1 .\" @(#) $Header: /tcpdump/master/tcpdump/Attic/tcpdump.1,v 1.69 1999-10-30 05:11:22 itojun Exp $ (LBL)
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23 .TH TCPDUMP 1 "30 June 1997"
25 tcpdump \- dump traffic on a network
68 \fITcpdump\fP prints out the headers of packets on a network interface
69 that match the boolean \fIexpression\fP.
71 .B Under SunOS with nit or bpf:
74 you must have read access to
78 .B Under Solaris with dlpi:
79 You must have read access to the network pseudo device, e.g.
81 .B Under HP-UX with dlpi:
82 You must be root or it must be installed setuid to root.
83 .B Under IRIX with snoop:
84 You must be root or it must be installed setuid to root.
86 You must be root or it must be installed setuid to root.
87 .B Under Ultrix and Digital UNIX:
88 Once the super-user has enabled promiscuous-mode operation using
93 You must have read access to
98 Attempt to convert network and broadcast addresses to names.
101 Exit after receiving \fIcount\fP packets.
104 Dump the compiled packet-matching code in a human readable form to
105 standard output and stop.
108 Dump packet-matching code as a
113 Dump packet-matching code as decimal numbers (preceded with a count).
116 Print the link-level header on each dump line.
119 Print `foreign' internet addresses numerically rather than symbolically
120 (this option is intended to get around serious brain damage in
121 Sun's yp server \(em usually it hangs forever translating non-local
125 Use \fIfile\fP as input for the filter expression.
126 An additional expression given on the command line is ignored.
129 Listen on \fIinterface\fP.
130 If unspecified, \fItcpdump\fP searches the system interface list for the
131 lowest numbered, configured up interface (excluding loopback).
132 Ties are broken by choosing the earliest match.
135 Make stdout line buffered. Useful if you want to see the data
136 while capturing it. E.g.,
138 ``tcpdump\ \ \-l\ \ |\ \ tee dat'' or
139 ``tcpdump\ \ \-l \ \ > dat\ \ &\ \ tail\ \ \-f\ \ dat''.
142 Don't convert addresses (i.e., host addresses, port numbers, etc.) to names.
145 Don't print domain name qualification of host names. E.g.,
146 if you give this flag then \fItcpdump\fP will print ``nic''
147 instead of ``nic.ddn.mil''.
150 Do not run the packet-matching code optimizer. This is useful only
151 if you suspect a bug in the optimizer.
154 \fIDon't\fP put the interface
155 into promiscuous mode. Note that the interface might be in promiscuous
156 mode for some other reason; hence, `-p' cannot be used as an abbreviation for
157 `ether host {local-hw-addr} or ether broadcast'.
160 Quick (quiet?) output. Print less protocol information so output
164 Read packets from \fIfile\fR (which was created with the -w option).
165 Standard input is used if \fIfile\fR is ``-''.
168 Snarf \fIsnaplen\fP bytes of data from each packet rather than the
169 default of 68 (with SunOS's NIT, the minimum is actually 96).
170 68 bytes is adequate for IP, ICMP, TCP
171 and UDP but may truncate protocol information from name server and NFS
172 packets (see below). Packets truncated because of a limited snapshot
173 are indicated in the output with ``[|\fIproto\fP]'', where \fIproto\fP
174 is the name of the protocol level at which the truncation has occurred.
175 Note that taking larger snapshots both increases
176 the amount of time it takes to process packets and, effectively,
177 decreases the amount of packet buffering. This may cause packets to be
178 lost. You should limit \fIsnaplen\fP to the smallest number that will
179 capture the protocol information you're interested in.
182 Force packets selected by "\fIexpression\fP" to be interpreted the
183 specified \fItype\fR. Currently known types are
184 \fBrpc\fR (Remote Procedure Call),
185 \fBrtp\fR (Real-Time Applications protocol),
186 \fBrtcp\fR (Real-Time Applications control protocol),
187 \fBvat\fR (Visual Audio Tool),
189 \fBwb\fR (distributed White Board).
192 Assume ESP/AH packets to be based on old specification (RFC1825 to RFC1829).
193 If specified, \fItcpdump\fP will not print replay prevention field.
194 Since there is no protocol version field in ESP/AH specification,
195 \fItcpdump\fP cannot deduce the version of ESP/AH protocol.
198 Print absolute, rather than relative, TCP sequence numbers.
201 \fIDon't\fP print a timestamp on each dump line.
204 Print an unformatted timestamp on each dump line.
207 (Slightly more) verbose output. For example, the time to live
208 and type of service information in an IP packet is printed.
211 Even more verbose output. For example, additional fields are
212 printed from NFS reply packets.
215 Write the raw packets to \fIfile\fR rather than parsing and printing
216 them out. They can later be printed with the \-r option.
217 Standard output is used if \fIfile\fR is ``-''.
220 Print each packet (minus its link level header) in hex.
221 The smaller of the entire packet or
223 bytes will be printed.
224 .IP "\fI expression\fP"
226 selects which packets will be dumped. If no \fIexpression\fP
227 is given, all packets on the net will be dumped. Otherwise,
228 only packets for which \fIexpression\fP is `true' will be dumped.
230 The \fIexpression\fP consists of one or more
232 Primitives usually consist of an
234 (name or number) preceded by one or more qualifiers. There are three
235 different kinds of qualifier:
237 qualifiers say what kind of thing the id name or number refers to.
243 E.g., `host foo', `net 128.3', `port 20'. If there is no type
248 qualifiers specify a particular transfer direction to and/or from
250 Possible directions are
257 E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'. If
258 there is no dir qualifier,
261 For `null' link layers (i.e. point to point protocols such as slip) the
265 qualifiers can be used to specify a desired direction.
267 qualifiers restrict the match to a particular protocol. Possible
285 E.g., `ether src foo', `arp net 128.3', `tcp port 21'. If there is
286 no proto qualifier, all protocols consistent with the type are
287 assumed. E.g., `src foo' means `(ip or arp or rarp) src foo'
288 (except the latter is not legal syntax), `net bar' means `(ip or
289 arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'.
291 [`fddi' is actually an alias for `ether'; the parser treats them
292 identically as meaning ``the data link level used on the specified
293 network interface.'' FDDI headers contain Ethernet-like source
294 and destination addresses, and often contain Ethernet-like packet
295 types, so you can filter on these FDDI fields just as with the
296 analogous Ethernet fields. FDDI headers also contain other fields,
297 but you cannot name them explicitly in a filter expression.]
299 In addition to the above, there are some special `primitive' keywords
300 that don't follow the pattern:
305 and arithmetic expressions. All of these are described below.
307 More complex filter expressions are built up by using the words
312 to combine primitives. E.g., `host foo and not port ftp and not port ftp-data'.
313 To save typing, identical qualifier lists can be omitted. E.g.,
314 `tcp dst port ftp or ftp-data or domain' is exactly the same as
315 `tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
317 Allowable primitives are:
318 .IP "\fBdst host \fIhost\fR"
319 True if the IPv4/v6 destination field of the packet is \fIhost\fP,
320 which may be either an address or a name.
321 .IP "\fBsrc host \fIhost\fR"
322 True if the IPv4/v6 source field of the packet is \fIhost\fP.
323 .IP "\fBhost \fIhost\fP
324 True if either the IPv4/v6 source or destination of the packet is \fIhost\fP.
325 Any of the above host expressions can be prepended with the keywords,
326 \fBip\fP, \fBarp\fP, \fBrarp\fP, or \fBip6\fP as in:
329 \fBip host \fIhost\fR
332 which is equivalent to:
335 \fBether proto \fI\\ip\fB and host \fIhost\fR
338 If \fIhost\fR is a name with multiple IP addresses, each address will
339 be checked for a match.
340 .IP "\fBether dst \fIehost\fP
341 True if the ethernet destination address is \fIehost\fP. \fIEhost\fP
342 may be either a name from /etc/ethers or a number (see
345 .IP "\fBether src \fIehost\fP
346 True if the ethernet source address is \fIehost\fP.
347 .IP "\fBether host \fIehost\fP
348 True if either the ethernet source or destination address is \fIehost\fP.
349 .IP "\fBgateway\fP \fIhost\fP
350 True if the packet used \fIhost\fP as a gateway. I.e., the ethernet
351 source or destination address was \fIhost\fP but neither the IP source
352 nor the IP destination was \fIhost\fP. \fIHost\fP must be a name and
353 must be found in both /etc/hosts and /etc/ethers. (An equivalent
357 \fBether host \fIehost \fBand not host \fIhost\fR
360 which can be used with either names or numbers for \fIhost / ehost\fP.)
361 This syntax does not work in IPv6-enabled configuration at this moment.
362 .IP "\fBdst net \fInet\fR"
363 True if the IPv4/v6 destination address of the packet has a network
364 number of \fInet\fP. \fINet\fP may be either a name from /etc/networks
365 or a network number (see \fInetworks(4)\fP for details).
366 .IP "\fBsrc net \fInet\fR"
367 True if the IPv4/v6 source address of the packet has a network
369 .IP "\fBnet \fInet\fR"
370 True if either the IPv4/v6 source or destination address of the packet has a network
372 .IP "\fBnet \fInet\fR \fBmask \fImask\fR"
373 True if the IP address matches \fInet\fR with the specific netmask.
374 May be qualified with \fBsrc\fR or \fBdst\fR.
375 Note that this syntax is not valid for IPv6 \fInet\fR.
376 .IP "\fBnet \fInet\fR/\fIlen\fR"
377 True if the IPv4/v6 address matches \fInet\fR a netmask \fIlen\fR bits wide.
378 May be qualified with \fBsrc\fR or \fBdst\fR.
379 .IP "\fBdst port \fIport\fR"
380 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a
381 destination port value of \fIport\fP.
382 The \fIport\fP can be a number or a name used in /etc/services (see
386 If a name is used, both the port
387 number and protocol are checked. If a number or ambiguous name is used,
388 only the port number is checked (e.g., \fBdst port 513\fR will print both
389 tcp/login traffic and udp/who traffic, and \fBport domain\fR will print
390 both tcp/domain and udp/domain traffic).
391 .IP "\fBsrc port \fIport\fR"
392 True if the packet has a source port value of \fIport\fP.
393 .IP "\fBport \fIport\fR"
394 True if either the source or destination port of the packet is \fIport\fP.
395 Any of the above port expressions can be prepended with the keywords,
396 \fBtcp\fP or \fBudp\fP, as in:
399 \fBtcp src port \fIport\fR
402 which matches only tcp packets whose source port is \fIport\fP.
403 .IP "\fBless \fIlength\fR"
404 True if the packet has a length less than or equal to \fIlength\fP.
405 This is equivalent to:
408 \fBlen <= \fIlength\fP.
411 .IP "\fBgreater \fIlength\fR"
412 True if the packet has a length greater than or equal to \fIlength\fP.
413 This is equivalent to:
416 \fBlen >= \fIlength\fP.
419 .IP "\fBip proto \fIprotocol\fR"
420 True if the packet is an ip packet (see
422 of protocol type \fIprotocol\fP.
423 \fIProtocol\fP can be a number or one of the names
424 \fIicmp\fP, \fIigrp\fP, \fIudp\fP, \fInd\fP, or \fItcp\fP.
425 Note that the identifiers \fItcp\fP, \fIudp\fP, and \fIicmp\fP are also
426 keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell.
427 Note that this primitive does not chase protocol header chain.
428 .IP "\fBip6 proto \fIprotocol\fR"
429 True if the packet is an IPv6 packet of protocol type \fIprotocol\fP.
430 Note that this primitive does not chase protocol header chain.
431 .IP "\fBip6 protochain \fIprotocol\fR"
432 True if the packet is IPv6 packet,
433 and contains protocol header with type \fIprotocol\fR
434 in its protocol header chain.
438 \fBip6 protochain 6\fR
441 matches any IPv6 packet with TCP protocol header in the protocol header chain.
442 The packet may contain, for example,
443 authentication header, routing header, or hop-by-hop option header,
444 between IPv6 header and TCP header.
445 The BPF code emitted by this primitive is complex and
446 cannot be optimized by BPF optimizer code in \fItcpdump\fP,
447 so this can be somewhat slow.
448 .IP "\fBip protochain \fIprotocol\fR"
449 Equivalent to \fBip6 protochain \fIprotocol\fR, but this is for IPv4.
450 .IP "\fBether broadcast\fR"
451 True if the packet is an ethernet broadcast packet. The \fIether\fP
453 .IP "\fBip broadcast\fR"
454 True if the packet is an IP broadcast packet. It checks for both
455 the all-zeroes and all-ones broadcast conventions, and looks up
456 the local subnet mask.
457 .IP "\fBether multicast\fR"
458 True if the packet is an ethernet multicast packet. The \fIether\fP
460 This is shorthand for `\fBether[0] & 1 != 0\fP'.
461 .IP "\fBip multicast\fR"
462 True if the packet is an IP multicast packet.
463 .IP "\fBip6 multicast\fR"
464 True if the packet is an IPv6 multicast packet.
465 .IP "\fBether proto \fIprotocol\fR"
466 True if the packet is of ether type \fIprotocol\fR.
467 \fIProtocol\fP can be a number or a name like
468 \fIip\fP, \fIip6\fP, \fIarp\fP, or \fIrarp\fP.
469 Note these identifiers are also keywords
470 and must be escaped via backslash (\\).
471 [In the case of FDDI (e.g., `\fBfddi protocol arp\fR'), the
472 protocol identification comes from the 802.2 Logical Link Control
473 (LLC) header, which is usually layered on top of the FDDI header.
474 \fITcpdump\fP assumes, when filtering on the protocol identifier,
475 that all FDDI packets include an LLC header, and that the LLC header
476 is in so-called SNAP format.]
477 .IP "\fBdecnet src \fIhost\fR"
478 True if the DECNET source address is
480 which may be an address of the form ``10.123'', or a DECNET host
481 name. [DECNET host name support is only available on Ultrix systems
482 that are configured to run DECNET.]
483 .IP "\fBdecnet dst \fIhost\fR"
484 True if the DECNET destination address is
486 .IP "\fBdecnet host \fIhost\fR"
487 True if either the DECNET source or destination address is
489 .IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBdecnet\fR"
493 \fBether proto \fIp\fR
496 where \fIp\fR is one of the above protocols.
497 .IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR"
501 \fBether proto \fIp\fR
504 where \fIp\fR is one of the above protocols.
506 \fItcpdump\fP does not currently know how to parse these protocols.
507 .IP "\fBtcp\fR, \fBudp\fR, \fBicmp\fR"
511 \fBip proto \fIp\fR\fB or ip6 proto \fIp\fR
514 where \fIp\fR is one of the above protocols.
515 .IP "\fIexpr relop expr\fR"
516 True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =, !=,
517 and \fIexpr\fR is an arithmetic expression composed of integer constants
518 (expressed in standard C syntax), the normal binary operators
519 [+, -, *, /, &, |], a length operator, and special packet data accessors.
521 data inside the packet, use the following syntax:
524 \fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR
527 \fIProto\fR is one of \fBether, fddi,
528 ip, arp, rarp, tcp, udp, icmp\fR or \fBip6\fR, and
529 indicates the protocol layer for the index operation.
530 Note that \fItcp, udp\fR and other upper-layer protocol types only
531 apply to IPv4, not IPv6 (this will be fixed in the future).
532 The byte offset, relative to the indicated protocol layer, is
534 \fISize\fR is optional and indicates the number of bytes in the
535 field of interest; it can be either one, two, or four, and defaults to one.
536 The length operator, indicated by the keyword \fBlen\fP, gives the
537 length of the packet.
539 For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic.
540 The expression `\fBip[0] & 0xf != 5\fP'
541 catches all IP packets with options. The expression
542 `\fBip[6:2] & 0x1fff = 0\fP'
543 catches only unfragmented datagrams and frag zero of fragmented datagrams.
544 This check is implicitly applied to the \fBtcp\fP and \fBudp\fP
546 For instance, \fBtcp[0]\fP always means the first
547 byte of the TCP \fIheader\fP, and never means the first byte of an
548 intervening fragment.
550 Primitives may be combined using:
552 A parenthesized group of primitives and operators
553 (parentheses are special to the Shell and must be escaped).
555 Negation (`\fB!\fP' or `\fBnot\fP').
557 Concatenation (`\fB&&\fP' or `\fBand\fP').
559 Alternation (`\fB||\fP' or `\fBor\fP').
561 Negation has highest precedence.
562 Alternation and concatenation have equal precedence and associate
563 left to right. Note that explicit \fBand\fR tokens, not juxtaposition,
564 are now required for concatenation.
566 If an identifier is given without a keyword, the most recent keyword
571 \fBnot host vs and ace\fR
577 \fBnot host vs and host ace\fR
580 which should not be confused with
583 \fBnot ( host vs or ace )\fR
587 Expression arguments can be passed to tcpdump as either a single argument
588 or as multiple arguments, whichever is more convenient.
589 Generally, if the expression contains Shell metacharacters, it is
590 easier to pass it as a single, quoted argument.
591 Multiple arguments are concatenated with spaces before being parsed.
594 To print all packets arriving at or departing from \fIsundown\fP:
597 \fBtcpdump host sundown\fP
601 To print traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR:
604 \fBtcpdump host helios and \\( hot or ace \\)\fP
608 To print all IP packets between \fIace\fR and any host except \fIhelios\fR:
611 \fBtcpdump ip host ace and not helios\fP
615 To print all traffic between local hosts and hosts at Berkeley:
619 tcpdump net ucb-ether
623 To print all ftp traffic through internet gateway \fIsnup\fP:
624 (note that the expression is quoted to prevent the shell from
625 (mis-)interpreting the parentheses):
629 tcpdump 'gateway snup and (port ftp or ftp-data)'
633 To print traffic neither sourced from nor destined for local hosts
634 (if you gateway to one other net, this stuff should never make it
635 onto your local net).
639 tcpdump ip and not net \fIlocalnet\fP
643 To print the start and end packets (the SYN and FIN packets) of each
644 TCP conversation that involves a non-local host.
648 tcpdump 'tcp[13] & 3 != 0 and not src and dst net \fIlocalnet\fP'
652 To print IP packets longer than 576 bytes sent through gateway \fIsnup\fP:
656 tcpdump 'gateway snup and ip[2:2] > 576'
660 To print IP broadcast or multicast packets that were
662 sent via ethernet broadcast or multicast:
666 tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'
670 To print all ICMP packets that are not echo requests/replies (i.e., not
675 tcpdump 'icmp[0] != 8 and icmp[0] != 0"
680 The output of \fItcpdump\fP is protocol dependent. The following
681 gives a brief description and examples of most of the formats.
689 If the '-e' option is given, the link level header is printed out.
690 On ethernets, the source and destination addresses, protocol,
691 and packet length are printed.
693 On FDDI networks, the '-e' option causes \fItcpdump\fP to print
694 the `frame control' field, the source and destination addresses,
695 and the packet length. (The `frame control' field governs the
696 interpretation of the rest of the packet. Normal packets (such
697 as those containing IP datagrams) are `async' packets, with a priority
698 value between 0 and 7; for example, `\fBasync4\fR'. Such packets
699 are assumed to contain an 802.2 Logical Link Control (LLC) packet;
700 the LLC header is printed if it is \fInot\fR an ISO datagram or a
701 so-called SNAP packet.
703 \fI(N.B.: The following description assumes familiarity with
704 the SLIP compression algorithm described in RFC-1144.)\fP
706 On SLIP links, a direction indicator (``I'' for inbound, ``O'' for outbound),
707 packet type, and compression information are printed out.
708 The packet type is printed first.
709 The three types are \fIip\fP, \fIutcp\fP, and \fIctcp\fP.
710 No further link information is printed for \fIip\fR packets.
711 For TCP packets, the connection identifier is printed following the type.
712 If the packet is compressed, its encoded header is printed out.
713 The special cases are printed out as
714 \fB*S+\fIn\fR and \fB*SA+\fIn\fR, where \fIn\fR is the amount by which
715 the sequence number (or sequence number and ack) has changed.
716 If it is not a special case,
717 zero or more changes are printed.
718 A change is indicated by U (urgent pointer), W (window), A (ack),
719 S (sequence number), and I (packet ID), followed by a delta (+n or -n),
721 Finally, the amount of data in the packet and compressed header length
724 For example, the following line shows an outbound compressed TCP packet,
725 with an implicit connection identifier; the ack has changed by 6,
726 the sequence number by 49, and the packet ID by 6; there are 3 bytes of
727 data and 6 bytes of compressed header:
730 \fBO ctcp * A+6 S+49 I+6 3 (6)\fP
736 Arp/rarp output shows the type of request and its arguments. The
737 format is intended to be self explanatory.
738 Here is a short sample taken from the start of an `rlogin' from
739 host \fIrtsg\fP to host \fIcsam\fP:
743 \f(CWarp who-has csam tell rtsg
744 arp reply csam is-at CSAM\fP
748 The first line says that rtsg sent an arp packet asking
749 for the ethernet address of internet host csam. Csam
750 replies with its ethernet address (in this example, ethernet addresses
751 are in caps and internet addresses in lower case).
753 This would look less redundant if we had done \fBtcpdump \-n\fP:
757 \f(CWarp who-has 128.3.254.6 tell 128.3.254.68
758 arp reply 128.3.254.6 is-at 02:07:01:00:01:c4\fP
762 If we had done \fBtcpdump \-e\fP, the fact that the first packet is
763 broadcast and the second is point-to-point would be visible:
767 \f(CWRTSG Broadcast 0806 64: arp who-has csam tell rtsg
768 CSAM RTSG 0806 64: arp reply csam is-at CSAM\fP
772 For the first packet this says the ethernet source address is RTSG, the
773 destination is the ethernet broadcast address, the type field
774 contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes.
778 \fI(N.B.:The following description assumes familiarity with
779 the TCP protocol described in RFC-793. If you are not familiar
780 with the protocol, neither this description nor tcpdump will
781 be of much use to you.)\fP
783 The general format of a tcp protocol line is:
787 \fIsrc > dst: flags data-seqno ack window urgent options\fP
791 \fISrc\fP and \fIdst\fP are the source and destination IP
792 addresses and ports. \fIFlags\fP are some combination of S (SYN),
793 F (FIN), P (PUSH) or R (RST) or a single `.' (no flags).
794 \fIData-seqno\fP describes the portion of sequence space covered
795 by the data in this packet (see example below).
796 \fIAck\fP is sequence number of the next data expected the other
797 direction on this connection.
798 \fIWindow\fP is the number of bytes of receive buffer space available
799 the other direction on this connection.
800 \fIUrg\fP indicates there is `urgent' data in the packet.
801 \fIOptions\fP are tcp options enclosed in angle brackets (e.g., <mss 1024>).
803 \fISrc, dst\fP and \fIflags\fP are always present. The other fields
804 depend on the contents of the packet's tcp protocol header and
805 are output only if appropriate.
807 Here is the opening portion of an rlogin from host \fIrtsg\fP to
812 \s-2\f(CWrtsg.1023 > csam.login: S 768512:768512(0) win 4096 <mss 1024>
813 csam.login > rtsg.1023: S 947648:947648(0) ack 768513 win 4096 <mss 1024>
814 rtsg.1023 > csam.login: . ack 1 win 4096
815 rtsg.1023 > csam.login: P 1:2(1) ack 1 win 4096
816 csam.login > rtsg.1023: . ack 2 win 4096
817 rtsg.1023 > csam.login: P 2:21(19) ack 1 win 4096
818 csam.login > rtsg.1023: P 1:2(1) ack 21 win 4077
819 csam.login > rtsg.1023: P 2:3(1) ack 21 win 4077 urg 1
820 csam.login > rtsg.1023: P 3:4(1) ack 21 win 4077 urg 1\fP\s+2
824 The first line says that tcp port 1023 on rtsg sent a packet
826 on csam. The \fBS\fP indicates that the \fISYN\fP flag was set.
827 The packet sequence number was 768512 and it contained no data.
828 (The notation is `first:last(nbytes)' which means `sequence
830 up to but not including \fIlast\fP which is \fInbytes\fP bytes of user data'.)
831 There was no piggy-backed ack, the available receive window was 4096
832 bytes and there was a max-segment-size option requesting an mss of
835 Csam replies with a similar packet except it includes a piggy-backed
836 ack for rtsg's SYN. Rtsg then acks csam's SYN. The `.' means no
838 The packet contained no data so there is no data sequence number.
839 Note that the ack sequence
840 number is a small integer (1). The first time \fBtcpdump\fP sees a
841 tcp `conversation', it prints the sequence number from the packet.
842 On subsequent packets of the conversation, the difference between
843 the current packet's sequence number and this initial sequence number
844 is printed. This means that sequence numbers after the
845 first can be interpreted
846 as relative byte positions in the conversation's data stream (with the
847 first data byte each direction being `1'). `-S' will override this
848 feature, causing the original sequence numbers to be output.
850 On the 6th line, rtsg sends csam 19 bytes of data (bytes 2 through 20
851 in the rtsg \(-> csam side of the conversation).
852 The PUSH flag is set in the packet.
853 On the 7th line, csam says it's received data sent by rtsg up to
854 but not including byte 21. Most of this data is apparently sitting in the
855 socket buffer since csam's receive window has gotten 19 bytes smaller.
856 Csam also sends one byte of data to rtsg in this packet.
857 On the 8th and 9th lines,
858 csam sends two bytes of urgent, pushed data to rtsg.
860 If the snapshot was small enough that \fBtcpdump\fP didn't capture
861 the full TCP header, it interprets as much of the header as it can
862 and then reports ``[|\fItcp\fP]'' to indicate the remainder could not
863 be interpreted. If the header contains a bogus option (one with a length
864 that's either too small or beyond the end of the header), tcpdump reports
865 it as ``[\fIbad opt\fP]'' and does not interpret any further options (since
866 it's impossible to tell where they start). If the header length indicates
867 options are present but the IP datagram length is not long enough for the
868 options to actually be there, tcpdump reports it as ``[\fIbad hdr length\fP]''.
873 UDP format is illustrated by this rwho packet:
877 \f(CWactinide.who > broadcast.who: udp 84\fP
881 This says that port \fIwho\fP on host \fIactinide\fP sent a udp
882 datagram to port \fIwho\fP on host \fIbroadcast\fP, the Internet
883 broadcast address. The packet contained 84 bytes of user data.
885 Some UDP services are recognized (from the source or destination
886 port number) and the higher level protocol information printed.
887 In particular, Domain Name service requests (RFC-1034/1035) and Sun
888 RPC calls (RFC-1050) to NFS.
890 UDP Name Server Requests
892 \fI(N.B.:The following description assumes familiarity with
893 the Domain Service protocol described in RFC-1035. If you are not familiar
894 with the protocol, the following description will appear to be written
897 Name server requests are formatted as
901 \fIsrc > dst: id op? flags qtype qclass name (len)\fP
903 \f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fP
907 Host \fIh2opolo\fP asked the domain server on \fIhelios\fP for an
908 address record (qtype=A) associated with the name \fIucbvax.berkeley.edu.\fP
909 The query id was `3'. The `+' indicates the \fIrecursion desired\fP flag
910 was set. The query length was 37 bytes, not including the UDP and
911 IP protocol headers. The query operation was the normal one, \fIQuery\fP,
912 so the op field was omitted. If the op had been anything else, it would
913 have been printed between the `3' and the `+'.
914 Similarly, the qclass was the normal one,
915 \fIC_IN\fP, and omitted. Any other qclass would have been printed
916 immediately after the `A'.
918 A few anomalies are checked and may result in extra fields enclosed in
919 square brackets: If a query contains an answer, name server or
925 are printed as `[\fIn\fPa]', `[\fIn\fPn]' or `[\fIn\fPau]' where \fIn\fP
926 is the appropriate count.
927 If any of the response bits are set (AA, RA or rcode) or any of the
928 `must be zero' bits are set in bytes two and three, `[b2&3=\fIx\fP]'
929 is printed, where \fIx\fP is the hex value of header bytes two and three.
931 UDP Name Server Responses
933 Name server responses are formatted as
937 \fIsrc > dst: id op rcode flags a/n/au type class data (len)\fP
939 \f(CWhelios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273)
940 helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fP
944 In the first example, \fIhelios\fP responds to query id 3 from \fIh2opolo\fP
945 with 3 answer records, 3 name server records and 7 authority records.
946 The first answer record is type A (address) and its data is internet
947 address 128.32.137.3. The total size of the response was 273 bytes,
948 excluding UDP and IP headers. The op (Query) and response code
949 (NoError) were omitted, as was the class (C_IN) of the A record.
951 In the second example, \fIhelios\fP responds to query 2 with a
952 response code of non-existent domain (NXDomain) with no answers,
953 one name server and no authority records. The `*' indicates that
954 the \fIauthoritative answer\fP bit was set. Since there were no
955 answers, no type, class or data were printed.
957 Other flag characters that might appear are `\-' (recursion available,
958 RA, \fInot\fP set) and `|' (truncated message, TC, set). If the
959 `question' section doesn't contain exactly one entry, `[\fIn\fPq]'
962 Note that name server requests and responses tend to be large and the
963 default \fIsnaplen\fP of 68 bytes may not capture enough of the packet
964 to print. Use the \fB\-s\fP flag to increase the snaplen if you
965 need to seriously investigate name server traffic. `\fB\-s 128\fP'
966 has worked well for me.
969 NFS Requests and Replies
971 Sun NFS (Network File System) requests and replies are printed as:
975 \fIsrc.xid > dst.nfs: len op args\fP
976 \fIsrc.nfs > dst.xid: reply stat len op results\fP
979 sushi.6709 > wrl.nfs: 112 readlink fh 21,24/10.73165
980 wrl.nfs > sushi.6709: reply ok 40 readlink "../var"
981 sushi.201b > wrl.nfs:
982 144 lookup fh 9,74/4096.6878 "xcolors"
983 wrl.nfs > sushi.201b:
984 reply ok 128 lookup fh 9,74/4134.3150
989 In the first line, host \fIsushi\fP sends a transaction with id \fI6709\fP
990 to \fIwrl\fP (note that the number following the src host is a
991 transaction id, \fInot\fP the source port). The request was 112 bytes,
992 excluding the UDP and IP headers. The operation was a \fIreadlink\fP
993 (read symbolic link) on file handle (\fIfh\fP) 21,24/10.731657119.
994 (If one is lucky, as in this case, the file handle can be interpreted
995 as a major,minor device number pair, followed by the inode number and
997 \fIWrl\fP replies `ok' with the contents of the link.
999 In the third line, \fIsushi\fP asks \fIwrl\fP to lookup the name
1000 `\fIxcolors\fP' in directory file 9,74/4096.6878. Note that the data printed
1001 depends on the operation type. The format is intended to be self
1002 explanatory if read in conjunction with
1003 an NFS protocol spec.
1005 If the \-v (verbose) flag is given, additional information is printed.
1011 sushi.1372a > wrl.nfs:
1012 148 read fh 21,11/12.195 8192 bytes @ 24576
1013 wrl.nfs > sushi.1372a:
1014 reply ok 1472 read REG 100664 ids 417/0 sz 29388
1019 (\-v also prints the IP header TTL, ID, and fragmentation fields,
1020 which have been omitted from this example.) In the first line,
1021 \fIsushi\fP asks \fIwrl\fP to read 8192 bytes from file 21,11/12.195,
1022 at byte offset 24576. \fIWrl\fP replies `ok'; the packet shown on the
1023 second line is the first fragment of the reply, and hence is only 1472
1024 bytes long (the other bytes will follow in subsequent fragments, but
1025 these fragments do not have NFS or even UDP headers and so might not be
1026 printed, depending on the filter expression used). Because the \-v flag
1027 is given, some of the file attributes (which are returned in addition
1028 to the file data) are printed: the file type (``REG'', for regular file),
1029 the file mode (in octal), the uid and gid, and the file size.
1031 If the \-v flag is given more than once, even more details are printed.
1033 Note that NFS requests are very large and much of the detail won't be printed
1034 unless \fIsnaplen\fP is increased. Try using `\fB\-s 192\fP' to watch
1037 NFS reply packets do not explicitly identify the RPC operation. Instead,
1038 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1039 replies using the transaction ID. If a reply does not closely follow the
1040 corresponding request, it might not be parsable.
1042 KIP Appletalk (DDP in UDP)
1044 Appletalk DDP packets encapsulated in UDP datagrams are de-encapsulated
1045 and dumped as DDP packets (i.e., all the UDP header information is
1046 discarded). The file
1048 is used to translate appletalk net and node numbers to names.
1049 Lines in this file have the form
1061 The first two lines give the names of appletalk networks. The third
1062 line gives the name of a particular host (a host is distinguished
1063 from a net by the 3rd octet in the number \-
1064 a net number \fImust\fP have two octets and a host number \fImust\fP
1065 have three octets.) The number and name should be separated by
1066 whitespace (blanks or tabs).
1069 file may contain blank lines or comment lines (lines starting with
1072 Appletalk addresses are printed in the form
1078 \f(CW144.1.209.2 > icsd-net.112.220
1079 office.2 > icsd-net.112.220
1080 jssmag.149.235 > icsd-net.2\fP
1086 doesn't exist or doesn't contain an entry for some appletalk
1087 host/net number, addresses are printed in numeric form.)
1088 In the first example, NBP (DDP port 2) on net 144.1 node 209
1089 is sending to whatever is listening on port 220 of net icsd node 112.
1090 The second line is the same except the full name of the source node
1091 is known (`office'). The third line is a send from port 235 on
1092 net jssmag node 149 to broadcast on the icsd-net NBP port (note that
1093 the broadcast address (255) is indicated by a net name with no host
1094 number \- for this reason it's a good idea to keep node names and
1095 net names distinct in /etc/atalk.names).
1097 NBP (name binding protocol) and ATP (Appletalk transaction protocol)
1098 packets have their contents interpreted. Other protocols just dump
1099 the protocol name (or number if no name is registered for the
1100 protocol) and packet size.
1102 \fBNBP packets\fP are formatted like the following examples:
1106 \s-2\f(CWicsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
1107 jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
1108 techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fP\s+2
1112 The first line is a name lookup request for laserwriters sent by net icsd host
1113 112 and broadcast on net jssmag. The nbp id for the lookup is 190.
1114 The second line shows a reply for this request (note that it has the
1115 same id) from host jssmag.209 saying that it has a laserwriter
1116 resource named "RM1140" registered on port 250. The third line is
1117 another reply to the same request saying host techpit has laserwriter
1118 "techpit" registered on port 186.
1120 \fBATP packet\fP formatting is demonstrated by the following example:
1124 \s-2\f(CWjssmag.209.165 > helios.132: atp-req 12266<0-7> 0xae030001
1125 helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
1126 helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
1127 helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
1128 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1129 helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
1130 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1131 helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
1132 helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
1133 jssmag.209.165 > helios.132: atp-req 12266<3,5> 0xae030001
1134 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1135 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1136 jssmag.209.165 > helios.132: atp-rel 12266<0-7> 0xae030001
1137 jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fP\s+2
1141 Jssmag.209 initiates transaction id 12266 with host helios by requesting
1142 up to 8 packets (the `<0-7>'). The hex number at the end of the line
1143 is the value of the `userdata' field in the request.
1145 Helios responds with 8 512-byte packets. The `:digit' following the
1146 transaction id gives the packet sequence number in the transaction
1147 and the number in parens is the amount of data in the packet,
1148 excluding the atp header. The `*' on packet 7 indicates that the
1151 Jssmag.209 then requests that packets 3 & 5 be retransmitted. Helios
1152 resends them then jssmag.209 releases the transaction. Finally,
1153 jssmag.209 initiates the next request. The `*' on the request
1154 indicates that XO (`exactly once') was \fInot\fP set.
1159 Fragmented Internet datagrams are printed as
1163 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR
1164 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR
1168 (The first form indicates there are more fragments. The second
1169 indicates this is the last fragment.)
1171 \fIId\fP is the fragment id. \fISize\fP is the fragment
1172 size (in bytes) excluding the IP header. \fIOffset\fP is this
1173 fragment's offset (in bytes) in the original datagram.
1175 The fragment information is output for each fragment. The first
1176 fragment contains the higher level protocol header and the frag
1177 info is printed after the protocol info. Fragments
1178 after the first contain no higher level protocol header and the
1179 frag info is printed after the source and destination addresses.
1180 For example, here is part of an ftp from arizona.edu to lbl-rtsg.arpa
1181 over a CSNET connection that doesn't appear to handle 576 byte datagrams:
1185 \s-2\f(CWarizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+)
1186 arizona > rtsg: (frag 595a:204@328)
1187 rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2
1191 There are a couple of things to note here: First, addresses in the
1192 2nd line don't include port numbers. This is because the TCP
1193 protocol information is all in the first fragment and we have no idea
1194 what the port or sequence numbers are when we print the later fragments.
1195 Second, the tcp sequence information in the first line is printed as if there
1196 were 308 bytes of user data when, in fact, there are 512 bytes (308 in
1197 the first frag and 204 in the second). If you are looking for holes
1198 in the sequence space or trying to match up acks
1199 with packets, this can fool you.
1201 A packet with the IP \fIdon't fragment\fP flag is marked with a
1202 trailing \fB(DF)\fP.
1206 By default, all output lines are preceded by a timestamp. The timestamp
1207 is the current clock time in the form
1213 and is as accurate as the kernel's clock.
1214 The timestamp reflects the time the kernel first saw the packet. No attempt
1215 is made to account for the time lag between when the
1216 ethernet interface removed the packet from the wire and when the kernel
1217 serviced the `new packet' interrupt.
1219 traffic(1C), nit(4P), bpf(4), pcap(3)
1223 Steven McCanne, all of the
1224 Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
1226 The current version is available via anonymous ftp:
1229 .I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z
1232 IPv6/IPsec support is added by WIDE/KAME project.
1233 This program uses Eric Young's SSLeay library, under specific configuration.
1235 Please send bug reports to tcpdump@ee.lbl.gov.
1237 NIT doesn't let you watch your own outbound traffic, BPF will.
1238 We recommend that you use the latter.
1240 Some attempt should be made to reassemble IP fragments or, at least
1241 to compute the right length for the higher level protocol.
1243 Name server inverse queries are not dumped correctly: The (empty)
1244 question section is printed rather than real query in the answer
1245 section. Some believe that inverse queries are themselves a bug and
1246 prefer to fix the program generating them rather than tcpdump.
1248 Apple Ethertalk DDP packets could be dumped as easily as KIP DDP
1250 Even if we were inclined to do anything to promote the use of
1251 Ethertalk (we aren't), LBL doesn't allow Ethertalk on any of its
1252 networks so we'd would have no way of testing this code.
1254 A packet trace that crosses a daylight savings time change will give
1255 skewed time stamps (the time change is ignored).
1257 Filters expressions that manipulate FDDI headers assume that all FDDI
1258 packets are encapsulated Ethernet packets. This is true for IP, ARP,
1259 and DECNET Phase IV, but is not true for protocols such as ISO CLNS.
1260 Therefore, the filter may inadvertently accept certain packets that
1261 do not properly match the filter expression.
1264 should chase header chain, but at this moment it does not.
1268 should chase header chain too.
projects / tcpdump / blob