] [	-M secret ]
	       [ -r file ] [ -s	snaplen	] [ -T type ] [	-w file	]
	       [ -W filecount ]
	       [ -E spi@ipaddr algo:secret,...	]
	       [ -y datalinktype ] [ -Z	user ]
	       [ -y datalinktype ]
	       [ expression ]

DESCRIPTION
       Tcpdump	prints	out a description of the contents of packets on	a net-
       work interface that match the boolean expression.  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.
       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.

       Reading packets from a network interface	may require that you have spe-
       cial privileges:

       Under SunOS 3.x or 4.x with NIT or BPF:
	      You must have read access	to /dev/nit or /dev/bpf*.

       Under Solaris with DLPI:
	      You must have read/write access to the  network  pseudo  device,
	      e.g.   /dev/le.	On at least some versions of Solaris, however,
	      this is not sufficient to	allow tcpdump to capture in  promiscu-
	      ous  mode;  on  those  versions of Solaris, you must be root, or
	      tcpdump must be installed	setuid to root,	in order to capture in
	      promiscuous  mode.  Note that, on	many (perhaps all) interfaces,
	      if you don't capture in promiscuous mode,	you will not  see  any
	      outgoing	packets, so a capture not done in promiscuous mode may
	      not be very useful.

       Under HP-UX with	DLPI:
	      You must be root or tcpdump must be installed setuid to root.

       Under IRIX with snoop:
	      You must be root or tcpdump must be installed setuid to root.

       Under Linux:
	      You must be root or tcpdump must be  installed  setuid  to  root
	      (unless  your distribution has a kernel that supports capability
	      bits such	as CAP_NET_RAW and code	to allow those capability bits
	      to be given to particular	accounts and to	cause those bits to be
	      set on a user's initial processes	when they  log	in,  in	 which
	      case  you	  must	have  CAP_NET_RAW  in  order  to  capture  and
	      CAP_NET_ADMIN to enumerate network devices  with,	 for  example,
	      the -D flag).

       Under ULTRIX and	Digital	UNIX/Tru64 UNIX:
	      Any  user	may capture network traffic with tcpdump.  However, no
	      user (not	even the super-user) can capture in  promiscuous  mode
	      on  an  interface	unless the super-user has enabled promiscuous-
	      mode operation on	that interface using pfconfig(8), and no  user
	      (not  even  the super-user) can capture unicast traffic received
	      by or sent by the	machine	on an interface	unless the  super-user
	      has  enabled copy-all-mode operation on that interface using pf-
	      config, so useful	packet capture on an  interface	 probably  re-
	      quires  that either promiscuous-mode or copy-all-mode operation,
	      or both modes of operation, be enabled on	that interface.

       Under BSD (this includes	Mac OS X):
	      You must have read access	to /dev/bpf*  on  systems  that	 don't
	      have  a  cloning	BPF device, or to /dev/bpf on systems that do.
	      On BSDs with a devfs (this includes Mac OS X),  this  might  in-
	      volve more than just having somebody with	super-user access set-
	      ting the ownership or permissions	on the BPF devices - it	 might
	      involve  configuring  devfs  to set the ownership	or permissions
	      every time the system is booted, if  the	system	even  supports
	      that;  if	 it  doesn't support that, you might have to find some
	      other way	to make	that happen at boot time.

       Reading a saved packet file doesn't require special privileges.

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

       -c     Exit after receiving count packets.

       -C     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
	      count).

       -D     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-
	      tion.

       -e     Print the	link-level header on each dump line.

       -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
	      seperation.

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

       -i     Listen  on interface.  If	unspecified, tcpdump searches the sys-
	      tem interface list for the lowest	numbered, configured up	inter-
	      face (excluding loopback).  Ties are broken by choosing the ear-
	      liest match.

	      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.

       -l     Make stdout line buffered.  Useful if you	want to	see  the  data
	      while capturing it.  E.g.,
	      ``tcpdump	 -l  |	tee	dat''	  or	 ``tcpdump  -l	     >
	      dat  &  tail  -f	dat''.

       -L     List the known data link types for the interface and exit.

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

       -M     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
	      ``nic.ddn.mil''.

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

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

       -R     Assume  ESP/AH packets to	be based on old	specification (RFC1825
	      to RFC1829).  If specified, tcpdump will not print  replay  pre-
	      vention  field.	Since  there  is  no protocol version field in
	      ESP/AH specification,  tcpdump  cannot  deduce  the  version  of
	      ESP/AH protocol.

       -r     Read  packets  from file (which was created with the -w option).
	      Standard input is	used if	file is	``-''.

       -S     Print absolute, rather than relative, TCP	sequence numbers.

       -s     Snarf snaplen bytes of data from each packet rather than the de-
	      fault  of	68 (with SunOS's NIT, the minimum is actually 96).  68
	      bytes is adequate	for IP,	ICMP, TCP and  UDP  but	 may  truncate
	      protocol	information  from name server and NFS packets (see be-
	      low).  Packets truncated because of a limited snapshot are indi-
	      cated  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 packets to be lost.
	      You should limit snaplen to the smallest number that  will  cap-
	      ture  the	 protocol  information	you're interested in.  Setting
	      snaplen to 0 means use the required length to catch whole	 pack-
	      ets.

       -T     Force  packets  selected	by  "expression" to be interpreted the
	      specified	type.  Currently known types are aodv  (Ad-hoc	On-de-
	      mand  Distance  Vector protocol),	cnfp (Cisco NetFlow protocol),
	      rpc (Remote Procedure Call), rtp (Real-Time Applications	proto-
	      col), rtcp (Real-Time Applications control protocol), snmp (Sim-
	      ple Network Management Protocol),	tftp  (Trivial	File  Transfer
	      Protocol),  vat  (Visual	Audio Tool), and wb (distributed White
	      Board).

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

       -tt    Print an unformatted timestamp on	each dump line.

       -ttt   Print a delta (in	micro-seconds) between	current	 and  previous
	      line on each dump	line.

       -tttt  Print  a	timestamp  in default format proceeded by date on each
	      dump line.

       -u     Print undecoded NFS handles.

       -U     Make output saved	via the	-w option  ``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-
	      tion.

       -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-
	      coded.

       -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.

       -w     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 ``-''.

       -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
	      correctly.

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

       -Z     Drops privileges (if root) and changes 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.

	expression
	      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.

	      The  expression  consists	of one or more primitives.  Primitives
	      usually consist of an id (name or	number)	 preceded  by  one  or
	      more qualifiers.	There are three	different kinds	of qualifier:

	      type   qualifiers	 say  what kind	of thing the id	name or	number
		     refers to.	 Possible types	are host, net ,	port and  por-
		     trange.   E.g., `host foo', `net 128.3', `port 20', `por-
		     trange 6000-6008'.	 If there is no	type  qualifier,  host
		     is	assumed.

	      dir    qualifiers	 specify  a  particular	 transfer direction to
		     and/or from id.  Possible directions are src, dst,	src or
		     dst  and  src and dst.  E.g., `src	foo', `dst net 128.3',
		     `src or dst port ftp-data'.  If there is  no  dir	quali-
		     fier,  src	or dst is assumed.  For	some link layers, such
		     as	SLIP and the ``cooked''	Linux capture  mode  used  for
		     the  ``any''  device and for some other device types, the
		     inbound and outbound qualifiers can be used to specify  a
		     desired direction.

	      proto  qualifiers	 restrict  the match to	a particular protocol.
		     Possible protos are: ether, fddi, tr, wlan, ip, ip6, arp,
		     rarp,  decnet,  lat,  sca,	moprc, mopdl, iso, esis, isis,
		     icmp, icmp6, tcp and udp.	E.g., `ether  src  foo',  `arp
		     net 128.3', `tcp port 21',	`udp portrange 7000-7009'.  If
		     there is no proto	qualifier,  all	 protocols  consistent
		     with the type are assumed.	 E.g., `src foo' means `(ip or
		     arp or rarp) src foo' (except the	latter	is  not	 legal
		     syntax),  `net  bar'  means `(ip or arp or	rarp) net bar'
		     and `port 53' means `(tcp or udp) port 53'.

	      [`fddi' is actually an alias for `ether';	the parser treats them
	      identically  as meaning ``the data link level used on the	speci-
	      fied network interface.''	 FDDI  headers	contain	 Ethernet-like
	      source  and  destination	addresses, and often contain Ethernet-
	      like packet types, so you	can filter on these FDDI  fields  just
	      as  with	the analogous Ethernet fields.	FDDI headers also con-
	      tain other fields, but you cannot	name them explicitly in	a fil-
	      ter expression.

	      Similarly, `tr' and `wlan' are aliases for `ether'; the previous
	      paragraph's statements about FDDI	headers	also  apply  to	 Token
	      Ring  and	 802.11	wireless LAN headers.  For 802.11 headers, the
	      destination address is the DA field and the  source  address  is
	      the SA field; the	BSSID, RA, and TA fields aren't	tested.]

	      In  addition  to	the  above, there are some special `primitive'
	      keywords that don't  follow  the	pattern:  gateway,  broadcast,
	      less,  greater and arithmetic expressions.  All of these are de-
	      scribed below.

	      More complex filter expressions are built	up by using the	 words
	      and,  or and not to combine primitives.  E.g., `host foo and not
	      port ftp and not port  ftp-data'.	  To  save  typing,  identical
	      qualifier	lists can be omitted.  E.g., `tcp dst port ftp or ftp-
	      data or domain' is exactly the same as `tcp dst port ftp or  tcp
	      dst port ftp-data	or tcp dst port	domain'.

	      Allowable	primitives are:

	      dst host host
		     True  if  the  IPv4/v6 destination	field of the packet is
		     host, which may be	either an address or a name.

	      src host host
		     True if the IPv4/v6 source	field of the packet is host.

	      host host
		     True if either the	IPv4/v6	source or destination  of  the
		     packet is host.

		     Any  of  the above	host expressions can be	prepended with
		     the keywords, ip, arp, rarp, or ip6 as in:
			  ip host host
		     which is equivalent to:
			  ether	proto \ip and host host
		     If	host is	a name with multiple IP	 addresses,  each  ad-
		     dress will	be checked for a match.

	      ether dst	ehost
		     True if the Ethernet destination address is ehost.	 Ehost
		     may be either a name from /etc/ethers or  a  number  (see
		     ethers(3N)	for numeric format).

	      ether src	ehost
		     True if the Ethernet source address is ehost.

	      ether host ehost
		     True if either the	Ethernet source	or destination address
		     is	ehost.

	      gateway host
		     True if the packet	used host as  a	 gateway.   I.e.,  the
		     Ethernet  source or destination address was host but nei-
		     ther the IP source	nor the	IP destination was host.  Host
		     must  be  a  name and must	be found both by the machine's
		     host-name-to-IP-address resolution	mechanisms (host  name
		     file,  DNS, NIS, etc.) and	by the machine's host-name-to-
		     Ethernet-address	resolution   mechanism	 (/etc/ethers,
		     etc.).  (An equivalent expression is
			  ether	host ehost and not host	host
		     which can be used with either names or numbers for	host /
		     ehost.)  This syntax does not work	in  IPv6-enabled  con-
		     figuration	at this	moment.

	      dst net net
		     True if the IPv4/v6 destination address of	the packet has
		     a network number of net.  Net may be either a  name  from
		     the  networks database (/etc/networks, etc.) or a network
		     number.  An IPv4 network number can be written as a  dot-
		     ted   quad	 (e.g.,	 192.168.1.0),	dotted	triple	(e.g.,
		     192.168.1), dotted	pair (e.g, 172.16), or	single	number
		     (e.g.,  10);  the netmask is 255.255.255.255 for a	dotted
		     quad  (which  means  that	it's  really  a	 host  match),
		     255.255.255.0 for a dotted	triple,	255.255.0.0 for	a dot-
		     ted pair, or 255.0.0.0 for	a single number.  An IPv6 net-
		     work  number  must	 be  written out fully;	the netmask is
		     ff:ff:ff:ff:ff:ff:ff:ff, so IPv6  "network"  matches  are
		     really  always host matches, and a	network	match requires
		     a netmask length.

	      src net net
		     True if the IPv4/v6 source	address	of the	packet	has  a
		     network number of net.

	      net net
		     True  if either the IPv4/v6 source	or destination address
		     of	the packet has a network number	of net.

	      net net mask netmask
		     True if the IPv4 address matches net  with	 the  specific
		     netmask.	May  be	 qualified with	src or dst.  Note that
		     this syntax is not	valid for IPv6 net.

	      net net/len
		     True if the IPv4/v6 address matches net  with  a  netmask
		     len bits wide.  May be qualified with src or dst.

	      dst port port
		     True  if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp
		     and has a destination port	value of port.	The  port  can
		     be	 a number or a name used in /etc/services (see tcp(4P)
		     and udp(4P)).  If a name is used, both  the  port	number
		     and  protocol are checked.	 If a number or	ambiguous name
		     is	used, only the port number is checked (e.g., dst  port
		     513  will	print both tcp/login traffic and udp/who traf-
		     fic, and port  domain  will  print	 both  tcp/domain  and
		     udp/domain	traffic).

	      src port port
		     True if the packet	has a source port value	of port.

	      port port
		     True  if  either  the  source  or destination port	of the
		     packet is port.

	      dst portrange port1-port2
		     True if the packet	is ip/tcp, ip/udp, ip6/tcp or  ip6/udp
		     and has a destination port	value between port1 and	port2.
		     port1 and port2 are interpreted in	the  same  fashion  as
		     the port parameter	for port.

	      src portrange port1-port2
		     True  if the packet has a source port value between port1
		     and port2.

	      portrange	port1-port2
		     True if either the	source	or  destination	 port  of  the
		     packet is between port1 and port2.

		     Any  of  the  above port or port range expressions	can be
		     prepended with the	keywords, tcp or udp, as in:
			  tcp src port port
		     which matches only	tcp packets whose source port is port.

	      less length
		     True if the packet	has a length less  than	 or  equal  to
		     length.  This is equivalent to:
			  len <= length.

	      greater length
		     True  if the packet has a length greater than or equal to
		     length.  This is equivalent to:
			  len >= length.

	      ip proto protocol
		     True if the packet	is an IPv4 packet (see ip(4P)) of pro-
		     tocol  type protocol.  Protocol can be a number or	one of
		     the names icmp, icmp6, igmp, igrp,	pim,  ah,  esp,	 vrrp,
		     udp,  or  tcp.   Note  that the identifiers tcp, udp, and
		     icmp are also keywords and	must be	escaped	via  backslash
		     (\),  which  is \\	in the C-shell.	 Note that this	primi-
		     tive does not chase the protocol header chain.

	      ip6 proto	protocol
		     True if the packet	is an IPv6  packet  of	protocol  type
		     protocol.	 Note  that  this primitive does not chase the
		     protocol header chain.

	      ip6 protochain protocol
		     True if the packet	is IPv6	packet,	and contains  protocol
		     header  with  type	protocol in its	protocol header	chain.
		     For example,
			  ip6 protochain 6
		     matches any IPv6 packet with TCP protocol header  in  the
		     protocol header chain.  The packet	may contain, for exam-
		     ple, authentication header, routing header, or hop-by-hop
		     option  header,  between IPv6 header and TCP header.  The
		     BPF code emitted by this primitive	is complex and	cannot
		     be	 optimized  by	BPF optimizer code in tcpdump, so this
		     can be somewhat slow.

	      ip protochain protocol
		     Equivalent	to ip6 protochain protocol, but	 this  is  for
		     IPv4.

	      ether broadcast
		     True  if the packet is an Ethernet	broadcast packet.  The
		     ether keyword is optional.

	      ip broadcast
		     True if the packet	 is  an	 IPv4  broadcast  packet.   It
		     checks  for  both	the  all-zeroes	and all-ones broadcast
		     conventions, and looks up the subnet mask on  the	inter-
		     face on which the capture is being	done.

		     If	 the subnet mask of the	interface on which the capture
		     is	being done is not available, either because the	inter-
		     face on which capture is being done has no	netmask	or be-
		     cause the capture is being	done on	the Linux "any"	inter-
		     face,  which can capture on more than one interface, this
		     check will	not work correctly.

	      ether multicast
		     True if the packet	is an Ethernet multicast packet.   The
		     ether   keyword  is  optional.   This  is	shorthand  for
		     `ether[0] & 1 != 0'.

	      ip multicast
		     True if the packet	is an IPv4 multicast packet.

	      ip6 multicast
		     True if the packet	is an IPv6 multicast packet.

	      ether proto protocol
		     True if the packet	is of ether type  protocol.   Protocol
		     can  be  a	number or one of the names ip, ip6, arp, rarp,
		     atalk, aarp, decnet, sca, lat, mopdl,  moprc,  iso,  stp,
		     ipx,  or  netbeui.	  Note these identifiers are also key-
		     words and must be escaped via backslash (\).

		     [In the case of FDDI (e.g., `fddi protocol	 arp'),	 Token
		     Ring  (e.g., `tr protocol arp'), and IEEE 802.11 wireless
		     LANS (e.g., `wlan protocol	arp'), for most	of those  pro-
		     tocols,  the protocol identification comes	from the 802.2
		     Logical Link Control (LLC)	header,	which is usually  lay-
		     ered on top of the	FDDI, Token Ring, or 802.11 header.

		     When filtering for	most protocol identifiers on FDDI, To-
		     ken Ring, or 802.11, tcpdump checks only the protocol  ID
		     field  of	an LLC header in so-called SNAP	format with an
		     Organizational Unit Identifier (OUI) of 0x000000, for en-
		     capsulated	 Ethernet; it doesn't check whether the	packet
		     is	in SNAP	format with an OUI of  0x000000.   The	excep-
		     tions are:

		     iso    tcpdump  checks  the DSAP (Destination Service Ac-
			    cess Point)	and SSAP (Source Service Access	Point)
			    fields of the LLC header;

		     stp and netbeui
			    tcpdump checks the DSAP of the LLC header;

		     atalk  tcpdump  checks  for  a SNAP-format	packet with an
			    OUI	of 0x080007 and	the AppleTalk etype.

		     In	the case of Ethernet, tcpdump checks the Ethernet type
		     field for most of those protocols.	 The exceptions	are:

		     iso, stp, and netbeui
			    tcpdump  checks for	an 802.3 frame and then	checks
			    the	LLC header as it does for  FDDI,  Token	 Ring,
			    and	802.11;

		     atalk  tcpdump  checks both for the AppleTalk etype in an
			    Ethernet frame and for a SNAP-format packet	as  it
			    does for FDDI, Token Ring, and 802.11;

		     aarp   tcpdump  checks for	the AppleTalk ARP etype	in ei-
			    ther an Ethernet frame or an 802.2 SNAP frame with
			    an OUI of 0x000000;

		     ipx    tcpdump  checks  for  the IPX etype	in an Ethernet
			    frame,  the	 IPX  DSAP  in	the  LLC  header,  the
			    802.3-with-no-LLC-header encapsulation of IPX, and
			    the	IPX etype in a SNAP frame.

	      decnet src host
		     True if the DECNET	source address is host,	which  may  be
		     an	address	of the form ``10.123'',	or a DECNET host name.
		     [DECNET host name support is  only	 available  on	ULTRIX
		     systems that are configured to run	DECNET.]

	      decnet dst host
		     True if the DECNET	destination address is host.

	      decnet host host
		     True  if  either the DECNET source	or destination address
		     is	host.

	      ifname interface
		     True if the packet	was logged as coming from  the	speci-
		     fied  interface  (applies only to packets logged by Open-
		     BSD's pf(4)).

	      on interface
		     Synonymous	with the ifname	modifier.

	      rnr num
		     True if the packet	was logged as matching	the  specified
		     PF	 rule  number (applies only to packets logged by Open-
		     BSD's pf(4)).

	      rulenum num
		     Synonomous	with the rnr modifier.

	      reason code
		     True if the packet	was logged with	the specified PF  rea-
		     son  code.	 The known codes are: match, bad-offset, frag-
		     ment, short, normalize, and memory	(applies only to pack-
		     ets logged	by OpenBSD's pf(4)).

	      rset name
		     True  if  the packet was logged as	matching the specified
		     PF	ruleset	name of	an anchored ruleset (applies  only  to
		     packets logged by pf(4)).

	      ruleset name
		     Synonomous	with the rset modifier.

	      srnr num
		     True  if  the packet was logged as	matching the specified
		     PF	rule number of an anchored ruleset  (applies  only  to
		     packets logged by pf(4)).

	      subrulenum num
		     Synonomous	with the srnr modifier.

	      action act
		     True  if PF took the specified action when	the packet was
		     logged.  Known actions are: pass and block	(applies  only
		     to	packets	logged by OpenBSD's pf(4)).

	      ip, ip6, arp, rarp, atalk, aarp, decnet, iso, stp, ipx, netbeui
		     Abbreviations for:
			  ether	proto p
		     where p is	one of the above protocols.

	      lat, moprc, mopdl
		     Abbreviations for:
			  ether	proto p
		     where p is	one of the above protocols.  Note that tcpdump
		     does not currently	know how to parse these	protocols.

	      vlan [vlan_id]
		     True if the packet	is an IEEE  802.1Q  VLAN  packet.   If
		     [vlan_id]	is  specified, only true if the	packet has the
		     specified vlan_id.	 Note that the first vlan keyword  en-
		     countered	in expression changes the decoding offsets for
		     the remainder of expression on the	 assumption  that  the
		     packet  is	 a VLAN	packet.	 The vlan [vlan_id] expression
		     may be used more than once, to  filter  on	 VLAN  hierar-
		     chies.  Each use of that expression increments the	filter
		     offsets by	4.

		     For example:
			  vlan 100 && vlan 200
		     filters on	VLAN 200 encapsulated within VLAN 100, and
			  vlan && vlan 300 && ip
		     filters IPv4 protocols encapsulated in VLAN 300  encapsu-
		     lated within any higher order VLAN.

	      mpls [label_num]
		     True  if the packet is an MPLS packet.  If	[label_num] is
		     specified,	only true is the packet	has the	specified  la-
		     bel_num.  Note that the first mpls	keyword	encountered in
		     expression	changes	the decoding offsets for the remainder
		     of	 expression  on	 the  assumption  that the packet is a
		     MPLS-encapsulated IP packet.  The	mpls  [label_num]  ex-
		     pression  may  be	used more than once, to	filter on MPLS
		     hierarchies.  Each	use of that expression increments  the
		     filter offsets by 4.

		     For example:
			  mpls 100000 && mpls 1024
		     filters  packets with an outer label of 100000 and	an in-
		     ner label of 1024,	and
			  mpls && mpls 1024 && host 192.9.200.1
		     filters packets to	or from	192.9.200.1 with an inner  la-
		     bel of 1024 and any outer label.

	      pppoed True  if  the  packet  is	a  PPP-over-Ethernet Discovery
		     packet (Ethernet type 0x8863).

	      pppoes True if the packet	is a PPP-over-Ethernet Session	packet
		     (Ethernet	type 0x8864).  Note that the first pppoes key-
		     word encountered in expression changes the	decoding  off-
		     sets  for	the  remainder of expression on	the assumption
		     that the packet is	a PPPoE	session	packet.

		     For example:
			  pppoes && ip
		     filters IPv4 protocols encapsulated in PPPoE.

	      tcp, udp,	icmp
		     Abbreviations for:
			  ip proto p or	ip6 proto p
		     where p is	one of the above protocols.

	      iso proto	protocol
		     True if the packet	is an OSI packet of protocol type pro-
		     tocol.   Protocol	can  be	 a  number or one of the names
		     clnp, esis, or isis.

	      clnp, esis, isis
		     Abbreviations for:
			  iso proto p
		     where p is	one of the above protocols.

	      l1, l2, iih, lsp,	snp, csnp, psnp
		     Abbreviations for IS-IS PDU types.

	      vpi n  True if the packet	is an ATM packet, for  SunATM  on  So-
		     laris, with a virtual path	identifier of n.

	      vci n  True  if  the  packet is an ATM packet, for SunATM	on So-
		     laris, with a virtual channel identifier of n.

	      lane   True if the packet	is an ATM packet, for  SunATM  on  So-
		     laris,  and  is  an ATM LANE packet.  Note	that the first
		     lane keyword encountered in expression changes the	 tests
		     done  in  the  remainder  of expression on	the assumption
		     that the packet is	either a LANE emulated Ethernet	packet
		     or	 a  LANE  LE Control packet.  If lane isn't specified,
		     the tests are done	under the assumption that  the	packet
		     is	an LLC-encapsulated packet.

	      llc    True  if  the  packet is an ATM packet, for SunATM	on So-
		     laris, and	is an LLC-encapsulated packet.

	      oamf4s True if the packet	is an ATM packet, for  SunATM  on  So-
		     laris, and	is a segment OAM F4 flow cell (VPI=0 & VCI=3).

	      oamf4e True  if  the  packet is an ATM packet, for SunATM	on So-
		     laris, and	is an end-to-end OAM F4	 flow  cell  (VPI=0  &
		     VCI=4).

	      oamf4  True  if  the  packet is an ATM packet, for SunATM	on So-
		     laris, and	is a segment or	end-to-end OAM	F4  flow  cell
		     (VPI=0 & (VCI=3 | VCI=4)).

	      oam    True  if  the  packet is an ATM packet, for SunATM	on So-
		     laris, and	is a segment or	end-to-end OAM	F4  flow  cell
		     (VPI=0 & (VCI=3 | VCI=4)).

	      metac  True  if  the  packet is an ATM packet, for SunATM	on So-
		     laris, and	is  on	a  meta	 signaling  circuit  (VPI=0  &
		     VCI=1).

	      bcc    True  if  the  packet is an ATM packet, for SunATM	on So-
		     laris, and	is on a	broadcast signaling circuit  (VPI=0  &
		     VCI=2).

	      sc     True  if  the  packet is an ATM packet, for SunATM	on So-
		     laris, and	is on a	signaling circuit (VPI=0 & VCI=5).

	      ilmic  True if the packet	is an ATM packet, for  SunATM  on  So-
		     laris, and	is on an ILMI circuit (VPI=0 & VCI=16).

	      connectmsg
		     True  if  the  packet is an ATM packet, for SunATM	on So-
		     laris, and	is on a	signaling  circuit  and	 is  a	Q.2931
		     Setup, Call Proceeding, Connect, Connect Ack, Release, or
		     Release Done message.

	      metaconnect
		     True if the packet	is an ATM packet, for  SunATM  on  So-
		     laris, and	is on a	meta signaling circuit and is a	Q.2931
		     Setup, Call Proceeding, Connect, Release, or Release Done
		     message.

	      expr relop expr
		     True  if  the relation holds, where relop is one of >, <,
		     >=, <=, =,	!=, and	expr is	an arithmetic expression  com-
		     posed  of integer constants (expressed in standard	C syn-
		     tax), the normal binary operators [+, -, *, /, &, |,  <<,
		     >>],  a  length  operator,	and special packet data	acces-
		     sors.  Note that all comparisons are unsigned,  so	 that,
		     for  example,  0x80000000 and 0xffffffff are > 0.	To ac-
		     cess data inside the packet, use the following syntax:
			  proto	[ expr : size ]
		     Proto is one of ether, fddi, tr, wlan, ppp,  slip,	 link,
		     ip,  arp,	rarp,  tcp, udp, icmp, ip6 or radio, and indi-
		     cates  the	 protocol  layer  for  the  index   operation.
		     (ether,  fddi,  wlan, tr, ppp, slip and link all refer to
		     the link layer. radio refers to the "radio	header"	 added
		     to	 some  802.11 captures.)  Note that tcp, udp and other
		     upper-layer protocol types	only apply to IPv4,  not  IPv6
		     (this  will  be  fixed  in	the future).  The byte offset,
		     relative to the indicated protocol	 layer,	 is  given  by
		     expr.  Size is optional and indicates the number of bytes
		     in	the field of interest; it can be either	one,  two,  or
		     four,  and	 defaults  to one.  The	length operator, indi-
		     cated by the keyword len, gives the length	of the packet.

		     For example, `ether[0] & 1	!= 0'  catches	all  multicast
		     traffic.	The  expression	`ip[0] & 0xf !=	5' catches all
		     IPv4 packets with options.	  The  expression  `ip[6:2]  &
		     0x1fff  = 0' catches only unfragmented IPv4 datagrams and
		     frag zero of fragmented IPv4 datagrams.   This  check  is
		     implicitly	 applied  to the tcp and udp index operations.
		     For instance, tcp[0] always means the first byte  of  the
		     TCP  header,  and never means the first byte of an	inter-
		     vening fragment.

		     Some offsets and field values may be expressed  as	 names
		     rather  than  as  numeric values.	The following protocol
		     header field offsets are available: icmptype  (ICMP  type
		     field),  icmpcode	(ICMP  code  field), and tcpflags (TCP
		     flags field).

		     The following ICMP	type field values are available: icmp-
		     echoreply,	 icmp-unreach,	icmp-sourcequench,  icmp-redi-
		     rect, icmp-echo,  icmp-routeradvert,  icmp-routersolicit,
		     icmp-timxceed,  icmp-paramprob,  icmp-tstamp, icmp-tstam-
		     preply, icmp-ireq,	 icmp-ireqreply,  icmp-maskreq,	 icmp-
		     maskreply.

		     The  following TCP	flags field values are available: tcp-
		     fin, tcp-syn, tcp-rst, tcp-push, tcp-ack, tcp-urg.

	      Primitives may be	combined using:

		     A parenthesized group of primitives and operators (paren-
		     theses are	special	to the Shell and must be escaped).

		     Negation (`!' or `not').

		     Concatenation (`&&' or `and').

		     Alternation (`||' or `or').

	      Negation	has highest precedence.	 Alternation and concatenation
	      have equal precedence and	associate left to  right.   Note  that
	      explicit	and  tokens,  not  juxtaposition, are now required for
	      concatenation.

	      If an identifier is given	without	a  keyword,  the  most	recent
	      keyword is assumed.  For example,
		   not host vs and ace
	      is short for
		   not host vs and host	ace
	      which should not be confused with
		   not ( host vs or ace	)

	      Expression arguments can be passed to tcpdump as either a	single
	      argument or as multiple arguments, whichever is more convenient.
	      Generally,  if  the expression contains Shell metacharacters, it
	      is easier	to pass	it as a	single,	quoted argument.  Multiple ar-
	      guments are concatenated with spaces before being	parsed.

EXAMPLES
       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
       parentheses):
	      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'

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

       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 128.3.254.6 tell 128.3.254.68
	      arp reply	128.3.254.6 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.

       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,
       neither this description	nor tcpdump will be of much use	to you.)

       The general format of a tcp protocol line is:
	      src _ dst: flags data-seqno ack window urgent options
       Src and dst are the source and  destination  IP	addresses  and	ports.
       Flags  are  some	 combination of	S (SYN), F (FIN), P (PUSH), R (RST), W
       (ECN CWR) or E (ECN-Echo), or a single `.' (no flags).  Data-seqno  de-
       scribes	the  portion  of  sequence  space  covered by the data in this
       packet (see example below).  Ack	is sequence number of  the  next  data
       expected	 the other direction on	this connection.  Window 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.  Op-
       tions are tcp options enclosed in angle brackets	(e.g., <mss 1024>).

       Src, dst	and flags are always present.  The other fields	depend on  the
       contents	of the packet's	tcp protocol header and	are output only	if ap-
       propriate.

       Here is the opening portion of an rlogin	from host rtsg to host csam.
	      rtsg.1023	> csam.login: S	768512:768512(0) win 4096 <mss 1024>
	      csam.login > rtsg.1023: S	947648:947648(0) ack 768513 win	4096 <mss 1024>
	      rtsg.1023	> csam.login: .	ack 1 win 4096
	      rtsg.1023	> csam.login: P	1:2(1) ack 1 win 4096
	      csam.login > rtsg.1023: .	ack 2 win 4096
	      rtsg.1023	> csam.login: P	2:21(19) ack 1 win 4096
	      csam.login > rtsg.1023: P	1:2(1) ack 21 win 4077
	      csam.login > rtsg.1023: P	2:3(1) ack 21 win 4077 urg 1
	      csam.login > rtsg.1023: P	3:4(1) ack 21 win 4077 urg 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(nbytes)'  which means `sequence numbers first up to but not
       including last which is nbytes bytes of	user  data'.)	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 no flags
       were set.  The packet contained no data so there	is  no	data  sequence
       number.	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  ini-
       tial  sequence number is	printed.  This means that sequence numbers af-
       ter the first can be interpreted	as relative byte positions in the con-
       versation'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
       length]''.

       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:

		       |	       |
		       |---------------|
		       |C|E|U|A|P|R|S|F|
		       |---------------|
		       |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:

		       |C|E|U|A|P|R|S|F|
		       |---------------|
		       |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

	      00000010

       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
       arrives:

	    |C|E|U|A|P|R|S|F|
	    |---------------|
	    |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

		   00010010

       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'

       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
       greek.)

       Name server requests are	formatted as
	      src _ dst: id op?	flags qtype qclass name	(len)
	      h2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)
       Host h2opolo asked the domain server on helios for  an  address	record
       (qtype=A)  associated  with the name ucbvax.berkeley.edu.  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 128.32.137.3 (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  128.32.137.3.  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
       printed.

       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.

       Note  that  name	server requests	and responses tend to be large and the
       default snaplen of 68 bytes may not capture enough  of  the  packet  to
       print.	Use  the  -s flag to increase the snaplen if you need to seri-
       ously investigate name server traffic.  `-s 128'	has  worked  well  for
       me.

       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 te fields  mean  see
       www.cifs.org   or  the  pub/samba/specs/	 directory  on	your  favorite
       samba.org mirror	site.  The SMB patches were written by Andrew Tridgell
       (tridge@samba.org).

       NFS Requests and	Replies

       Sun NFS (Network	File System) requests and replies are printed as:
	      src.xid _	dst.nfs: len op	args
	      src.nfs _	dst.xid: reply stat len	op results
	      sushi.6709 > wrl.nfs: 112	readlink fh 21,24/10.73165
	      wrl.nfs >	sushi.6709: reply ok 40	readlink "../var"
	      sushi.201b > wrl.nfs:
		   144 lookup fh 9,74/4096.6878	"xcolors"
	      wrl.nfs >	sushi.201b:
		   reply ok 128	lookup fh 9,74/4134.3150
       In  the	first line, host sushi sends a transaction with	id 6709	to wrl
       (note that the number following the src host is a transaction  id,  not
       the  source port).  The request was 112 bytes, excluding	the UDP	and IP
       headers.	 The operation 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.)  Wrl replies `ok'
       with the	contents of the	link.

       In the third line, sushi	asks wrl to lookup the name `xcolors'  in  di-
       rectory file 9,74/4096.6878.  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.

       If  the	-v (verbose) flag is given, additional information is printed.
       For example:
	      sushi.1372a > wrl.nfs:
		   148 read fh 21,11/12.195 8192 bytes @ 24576
	      wrl.nfs >	sushi.1372a:
		   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
       traffic.

       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:

	      src.sport	_ dst.dport: rx	packet-type
	      src.sport	_ dst.dport: rx	packet-type service call call-name args
	      src.sport	_ dst.dport: rx	packet-type service reply call-name args
	      elvis.7001 > pike.afsfs:
		   rx data fs call rename old fid 536876964/1/1	".newsrc.new"
		   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 `.newsrc.new', 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
       RX.

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

	      144.1.209.2 > 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
       /etc/atalk.names).

       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.

       IP Fragmentation

       Fragmented Internet datagrams are printed as
	      (frag id:size@offset+)
	      (frag id:size@offset)
       (The first form indicates there are more	fragments.  The	 second	 indi-
       cates this is the last fragment.)

       Id  is the fragment id.	Size is	the fragment size (in bytes) excluding
       the IP header.  Offset is this fragment's  offset  (in  bytes)  in  the
       original	datagram.

       The  fragment information is output for each fragment.  The first frag-
       ment contains the higher	level protocol header and  the	frag  info  is
       printed	after the protocol info.  Fragments after the first contain no
       higher level protocol header and	the frag info  is  printed  after  the
       source  and destination addresses.  For example,	here is	part of	an ftp
       from arizona.edu	to lbl-rtsg.arpa over a	CSNET connection that  doesn't
       appear to handle	576 byte datagrams:
	      arizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+)
	      arizona >	rtsg: (frag 595a:204@328)
	      rtsg.1170	> arizona.ftp-data: . ack 1536 win 2560
       There are a couple of things to note here:  First, addresses in the 2nd
       line don't include port numbers.	 This is because the TCP protocol  in-
       formation  is  all  in  the first fragment and we have no idea what the
       port or sequence	numbers	are when we print the later  fragments.	  Sec-
       ond,  the  tcp  sequence	information in the first line is printed as if
       there were 308 bytes of user data when, in fact,	there  are  512	 bytes
       (308  in	the first frag and 204 in the second).	If you are looking for
       holes in	the sequence space or trying to	match up  acks	with  packets,
       this can	fool you.

       A  packet  with	the  IP	 don't fragment	flag is	marked with a trailing
       (DF).

       Timestamps

       By default, all output lines are	preceded by a  timestamp.   The	 time-
       stamp is	the current clock time in the form
	      hh:mm:ss.frac
       and  is	as accurate as the kernel's clock.  The	timestamp reflects the
       time the	kernel first saw the packet.  No attempt is  made  to  account
       for the time lag	between	when the Ethernet interface removed the	packet
       from the	wire and when the kernel serviced the `new packet' interrupt.

SEE ALSO
       bpf(4), pcap(3)

AUTHORS
       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 tcpdump.org.

       The current version is available	via http:

	      http://www.tcpdump.org/

       The original distribution is available via anonymous ftp:

	      ftp://ftp.ee.lbl.gov/tcpdump.tar.Z

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

BUGS
       Please send problems, bugs, questions, desirable	enhancements, etc. to:

	      tcpdump-workers@tcpdump.org

       Please send source code contributions, etc. to:

	      patches@tcpdump.org

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

       When running tcpdump with the -v	option on a network interface support-
       ing checksum off-loading, IP packets sourced  from  this	 machine  will
       have many false 'bad cksum 0' errors.

       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
       set.

       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.

				 18 April 2005			    TCPDUMP(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLES | OUTPUT FORMAT | SEE ALSO | AUTHORS | BUGS

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