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TCPDUMP(1)							    TCPDUMP(1)

NAME
       tcpdump - dump traffic on a network

SYNOPSIS
       tcpdump [ -adeflnNOpqRStuvxX ] [ -c count ]
	       [ -C file_size ] [ -F file ]
	       [ -i interface ] [ -m module ] [ -r file ]
	       [ -s snaplen ] [ -T type ] [ -w file ]
	       [ -E algo:secret ] [ expression ]

DESCRIPTION
       Tcpdump	prints	out the headers of packets on a network 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 -b 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  ``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 on other OSes it
	      counts only packets that were matched by the  filter  expression
	      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, it
       will report those counts when it receives a SIGINFO signal  (generated,
       for  example, by typing your ``status'' character, typically control-T)
       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.

       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.

       Under Ultrix and Digital UNIX:
	      Once the super-user has enabled promiscuous-mode operation using
	      pfconfig(8), any user may capture network traffic with tcpdump.

       Under BSD:
	      You must have read access to /dev/bpf*.

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

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

       -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 2 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).

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

       -E     Use  algo:secret	for  decrypting IPsec ESP packets.  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	 the ascii text for ESP secret key.  We cannot
	      take arbitrary binary value at this moment.  The option  assumes
	      RFC2406  ESP, not RFC1827 ESP.  The option is only for debugging
	      purposes, and the use of this option with truly `secret' key  is
	      discouraged.   By	 presenting IPsec secret key onto command line
	      you make it visible to others, via ps(1) and other occasions.

       -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 translating
	      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.

	      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.

       -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''.

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

       -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
	      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.   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 cnfp (Cisco NetFlow
	      protocol), rpc (Remote Procedure Call), rtp (Real-Time  Applica‐
	      tions protocol), rtcp (Real-Time Applications control protocol),
	      snmp (Simple Network Management  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.

       -v     (Slightly	 more) verbose output.	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.

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

       -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 ``-''.

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

       -X     When printing hex, print ascii too.  Thus if -x is also set, the
	      packet  is  printed  in  hex/ascii.   This  is  very  handy  for
	      analysing new protocols.	Even if -x is not also set, some parts
	      of some packets may be printed in hex/ascii.

	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, tr, ip, ip6, arp, rarp,
		     decnet, 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.

	      Similarly,  `tr'	is  an	alias  for `ether'; the previous para‐
	      graph's statements about FDDI headers also apply to  Token  Ring
	      headers.]

	      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  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
		     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 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
		     /etc/networks  or	a  network number (see networks(4) for
		     details).

	      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 IP address matches net with the specific net‐
		     mask.   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.  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,	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 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.

	      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') and
		     Token Ring (e.g., `tr protocol arp'), for most  of	 those
		     protocols,	 the  protocol	identification	comes from the
		     802.2 Logical Link Control (LLC) header, which is usually
		     layered on top of the FDDI or Token Ring header.

		     When  filtering  for most protocol identifiers on FDDI or
		     Token Ring, tcpdump checks only the protocol ID field  of
		     an	 LLC header in so-called SNAP format with an Organiza‐
		     tional Unit Identifier (OUI) of  0x000000,	 for  encapsu‐
		     lated Ethernet; it doesn't check whether the packet is in
		     SNAP format with an OUI of 0x000000.

		     The exceptions are iso, for  which	 it  checks  the  DSAP
		     (Destination  Service Access Point) and SSAP (Source Ser‐
		     vice Access Point) fields of the LLC header, stp and net‐
		     beui,  where  it  checks  the DSAP of the LLC header, and
		     atalk, where it 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,  sap,	 and netbeui, for which it checks for an 802.3
		     frame and then checks the LLC header as it does for  FDDI
		     and  Token	 Ring,	atalk,	where  it  checks both for the
		     Appletalk etype in an Ethernet frame and for a  SNAP-for‐
		     mat  packet  as  it  does	for FDDI and Token Ring, aarp,
		     where it checks for the Appletalk ARP etype in either  an
		     Ethernet  frame  or  an  802.2  SNAP frame with an OUI of
		     0x000000, and ipx, where it 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.

	      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 is the packet has the
		     specified vlan_id.	 Note  that  the  first	 vlan  keyword
		     encountered  in  expression  changes the decoding offsets
		     for the remainder of expression on	 the  assumption  that
		     the packet is a VLAN packet.

	      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.  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, tr, ip, arp, rarp, tcp, udp,
		     icmp or ip6, and indicates the  protocol  layer  for  the
		     index  operation.	 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, 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.

		     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-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
	      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[tcpflags] & (tcp-syn|tcp-fin) != 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[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
       assumed 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.

       (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]''.

       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
       (binary 00000010), so we know that for packets with SYN set the follow‐
       ing 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
       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.

       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.

       If you are decoding SMB sessions containing unicode  strings  then  you
       may  wish to set the environment variable USE_UNICODE to 1.  A patch to
       auto-detect unicode srings would be welcome.

       For information on SMB packet formats and what all te fields  mean  see
       www.cifs.org  or	 the  pub/samba/specs/	directory  on  your  favourite
       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
       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,  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.
       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.

       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.
       Instead,	 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
       (`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
       traffic(1C), nit(4P), 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.

       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).

       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 that manipulate FDDI or Token	 Ring  headers	assume
       that  all  FDDI	and  Token Ring packets are SNAP-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 inad‐
       vertently accept certain packets that do not properly match the	filter
       expression.

       Filter  expressions  on	fields	other than those that manipulate Token
       Ring headers will not correctly handle source-routed Token  Ring	 pack‐
       ets.

       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.

				3 January 2001			    TCPDUMP(1)
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