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TCPDUMP(1)							    TCPDUMP(1)

NAME
       tcpdump - dump traffic on a network

SYNOPSIS
       tcpdump [ -adeflnNOpqStvx ] [ -c	count ]	[ -F file ]
	       [ -i interface ]	[ -r file ] [ -s snaplen ]
	       [ -T type ] [ -w	file ] [ expression ]

DESCRIPTION
       Tcpdump	prints	out the	headers	of packets on a	network	interface that
       match the boolean expression.

       Under SunOS with	nit or bpf: To run tcpdump you must have  read	access
       to  /dev/nit or /dev/bpf*.  Under Solaris with dlpi: You	must have read
       access to the network pseudo device, e.g.  /dev/le.  Under  HP-UX  with
       dlpi:  You  must	be root	or it must be installed	setuid to root.	 Under
       IRIX with snoop:	You must be root or it must  be	 installed  setuid  to
       root.   Under Linux: You	must be	root or	it must	be installed setuid to
       root.  Under Ultrix and Digital UNIX: Once the super-user  has  enabled
       promiscuous-mode	operation using	pfconfig(8), any user may run tcpdump.
       Under BSD: You must have	read access to /dev/bpf*.

OPTIONS
       -a     Attempt to convert network and broadcast addresses to names.

       -c     Exit after receiving count packets.

       -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).

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

       -f     Print `foreign' internet addresses numerically rather than  sym-
	      bolically	 (this	option is intended to get around serious brain
	      damage in	Sun's yp server	-- usually it hangs forever  translat-
	      ing non-local internet numbers).

       -F     Use  file	 as  input  for	 the filter expression.	 An additional
	      expression 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.

       -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''.

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

       -s     Snarf snaplen bytes of data from each  packet  rather  than  the
	      default  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
	      below).  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 packets to be lost.
	      You should limit snaplen to the smallest number that  will  cap-
	      ture the protocol	information you're interested in.

       -T     Force  packets  selected	by  "expression" to be interpreted the
	      specified	type. Currently	known types are	rpc (Remote  Procedure
	      Call),  rtp  (Real-Time  Applications protocol), rtcp (Real-Time
	      Applications control protocol), vat (Visual Audio	Tool), and  wb
	      (distributed White Board).

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

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

       -tt    Print an unformatted timestamp on	each dump line.

       -v     (Slightly	 more)	verbose	output.	 For example, the time to live
	      and type of service information in an IP packet is printed.

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

       -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 ``-''.

       -x     Print  each  packet  (minus  its link level header) in hex.  The
	      smaller of the entire packet or snaplen bytes will be printed.

	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 and port.	 E.g.,
		     `host foo', `net 128.3', `port 20'.  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 `null' link	layers
		     (i.e. point to point protocols such as slip) 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,	ip, arp, rarp, decnet,
		     lat, sca, moprc, mopdl, iso, esis,	 isis,	tcp  and  udp.
		     E.g.,  `ether  src	 foo', `arp net	128.3',	`tcp port 21'.
		     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.]

	      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
	      described	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 IP destination field	of the packet is host,
		     which may be either an address or a name.

	      src host host
		     True if the IP source field of the	packet is host.

	      host host
		     True if either the	IP source or destination of the	packet
		     is	 host.	 Any  of  the  above  host  expressions	can be
		     prepended with the	keywords, ip, arp, or rarp 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
		     address 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	in both	/etc/hosts and
		     /etc/ethers.  (An equivalent expression is
			  ether	host ehost and not host	host
		     which can be used with either names or numbers for	host /
		     ehost.)

	      dst net net
		     True  if  the  IP destination address of the packet has a
		     network number of net. Net	may  be	 either	 a  name  from
		     /etc/networks  or	a  network number (see networks(4) for
		     details).

	      src net net
		     True if the IP source address of the packet has a network
		     number of net.

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

	      net net mask mask
		     True if the IP address matches net	with the specific net-
		     mask.  May	be qualified with src or dst.

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

	      dst port port
		     True if the packet	is ip/tcp or ip/udp and	has a destina-
		     tion  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  traffic,  and  port
		     domain  will  print  both tcp/domain and udp/domain traf-
		     fic).

	      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.  Any of the above port 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 ip packet	(see ip(4P)) of	proto-
		     col type protocol.	 Protocol can be a number  or  one  of
		     the  names	 icmp,	igrp,  udp, nd,	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.

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

	      ip broadcast
		     True  if the packet is an IP broadcast packet.  It	checks
		     for both the all-zeroes and  all-ones  broadcast  conven-
		     tions, and	looks up the local subnet mask.

	      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 IP multicast packet.

	      ether proto protocol
		     True  if  the packet is of	ether type protocol.  Protocol
		     can be a number or	a name like ip,	arp,  or  rarp.	  Note
		     these  identifiers	 are also keywords and must be escaped
		     via backslash (\).	 [In the case  of  FDDI	 (e.g.,	 `fddi
		     protocol  arp'),  the  protocol identification comes from
		     the 802.2 Logical Link Control  (LLC)  header,  which  is
		     usually  layered  on  top	of  the	 FDDI header.  Tcpdump
		     assumes, when filtering on	the protocol identifier,  that
		     all  FDDI packets include an LLC header, and that the LLC
		     header is in so-called SNAP format.]

	      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.

	      ip, arp, rarp, decnet, iso
		     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.

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

	      esis, isis
		     Abbreviations for:
			  iso proto p
		     where p is	one of the above protocols.  Note that tcpdump
		     does an incomplete	job of parsing these protocols.

	      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  accessors.   To
		     access data inside	the packet, use	the following syntax:
			  proto	[ expr : size ]
		     Proto  is one of ether, fddi, ip, arp, rarp, tcp, udp, or
		     icmp, and indicates the  protocol	layer  for  the	 index
		     operation.	  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, indicated 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
		     IP	packets	with options. The expression `ip[6:2] &	0x1fff
		     = 0' catches only unfragmented datagrams and frag zero of
		     fragmented	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 intervening fragment.

	      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
	      arguments	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[13] & 3 != 0	and not	src and	dst net	localnet'

       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[0] != 8 and	icmp[0]	!= 0'

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.

       (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
       indicated  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
       address	(in  this example, ethernet addresses are in caps and internet
       addresses 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)	or R (RST)  or
       a  single `.' (no flags).  Data-seqno describes 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.	Options	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
       appropriate.

       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
       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
       reports	``[|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]''.

       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,	name server or author-
       ity 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 authority records.  The
       first answer record is type  A  (address)  and  its  data  is  internet
       address	128.32.137.3.	The  total size	of the response	was 273	bytes,
       excluding UDP and IP headers.  The op (Query) and response code	(NoEr-
       ror) 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.

       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
       directory  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, 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	offset	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.
       Instead,	tcpdump	keeps track of ``recent'' requests, and	 matches  them
       to  the	replies	using the transaction 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
       (`office').  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
       another 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
       information 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
       Van Jacobson, Craig Leres and  Steven  McCanne,	all  of	 the  Lawrence
       Berkeley	National Laboratory, University	of California, Berkeley, CA.

       The current version is available	via anonymous ftp:

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

BUGS
       Please send bug reports to tcpdump@ee.lbl.gov.

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

       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.

       Apple Ethertalk DDP packets could be dumped as easily as	KIP DDP	 pack-
       ets but aren't.	Even if	we were	inclined to do anything	to promote the
       use of Ethertalk	(we aren't), LBL doesn't allow Ethertalk on any	of its
       networks	so we'd	would have no way of testing this code.

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

       Filters expressions that	manipulate FDDI	headers	assume that  all  FDDI
       packets	are  encapsulated Ethernet packets.  This is true for IP, ARP,
       and DECNET Phase	IV, but	is not true for	protocols such	as  ISO	 CLNS.
       Therefore,  the filter may inadvertently	accept certain packets that do
       not properly match the filter expression.

				 30 June 1997			    TCPDUMP(1)

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

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