1 .\" @(#) $Header: /tcpdump/master/tcpdump/Attic/tcpdump.1,v 1.118 2002-04-24 06:55:55 guy Exp $ (LBL)
3 .\" Copyright (c) 1987, 1988, 1989, 1990, 1991, 1992, 1994, 1995, 1996, 1997
4 .\" The Regents of the University of California. All rights reserved.
5 .\" All rights reserved.
7 .\" Redistribution and use in source and binary forms, with or without
8 .\" modification, are permitted provided that: (1) source code distributions
9 .\" retain the above copyright notice and this paragraph in its entirety, (2)
10 .\" distributions including binary code include the above copyright notice and
11 .\" this paragraph in its entirety in the documentation or other materials
12 .\" provided with the distribution, and (3) all advertising materials mentioning
13 .\" features or use of this software display the following acknowledgement:
14 .\" ``This product includes software developed by the University of California,
15 .\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
16 .\" the University nor the names of its contributors may be used to endorse
17 .\" or promote products derived from this software without specific prior
18 .\" written permission.
19 .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
20 .\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
21 .\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
23 .TH TCPDUMP 1 "3 January 2001"
25 tcpdump \- dump traffic on a network
30 .B \-aAdeflnNOpqRStuvxX
85 \fITcpdump\fP prints out the headers of packets on a network interface
86 that match the boolean \fIexpression\fP. It can also be run with the
88 flag, which causes it to save the packet data to a file for later
89 analysis, and/or with the
91 flag, which causes it to read from a saved packet file rather than to
92 read packets from a network interface. In all cases, only packets that
99 will, if not run with the
101 flag, continue capturing packets until it is interrupted by a SIGINT
102 signal (generated, for example, by typing your interrupt character,
103 typically control-C) or a SIGTERM signal (typically generated with the
105 command); if run with the
107 flag, it will capture packets until it is interrupted by a SIGINT or
108 SIGTERM signal or the specified number of packets have been processed.
112 finishes capturing packets, it will report counts of:
114 packets ``received by filter'' (the meaning of this depends on the OS on
117 and possibly on the way the OS was configured - if a filter was
118 specified on the command line, on some OSes it counts packets regardless
119 of whether they were matched by the filter expression, and on other OSes
120 it counts only packets that were matched by the filter expression and
124 packets ``dropped by kernel'' (this is the number of packets that were
125 dropped, due to a lack of buffer space, by the packet capture mechanism
128 is running, if the OS reports that information to applications; if not,
129 it will be reported as 0).
131 On platforms that support the SIGINFO signal, such as most BSDs, it will
132 report those counts when it receives a SIGINFO signal (generated, for
133 example, by typing your ``status'' character, typically control-T) and
134 will continue capturing packets.
136 Reading packets from a network interface may require that you have
139 .B Under SunOS 3.x or 4.x with NIT or BPF:
140 You must have read access to
145 .B Under Solaris with DLPI:
146 You must have read/write access to the network pseudo device, e.g.
148 On at least some versions of Solaris, however, this is not sufficient to
151 to capture in promiscuous mode; on those versions of Solaris, you must
154 must be installed setuid to root, in order to capture in promiscuous
155 mode. Note that, on many (perhaps all) interfaces, if you don't capture
156 in promiscuous mode, you will not see any outgoing packets, so a capture
157 not done in promiscuous mode may not be very useful.
159 .B Under HP-UX with DLPI:
162 must be installed setuid to root.
164 .B Under IRIX with snoop:
167 must be installed setuid to root.
172 must be installed setuid to root.
174 .B Under Ultrix and Digital UNIX:
175 Once the super-user has enabled promiscuous-mode operation using
177 any user may capture network traffic with
181 You must have read access to
184 Reading a saved packet file doesn't require special privileges.
189 Print each packet (minus its link level header) in ASCII. Handy for
192 Attempt to convert network and broadcast addresses to names.
195 Exit after receiving \fIcount\fP packets.
198 Before writing a raw packet to a savefile, check whether the file is
199 currently larger than \fIfile_size\fP and, if so, close the current
200 savefile and open a new one. Savefiles after the first savefile will
201 have the name specified with the
203 flag, with a number after it, starting at 2 and continuing upward.
204 The units of \fIfile_size\fP are millions of bytes (1,000,000 bytes,
205 not 1,048,576 bytes).
208 Dump the compiled packet-matching code in a human readable form to
209 standard output and stop.
212 Dump packet-matching code as a
217 Dump packet-matching code as decimal numbers (preceded with a count).
220 Print the link-level header on each dump line.
223 Use \fIalgo:secret\fP for decrypting IPsec ESP packets.
229 \fBcast128-cbc\fP, or
231 The default is \fBdes-cbc\fP.
232 The ability to decrypt packets is only present if \fItcpdump\fP was compiled
233 with cryptography enabled.
234 \fIsecret\fP the ascii text for ESP secret key.
235 We cannot take arbitrary binary value at this moment.
236 The option assumes RFC2406 ESP, not RFC1827 ESP.
237 The option is only for debugging purposes, and
238 the use of this option with truly `secret' key is discouraged.
239 By presenting IPsec secret key onto command line
240 you make it visible to others, via
245 Print `foreign' internet addresses numerically rather than symbolically
246 (this option is intended to get around serious brain damage in
247 Sun's yp server \(em usually it hangs forever translating non-local
251 Use \fIfile\fP as input for the filter expression.
252 An additional expression given on the command line is ignored.
255 Listen on \fIinterface\fP.
256 If unspecified, \fItcpdump\fP searches the system interface list for the
257 lowest numbered, configured up interface (excluding loopback).
258 Ties are broken by choosing the earliest match.
260 On Linux systems with 2.2 or later kernels, an
262 argument of ``any'' can be used to capture packets from all interfaces.
263 Note that captures on the ``any'' device will not be done in promiscuous
267 Make stdout line buffered.
268 Useful if you want to see the data
272 ``tcpdump\ \ \-l\ \ |\ \ tee dat'' or
273 ``tcpdump\ \ \-l \ \ > dat\ \ &\ \ tail\ \ \-f\ \ dat''.
276 Load SMI MIB module definitions from file \fImodule\fR.
278 can be used several times to load several MIB modules into \fItcpdump\fP.
281 Don't convert addresses (i.e., host addresses, port numbers, etc.) to names.
284 Don't print domain name qualification of host names.
286 if you give this flag then \fItcpdump\fP will print ``nic''
287 instead of ``nic.ddn.mil''.
290 Do not run the packet-matching code optimizer.
292 if you suspect a bug in the optimizer.
295 \fIDon't\fP put the interface
296 into promiscuous mode.
297 Note that the interface might be in promiscuous
298 mode for some other reason; hence, `-p' cannot be used as an abbreviation for
299 `ether host {local-hw-addr} or ether broadcast'.
302 Quick (quiet?) output.
303 Print less protocol information so output
307 Assume ESP/AH packets to be based on old specification (RFC1825 to RFC1829).
308 If specified, \fItcpdump\fP will not print replay prevention field.
309 Since there is no protocol version field in ESP/AH specification,
310 \fItcpdump\fP cannot deduce the version of ESP/AH protocol.
313 Read packets from \fIfile\fR (which was created with the -w option).
314 Standard input is used if \fIfile\fR is ``-''.
317 Print absolute, rather than relative, TCP sequence numbers.
320 Snarf \fIsnaplen\fP bytes of data from each packet rather than the
321 default of 68 (with SunOS's NIT, the minimum is actually 96).
322 68 bytes is adequate for IP, ICMP, TCP
323 and UDP but may truncate protocol information from name server and NFS
325 Packets truncated because of a limited snapshot
326 are indicated in the output with ``[|\fIproto\fP]'', where \fIproto\fP
327 is the name of the protocol level at which the truncation has occurred.
328 Note that taking larger snapshots both increases
329 the amount of time it takes to process packets and, effectively,
330 decreases the amount of packet buffering.
331 This may cause packets to be
333 You should limit \fIsnaplen\fP to the smallest number that will
334 capture the protocol information you're interested in.
336 \fIsnaplen\fP to 0 means use the required length to catch whole packets.
339 Force packets selected by "\fIexpression\fP" to be interpreted the
340 specified \fItype\fR.
341 Currently known types are
342 \fBcnfp\fR (Cisco NetFlow protocol),
343 \fBrpc\fR (Remote Procedure Call),
344 \fBrtp\fR (Real-Time Applications protocol),
345 \fBrtcp\fR (Real-Time Applications control protocol),
346 \fBsnmp\fR (Simple Network Management Protocol),
347 \fBvat\fR (Visual Audio Tool),
349 \fBwb\fR (distributed White Board).
352 \fIDon't\fP print a timestamp on each dump line.
355 Print an unformatted timestamp on each dump line.
358 Print a delta (in micro-seconds) between current and previous line
362 Print a timestamp in default format proceeded by date on each dump line.
364 Print undecoded NFS handles.
367 (Slightly more) verbose output.
368 For example, the time to live,
369 identification, total length and options in an IP packet are printed.
370 Also enables additional packet integrity checks such as verifying the
371 IP and ICMP header checksum.
374 Even more verbose output.
375 For example, additional fields are
376 printed from NFS reply packets, and SMB packets are fully decoded.
379 Even more verbose output.
381 telnet \fBSB\fP ... \fBSE\fP options
385 telnet options are printed in hex as well.
388 Write the raw packets to \fIfile\fR rather than parsing and printing
390 They can later be printed with the \-r option.
391 Standard output is used if \fIfile\fR is ``-''.
394 Print each packet (minus its link level header) in hex.
395 The smaller of the entire packet or
397 bytes will be printed.
400 When printing hex, print ascii too.
403 is also set, the packet is printed in hex/ascii.
404 This is very handy for analysing new protocols.
407 is not also set, some parts of some packets may be printed
409 .IP "\fI expression\fP"
411 selects which packets will be dumped.
412 If no \fIexpression\fP
413 is given, all packets on the net will be dumped.
415 only packets for which \fIexpression\fP is `true' will be dumped.
417 The \fIexpression\fP consists of one or more
419 Primitives usually consist of an
421 (name or number) preceded by one or more qualifiers.
423 different kinds of qualifier:
425 qualifiers say what kind of thing the id name or number refers to.
431 E.g., `host foo', `net 128.3', `port 20'.
437 qualifiers specify a particular transfer direction to and/or from
439 Possible directions are
446 E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'.
448 there is no dir qualifier,
451 For `null' link layers (i.e. point to point protocols such as slip) the
455 qualifiers can be used to specify a desired direction.
457 qualifiers restrict the match to a particular protocol.
471 E.g., `ether src foo', `arp net 128.3', `tcp port 21'.
473 no proto qualifier, all protocols consistent with the type are
475 E.g., `src foo' means `(ip or arp or rarp) src foo'
476 (except the latter is not legal syntax), `net bar' means `(ip or
477 arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'.
479 [`fddi' is actually an alias for `ether'; the parser treats them
480 identically as meaning ``the data link level used on the specified
481 network interface.'' FDDI headers contain Ethernet-like source
482 and destination addresses, and often contain Ethernet-like packet
483 types, so you can filter on these FDDI fields just as with the
484 analogous Ethernet fields.
485 FDDI headers also contain other fields,
486 but you cannot name them explicitly in a filter expression.
488 Similarly, `tr' is an alias for `ether'; the previous paragraph's
489 statements about FDDI headers also apply to Token Ring headers.]
491 In addition to the above, there are some special `primitive' keywords
492 that don't follow the pattern:
497 and arithmetic expressions.
498 All of these are described below.
500 More complex filter expressions are built up by using the words
505 to combine primitives.
506 E.g., `host foo and not port ftp and not port ftp-data'.
507 To save typing, identical qualifier lists can be omitted.
509 `tcp dst port ftp or ftp-data or domain' is exactly the same as
510 `tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
512 Allowable primitives are:
513 .IP "\fBdst host \fIhost\fR"
514 True if the IPv4/v6 destination field of the packet is \fIhost\fP,
515 which may be either an address or a name.
516 .IP "\fBsrc host \fIhost\fR"
517 True if the IPv4/v6 source field of the packet is \fIhost\fP.
518 .IP "\fBhost \fIhost\fP
519 True if either the IPv4/v6 source or destination of the packet is \fIhost\fP.
520 Any of the above host expressions can be prepended with the keywords,
521 \fBip\fP, \fBarp\fP, \fBrarp\fP, or \fBip6\fP as in:
524 \fBip host \fIhost\fR
527 which is equivalent to:
530 \fBether proto \fI\\ip\fB and host \fIhost\fR
533 If \fIhost\fR is a name with multiple IP addresses, each address will
534 be checked for a match.
535 .IP "\fBether dst \fIehost\fP
536 True if the ethernet destination address is \fIehost\fP.
538 may be either a name from /etc/ethers or a number (see
541 .IP "\fBether src \fIehost\fP
542 True if the ethernet source address is \fIehost\fP.
543 .IP "\fBether host \fIehost\fP
544 True if either the ethernet source or destination address is \fIehost\fP.
545 .IP "\fBgateway\fP \fIhost\fP
546 True if the packet used \fIhost\fP as a gateway.
548 source or destination address was \fIhost\fP but neither the IP source
549 nor the IP destination was \fIhost\fP.
550 \fIHost\fP must be a name and
551 must be found both by the machine's host-name-to-IP-address resolution
552 mechanisms (host name file, DNS, NIS, etc.) and by the machine's
553 host-name-to-Ethernet-address resolution mechanism (/etc/ethers, etc.).
554 (An equivalent expression is
557 \fBether host \fIehost \fBand not host \fIhost\fR
560 which can be used with either names or numbers for \fIhost / ehost\fP.)
561 This syntax does not work in IPv6-enabled configuration at this moment.
562 .IP "\fBdst net \fInet\fR"
563 True if the IPv4/v6 destination address of the packet has a network
565 \fINet\fP may be either a name from /etc/networks
566 or a network number (see \fInetworks(4)\fP for details).
567 .IP "\fBsrc net \fInet\fR"
568 True if the IPv4/v6 source address of the packet has a network
570 .IP "\fBnet \fInet\fR"
571 True if either the IPv4/v6 source or destination address of the packet has a network
573 .IP "\fBnet \fInet\fR \fBmask \fInetmask\fR"
574 True if the IP address matches \fInet\fR with the specific \fInetmask\fR.
575 May be qualified with \fBsrc\fR or \fBdst\fR.
576 Note that this syntax is not valid for IPv6 \fInet\fR.
577 .IP "\fBnet \fInet\fR/\fIlen\fR"
578 True if the IPv4/v6 address matches \fInet\fR with a netmask \fIlen\fR
580 May be qualified with \fBsrc\fR or \fBdst\fR.
581 .IP "\fBdst port \fIport\fR"
582 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a
583 destination port value of \fIport\fP.
584 The \fIport\fP can be a number or a name used in /etc/services (see
588 If a name is used, both the port
589 number and protocol are checked.
590 If a number or ambiguous name is used,
591 only the port number is checked (e.g., \fBdst port 513\fR will print both
592 tcp/login traffic and udp/who traffic, and \fBport domain\fR will print
593 both tcp/domain and udp/domain traffic).
594 .IP "\fBsrc port \fIport\fR"
595 True if the packet has a source port value of \fIport\fP.
596 .IP "\fBport \fIport\fR"
597 True if either the source or destination port of the packet is \fIport\fP.
598 Any of the above port expressions can be prepended with the keywords,
599 \fBtcp\fP or \fBudp\fP, as in:
602 \fBtcp src port \fIport\fR
605 which matches only tcp packets whose source port is \fIport\fP.
606 .IP "\fBless \fIlength\fR"
607 True if the packet has a length less than or equal to \fIlength\fP.
608 This is equivalent to:
611 \fBlen <= \fIlength\fP.
614 .IP "\fBgreater \fIlength\fR"
615 True if the packet has a length greater than or equal to \fIlength\fP.
616 This is equivalent to:
619 \fBlen >= \fIlength\fP.
622 .IP "\fBip proto \fIprotocol\fR"
623 True if the packet is an IP packet (see
625 of protocol type \fIprotocol\fP.
626 \fIProtocol\fP can be a number or one of the names
627 \fIicmp\fP, \fIicmp6\fP, \fIigmp\fP, \fIigrp\fP, \fIpim\fP, \fIah\fP,
628 \fIesp\fP, \fIvrrp\fP, \fIudp\fP, or \fItcp\fP.
629 Note that the identifiers \fItcp\fP, \fIudp\fP, and \fIicmp\fP are also
630 keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell.
631 Note that this primitive does not chase the protocol header chain.
632 .IP "\fBip6 proto \fIprotocol\fR"
633 True if the packet is an IPv6 packet of protocol type \fIprotocol\fP.
634 Note that this primitive does not chase the protocol header chain.
635 .IP "\fBip6 protochain \fIprotocol\fR"
636 True if the packet is IPv6 packet,
637 and contains protocol header with type \fIprotocol\fR
638 in its protocol header chain.
642 \fBip6 protochain 6\fR
645 matches any IPv6 packet with TCP protocol header in the protocol header chain.
646 The packet may contain, for example,
647 authentication header, routing header, or hop-by-hop option header,
648 between IPv6 header and TCP header.
649 The BPF code emitted by this primitive is complex and
650 cannot be optimized by BPF optimizer code in \fItcpdump\fP,
651 so this can be somewhat slow.
652 .IP "\fBip protochain \fIprotocol\fR"
653 Equivalent to \fBip6 protochain \fIprotocol\fR, but this is for IPv4.
654 .IP "\fBether broadcast\fR"
655 True if the packet is an ethernet broadcast packet.
658 .IP "\fBip broadcast\fR"
659 True if the packet is an IP broadcast packet.
661 the all-zeroes and all-ones broadcast conventions, and looks up
662 the local subnet mask.
663 .IP "\fBether multicast\fR"
664 True if the packet is an ethernet multicast packet.
667 This is shorthand for `\fBether[0] & 1 != 0\fP'.
668 .IP "\fBip multicast\fR"
669 True if the packet is an IP multicast packet.
670 .IP "\fBip6 multicast\fR"
671 True if the packet is an IPv6 multicast packet.
672 .IP "\fBether proto \fIprotocol\fR"
673 True if the packet is of ether type \fIprotocol\fR.
674 \fIProtocol\fP can be a number or one of the names
675 \fIip\fP, \fIip6\fP, \fIarp\fP, \fIrarp\fP, \fIatalk\fP, \fIaarp\fP,
676 \fIdecnet\fP, \fIsca\fP, \fIlat\fP, \fImopdl\fP, \fImoprc\fP,
677 \fIiso\fP, \fIstp\fP, \fIipx\fP, or \fInetbeui\fP.
678 Note these identifiers are also keywords
679 and must be escaped via backslash (\\).
681 [In the case of FDDI (e.g., `\fBfddi protocol arp\fR') and Token Ring
682 (e.g., `\fBtr protocol arp\fR'), for most of those protocols, the
683 protocol identification comes from the 802.2 Logical Link Control (LLC)
684 header, which is usually layered on top of the FDDI or Token Ring
687 When filtering for most protocol identifiers on FDDI or Token Ring,
688 \fItcpdump\fR checks only the protocol ID field of an LLC header in
689 so-called SNAP format with an Organizational Unit Identifier (OUI) of
690 0x000000, for encapsulated Ethernet; it doesn't check whether the packet
691 is in SNAP format with an OUI of 0x000000.
693 The exceptions are \fIiso\fP, for which it checks the DSAP (Destination
694 Service Access Point) and SSAP (Source Service Access Point) fields of
695 the LLC header, \fIstp\fP and \fInetbeui\fP, where it checks the DSAP of
696 the LLC header, and \fIatalk\fP, where it checks for a SNAP-format
697 packet with an OUI of 0x080007 and the Appletalk etype.
699 In the case of Ethernet, \fItcpdump\fR checks the Ethernet type field
700 for most of those protocols; the exceptions are \fIiso\fP, \fIsap\fP,
701 and \fInetbeui\fP, for which it checks for an 802.3 frame and then
702 checks the LLC header as it does for FDDI and Token Ring, \fIatalk\fP,
703 where it checks both for the Appletalk etype in an Ethernet frame and
704 for a SNAP-format packet as it does for FDDI and Token Ring, \fIaarp\fP,
705 where it checks for the Appletalk ARP etype in either an Ethernet frame
706 or an 802.2 SNAP frame with an OUI of 0x000000, and \fIipx\fP, where it
707 checks for the IPX etype in an Ethernet frame, the IPX DSAP in the LLC
708 header, the 802.3 with no LLC header encapsulation of IPX, and the IPX
709 etype in a SNAP frame.]
710 .IP "\fBdecnet src \fIhost\fR"
711 True if the DECNET source address is
713 which may be an address of the form ``10.123'', or a DECNET host
715 [DECNET host name support is only available on Ultrix systems
716 that are configured to run DECNET.]
717 .IP "\fBdecnet dst \fIhost\fR"
718 True if the DECNET destination address is
720 .IP "\fBdecnet host \fIhost\fR"
721 True if either the DECNET source or destination address is
723 .IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBatalk\fR, \fBaarp\fR, \fBdecnet\fR, \fBiso\fR, \fBstp\fR, \fBipx\fR, \fInetbeui\fP"
727 \fBether proto \fIp\fR
730 where \fIp\fR is one of the above protocols.
731 .IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR"
735 \fBether proto \fIp\fR
738 where \fIp\fR is one of the above protocols.
740 \fItcpdump\fP does not currently know how to parse these protocols.
741 .IP "\fBvlan \fI[vlan_id]\fR"
742 True if the packet is an IEEE 802.1Q VLAN packet.
743 If \fI[vlan_id]\fR is specified, only true is the packet has the specified
745 Note that the first \fBvlan\fR keyword encountered in \fIexpression\fR
746 changes the decoding offsets for the remainder of \fIexpression\fR
747 on the assumption that the packet is a VLAN packet.
748 .IP "\fBtcp\fR, \fBudp\fR, \fBicmp\fR"
752 \fBip proto \fIp\fR\fB or ip6 proto \fIp\fR
755 where \fIp\fR is one of the above protocols.
756 .IP "\fBiso proto \fIprotocol\fR"
757 True if the packet is an OSI packet of protocol type \fIprotocol\fP.
758 \fIProtocol\fP can be a number or one of the names
759 \fIclnp\fP, \fIesis\fP, or \fIisis\fP.
760 .IP "\fBclnp\fR, \fBesis\fR, \fBisis\fR"
767 where \fIp\fR is one of the above protocols.
768 Note that \fItcpdump\fR does an incomplete job of parsing these protocols.
769 .IP "\fIexpr relop expr\fR"
770 True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =, !=,
771 and \fIexpr\fR is an arithmetic expression composed of integer constants
772 (expressed in standard C syntax), the normal binary operators
773 [+, -, *, /, &, |], a length operator, and special packet data accessors.
775 data inside the packet, use the following syntax:
778 \fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR
781 \fIProto\fR is one of \fBether, fddi, tr, ppp, slip, link,
782 ip, arp, rarp, tcp, udp, icmp\fR or \fBip6\fR, and
783 indicates the protocol layer for the index operation.
784 (\fBether, fddi, tr, ppp, slip\fR and \fBlink\fR all refer to the link
786 Note that \fItcp, udp\fR and other upper-layer protocol types only
787 apply to IPv4, not IPv6 (this will be fixed in the future).
788 The byte offset, relative to the indicated protocol layer, is
790 \fISize\fR is optional and indicates the number of bytes in the
791 field of interest; it can be either one, two, or four, and defaults to one.
792 The length operator, indicated by the keyword \fBlen\fP, gives the
793 length of the packet.
795 For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic.
796 The expression `\fBip[0] & 0xf != 5\fP'
797 catches all IP packets with options.
799 `\fBip[6:2] & 0x1fff = 0\fP'
800 catches only unfragmented datagrams and frag zero of fragmented datagrams.
801 This check is implicitly applied to the \fBtcp\fP and \fBudp\fP
803 For instance, \fBtcp[0]\fP always means the first
804 byte of the TCP \fIheader\fP, and never means the first byte of an
805 intervening fragment.
807 Some offsets and field values may be expressed as names rather than
809 The following protocol header field offsets are
810 available: \fBicmptype\fP (ICMP type field), \fBicmpcode\fP (ICMP
811 code field), and \fBtcpflags\fP (TCP flags field).
813 The following ICMP type field values are available: \fBicmp-echoreply\fP,
814 \fBicmp-unreach\fP, \fBicmp-sourcequench\fP, \fBicmp-redirect\fP,
815 \fBicmp-echo\fP, \fBicmp-routeradvert\fP, \fBicmp-routersolicit\fP,
816 \fBicmp-timxceed\fP, \fBicmp-paramprob\fP, \fBicmp-tstamp\fP,
817 \fBicmp-tstampreply\fP, \fBicmp-ireq\fP, \fBicmp-ireqreply\fP,
818 \fBicmp-maskreq\fP, \fBicmp-maskreply\fP.
820 The following TCP flags field values are available: \fBtcp-fin\fP,
821 \fBtcp-syn\fP, \fBtcp-rst\fP, \fBtcp-push\fP, \fBtcp-push\fP,
822 \fBtcp-ack\fP, \fBtcp-urg\fP.
824 Primitives may be combined using:
826 A parenthesized group of primitives and operators
827 (parentheses are special to the Shell and must be escaped).
829 Negation (`\fB!\fP' or `\fBnot\fP').
831 Concatenation (`\fB&&\fP' or `\fBand\fP').
833 Alternation (`\fB||\fP' or `\fBor\fP').
835 Negation has highest precedence.
836 Alternation and concatenation have equal precedence and associate
838 Note that explicit \fBand\fR tokens, not juxtaposition,
839 are now required for concatenation.
841 If an identifier is given without a keyword, the most recent keyword
846 \fBnot host vs and ace\fR
852 \fBnot host vs and host ace\fR
855 which should not be confused with
858 \fBnot ( host vs or ace )\fR
862 Expression arguments can be passed to \fItcpdump\fP as either a single
863 argument or as multiple arguments, whichever is more convenient.
864 Generally, if the expression contains Shell metacharacters, it is
865 easier to pass it as a single, quoted argument.
866 Multiple arguments are concatenated with spaces before being parsed.
869 To print all packets arriving at or departing from \fIsundown\fP:
872 \fBtcpdump host sundown\fP
876 To print traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR:
879 \fBtcpdump host helios and \\( hot or ace \\)\fP
883 To print all IP packets between \fIace\fR and any host except \fIhelios\fR:
886 \fBtcpdump ip host ace and not helios\fP
890 To print all traffic between local hosts and hosts at Berkeley:
894 tcpdump net ucb-ether
898 To print all ftp traffic through internet gateway \fIsnup\fP:
899 (note that the expression is quoted to prevent the shell from
900 (mis-)interpreting the parentheses):
904 tcpdump 'gateway snup and (port ftp or ftp-data)'
908 To print traffic neither sourced from nor destined for local hosts
909 (if you gateway to one other net, this stuff should never make it
910 onto your local net).
914 tcpdump ip and not net \fIlocalnet\fP
918 To print the start and end packets (the SYN and FIN packets) of each
919 TCP conversation that involves a non-local host.
923 tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net \fIlocalnet\fP'
927 To print IP packets longer than 576 bytes sent through gateway \fIsnup\fP:
931 tcpdump 'gateway snup and ip[2:2] > 576'
935 To print IP broadcast or multicast packets that were
937 sent via ethernet broadcast or multicast:
941 tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'
945 To print all ICMP packets that are not echo requests/replies (i.e., not
950 tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'
955 The output of \fItcpdump\fP is protocol dependent.
957 gives a brief description and examples of most of the formats.
965 If the '-e' option is given, the link level header is printed out.
966 On ethernets, the source and destination addresses, protocol,
967 and packet length are printed.
969 On FDDI networks, the '-e' option causes \fItcpdump\fP to print
970 the `frame control' field, the source and destination addresses,
971 and the packet length.
972 (The `frame control' field governs the
973 interpretation of the rest of the packet.
975 as those containing IP datagrams) are `async' packets, with a priority
976 value between 0 and 7; for example, `\fBasync4\fR'.
978 are assumed to contain an 802.2 Logical Link Control (LLC) packet;
979 the LLC header is printed if it is \fInot\fR an ISO datagram or a
980 so-called SNAP packet.
982 On Token Ring networks, the '-e' option causes \fItcpdump\fP to print
983 the `access control' and `frame control' fields, the source and
984 destination addresses, and the packet length.
986 packets are assumed to contain an LLC packet.
987 Regardless of whether
988 the '-e' option is specified or not, the source routing information is
989 printed for source-routed packets.
991 \fI(N.B.: The following description assumes familiarity with
992 the SLIP compression algorithm described in RFC-1144.)\fP
994 On SLIP links, a direction indicator (``I'' for inbound, ``O'' for outbound),
995 packet type, and compression information are printed out.
996 The packet type is printed first.
997 The three types are \fIip\fP, \fIutcp\fP, and \fIctcp\fP.
998 No further link information is printed for \fIip\fR packets.
999 For TCP packets, the connection identifier is printed following the type.
1000 If the packet is compressed, its encoded header is printed out.
1001 The special cases are printed out as
1002 \fB*S+\fIn\fR and \fB*SA+\fIn\fR, where \fIn\fR is the amount by which
1003 the sequence number (or sequence number and ack) has changed.
1004 If it is not a special case,
1005 zero or more changes are printed.
1006 A change is indicated by U (urgent pointer), W (window), A (ack),
1007 S (sequence number), and I (packet ID), followed by a delta (+n or -n),
1008 or a new value (=n).
1009 Finally, the amount of data in the packet and compressed header length
1012 For example, the following line shows an outbound compressed TCP packet,
1013 with an implicit connection identifier; the ack has changed by 6,
1014 the sequence number by 49, and the packet ID by 6; there are 3 bytes of
1015 data and 6 bytes of compressed header:
1018 \fBO ctcp * A+6 S+49 I+6 3 (6)\fP
1024 Arp/rarp output shows the type of request and its arguments.
1026 format is intended to be self explanatory.
1027 Here is a short sample taken from the start of an `rlogin' from
1028 host \fIrtsg\fP to host \fIcsam\fP:
1032 \f(CWarp who-has csam tell rtsg
1033 arp reply csam is-at CSAM\fR
1037 The first line says that rtsg sent an arp packet asking
1038 for the ethernet address of internet host csam.
1040 replies with its ethernet address (in this example, ethernet addresses
1041 are in caps and internet addresses in lower case).
1043 This would look less redundant if we had done \fItcpdump \-n\fP:
1047 \f(CWarp who-has 128.3.254.6 tell 128.3.254.68
1048 arp reply 128.3.254.6 is-at 02:07:01:00:01:c4\fP
1052 If we had done \fItcpdump \-e\fP, the fact that the first packet is
1053 broadcast and the second is point-to-point would be visible:
1057 \f(CWRTSG Broadcast 0806 64: arp who-has csam tell rtsg
1058 CSAM RTSG 0806 64: arp reply csam is-at CSAM\fR
1062 For the first packet this says the ethernet source address is RTSG, the
1063 destination is the ethernet broadcast address, the type field
1064 contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes.
1068 \fI(N.B.:The following description assumes familiarity with
1069 the TCP protocol described in RFC-793.
1070 If you are not familiar
1071 with the protocol, neither this description nor \fItcpdump\fP will
1072 be of much use to you.)\fP
1074 The general format of a tcp protocol line is:
1078 \fIsrc > dst: flags data-seqno ack window urgent options\fP
1082 \fISrc\fP and \fIdst\fP are the source and destination IP
1083 addresses and ports.
1084 \fIFlags\fP are some combination of S (SYN),
1085 F (FIN), P (PUSH) or R (RST) or a single `.' (no flags).
1086 \fIData-seqno\fP describes the portion of sequence space covered
1087 by the data in this packet (see example below).
1088 \fIAck\fP is sequence number of the next data expected the other
1089 direction on this connection.
1090 \fIWindow\fP is the number of bytes of receive buffer space available
1091 the other direction on this connection.
1092 \fIUrg\fP indicates there is `urgent' data in the packet.
1093 \fIOptions\fP are tcp options enclosed in angle brackets (e.g., <mss 1024>).
1095 \fISrc, dst\fP and \fIflags\fP are always present.
1097 depend on the contents of the packet's tcp protocol header and
1098 are output only if appropriate.
1100 Here is the opening portion of an rlogin from host \fIrtsg\fP to
1105 \s-2\f(CWrtsg.1023 > csam.login: S 768512:768512(0) win 4096 <mss 1024>
1106 csam.login > rtsg.1023: S 947648:947648(0) ack 768513 win 4096 <mss 1024>
1107 rtsg.1023 > csam.login: . ack 1 win 4096
1108 rtsg.1023 > csam.login: P 1:2(1) ack 1 win 4096
1109 csam.login > rtsg.1023: . ack 2 win 4096
1110 rtsg.1023 > csam.login: P 2:21(19) ack 1 win 4096
1111 csam.login > rtsg.1023: P 1:2(1) ack 21 win 4077
1112 csam.login > rtsg.1023: P 2:3(1) ack 21 win 4077 urg 1
1113 csam.login > rtsg.1023: P 3:4(1) ack 21 win 4077 urg 1\fR\s+2
1117 The first line says that tcp port 1023 on rtsg sent a packet
1120 The \fBS\fP indicates that the \fISYN\fP flag was set.
1121 The packet sequence number was 768512 and it contained no data.
1122 (The notation is `first:last(nbytes)' which means `sequence
1124 up to but not including \fIlast\fP which is \fInbytes\fP bytes of user data'.)
1125 There was no piggy-backed ack, the available receive window was 4096
1126 bytes and there was a max-segment-size option requesting an mss of
1129 Csam replies with a similar packet except it includes a piggy-backed
1131 Rtsg then acks csam's SYN.
1134 The packet contained no data so there is no data sequence number.
1135 Note that the ack sequence
1136 number is a small integer (1).
1137 The first time \fItcpdump\fP sees a
1138 tcp `conversation', it prints the sequence number from the packet.
1139 On subsequent packets of the conversation, the difference between
1140 the current packet's sequence number and this initial sequence number
1142 This means that sequence numbers after the
1143 first can be interpreted
1144 as relative byte positions in the conversation's data stream (with the
1145 first data byte each direction being `1').
1146 `-S' will override this
1147 feature, causing the original sequence numbers to be output.
1149 On the 6th line, rtsg sends csam 19 bytes of data (bytes 2 through 20
1150 in the rtsg \(-> csam side of the conversation).
1151 The PUSH flag is set in the packet.
1152 On the 7th line, csam says it's received data sent by rtsg up to
1153 but not including byte 21.
1154 Most of this data is apparently sitting in the
1155 socket buffer since csam's receive window has gotten 19 bytes smaller.
1156 Csam also sends one byte of data to rtsg in this packet.
1157 On the 8th and 9th lines,
1158 csam sends two bytes of urgent, pushed data to rtsg.
1160 If the snapshot was small enough that \fItcpdump\fP didn't capture
1161 the full TCP header, it interprets as much of the header as it can
1162 and then reports ``[|\fItcp\fP]'' to indicate the remainder could not
1164 If the header contains a bogus option (one with a length
1165 that's either too small or beyond the end of the header), \fItcpdump\fP
1166 reports it as ``[\fIbad opt\fP]'' and does not interpret any further
1167 options (since it's impossible to tell where they start).
1169 length indicates options are present but the IP datagram length is not
1170 long enough for the options to actually be there, \fItcpdump\fP reports
1171 it as ``[\fIbad hdr length\fP]''.
1173 .B Capturing TCP packets with particular flag combinations (SYN-ACK, URG-ACK, etc.)
1175 There are 8 bits in the control bits section of the TCP header:
1177 .I CWR | ECE | URG | ACK | PSH | RST | SYN | FIN
1179 Let's assume that we want to watch packets used in establishing
1181 Recall that TCP uses a 3-way handshake protocol
1182 when it initializes a new connection; the connection sequence with
1183 regard to the TCP control bits is
1189 2) Recipient responds with SYN, ACK
1195 Now we're interested in capturing packets that have only the
1196 SYN bit set (Step 1).
1197 Note that we don't want packets from step 2
1198 (SYN-ACK), just a plain initial SYN.
1199 What we need is a correct filter
1200 expression for \fItcpdump\fP.
1202 Recall the structure of a TCP header without options:
1206 -----------------------------------------------------------------
1207 | source port | destination port |
1208 -----------------------------------------------------------------
1210 -----------------------------------------------------------------
1211 | acknowledgment number |
1212 -----------------------------------------------------------------
1213 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1214 -----------------------------------------------------------------
1215 | TCP checksum | urgent pointer |
1216 -----------------------------------------------------------------
1219 A TCP header usually holds 20 octets of data, unless options are
1221 The first line of the graph contains octets 0 - 3, the
1222 second line shows octets 4 - 7 etc.
1224 Starting to count with 0, the relevant TCP control bits are contained
1229 ----------------|---------------|---------------|----------------
1230 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1231 ----------------|---------------|---------------|----------------
1232 | | 13th octet | | |
1235 Let's have a closer look at octet no. 13:
1245 These are the TCP control bits we are interested
1247 We have numbered the bits in this octet from 0 to 7, right to
1248 left, so the PSH bit is bit number 3, while the URG bit is number 5.
1250 Recall that we want to capture packets with only SYN set.
1251 Let's see what happens to octet 13 if a TCP datagram arrives
1252 with the SYN bit set in its header:
1263 control bits section we see that only bit number 1 (SYN) is set.
1265 Assuming that octet number 13 is an 8-bit unsigned integer in
1266 network byte order, the binary value of this octet is
1270 and its decimal representation is
1274 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 1*2 + 0*2 = 2
1277 We're almost done, because now we know that if only SYN is set,
1278 the value of the 13th octet in the TCP header, when interpreted
1279 as a 8-bit unsigned integer in network byte order, must be exactly 2.
1281 This relationship can be expressed as
1287 We can use this expression as the filter for \fItcpdump\fP in order
1288 to watch packets which have only SYN set:
1291 tcpdump -i xl0 tcp[13] == 2
1294 The expression says "let the 13th octet of a TCP datagram have
1295 the decimal value 2", which is exactly what we want.
1297 Now, let's assume that we need to capture SYN packets, but we
1298 don't care if ACK or any other TCP control bit is set at the
1300 Let's see what happens to octet 13 when a TCP datagram
1301 with SYN-ACK set arrives:
1311 Now bits 1 and 4 are set in the 13th octet.
1317 which translates to decimal
1321 0*2 + 0*2 + 0*2 + 1*2 + 0*2 + 0*2 + 1*2 + 0*2 = 18
1324 Now we can't just use 'tcp[13] == 18' in the \fItcpdump\fP filter
1325 expression, because that would select only those packets that have
1326 SYN-ACK set, but not those with only SYN set.
1327 Remember that we don't care
1328 if ACK or any other control bit is set as long as SYN is set.
1330 In order to achieve our goal, we need to logically AND the
1331 binary value of octet 13 with some other value to preserve
1333 We know that we want SYN to be set in any case,
1334 so we'll logically AND the value in the 13th octet with
1335 the binary value of a SYN:
1339 00010010 SYN-ACK 00000010 SYN
1340 AND 00000010 (we want SYN) AND 00000010 (we want SYN)
1342 = 00000010 = 00000010
1345 We see that this AND operation delivers the same result
1346 regardless whether ACK or another TCP control bit is set.
1347 The decimal representation of the AND value as well as
1348 the result of this operation is 2 (binary 00000010),
1349 so we know that for packets with SYN set the following
1350 relation must hold true:
1352 ( ( value of octet 13 ) AND ( 2 ) ) == ( 2 )
1354 This points us to the \fItcpdump\fP filter expression
1357 tcpdump -i xl0 'tcp[13] & 2 == 2'
1360 Note that you should use single quotes or a backslash
1361 in the expression to hide the AND ('&') special character
1367 UDP format is illustrated by this rwho packet:
1371 \f(CWactinide.who > broadcast.who: udp 84\fP
1375 This says that port \fIwho\fP on host \fIactinide\fP sent a udp
1376 datagram to port \fIwho\fP on host \fIbroadcast\fP, the Internet
1378 The packet contained 84 bytes of user data.
1380 Some UDP services are recognized (from the source or destination
1381 port number) and the higher level protocol information printed.
1382 In particular, Domain Name service requests (RFC-1034/1035) and Sun
1383 RPC calls (RFC-1050) to NFS.
1385 UDP Name Server Requests
1387 \fI(N.B.:The following description assumes familiarity with
1388 the Domain Service protocol described in RFC-1035.
1389 If you are not familiar
1390 with the protocol, the following description will appear to be written
1393 Name server requests are formatted as
1397 \fIsrc > dst: id op? flags qtype qclass name (len)\fP
1399 \f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fR
1403 Host \fIh2opolo\fP asked the domain server on \fIhelios\fP for an
1404 address record (qtype=A) associated with the name \fIucbvax.berkeley.edu.\fP
1405 The query id was `3'.
1406 The `+' indicates the \fIrecursion desired\fP flag
1408 The query length was 37 bytes, not including the UDP and
1409 IP protocol headers.
1410 The query operation was the normal one, \fIQuery\fP,
1411 so the op field was omitted.
1412 If the op had been anything else, it would
1413 have been printed between the `3' and the `+'.
1414 Similarly, the qclass was the normal one,
1415 \fIC_IN\fP, and omitted.
1416 Any other qclass would have been printed
1417 immediately after the `A'.
1419 A few anomalies are checked and may result in extra fields enclosed in
1420 square brackets: If a query contains an answer, authority records or
1421 additional records section,
1426 are printed as `[\fIn\fPa]', `[\fIn\fPn]' or `[\fIn\fPau]' where \fIn\fP
1427 is the appropriate count.
1428 If any of the response bits are set (AA, RA or rcode) or any of the
1429 `must be zero' bits are set in bytes two and three, `[b2&3=\fIx\fP]'
1430 is printed, where \fIx\fP is the hex value of header bytes two and three.
1432 UDP Name Server Responses
1434 Name server responses are formatted as
1438 \fIsrc > dst: id op rcode flags a/n/au type class data (len)\fP
1440 \f(CWhelios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273)
1441 helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fR
1445 In the first example, \fIhelios\fP responds to query id 3 from \fIh2opolo\fP
1446 with 3 answer records, 3 name server records and 7 additional records.
1447 The first answer record is type A (address) and its data is internet
1448 address 128.32.137.3.
1449 The total size of the response was 273 bytes,
1450 excluding UDP and IP headers.
1451 The op (Query) and response code
1452 (NoError) were omitted, as was the class (C_IN) of the A record.
1454 In the second example, \fIhelios\fP responds to query 2 with a
1455 response code of non-existent domain (NXDomain) with no answers,
1456 one name server and no authority records.
1457 The `*' indicates that
1458 the \fIauthoritative answer\fP bit was set.
1460 answers, no type, class or data were printed.
1462 Other flag characters that might appear are `\-' (recursion available,
1463 RA, \fInot\fP set) and `|' (truncated message, TC, set).
1465 `question' section doesn't contain exactly one entry, `[\fIn\fPq]'
1468 Note that name server requests and responses tend to be large and the
1469 default \fIsnaplen\fP of 68 bytes may not capture enough of the packet
1471 Use the \fB\-s\fP flag to increase the snaplen if you
1472 need to seriously investigate name server traffic.
1474 has worked well for me.
1479 \fItcpdump\fP now includes fairly extensive SMB/CIFS/NBT decoding for data
1480 on UDP/137, UDP/138 and TCP/139.
1481 Some primitive decoding of IPX and
1482 NetBEUI SMB data is also done.
1484 By default a fairly minimal decode is done, with a much more detailed
1485 decode done if -v is used.
1486 Be warned that with -v a single SMB packet
1487 may take up a page or more, so only use -v if you really want all the
1490 If you are decoding SMB sessions containing unicode strings then you
1491 may wish to set the environment variable USE_UNICODE to 1.
1493 auto-detect unicode srings would be welcome.
1495 For information on SMB packet formats and what all te fields mean see
1496 www.cifs.org or the pub/samba/specs/ directory on your favourite
1497 samba.org mirror site.
1498 The SMB patches were written by Andrew Tridgell
1502 NFS Requests and Replies
1504 Sun NFS (Network File System) requests and replies are printed as:
1508 \fIsrc.xid > dst.nfs: len op args\fP
1509 \fIsrc.nfs > dst.xid: reply stat len op results\fP
1512 sushi.6709 > wrl.nfs: 112 readlink fh 21,24/10.73165
1513 wrl.nfs > sushi.6709: reply ok 40 readlink "../var"
1514 sushi.201b > wrl.nfs:
1515 144 lookup fh 9,74/4096.6878 "xcolors"
1516 wrl.nfs > sushi.201b:
1517 reply ok 128 lookup fh 9,74/4134.3150
1522 In the first line, host \fIsushi\fP sends a transaction with id \fI6709\fP
1523 to \fIwrl\fP (note that the number following the src host is a
1524 transaction id, \fInot\fP the source port).
1525 The request was 112 bytes,
1526 excluding the UDP and IP headers.
1527 The operation was a \fIreadlink\fP
1528 (read symbolic link) on file handle (\fIfh\fP) 21,24/10.731657119.
1529 (If one is lucky, as in this case, the file handle can be interpreted
1530 as a major,minor device number pair, followed by the inode number and
1532 \fIWrl\fP replies `ok' with the contents of the link.
1534 In the third line, \fIsushi\fP asks \fIwrl\fP to lookup the name
1535 `\fIxcolors\fP' in directory file 9,74/4096.6878.
1536 Note that the data printed
1537 depends on the operation type.
1538 The format is intended to be self
1539 explanatory if read in conjunction with
1540 an NFS protocol spec.
1542 If the \-v (verbose) flag is given, additional information is printed.
1548 sushi.1372a > wrl.nfs:
1549 148 read fh 21,11/12.195 8192 bytes @ 24576
1550 wrl.nfs > sushi.1372a:
1551 reply ok 1472 read REG 100664 ids 417/0 sz 29388
1556 (\-v also prints the IP header TTL, ID, length, and fragmentation fields,
1557 which have been omitted from this example.) In the first line,
1558 \fIsushi\fP asks \fIwrl\fP to read 8192 bytes from file 21,11/12.195,
1559 at byte offset 24576.
1560 \fIWrl\fP replies `ok'; the packet shown on the
1561 second line is the first fragment of the reply, and hence is only 1472
1562 bytes long (the other bytes will follow in subsequent fragments, but
1563 these fragments do not have NFS or even UDP headers and so might not be
1564 printed, depending on the filter expression used).
1565 Because the \-v flag
1566 is given, some of the file attributes (which are returned in addition
1567 to the file data) are printed: the file type (``REG'', for regular file),
1568 the file mode (in octal), the uid and gid, and the file size.
1570 If the \-v flag is given more than once, even more details are printed.
1572 Note that NFS requests are very large and much of the detail won't be printed
1573 unless \fIsnaplen\fP is increased.
1574 Try using `\fB\-s 192\fP' to watch
1577 NFS reply packets do not explicitly identify the RPC operation.
1579 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1580 replies using the transaction ID.
1581 If a reply does not closely follow the
1582 corresponding request, it might not be parsable.
1584 AFS Requests and Replies
1586 Transarc AFS (Andrew File System) requests and replies are printed
1592 \fIsrc.sport > dst.dport: rx packet-type\fP
1593 \fIsrc.sport > dst.dport: rx packet-type service call call-name args\fP
1594 \fIsrc.sport > dst.dport: rx packet-type service reply call-name args\fP
1597 elvis.7001 > pike.afsfs:
1598 rx data fs call rename old fid 536876964/1/1 ".newsrc.new"
1599 new fid 536876964/1/1 ".newsrc"
1600 pike.afsfs > elvis.7001: rx data fs reply rename
1605 In the first line, host elvis sends a RX packet to pike.
1607 a RX data packet to the fs (fileserver) service, and is the start of
1609 The RPC call was a rename, with the old directory file id
1610 of 536876964/1/1 and an old filename of `.newsrc.new', and a new directory
1611 file id of 536876964/1/1 and a new filename of `.newsrc'.
1613 responds with a RPC reply to the rename call (which was successful, because
1614 it was a data packet and not an abort packet).
1616 In general, all AFS RPCs are decoded at least by RPC call name.
1618 AFS RPCs have at least some of the arguments decoded (generally only
1619 the `interesting' arguments, for some definition of interesting).
1621 The format is intended to be self-describing, but it will probably
1622 not be useful to people who are not familiar with the workings of
1625 If the -v (verbose) flag is given twice, acknowledgement packets and
1626 additional header information is printed, such as the the RX call ID,
1627 call number, sequence number, serial number, and the RX packet flags.
1629 If the -v flag is given twice, additional information is printed,
1630 such as the the RX call ID, serial number, and the RX packet flags.
1631 The MTU negotiation information is also printed from RX ack packets.
1633 If the -v flag is given three times, the security index and service id
1636 Error codes are printed for abort packets, with the exception of Ubik
1637 beacon packets (because abort packets are used to signify a yes vote
1638 for the Ubik protocol).
1640 Note that AFS requests are very large and many of the arguments won't
1641 be printed unless \fIsnaplen\fP is increased.
1642 Try using `\fB-s 256\fP'
1643 to watch AFS traffic.
1645 AFS reply packets do not explicitly identify the RPC operation.
1647 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1648 replies using the call number and service ID.
1649 If a reply does not closely
1651 corresponding request, it might not be parsable.
1654 KIP Appletalk (DDP in UDP)
1656 Appletalk DDP packets encapsulated in UDP datagrams are de-encapsulated
1657 and dumped as DDP packets (i.e., all the UDP header information is
1661 is used to translate appletalk net and node numbers to names.
1662 Lines in this file have the form
1674 The first two lines give the names of appletalk networks.
1676 line gives the name of a particular host (a host is distinguished
1677 from a net by the 3rd octet in the number \-
1678 a net number \fImust\fP have two octets and a host number \fImust\fP
1679 have three octets.) The number and name should be separated by
1680 whitespace (blanks or tabs).
1683 file may contain blank lines or comment lines (lines starting with
1686 Appletalk addresses are printed in the form
1692 \f(CW144.1.209.2 > icsd-net.112.220
1693 office.2 > icsd-net.112.220
1694 jssmag.149.235 > icsd-net.2\fR
1700 doesn't exist or doesn't contain an entry for some appletalk
1701 host/net number, addresses are printed in numeric form.)
1702 In the first example, NBP (DDP port 2) on net 144.1 node 209
1703 is sending to whatever is listening on port 220 of net icsd node 112.
1704 The second line is the same except the full name of the source node
1705 is known (`office').
1706 The third line is a send from port 235 on
1707 net jssmag node 149 to broadcast on the icsd-net NBP port (note that
1708 the broadcast address (255) is indicated by a net name with no host
1709 number \- for this reason it's a good idea to keep node names and
1710 net names distinct in /etc/atalk.names).
1712 NBP (name binding protocol) and ATP (Appletalk transaction protocol)
1713 packets have their contents interpreted.
1714 Other protocols just dump
1715 the protocol name (or number if no name is registered for the
1716 protocol) and packet size.
1718 \fBNBP packets\fP are formatted like the following examples:
1722 \s-2\f(CWicsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
1723 jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
1724 techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fR\s+2
1728 The first line is a name lookup request for laserwriters sent by net icsd host
1729 112 and broadcast on net jssmag.
1730 The nbp id for the lookup is 190.
1731 The second line shows a reply for this request (note that it has the
1732 same id) from host jssmag.209 saying that it has a laserwriter
1733 resource named "RM1140" registered on port 250.
1735 another reply to the same request saying host techpit has laserwriter
1736 "techpit" registered on port 186.
1738 \fBATP packet\fP formatting is demonstrated by the following example:
1742 \s-2\f(CWjssmag.209.165 > helios.132: atp-req 12266<0-7> 0xae030001
1743 helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
1744 helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
1745 helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
1746 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1747 helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
1748 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1749 helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
1750 helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
1751 jssmag.209.165 > helios.132: atp-req 12266<3,5> 0xae030001
1752 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1753 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1754 jssmag.209.165 > helios.132: atp-rel 12266<0-7> 0xae030001
1755 jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fR\s+2
1759 Jssmag.209 initiates transaction id 12266 with host helios by requesting
1760 up to 8 packets (the `<0-7>').
1761 The hex number at the end of the line
1762 is the value of the `userdata' field in the request.
1764 Helios responds with 8 512-byte packets.
1765 The `:digit' following the
1766 transaction id gives the packet sequence number in the transaction
1767 and the number in parens is the amount of data in the packet,
1768 excluding the atp header.
1769 The `*' on packet 7 indicates that the
1772 Jssmag.209 then requests that packets 3 & 5 be retransmitted.
1774 resends them then jssmag.209 releases the transaction.
1776 jssmag.209 initiates the next request.
1777 The `*' on the request
1778 indicates that XO (`exactly once') was \fInot\fP set.
1783 Fragmented Internet datagrams are printed as
1787 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR
1788 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR
1792 (The first form indicates there are more fragments.
1794 indicates this is the last fragment.)
1796 \fIId\fP is the fragment id.
1797 \fISize\fP is the fragment
1798 size (in bytes) excluding the IP header.
1799 \fIOffset\fP is this
1800 fragment's offset (in bytes) in the original datagram.
1802 The fragment information is output for each fragment.
1804 fragment contains the higher level protocol header and the frag
1805 info is printed after the protocol info.
1807 after the first contain no higher level protocol header and the
1808 frag info is printed after the source and destination addresses.
1809 For example, here is part of an ftp from arizona.edu to lbl-rtsg.arpa
1810 over a CSNET connection that doesn't appear to handle 576 byte datagrams:
1814 \s-2\f(CWarizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+)
1815 arizona > rtsg: (frag 595a:204@328)
1816 rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2
1820 There are a couple of things to note here: First, addresses in the
1821 2nd line don't include port numbers.
1822 This is because the TCP
1823 protocol information is all in the first fragment and we have no idea
1824 what the port or sequence numbers are when we print the later fragments.
1825 Second, the tcp sequence information in the first line is printed as if there
1826 were 308 bytes of user data when, in fact, there are 512 bytes (308 in
1827 the first frag and 204 in the second).
1828 If you are looking for holes
1829 in the sequence space or trying to match up acks
1830 with packets, this can fool you.
1832 A packet with the IP \fIdon't fragment\fP flag is marked with a
1833 trailing \fB(DF)\fP.
1837 By default, all output lines are preceded by a timestamp.
1839 is the current clock time in the form
1845 and is as accurate as the kernel's clock.
1846 The timestamp reflects the time the kernel first saw the packet.
1848 is made to account for the time lag between when the
1849 ethernet interface removed the packet from the wire and when the kernel
1850 serviced the `new packet' interrupt.
1852 traffic(1C), nit(4P), bpf(4), pcap(3)
1854 The original authors are:
1858 Steven McCanne, all of the
1859 Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
1861 It is currently being maintained by tcpdump.org.
1863 The current version is available via http:
1866 .I http://www.tcpdump.org/
1869 The original distribution is available via anonymous ftp:
1872 .I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z
1875 IPv6/IPsec support is added by WIDE/KAME project.
1876 This program uses Eric Young's SSLeay library, under specific configuration.
1878 Please send problems, bugs, questions, desirable enhancements, etc. to:
1881 tcpdump-workers@tcpdump.org
1884 Please send source code contributions, etc. to:
1890 NIT doesn't let you watch your own outbound traffic, BPF will.
1891 We recommend that you use the latter.
1893 On Linux systems with 2.0[.x] kernels:
1895 packets on the loopback device will be seen twice;
1897 packet filtering cannot be done in the kernel, so that all packets must
1898 be copied from the kernel in order to be filtered in user mode;
1900 all of a packet, not just the part that's within the snapshot length,
1901 will be copied from the kernel (the 2.0[.x] packet capture mechanism, if
1902 asked to copy only part of a packet to userland, will not report the
1903 true length of the packet; this would cause most IP packets to get an
1907 capturing on some PPP devices won't work correctly.
1909 We recommend that you upgrade to a 2.2 or later kernel.
1911 Some attempt should be made to reassemble IP fragments or, at least
1912 to compute the right length for the higher level protocol.
1914 Name server inverse queries are not dumped correctly: the (empty)
1915 question section is printed rather than real query in the answer
1917 Some believe that inverse queries are themselves a bug and
1918 prefer to fix the program generating them rather than \fItcpdump\fP.
1920 A packet trace that crosses a daylight savings time change will give
1921 skewed time stamps (the time change is ignored).
1923 Filter expressions that manipulate FDDI or Token Ring headers assume
1924 that all FDDI and Token Ring packets are SNAP-encapsulated Ethernet
1926 This is true for IP, ARP, and DECNET Phase IV, but is not true
1927 for protocols such as ISO CLNS.
1928 Therefore, the filter may inadvertently
1929 accept certain packets that do not properly match the filter expression.
1931 Filter expressions on fields other than those that manipulate Token Ring
1932 headers will not correctly handle source-routed Token Ring packets.
1935 should chase header chain, but at this moment it does not.
1936 .BR "ip6 protochain"
1937 is supplied for this behavior.
1939 Arithmetic expression against transport layer headers, like \fBtcp[0]\fP,
1940 does not work against IPv6 packets.
1941 It only looks at IPv4 packets.
projects / tcpdump / blob