1 .\" @(#) $Header: /tcpdump/master/tcpdump/tcpdump.1,v 1.148.2.6 2004/03/28 21:25:03 fenner Exp $ (LBL)
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27 .TH TCPDUMP 1 "7 January 2004"
29 tcpdump \- dump traffic on a network
34 .B \-AdDeflLnNOpqRStuUvxX
80 .I spi@ipaddr algo:secret,...
101 \fITcpdump\fP prints out the headers of packets on a network interface
102 that match the boolean \fIexpression\fP. It can also be run with the
104 flag, which causes it to save the packet data to a file for later
105 analysis, and/or with the
107 flag, which causes it to read from a saved packet file rather than to
108 read packets from a network interface. In all cases, only packets that
115 will, if not run with the
117 flag, continue capturing packets until it is interrupted by a SIGINT
118 signal (generated, for example, by typing your interrupt character,
119 typically control-C) or a SIGTERM signal (typically generated with the
121 command); if run with the
123 flag, it will capture packets until it is interrupted by a SIGINT or
124 SIGTERM signal or the specified number of packets have been processed.
128 finishes capturing packets, it will report counts of:
130 packets ``captured'' (this is the number of packets that
132 has received and processed);
134 packets ``received by filter'' (the meaning of this depends on the OS on
137 and possibly on the way the OS was configured - if a filter was
138 specified on the command line, on some OSes it counts packets regardless
139 of whether they were matched by the filter expression and, even if they
140 were matched by the filter expression, regardless of whether
142 has read and processed them yet, on other OSes it counts only packets that were
143 matched by the filter expression regardless of whether
145 has read and processed them yet, and on other OSes it counts only
146 packets that were matched by the filter expression and were processed by
149 packets ``dropped by kernel'' (this is the number of packets that were
150 dropped, due to a lack of buffer space, by the packet capture mechanism
153 is running, if the OS reports that information to applications; if not,
154 it will be reported as 0).
156 On platforms that support the SIGINFO signal, such as most BSDs
157 (including Mac OS X) and Digital/Tru64 UNIX, it will report those counts
158 when it receives a SIGINFO signal (generated, for example, by typing
159 your ``status'' character, typically control-T, although on some
160 platforms, such as Mac OS X, the ``status'' character is not set by
161 default, so you must set it with
163 in order to use it) and will continue capturing packets.
165 Reading packets from a network interface may require that you have
168 .B Under SunOS 3.x or 4.x with NIT or BPF:
169 You must have read access to
174 .B Under Solaris with DLPI:
175 You must have read/write access to the network pseudo device, e.g.
177 On at least some versions of Solaris, however, this is not sufficient to
180 to capture in promiscuous mode; on those versions of Solaris, you must
183 must be installed setuid to root, in order to capture in promiscuous
184 mode. Note that, on many (perhaps all) interfaces, if you don't capture
185 in promiscuous mode, you will not see any outgoing packets, so a capture
186 not done in promiscuous mode may not be very useful.
188 .B Under HP-UX with DLPI:
191 must be installed setuid to root.
193 .B Under IRIX with snoop:
196 must be installed setuid to root.
201 must be installed setuid to root (unless your distribution has a kernel
202 that supports capability bits such as CAP_NET_RAW and code to allow
203 those capability bits to be given to particular accounts and to cause
204 those bits to be set on a user's initial processes when they log in, in
205 which case you must have CAP_NET_RAW in order to capture and
206 CAP_NET_ADMIN to enumerate network devices with, for example, the
210 .B Under ULTRIX and Digital UNIX/Tru64 UNIX:
211 Any user may capture network traffic with
213 However, no user (not even the super-user) can capture in promiscuous
214 mode on an interface unless the super-user has enabled promiscuous-mode
215 operation on that interface using
217 and no user (not even the super-user) can capture unicast traffic
218 received by or sent by the machine on an interface unless the super-user
219 has enabled copy-all-mode operation on that interface using
223 packet capture on an interface probably requires that either
224 promiscuous-mode or copy-all-mode operation, or both modes of
225 operation, be enabled on that interface.
227 .B Under BSD (this includes Mac OS X):
228 You must have read access to
230 On BSDs with a devfs (this includes Mac OS X), this might involve more
231 than just having somebody with super-user access setting the ownership
232 or permissions on the BPF devices - it might involve configuring devfs
233 to set the ownership or permissions every time the system is booted,
234 if the system even supports that; if it doesn't support that, you might
235 have to find some other way to make that happen at boot time.
237 Reading a saved packet file doesn't require special privileges.
241 Print each packet (minus its link level header) in ASCII. Handy for
245 Exit after receiving \fIcount\fP packets.
248 Before writing a raw packet to a savefile, check whether the file is
249 currently larger than \fIfile_size\fP and, if so, close the current
250 savefile and open a new one. Savefiles after the first savefile will
251 have the name specified with the
253 flag, with a number after it, starting at 2 and continuing upward.
254 The units of \fIfile_size\fP are millions of bytes (1,000,000 bytes,
255 not 1,048,576 bytes).
258 Dump the compiled packet-matching code in a human readable form to
259 standard output and stop.
262 Dump packet-matching code as a
267 Dump packet-matching code as decimal numbers (preceded with a count).
270 Print the list of the network interfaces available on the system and on
273 can capture packets. For each network interface, a number and an
274 interface name, possibly followed by a text description of the
275 interface, is printed. The interface name or the number can be supplied
278 flag to specify an interface on which to capture.
280 This can be useful on systems that don't have a command to list them
281 (e.g., Windows systems, or UNIX systems lacking
282 .BR "ifconfig \-a" );
283 the number can be useful on Windows 2000 and later systems, where the
284 interface name is a somewhat complex string.
288 flag will not be supported if
290 was built with an older version of
293 .B pcap_findalldevs()
297 Print the link-level header on each dump line.
300 Use \fIspi@ipaddr algo:secret\fP for decrypting IPsec ESP packets that
301 are addressed to \fIaddr\fP and contain Security Parameter Index value
302 \fIspi\fP. This combination may be repeated with comma or newline seperation.
304 Note that setting the secret for IPv4 ESP packets is supported at this time.
311 \fBcast128-cbc\fP, or
313 The default is \fBdes-cbc\fP.
314 The ability to decrypt packets is only present if \fItcpdump\fP was compiled
315 with cryptography enabled.
317 \fIsecret\fP is the ASCII text for ESP secret key.
318 If preceeded by 0x, then a hex value will be read.
320 The option assumes RFC2406 ESP, not RFC1827 ESP.
321 The option is only for debugging purposes, and
322 the use of this option with a true `secret' key is discouraged.
323 By presenting IPsec secret key onto command line
324 you make it visible to others, via
328 In addition to the above syntax, the syntax \fIfile name\fP may be used
329 to have tcpdump read the provided file in. The file is opened upon
330 receiving the first ESP packet, so any special permissions that tcpdump
331 may have been given should already have been given up.
334 Print `foreign' IPv4 addresses numerically rather than symbolically
335 (this option is intended to get around serious brain damage in
336 Sun's NIS server \(em usually it hangs forever translating non-local
339 The test for `foreign' IPv4 addresses is done using the IPv4 address and
340 netmask of the interface on which capture is being done. If that
341 address or netmask are not available, available, either because the
342 interface on which capture is being done has no address or netmask or
343 because the capture is being done on the Linux "any" interface, which
344 can capture on more than one interface, this option will not work
348 Use \fIfile\fP as input for the filter expression.
349 An additional expression given on the command line is ignored.
352 Listen on \fIinterface\fP.
353 If unspecified, \fItcpdump\fP searches the system interface list for the
354 lowest numbered, configured up interface (excluding loopback).
355 Ties are broken by choosing the earliest match.
357 On Linux systems with 2.2 or later kernels, an
359 argument of ``any'' can be used to capture packets from all interfaces.
360 Note that captures on the ``any'' device will not be done in promiscuous
365 flag is supported, an interface number as printed by that flag can be
371 Make stdout line buffered.
372 Useful if you want to see the data
376 ``tcpdump\ \ \-l\ \ |\ \ tee dat'' or
377 ``tcpdump\ \ \-l \ \ > dat\ \ &\ \ tail\ \ \-f\ \ dat''.
380 List the known data link types for the interface and exit.
383 Load SMI MIB module definitions from file \fImodule\fR.
385 can be used several times to load several MIB modules into \fItcpdump\fP.
388 Don't convert addresses (i.e., host addresses, port numbers, etc.) to names.
391 Don't print domain name qualification of host names.
393 if you give this flag then \fItcpdump\fP will print ``nic''
394 instead of ``nic.ddn.mil''.
397 Do not run the packet-matching code optimizer.
399 if you suspect a bug in the optimizer.
402 \fIDon't\fP put the interface
403 into promiscuous mode.
404 Note that the interface might be in promiscuous
405 mode for some other reason; hence, `-p' cannot be used as an abbreviation for
406 `ether host {local-hw-addr} or ether broadcast'.
409 Quick (quiet?) output.
410 Print less protocol information so output
414 Assume ESP/AH packets to be based on old specification (RFC1825 to RFC1829).
415 If specified, \fItcpdump\fP will not print replay prevention field.
416 Since there is no protocol version field in ESP/AH specification,
417 \fItcpdump\fP cannot deduce the version of ESP/AH protocol.
420 Read packets from \fIfile\fR (which was created with the
423 Standard input is used if \fIfile\fR is ``-''.
426 Print absolute, rather than relative, TCP sequence numbers.
429 Snarf \fIsnaplen\fP bytes of data from each packet rather than the
430 default of 68 (with SunOS's NIT, the minimum is actually 96).
431 68 bytes is adequate for IP, ICMP, TCP
432 and UDP but may truncate protocol information from name server and NFS
434 Packets truncated because of a limited snapshot
435 are indicated in the output with ``[|\fIproto\fP]'', where \fIproto\fP
436 is the name of the protocol level at which the truncation has occurred.
437 Note that taking larger snapshots both increases
438 the amount of time it takes to process packets and, effectively,
439 decreases the amount of packet buffering.
440 This may cause packets to be
442 You should limit \fIsnaplen\fP to the smallest number that will
443 capture the protocol information you're interested in.
445 \fIsnaplen\fP to 0 means use the required length to catch whole packets.
448 Force packets selected by "\fIexpression\fP" to be interpreted the
449 specified \fItype\fR.
450 Currently known types are
451 \fBaodv\fR (Ad-hoc On-demand Distance Vector protocol),
452 \fBcnfp\fR (Cisco NetFlow protocol),
453 \fBrpc\fR (Remote Procedure Call),
454 \fBrtp\fR (Real-Time Applications protocol),
455 \fBrtcp\fR (Real-Time Applications control protocol),
456 \fBsnmp\fR (Simple Network Management Protocol),
457 \fBtftp\fR (Trivial File Transfer Protocol),
458 \fBvat\fR (Visual Audio Tool),
460 \fBwb\fR (distributed White Board).
463 \fIDon't\fP print a timestamp on each dump line.
466 Print an unformatted timestamp on each dump line.
469 Print a delta (in micro-seconds) between current and previous line
473 Print a timestamp in default format proceeded by date on each dump line.
476 Print undecoded NFS handles.
479 Make output saved via the
481 option ``packet-buffered''; i.e., as each packet is saved, it will be
482 written to the output file, rather than being written only when the
487 flag will not be supported if
489 was built with an older version of
496 (Slightly more) verbose output.
497 For example, the time to live,
498 identification, total length and options in an IP packet are printed.
499 Also enables additional packet integrity checks such as verifying the
500 IP and ICMP header checksum.
503 Even more verbose output.
504 For example, additional fields are
505 printed from NFS reply packets, and SMB packets are fully decoded.
508 Even more verbose output.
510 telnet \fBSB\fP ... \fBSE\fP options
514 Telnet options are printed in hex as well.
517 Write the raw packets to \fIfile\fR rather than parsing and printing
519 They can later be printed with the \-r option.
520 Standard output is used if \fIfile\fR is ``-''.
523 Print each packet (minus its link level header) in hex.
524 The smaller of the entire packet or
526 bytes will be printed. Note that this is the entire link-layer
527 packet, so for link layers that pad (e.g. Ethernet), the padding bytes
528 will also be printed when the higher layer packet is shorter than the
534 its link level header, in hex.
537 Print each packet (minus its link level header) in hex and ASCII.
538 This is very handy for analysing new protocols.
543 its link level header, in hex and ASCII.
546 Set the data link type to use while capturing packets to \fIdatalinktype\fP.
547 .IP "\fI expression\fP"
549 selects which packets will be dumped.
550 If no \fIexpression\fP
551 is given, all packets on the net will be dumped.
553 only packets for which \fIexpression\fP is `true' will be dumped.
555 The \fIexpression\fP consists of one or more
557 Primitives usually consist of an
559 (name or number) preceded by one or more qualifiers.
561 different kinds of qualifier:
563 qualifiers say what kind of thing the id name or number refers to.
569 E.g., `host foo', `net 128.3', `port 20'.
575 qualifiers specify a particular transfer direction to and/or from
577 Possible directions are
584 E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'.
586 there is no dir qualifier,
589 For some link layers, such as SLIP and the ``cooked'' Linux capture mode
590 used for the ``any'' device and for some other device types, the
594 qualifiers can be used to specify a desired direction.
596 qualifiers restrict the match to a particular protocol.
620 E.g., `ether src foo', `arp net 128.3', `tcp port 21'.
622 no proto qualifier, all protocols consistent with the type are
624 E.g., `src foo' means `(ip or arp or rarp) src foo'
625 (except the latter is not legal syntax), `net bar' means `(ip or
626 arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'.
628 [`fddi' is actually an alias for `ether'; the parser treats them
629 identically as meaning ``the data link level used on the specified
630 network interface.'' FDDI headers contain Ethernet-like source
631 and destination addresses, and often contain Ethernet-like packet
632 types, so you can filter on these FDDI fields just as with the
633 analogous Ethernet fields.
634 FDDI headers also contain other fields,
635 but you cannot name them explicitly in a filter expression.
637 Similarly, `tr' and `wlan' are aliases for `ether'; the previous
638 paragraph's statements about FDDI headers also apply to Token Ring
639 and 802.11 wireless LAN headers. For 802.11 headers, the destination
640 address is the DA field and the source address is the SA field; the
641 BSSID, RA, and TA fields aren't tested.]
643 In addition to the above, there are some special `primitive' keywords
644 that don't follow the pattern:
649 and arithmetic expressions.
650 All of these are described below.
652 More complex filter expressions are built up by using the words
657 to combine primitives.
658 E.g., `host foo and not port ftp and not port ftp-data'.
659 To save typing, identical qualifier lists can be omitted.
661 `tcp dst port ftp or ftp-data or domain' is exactly the same as
662 `tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
664 Allowable primitives are:
665 .IP "\fBdst host \fIhost\fR"
666 True if the IPv4/v6 destination field of the packet is \fIhost\fP,
667 which may be either an address or a name.
668 .IP "\fBsrc host \fIhost\fR"
669 True if the IPv4/v6 source field of the packet is \fIhost\fP.
670 .IP "\fBhost \fIhost\fP
671 True if either the IPv4/v6 source or destination of the packet is \fIhost\fP.
672 Any of the above host expressions can be prepended with the keywords,
673 \fBip\fP, \fBarp\fP, \fBrarp\fP, or \fBip6\fP as in:
676 \fBip host \fIhost\fR
679 which is equivalent to:
682 \fBether proto \fI\\ip\fB and host \fIhost\fR
685 If \fIhost\fR is a name with multiple IP addresses, each address will
686 be checked for a match.
687 .IP "\fBether dst \fIehost\fP
688 True if the ethernet destination address is \fIehost\fP.
690 may be either a name from /etc/ethers or a number (see
693 .IP "\fBether src \fIehost\fP
694 True if the ethernet source address is \fIehost\fP.
695 .IP "\fBether host \fIehost\fP
696 True if either the ethernet source or destination address is \fIehost\fP.
697 .IP "\fBgateway\fP \fIhost\fP
698 True if the packet used \fIhost\fP as a gateway.
700 source or destination address was \fIhost\fP but neither the IP source
701 nor the IP destination was \fIhost\fP.
702 \fIHost\fP must be a name and
703 must be found both by the machine's host-name-to-IP-address resolution
704 mechanisms (host name file, DNS, NIS, etc.) and by the machine's
705 host-name-to-Ethernet-address resolution mechanism (/etc/ethers, etc.).
706 (An equivalent expression is
709 \fBether host \fIehost \fBand not host \fIhost\fR
712 which can be used with either names or numbers for \fIhost / ehost\fP.)
713 This syntax does not work in IPv6-enabled configuration at this moment.
714 .IP "\fBdst net \fInet\fR"
715 True if the IPv4/v6 destination address of the packet has a network
717 \fINet\fP may be either a name from /etc/networks
718 or a network number (see \fInetworks(4)\fP for details).
719 .IP "\fBsrc net \fInet\fR"
720 True if the IPv4/v6 source address of the packet has a network
722 .IP "\fBnet \fInet\fR"
723 True if either the IPv4/v6 source or destination address of the packet has a network
725 .IP "\fBnet \fInet\fR \fBmask \fInetmask\fR"
726 True if the IP address matches \fInet\fR with the specific \fInetmask\fR.
727 May be qualified with \fBsrc\fR or \fBdst\fR.
728 Note that this syntax is not valid for IPv6 \fInet\fR.
729 .IP "\fBnet \fInet\fR/\fIlen\fR"
730 True if the IPv4/v6 address matches \fInet\fR with a netmask \fIlen\fR
732 May be qualified with \fBsrc\fR or \fBdst\fR.
733 .IP "\fBdst port \fIport\fR"
734 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a
735 destination port value of \fIport\fP.
736 The \fIport\fP can be a number or a name used in /etc/services (see
740 If a name is used, both the port
741 number and protocol are checked.
742 If a number or ambiguous name is used,
743 only the port number is checked (e.g., \fBdst port 513\fR will print both
744 tcp/login traffic and udp/who traffic, and \fBport domain\fR will print
745 both tcp/domain and udp/domain traffic).
746 .IP "\fBsrc port \fIport\fR"
747 True if the packet has a source port value of \fIport\fP.
748 .IP "\fBport \fIport\fR"
749 True if either the source or destination port of the packet is \fIport\fP.
750 Any of the above port expressions can be prepended with the keywords,
751 \fBtcp\fP or \fBudp\fP, as in:
754 \fBtcp src port \fIport\fR
757 which matches only tcp packets whose source port is \fIport\fP.
758 .IP "\fBless \fIlength\fR"
759 True if the packet has a length less than or equal to \fIlength\fP.
760 This is equivalent to:
763 \fBlen <= \fIlength\fP.
766 .IP "\fBgreater \fIlength\fR"
767 True if the packet has a length greater than or equal to \fIlength\fP.
768 This is equivalent to:
771 \fBlen >= \fIlength\fP.
774 .IP "\fBip proto \fIprotocol\fR"
775 True if the packet is an IP packet (see
777 of protocol type \fIprotocol\fP.
778 \fIProtocol\fP can be a number or one of the names
779 \fIicmp\fP, \fIicmp6\fP, \fIigmp\fP, \fIigrp\fP, \fIpim\fP, \fIah\fP,
780 \fIesp\fP, \fIvrrp\fP, \fIudp\fP, or \fItcp\fP.
781 Note that the identifiers \fItcp\fP, \fIudp\fP, and \fIicmp\fP are also
782 keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell.
783 Note that this primitive does not chase the protocol header chain.
784 .IP "\fBip6 proto \fIprotocol\fR"
785 True if the packet is an IPv6 packet of protocol type \fIprotocol\fP.
786 Note that this primitive does not chase the protocol header chain.
787 .IP "\fBip6 protochain \fIprotocol\fR"
788 True if the packet is IPv6 packet,
789 and contains protocol header with type \fIprotocol\fR
790 in its protocol header chain.
794 \fBip6 protochain 6\fR
797 matches any IPv6 packet with TCP protocol header in the protocol header chain.
798 The packet may contain, for example,
799 authentication header, routing header, or hop-by-hop option header,
800 between IPv6 header and TCP header.
801 The BPF code emitted by this primitive is complex and
802 cannot be optimized by BPF optimizer code in \fItcpdump\fP,
803 so this can be somewhat slow.
804 .IP "\fBip protochain \fIprotocol\fR"
805 Equivalent to \fBip6 protochain \fIprotocol\fR, but this is for IPv4.
806 .IP "\fBether broadcast\fR"
807 True if the packet is an ethernet broadcast packet.
810 .IP "\fBip broadcast\fR"
811 True if the packet is an IPv4 broadcast packet.
812 It checks for both the all-zeroes and all-ones broadcast conventions,
813 and looks up the subnet mask on the interface on which the capture is
816 If the subnet mask of the interface on which the capture is being done
817 is not available, either because the interface on which capture is being
818 done has no netmask or because the capture is being done on the Linux
819 "any" interface, which can capture on more than one interface, this
820 check will not work correctly.
821 .IP "\fBether multicast\fR"
822 True if the packet is an ethernet multicast packet.
825 This is shorthand for `\fBether[0] & 1 != 0\fP'.
826 .IP "\fBip multicast\fR"
827 True if the packet is an IP multicast packet.
828 .IP "\fBip6 multicast\fR"
829 True if the packet is an IPv6 multicast packet.
830 .IP "\fBether proto \fIprotocol\fR"
831 True if the packet is of ether type \fIprotocol\fR.
832 \fIProtocol\fP can be a number or one of the names
833 \fIip\fP, \fIip6\fP, \fIarp\fP, \fIrarp\fP, \fIatalk\fP, \fIaarp\fP,
834 \fIdecnet\fP, \fIsca\fP, \fIlat\fP, \fImopdl\fP, \fImoprc\fP,
835 \fIiso\fP, \fIstp\fP, \fIipx\fP, or \fInetbeui\fP.
836 Note these identifiers are also keywords
837 and must be escaped via backslash (\\).
839 [In the case of FDDI (e.g., `\fBfddi protocol arp\fR'), Token Ring
840 (e.g., `\fBtr protocol arp\fR'), and IEEE 802.11 wireless LANS (e.g.,
841 `\fBwlan protocol arp\fR'), for most of those protocols, the
842 protocol identification comes from the 802.2 Logical Link Control (LLC)
843 header, which is usually layered on top of the FDDI, Token Ring, or
846 When filtering for most protocol identifiers on FDDI, Token Ring, or
847 802.11, \fItcpdump\fR checks only the protocol ID field of an LLC header
848 in so-called SNAP format with an Organizational Unit Identifier (OUI) of
849 0x000000, for encapsulated Ethernet; it doesn't check whether the packet
850 is in SNAP format with an OUI of 0x000000.
855 \fItcpdump\fR checks the DSAP (Destination Service Access Point) and
856 SSAP (Source Service Access Point) fields of the LLC header;
858 \fBstp\fP and \fInetbeui\fP
859 \fItcpdump\fR checks the DSAP of the LLC header;
862 \fItcpdump\fR checks for a SNAP-format packet with an OUI of 0x080007
863 and the AppleTalk etype.
866 In the case of Ethernet, \fItcpdump\fR checks the Ethernet type field
867 for most of those protocols. The exceptions are:
870 \fBiso\fP, \fBsap\fP, and \fBnetbeui\fP
871 \fItcpdump\fR checks for an 802.3 frame and then checks the LLC header as
872 it does for FDDI, Token Ring, and 802.11;
875 \fItcpdump\fR checks both for the AppleTalk etype in an Ethernet frame and
876 for a SNAP-format packet as it does for FDDI, Token Ring, and 802.11;
879 \fItcpdump\fR checks for the AppleTalk ARP etype in either an Ethernet
880 frame or an 802.2 SNAP frame with an OUI of 0x000000;
883 \fItcpdump\fR checks for the IPX etype in an Ethernet frame, the IPX
884 DSAP in the LLC header, the 802.3-with-no-LLC-header encapsulation of
885 IPX, and the IPX etype in a SNAP frame.
887 .IP "\fBdecnet src \fIhost\fR"
888 True if the DECNET source address is
890 which may be an address of the form ``10.123'', or a DECNET host
892 [DECNET host name support is only available on ULTRIX systems
893 that are configured to run DECNET.]
894 .IP "\fBdecnet dst \fIhost\fR"
895 True if the DECNET destination address is
897 .IP "\fBdecnet host \fIhost\fR"
898 True if either the DECNET source or destination address is
900 .IP "\fBifname \fIinterface\fR"
901 True if the packet was logged as coming from the specified interface (applies
902 only to packets logged by OpenBSD's
904 .IP "\fBon \fIinterface\fR"
908 .IP "\fBrnr \fInum\fR"
909 True if the packet was logged as matching the specified PF rule number
910 (applies only to packets logged by OpenBSD's
912 .IP "\fBrulenum \fInum\fR"
916 .IP "\fBreason \fIcode\fR"
917 True if the packet was logged with the specified PF reason code. The known
926 (applies only to packets logged by OpenBSD's
928 .IP "\fBrset \fIname\fR"
929 True if the packet was logged as matching the specified PF ruleset
930 name of an anchored ruleset (applies only to packets logged by
932 .IP "\fBruleset \fIname\fR"
936 .IP "\fBsrnr \fInum\fR"
937 True if the packet was logged as matching the specified PF rule number
938 of an anchored ruleset (applies only to packets logged by
940 .IP "\fBsubrulenum \fInum\fR"
944 .IP "\fBaction \fIact\fR"
945 True if PF took the specified action when the packet was logged. Known actions
950 (applies only to packets logged by OpenBSD's
952 .IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBatalk\fR, \fBaarp\fR, \fBdecnet\fR, \fBiso\fR, \fBstp\fR, \fBipx\fR, \fInetbeui\fP"
956 \fBether proto \fIp\fR
959 where \fIp\fR is one of the above protocols.
960 .IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR"
964 \fBether proto \fIp\fR
967 where \fIp\fR is one of the above protocols.
969 \fItcpdump\fP does not currently know how to parse these protocols.
970 .IP "\fBvlan \fI[vlan_id]\fR"
971 True if the packet is an IEEE 802.1Q VLAN packet.
972 If \fI[vlan_id]\fR is specified, only true is the packet has the specified
974 Note that the first \fBvlan\fR keyword encountered in \fIexpression\fR
975 changes the decoding offsets for the remainder of \fIexpression\fR
976 on the assumption that the packet is a VLAN packet.
977 .IP "\fBtcp\fR, \fBudp\fR, \fBicmp\fR"
981 \fBip proto \fIp\fR\fB or ip6 proto \fIp\fR
984 where \fIp\fR is one of the above protocols.
985 .IP "\fBiso proto \fIprotocol\fR"
986 True if the packet is an OSI packet of protocol type \fIprotocol\fP.
987 \fIProtocol\fP can be a number or one of the names
988 \fIclnp\fP, \fIesis\fP, or \fIisis\fP.
989 .IP "\fBclnp\fR, \fBesis\fR, \fBisis\fR"
996 where \fIp\fR is one of the above protocols.
997 .IP "\fBl1\fR, \fBl2\fR, \fBiih\fR, \fBlsp\fR, \fBsnp\fR, \fBcsnp\fR, \fBpsnp\fR"
998 Abbreviations for IS-IS PDU types.
999 .IP "\fBvpi\fP \fIn\fR
1000 True if the packet is an ATM packet, for SunATM on Solaris, with a
1001 virtual path identifier of
1003 .IP "\fBvci\fP \fIn\fR
1004 True if the packet is an ATM packet, for SunATM on Solaris, with a
1005 virtual channel identifier of
1008 True if the packet is an ATM packet, for SunATM on Solaris, and is
1010 Note that the first \fBlane\fR keyword encountered in \fIexpression\fR
1011 changes the tests done in the remainder of \fIexpression\fR
1012 on the assumption that the packet is either a LANE emulated Ethernet
1013 packet or a LANE LE Control packet. If \fBlane\fR isn't specified, the
1014 tests are done under the assumption that the packet is an
1015 LLC-encapsulated packet.
1017 True if the packet is an ATM packet, for SunATM on Solaris, and is
1018 an LLC-encapsulated packet.
1020 True if the packet is an ATM packet, for SunATM on Solaris, and is
1021 a segment OAM F4 flow cell (VPI=0 & VCI=3).
1023 True if the packet is an ATM packet, for SunATM on Solaris, and is
1024 an end-to-end OAM F4 flow cell (VPI=0 & VCI=4).
1026 True if the packet is an ATM packet, for SunATM on Solaris, and is
1027 a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).
1029 True if the packet is an ATM packet, for SunATM on Solaris, and is
1030 a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).
1032 True if the packet is an ATM packet, for SunATM on Solaris, and is
1033 on a meta signaling circuit (VPI=0 & VCI=1).
1035 True if the packet is an ATM packet, for SunATM on Solaris, and is
1036 on a broadcast signaling circuit (VPI=0 & VCI=2).
1038 True if the packet is an ATM packet, for SunATM on Solaris, and is
1039 on a signaling circuit (VPI=0 & VCI=5).
1041 True if the packet is an ATM packet, for SunATM on Solaris, and is
1042 on an ILMI circuit (VPI=0 & VCI=16).
1043 .IP \fBconnectmsg\fP
1044 True if the packet is an ATM packet, for SunATM on Solaris, and is
1045 on a signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect,
1046 Connect Ack, Release, or Release Done message.
1047 .IP \fBmetaconnect\fP
1048 True if the packet is an ATM packet, for SunATM on Solaris, and is
1049 on a meta signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect,
1050 Release, or Release Done message.
1051 .IP "\fIexpr relop expr\fR"
1052 True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =,
1053 !=, and \fIexpr\fR is an arithmetic expression composed of integer
1054 constants (expressed in standard C syntax), the normal binary operators
1055 [+, -, *, /, &, |, <<, >>], a length operator, and special packet data
1058 data inside the packet, use the following syntax:
1061 \fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR
1064 \fIProto\fR is one of \fBether, fddi, tr, wlan, ppp, slip, link,
1065 ip, arp, rarp, tcp, udp, icmp\fR or \fBip6\fR, and
1066 indicates the protocol layer for the index operation.
1067 (\fBether, fddi, wlan, tr, ppp, slip\fR and \fBlink\fR all refer to the
1069 Note that \fItcp, udp\fR and other upper-layer protocol types only
1070 apply to IPv4, not IPv6 (this will be fixed in the future).
1071 The byte offset, relative to the indicated protocol layer, is
1072 given by \fIexpr\fR.
1073 \fISize\fR is optional and indicates the number of bytes in the
1074 field of interest; it can be either one, two, or four, and defaults to one.
1075 The length operator, indicated by the keyword \fBlen\fP, gives the
1076 length of the packet.
1078 For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic.
1079 The expression `\fBip[0] & 0xf != 5\fP'
1080 catches all IP packets with options.
1082 `\fBip[6:2] & 0x1fff = 0\fP'
1083 catches only unfragmented datagrams and frag zero of fragmented datagrams.
1084 This check is implicitly applied to the \fBtcp\fP and \fBudp\fP
1086 For instance, \fBtcp[0]\fP always means the first
1087 byte of the TCP \fIheader\fP, and never means the first byte of an
1088 intervening fragment.
1090 Some offsets and field values may be expressed as names rather than
1092 The following protocol header field offsets are
1093 available: \fBicmptype\fP (ICMP type field), \fBicmpcode\fP (ICMP
1094 code field), and \fBtcpflags\fP (TCP flags field).
1096 The following ICMP type field values are available: \fBicmp-echoreply\fP,
1097 \fBicmp-unreach\fP, \fBicmp-sourcequench\fP, \fBicmp-redirect\fP,
1098 \fBicmp-echo\fP, \fBicmp-routeradvert\fP, \fBicmp-routersolicit\fP,
1099 \fBicmp-timxceed\fP, \fBicmp-paramprob\fP, \fBicmp-tstamp\fP,
1100 \fBicmp-tstampreply\fP, \fBicmp-ireq\fP, \fBicmp-ireqreply\fP,
1101 \fBicmp-maskreq\fP, \fBicmp-maskreply\fP.
1103 The following TCP flags field values are available: \fBtcp-fin\fP,
1104 \fBtcp-syn\fP, \fBtcp-rst\fP, \fBtcp-push\fP,
1105 \fBtcp-ack\fP, \fBtcp-urg\fP.
1107 Primitives may be combined using:
1109 A parenthesized group of primitives and operators
1110 (parentheses are special to the Shell and must be escaped).
1112 Negation (`\fB!\fP' or `\fBnot\fP').
1114 Concatenation (`\fB&&\fP' or `\fBand\fP').
1116 Alternation (`\fB||\fP' or `\fBor\fP').
1118 Negation has highest precedence.
1119 Alternation and concatenation have equal precedence and associate
1121 Note that explicit \fBand\fR tokens, not juxtaposition,
1122 are now required for concatenation.
1124 If an identifier is given without a keyword, the most recent keyword
1129 \fBnot host vs and ace\fR
1135 \fBnot host vs and host ace\fR
1138 which should not be confused with
1141 \fBnot ( host vs or ace )\fR
1145 Expression arguments can be passed to \fItcpdump\fP as either a single
1146 argument or as multiple arguments, whichever is more convenient.
1147 Generally, if the expression contains Shell metacharacters, it is
1148 easier to pass it as a single, quoted argument.
1149 Multiple arguments are concatenated with spaces before being parsed.
1152 To print all packets arriving at or departing from \fIsundown\fP:
1155 \fBtcpdump host sundown\fP
1159 To print traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR:
1162 \fBtcpdump host helios and \\( hot or ace \\)\fP
1166 To print all IP packets between \fIace\fR and any host except \fIhelios\fR:
1169 \fBtcpdump ip host ace and not helios\fP
1173 To print all traffic between local hosts and hosts at Berkeley:
1177 tcpdump net ucb-ether
1181 To print all ftp traffic through internet gateway \fIsnup\fP:
1182 (note that the expression is quoted to prevent the shell from
1183 (mis-)interpreting the parentheses):
1187 tcpdump 'gateway snup and (port ftp or ftp-data)'
1191 To print traffic neither sourced from nor destined for local hosts
1192 (if you gateway to one other net, this stuff should never make it
1193 onto your local net).
1197 tcpdump ip and not net \fIlocalnet\fP
1201 To print the start and end packets (the SYN and FIN packets) of each
1202 TCP conversation that involves a non-local host.
1206 tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net \fIlocalnet\fP'
1210 To print IP packets longer than 576 bytes sent through gateway \fIsnup\fP:
1214 tcpdump 'gateway snup and ip[2:2] > 576'
1218 To print IP broadcast or multicast packets that were
1220 sent via ethernet broadcast or multicast:
1224 tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'
1228 To print all ICMP packets that are not echo requests/replies (i.e., not
1233 tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'
1238 The output of \fItcpdump\fP is protocol dependent.
1240 gives a brief description and examples of most of the formats.
1248 If the '-e' option is given, the link level header is printed out.
1249 On ethernets, the source and destination addresses, protocol,
1250 and packet length are printed.
1252 On FDDI networks, the '-e' option causes \fItcpdump\fP to print
1253 the `frame control' field, the source and destination addresses,
1254 and the packet length.
1255 (The `frame control' field governs the
1256 interpretation of the rest of the packet.
1257 Normal packets (such
1258 as those containing IP datagrams) are `async' packets, with a priority
1259 value between 0 and 7; for example, `\fBasync4\fR'.
1261 are assumed to contain an 802.2 Logical Link Control (LLC) packet;
1262 the LLC header is printed if it is \fInot\fR an ISO datagram or a
1263 so-called SNAP packet.
1265 On Token Ring networks, the '-e' option causes \fItcpdump\fP to print
1266 the `access control' and `frame control' fields, the source and
1267 destination addresses, and the packet length.
1268 As on FDDI networks,
1269 packets are assumed to contain an LLC packet.
1270 Regardless of whether
1271 the '-e' option is specified or not, the source routing information is
1272 printed for source-routed packets.
1274 On 802.11 networks, the '-e' option causes \fItcpdump\fP to print
1275 the `frame control' fields, all of the addresses in the 802.11 header,
1276 and the packet length.
1277 As on FDDI networks,
1278 packets are assumed to contain an LLC packet.
1280 \fI(N.B.: The following description assumes familiarity with
1281 the SLIP compression algorithm described in RFC-1144.)\fP
1283 On SLIP links, a direction indicator (``I'' for inbound, ``O'' for outbound),
1284 packet type, and compression information are printed out.
1285 The packet type is printed first.
1286 The three types are \fIip\fP, \fIutcp\fP, and \fIctcp\fP.
1287 No further link information is printed for \fIip\fR packets.
1288 For TCP packets, the connection identifier is printed following the type.
1289 If the packet is compressed, its encoded header is printed out.
1290 The special cases are printed out as
1291 \fB*S+\fIn\fR and \fB*SA+\fIn\fR, where \fIn\fR is the amount by which
1292 the sequence number (or sequence number and ack) has changed.
1293 If it is not a special case,
1294 zero or more changes are printed.
1295 A change is indicated by U (urgent pointer), W (window), A (ack),
1296 S (sequence number), and I (packet ID), followed by a delta (+n or -n),
1297 or a new value (=n).
1298 Finally, the amount of data in the packet and compressed header length
1301 For example, the following line shows an outbound compressed TCP packet,
1302 with an implicit connection identifier; the ack has changed by 6,
1303 the sequence number by 49, and the packet ID by 6; there are 3 bytes of
1304 data and 6 bytes of compressed header:
1307 \fBO ctcp * A+6 S+49 I+6 3 (6)\fP
1313 Arp/rarp output shows the type of request and its arguments.
1315 format is intended to be self explanatory.
1316 Here is a short sample taken from the start of an `rlogin' from
1317 host \fIrtsg\fP to host \fIcsam\fP:
1321 \f(CWarp who-has csam tell rtsg
1322 arp reply csam is-at CSAM\fR
1326 The first line says that rtsg sent an arp packet asking
1327 for the ethernet address of internet host csam.
1329 replies with its ethernet address (in this example, ethernet addresses
1330 are in caps and internet addresses in lower case).
1332 This would look less redundant if we had done \fItcpdump \-n\fP:
1336 \f(CWarp who-has 128.3.254.6 tell 128.3.254.68
1337 arp reply 128.3.254.6 is-at 02:07:01:00:01:c4\fP
1341 If we had done \fItcpdump \-e\fP, the fact that the first packet is
1342 broadcast and the second is point-to-point would be visible:
1346 \f(CWRTSG Broadcast 0806 64: arp who-has csam tell rtsg
1347 CSAM RTSG 0806 64: arp reply csam is-at CSAM\fR
1351 For the first packet this says the ethernet source address is RTSG, the
1352 destination is the ethernet broadcast address, the type field
1353 contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes.
1357 \fI(N.B.:The following description assumes familiarity with
1358 the TCP protocol described in RFC-793.
1359 If you are not familiar
1360 with the protocol, neither this description nor \fItcpdump\fP will
1361 be of much use to you.)\fP
1363 The general format of a tcp protocol line is:
1367 \fIsrc > dst: flags data-seqno ack window urgent options\fP
1371 \fISrc\fP and \fIdst\fP are the source and destination IP
1372 addresses and ports.
1373 \fIFlags\fP are some combination of S (SYN),
1374 F (FIN), P (PUSH), R (RST), W (ECN CWR) or E (ECN-Echo), or a single
1376 \fIData-seqno\fP describes the portion of sequence space covered
1377 by the data in this packet (see example below).
1378 \fIAck\fP is sequence number of the next data expected the other
1379 direction on this connection.
1380 \fIWindow\fP is the number of bytes of receive buffer space available
1381 the other direction on this connection.
1382 \fIUrg\fP indicates there is `urgent' data in the packet.
1383 \fIOptions\fP are tcp options enclosed in angle brackets (e.g., <mss 1024>).
1385 \fISrc, dst\fP and \fIflags\fP are always present.
1387 depend on the contents of the packet's tcp protocol header and
1388 are output only if appropriate.
1390 Here is the opening portion of an rlogin from host \fIrtsg\fP to
1395 \s-2\f(CWrtsg.1023 > csam.login: S 768512:768512(0) win 4096 <mss 1024>
1396 csam.login > rtsg.1023: S 947648:947648(0) ack 768513 win 4096 <mss 1024>
1397 rtsg.1023 > csam.login: . ack 1 win 4096
1398 rtsg.1023 > csam.login: P 1:2(1) ack 1 win 4096
1399 csam.login > rtsg.1023: . ack 2 win 4096
1400 rtsg.1023 > csam.login: P 2:21(19) ack 1 win 4096
1401 csam.login > rtsg.1023: P 1:2(1) ack 21 win 4077
1402 csam.login > rtsg.1023: P 2:3(1) ack 21 win 4077 urg 1
1403 csam.login > rtsg.1023: P 3:4(1) ack 21 win 4077 urg 1\fR\s+2
1407 The first line says that tcp port 1023 on rtsg sent a packet
1410 The \fBS\fP indicates that the \fISYN\fP flag was set.
1411 The packet sequence number was 768512 and it contained no data.
1412 (The notation is `first:last(nbytes)' which means `sequence
1414 up to but not including \fIlast\fP which is \fInbytes\fP bytes of user data'.)
1415 There was no piggy-backed ack, the available receive window was 4096
1416 bytes and there was a max-segment-size option requesting an mss of
1419 Csam replies with a similar packet except it includes a piggy-backed
1421 Rtsg then acks csam's SYN.
1424 The packet contained no data so there is no data sequence number.
1425 Note that the ack sequence
1426 number is a small integer (1).
1427 The first time \fItcpdump\fP sees a
1428 tcp `conversation', it prints the sequence number from the packet.
1429 On subsequent packets of the conversation, the difference between
1430 the current packet's sequence number and this initial sequence number
1432 This means that sequence numbers after the
1433 first can be interpreted
1434 as relative byte positions in the conversation's data stream (with the
1435 first data byte each direction being `1').
1436 `-S' will override this
1437 feature, causing the original sequence numbers to be output.
1439 On the 6th line, rtsg sends csam 19 bytes of data (bytes 2 through 20
1440 in the rtsg \(-> csam side of the conversation).
1441 The PUSH flag is set in the packet.
1442 On the 7th line, csam says it's received data sent by rtsg up to
1443 but not including byte 21.
1444 Most of this data is apparently sitting in the
1445 socket buffer since csam's receive window has gotten 19 bytes smaller.
1446 Csam also sends one byte of data to rtsg in this packet.
1447 On the 8th and 9th lines,
1448 csam sends two bytes of urgent, pushed data to rtsg.
1450 If the snapshot was small enough that \fItcpdump\fP didn't capture
1451 the full TCP header, it interprets as much of the header as it can
1452 and then reports ``[|\fItcp\fP]'' to indicate the remainder could not
1454 If the header contains a bogus option (one with a length
1455 that's either too small or beyond the end of the header), \fItcpdump\fP
1456 reports it as ``[\fIbad opt\fP]'' and does not interpret any further
1457 options (since it's impossible to tell where they start).
1459 length indicates options are present but the IP datagram length is not
1460 long enough for the options to actually be there, \fItcpdump\fP reports
1461 it as ``[\fIbad hdr length\fP]''.
1463 .B Capturing TCP packets with particular flag combinations (SYN-ACK, URG-ACK, etc.)
1465 There are 8 bits in the control bits section of the TCP header:
1467 .I CWR | ECE | URG | ACK | PSH | RST | SYN | FIN
1469 Let's assume that we want to watch packets used in establishing
1471 Recall that TCP uses a 3-way handshake protocol
1472 when it initializes a new connection; the connection sequence with
1473 regard to the TCP control bits is
1479 2) Recipient responds with SYN, ACK
1485 Now we're interested in capturing packets that have only the
1486 SYN bit set (Step 1).
1487 Note that we don't want packets from step 2
1488 (SYN-ACK), just a plain initial SYN.
1489 What we need is a correct filter
1490 expression for \fItcpdump\fP.
1492 Recall the structure of a TCP header without options:
1496 -----------------------------------------------------------------
1497 | source port | destination port |
1498 -----------------------------------------------------------------
1500 -----------------------------------------------------------------
1501 | acknowledgment number |
1502 -----------------------------------------------------------------
1503 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1504 -----------------------------------------------------------------
1505 | TCP checksum | urgent pointer |
1506 -----------------------------------------------------------------
1509 A TCP header usually holds 20 octets of data, unless options are
1511 The first line of the graph contains octets 0 - 3, the
1512 second line shows octets 4 - 7 etc.
1514 Starting to count with 0, the relevant TCP control bits are contained
1519 ----------------|---------------|---------------|----------------
1520 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1521 ----------------|---------------|---------------|----------------
1522 | | 13th octet | | |
1525 Let's have a closer look at octet no. 13:
1535 These are the TCP control bits we are interested
1537 We have numbered the bits in this octet from 0 to 7, right to
1538 left, so the PSH bit is bit number 3, while the URG bit is number 5.
1540 Recall that we want to capture packets with only SYN set.
1541 Let's see what happens to octet 13 if a TCP datagram arrives
1542 with the SYN bit set in its header:
1553 control bits section we see that only bit number 1 (SYN) is set.
1555 Assuming that octet number 13 is an 8-bit unsigned integer in
1556 network byte order, the binary value of this octet is
1560 and its decimal representation is
1564 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 1*2 + 0*2 = 2
1567 We're almost done, because now we know that if only SYN is set,
1568 the value of the 13th octet in the TCP header, when interpreted
1569 as a 8-bit unsigned integer in network byte order, must be exactly 2.
1571 This relationship can be expressed as
1577 We can use this expression as the filter for \fItcpdump\fP in order
1578 to watch packets which have only SYN set:
1581 tcpdump -i xl0 tcp[13] == 2
1584 The expression says "let the 13th octet of a TCP datagram have
1585 the decimal value 2", which is exactly what we want.
1587 Now, let's assume that we need to capture SYN packets, but we
1588 don't care if ACK or any other TCP control bit is set at the
1590 Let's see what happens to octet 13 when a TCP datagram
1591 with SYN-ACK set arrives:
1601 Now bits 1 and 4 are set in the 13th octet.
1607 which translates to decimal
1611 0*2 + 0*2 + 0*2 + 1*2 + 0*2 + 0*2 + 1*2 + 0*2 = 18
1614 Now we can't just use 'tcp[13] == 18' in the \fItcpdump\fP filter
1615 expression, because that would select only those packets that have
1616 SYN-ACK set, but not those with only SYN set.
1617 Remember that we don't care
1618 if ACK or any other control bit is set as long as SYN is set.
1620 In order to achieve our goal, we need to logically AND the
1621 binary value of octet 13 with some other value to preserve
1623 We know that we want SYN to be set in any case,
1624 so we'll logically AND the value in the 13th octet with
1625 the binary value of a SYN:
1629 00010010 SYN-ACK 00000010 SYN
1630 AND 00000010 (we want SYN) AND 00000010 (we want SYN)
1632 = 00000010 = 00000010
1635 We see that this AND operation delivers the same result
1636 regardless whether ACK or another TCP control bit is set.
1637 The decimal representation of the AND value as well as
1638 the result of this operation is 2 (binary 00000010),
1639 so we know that for packets with SYN set the following
1640 relation must hold true:
1642 ( ( value of octet 13 ) AND ( 2 ) ) == ( 2 )
1644 This points us to the \fItcpdump\fP filter expression
1647 tcpdump -i xl0 'tcp[13] & 2 == 2'
1650 Note that you should use single quotes or a backslash
1651 in the expression to hide the AND ('&') special character
1657 UDP format is illustrated by this rwho packet:
1661 \f(CWactinide.who > broadcast.who: udp 84\fP
1665 This says that port \fIwho\fP on host \fIactinide\fP sent a udp
1666 datagram to port \fIwho\fP on host \fIbroadcast\fP, the Internet
1668 The packet contained 84 bytes of user data.
1670 Some UDP services are recognized (from the source or destination
1671 port number) and the higher level protocol information printed.
1672 In particular, Domain Name service requests (RFC-1034/1035) and Sun
1673 RPC calls (RFC-1050) to NFS.
1675 UDP Name Server Requests
1677 \fI(N.B.:The following description assumes familiarity with
1678 the Domain Service protocol described in RFC-1035.
1679 If you are not familiar
1680 with the protocol, the following description will appear to be written
1683 Name server requests are formatted as
1687 \fIsrc > dst: id op? flags qtype qclass name (len)\fP
1689 \f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fR
1693 Host \fIh2opolo\fP asked the domain server on \fIhelios\fP for an
1694 address record (qtype=A) associated with the name \fIucbvax.berkeley.edu.\fP
1695 The query id was `3'.
1696 The `+' indicates the \fIrecursion desired\fP flag
1698 The query length was 37 bytes, not including the UDP and
1699 IP protocol headers.
1700 The query operation was the normal one, \fIQuery\fP,
1701 so the op field was omitted.
1702 If the op had been anything else, it would
1703 have been printed between the `3' and the `+'.
1704 Similarly, the qclass was the normal one,
1705 \fIC_IN\fP, and omitted.
1706 Any other qclass would have been printed
1707 immediately after the `A'.
1709 A few anomalies are checked and may result in extra fields enclosed in
1710 square brackets: If a query contains an answer, authority records or
1711 additional records section,
1716 are printed as `[\fIn\fPa]', `[\fIn\fPn]' or `[\fIn\fPau]' where \fIn\fP
1717 is the appropriate count.
1718 If any of the response bits are set (AA, RA or rcode) or any of the
1719 `must be zero' bits are set in bytes two and three, `[b2&3=\fIx\fP]'
1720 is printed, where \fIx\fP is the hex value of header bytes two and three.
1722 UDP Name Server Responses
1724 Name server responses are formatted as
1728 \fIsrc > dst: id op rcode flags a/n/au type class data (len)\fP
1730 \f(CWhelios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273)
1731 helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fR
1735 In the first example, \fIhelios\fP responds to query id 3 from \fIh2opolo\fP
1736 with 3 answer records, 3 name server records and 7 additional records.
1737 The first answer record is type A (address) and its data is internet
1738 address 128.32.137.3.
1739 The total size of the response was 273 bytes,
1740 excluding UDP and IP headers.
1741 The op (Query) and response code
1742 (NoError) were omitted, as was the class (C_IN) of the A record.
1744 In the second example, \fIhelios\fP responds to query 2 with a
1745 response code of non-existent domain (NXDomain) with no answers,
1746 one name server and no authority records.
1747 The `*' indicates that
1748 the \fIauthoritative answer\fP bit was set.
1750 answers, no type, class or data were printed.
1752 Other flag characters that might appear are `\-' (recursion available,
1753 RA, \fInot\fP set) and `|' (truncated message, TC, set).
1755 `question' section doesn't contain exactly one entry, `[\fIn\fPq]'
1758 Note that name server requests and responses tend to be large and the
1759 default \fIsnaplen\fP of 68 bytes may not capture enough of the packet
1761 Use the \fB\-s\fP flag to increase the snaplen if you
1762 need to seriously investigate name server traffic.
1764 has worked well for me.
1769 \fItcpdump\fP now includes fairly extensive SMB/CIFS/NBT decoding for data
1770 on UDP/137, UDP/138 and TCP/139.
1771 Some primitive decoding of IPX and
1772 NetBEUI SMB data is also done.
1774 By default a fairly minimal decode is done, with a much more detailed
1775 decode done if -v is used.
1776 Be warned that with -v a single SMB packet
1777 may take up a page or more, so only use -v if you really want all the
1780 If you are decoding SMB sessions containing unicode strings then you
1781 may wish to set the environment variable USE_UNICODE to 1.
1783 auto-detect unicode strings would be welcome.
1785 For information on SMB packet formats and what all te fields mean see
1786 www.cifs.org or the pub/samba/specs/ directory on your favorite
1787 samba.org mirror site.
1788 The SMB patches were written by Andrew Tridgell
1792 NFS Requests and Replies
1794 Sun NFS (Network File System) requests and replies are printed as:
1798 \fIsrc.xid > dst.nfs: len op args\fP
1799 \fIsrc.nfs > dst.xid: reply stat len op results\fP
1802 sushi.6709 > wrl.nfs: 112 readlink fh 21,24/10.73165
1803 wrl.nfs > sushi.6709: reply ok 40 readlink "../var"
1804 sushi.201b > wrl.nfs:
1805 144 lookup fh 9,74/4096.6878 "xcolors"
1806 wrl.nfs > sushi.201b:
1807 reply ok 128 lookup fh 9,74/4134.3150
1812 In the first line, host \fIsushi\fP sends a transaction with id \fI6709\fP
1813 to \fIwrl\fP (note that the number following the src host is a
1814 transaction id, \fInot\fP the source port).
1815 The request was 112 bytes,
1816 excluding the UDP and IP headers.
1817 The operation was a \fIreadlink\fP
1818 (read symbolic link) on file handle (\fIfh\fP) 21,24/10.731657119.
1819 (If one is lucky, as in this case, the file handle can be interpreted
1820 as a major,minor device number pair, followed by the inode number and
1822 \fIWrl\fP replies `ok' with the contents of the link.
1824 In the third line, \fIsushi\fP asks \fIwrl\fP to lookup the name
1825 `\fIxcolors\fP' in directory file 9,74/4096.6878.
1826 Note that the data printed
1827 depends on the operation type.
1828 The format is intended to be self
1829 explanatory if read in conjunction with
1830 an NFS protocol spec.
1832 If the \-v (verbose) flag is given, additional information is printed.
1838 sushi.1372a > wrl.nfs:
1839 148 read fh 21,11/12.195 8192 bytes @ 24576
1840 wrl.nfs > sushi.1372a:
1841 reply ok 1472 read REG 100664 ids 417/0 sz 29388
1846 (\-v also prints the IP header TTL, ID, length, and fragmentation fields,
1847 which have been omitted from this example.) In the first line,
1848 \fIsushi\fP asks \fIwrl\fP to read 8192 bytes from file 21,11/12.195,
1849 at byte offset 24576.
1850 \fIWrl\fP replies `ok'; the packet shown on the
1851 second line is the first fragment of the reply, and hence is only 1472
1852 bytes long (the other bytes will follow in subsequent fragments, but
1853 these fragments do not have NFS or even UDP headers and so might not be
1854 printed, depending on the filter expression used).
1855 Because the \-v flag
1856 is given, some of the file attributes (which are returned in addition
1857 to the file data) are printed: the file type (``REG'', for regular file),
1858 the file mode (in octal), the uid and gid, and the file size.
1860 If the \-v flag is given more than once, even more details are printed.
1862 Note that NFS requests are very large and much of the detail won't be printed
1863 unless \fIsnaplen\fP is increased.
1864 Try using `\fB\-s 192\fP' to watch
1867 NFS reply packets do not explicitly identify the RPC operation.
1869 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1870 replies using the transaction ID.
1871 If a reply does not closely follow the
1872 corresponding request, it might not be parsable.
1874 AFS Requests and Replies
1876 Transarc AFS (Andrew File System) requests and replies are printed
1882 \fIsrc.sport > dst.dport: rx packet-type\fP
1883 \fIsrc.sport > dst.dport: rx packet-type service call call-name args\fP
1884 \fIsrc.sport > dst.dport: rx packet-type service reply call-name args\fP
1887 elvis.7001 > pike.afsfs:
1888 rx data fs call rename old fid 536876964/1/1 ".newsrc.new"
1889 new fid 536876964/1/1 ".newsrc"
1890 pike.afsfs > elvis.7001: rx data fs reply rename
1895 In the first line, host elvis sends a RX packet to pike.
1897 a RX data packet to the fs (fileserver) service, and is the start of
1899 The RPC call was a rename, with the old directory file id
1900 of 536876964/1/1 and an old filename of `.newsrc.new', and a new directory
1901 file id of 536876964/1/1 and a new filename of `.newsrc'.
1903 responds with a RPC reply to the rename call (which was successful, because
1904 it was a data packet and not an abort packet).
1906 In general, all AFS RPCs are decoded at least by RPC call name.
1908 AFS RPCs have at least some of the arguments decoded (generally only
1909 the `interesting' arguments, for some definition of interesting).
1911 The format is intended to be self-describing, but it will probably
1912 not be useful to people who are not familiar with the workings of
1915 If the -v (verbose) flag is given twice, acknowledgement packets and
1916 additional header information is printed, such as the the RX call ID,
1917 call number, sequence number, serial number, and the RX packet flags.
1919 If the -v flag is given twice, additional information is printed,
1920 such as the the RX call ID, serial number, and the RX packet flags.
1921 The MTU negotiation information is also printed from RX ack packets.
1923 If the -v flag is given three times, the security index and service id
1926 Error codes are printed for abort packets, with the exception of Ubik
1927 beacon packets (because abort packets are used to signify a yes vote
1928 for the Ubik protocol).
1930 Note that AFS requests are very large and many of the arguments won't
1931 be printed unless \fIsnaplen\fP is increased.
1932 Try using `\fB-s 256\fP'
1933 to watch AFS traffic.
1935 AFS reply packets do not explicitly identify the RPC operation.
1937 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1938 replies using the call number and service ID.
1939 If a reply does not closely
1941 corresponding request, it might not be parsable.
1944 KIP AppleTalk (DDP in UDP)
1946 AppleTalk DDP packets encapsulated in UDP datagrams are de-encapsulated
1947 and dumped as DDP packets (i.e., all the UDP header information is
1951 is used to translate AppleTalk net and node numbers to names.
1952 Lines in this file have the form
1964 The first two lines give the names of AppleTalk networks.
1966 line gives the name of a particular host (a host is distinguished
1967 from a net by the 3rd octet in the number \-
1968 a net number \fImust\fP have two octets and a host number \fImust\fP
1969 have three octets.) The number and name should be separated by
1970 whitespace (blanks or tabs).
1973 file may contain blank lines or comment lines (lines starting with
1976 AppleTalk addresses are printed in the form
1982 \f(CW144.1.209.2 > icsd-net.112.220
1983 office.2 > icsd-net.112.220
1984 jssmag.149.235 > icsd-net.2\fR
1990 doesn't exist or doesn't contain an entry for some AppleTalk
1991 host/net number, addresses are printed in numeric form.)
1992 In the first example, NBP (DDP port 2) on net 144.1 node 209
1993 is sending to whatever is listening on port 220 of net icsd node 112.
1994 The second line is the same except the full name of the source node
1995 is known (`office').
1996 The third line is a send from port 235 on
1997 net jssmag node 149 to broadcast on the icsd-net NBP port (note that
1998 the broadcast address (255) is indicated by a net name with no host
1999 number \- for this reason it's a good idea to keep node names and
2000 net names distinct in /etc/atalk.names).
2002 NBP (name binding protocol) and ATP (AppleTalk transaction protocol)
2003 packets have their contents interpreted.
2004 Other protocols just dump
2005 the protocol name (or number if no name is registered for the
2006 protocol) and packet size.
2008 \fBNBP packets\fP are formatted like the following examples:
2012 \s-2\f(CWicsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
2013 jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
2014 techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fR\s+2
2018 The first line is a name lookup request for laserwriters sent by net icsd host
2019 112 and broadcast on net jssmag.
2020 The nbp id for the lookup is 190.
2021 The second line shows a reply for this request (note that it has the
2022 same id) from host jssmag.209 saying that it has a laserwriter
2023 resource named "RM1140" registered on port 250.
2025 another reply to the same request saying host techpit has laserwriter
2026 "techpit" registered on port 186.
2028 \fBATP packet\fP formatting is demonstrated by the following example:
2032 \s-2\f(CWjssmag.209.165 > helios.132: atp-req 12266<0-7> 0xae030001
2033 helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
2034 helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
2035 helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
2036 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
2037 helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
2038 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
2039 helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
2040 helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
2041 jssmag.209.165 > helios.132: atp-req 12266<3,5> 0xae030001
2042 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
2043 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
2044 jssmag.209.165 > helios.132: atp-rel 12266<0-7> 0xae030001
2045 jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fR\s+2
2049 Jssmag.209 initiates transaction id 12266 with host helios by requesting
2050 up to 8 packets (the `<0-7>').
2051 The hex number at the end of the line
2052 is the value of the `userdata' field in the request.
2054 Helios responds with 8 512-byte packets.
2055 The `:digit' following the
2056 transaction id gives the packet sequence number in the transaction
2057 and the number in parens is the amount of data in the packet,
2058 excluding the atp header.
2059 The `*' on packet 7 indicates that the
2062 Jssmag.209 then requests that packets 3 & 5 be retransmitted.
2064 resends them then jssmag.209 releases the transaction.
2066 jssmag.209 initiates the next request.
2067 The `*' on the request
2068 indicates that XO (`exactly once') was \fInot\fP set.
2073 Fragmented Internet datagrams are printed as
2077 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR
2078 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR
2082 (The first form indicates there are more fragments.
2084 indicates this is the last fragment.)
2086 \fIId\fP is the fragment id.
2087 \fISize\fP is the fragment
2088 size (in bytes) excluding the IP header.
2089 \fIOffset\fP is this
2090 fragment's offset (in bytes) in the original datagram.
2092 The fragment information is output for each fragment.
2094 fragment contains the higher level protocol header and the frag
2095 info is printed after the protocol info.
2097 after the first contain no higher level protocol header and the
2098 frag info is printed after the source and destination addresses.
2099 For example, here is part of an ftp from arizona.edu to lbl-rtsg.arpa
2100 over a CSNET connection that doesn't appear to handle 576 byte datagrams:
2104 \s-2\f(CWarizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+)
2105 arizona > rtsg: (frag 595a:204@328)
2106 rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2
2110 There are a couple of things to note here: First, addresses in the
2111 2nd line don't include port numbers.
2112 This is because the TCP
2113 protocol information is all in the first fragment and we have no idea
2114 what the port or sequence numbers are when we print the later fragments.
2115 Second, the tcp sequence information in the first line is printed as if there
2116 were 308 bytes of user data when, in fact, there are 512 bytes (308 in
2117 the first frag and 204 in the second).
2118 If you are looking for holes
2119 in the sequence space or trying to match up acks
2120 with packets, this can fool you.
2122 A packet with the IP \fIdon't fragment\fP flag is marked with a
2123 trailing \fB(DF)\fP.
2127 By default, all output lines are preceded by a timestamp.
2129 is the current clock time in the form
2135 and is as accurate as the kernel's clock.
2136 The timestamp reflects the time the kernel first saw the packet.
2138 is made to account for the time lag between when the
2139 ethernet interface removed the packet from the wire and when the kernel
2140 serviced the `new packet' interrupt.
2144 The original authors are:
2148 Steven McCanne, all of the
2149 Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
2151 It is currently being maintained by tcpdump.org.
2153 The current version is available via http:
2156 .I http://www.tcpdump.org/
2159 The original distribution is available via anonymous ftp:
2162 .I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z
2165 IPv6/IPsec support is added by WIDE/KAME project.
2166 This program uses Eric Young's SSLeay library, under specific configuration.
2168 Please send problems, bugs, questions, desirable enhancements, etc. to:
2171 tcpdump-workers@tcpdump.org
2174 Please send source code contributions, etc. to:
2180 NIT doesn't let you watch your own outbound traffic, BPF will.
2181 We recommend that you use the latter.
2183 On Linux systems with 2.0[.x] kernels:
2185 packets on the loopback device will be seen twice;
2187 packet filtering cannot be done in the kernel, so that all packets must
2188 be copied from the kernel in order to be filtered in user mode;
2190 all of a packet, not just the part that's within the snapshot length,
2191 will be copied from the kernel (the 2.0[.x] packet capture mechanism, if
2192 asked to copy only part of a packet to userland, will not report the
2193 true length of the packet; this would cause most IP packets to get an
2197 capturing on some PPP devices won't work correctly.
2199 We recommend that you upgrade to a 2.2 or later kernel.
2201 Some attempt should be made to reassemble IP fragments or, at least
2202 to compute the right length for the higher level protocol.
2204 Name server inverse queries are not dumped correctly: the (empty)
2205 question section is printed rather than real query in the answer
2207 Some believe that inverse queries are themselves a bug and
2208 prefer to fix the program generating them rather than \fItcpdump\fP.
2210 A packet trace that crosses a daylight savings time change will give
2211 skewed time stamps (the time change is ignored).
2213 Filter expressions on fields other than those in Token Ring headers will
2214 not correctly handle source-routed Token Ring packets.
2216 Filter expressions on fields other than those in 802.11 headers will not
2217 correctly handle 802.11 data packets with both To DS and From DS set.
2220 should chase header chain, but at this moment it does not.
2221 .BR "ip6 protochain"
2222 is supplied for this behavior.
2224 Arithmetic expression against transport layer headers, like \fBtcp[0]\fP,
2225 does not work against IPv6 packets.
2226 It only looks at IPv4 packets.
projects / FreeBSD / FreeBSD.git / blob