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23 .TH TCPDUMP 1 "21 December 2002"
25 tcpdump \- dump traffic on a network
30 .B \-aAdDeflLnNOpqRStuUvxX
76 .I spi@ipaddr algo:secret,...
92 \fITcpdump\fP prints out the headers of packets on a network interface
93 that match the boolean \fIexpression\fP. It can also be run with the
95 flag, which causes it to save the packet data to a file for later
96 analysis, and/or with the
98 flag, which causes it to read from a saved packet file rather than to
99 read packets from a network interface. In all cases, only packets that
106 will, if not run with the
108 flag, continue capturing packets until it is interrupted by a SIGINT
109 signal (generated, for example, by typing your interrupt character,
110 typically control-C) or a SIGTERM signal (typically generated with the
112 command); if run with the
114 flag, it will capture packets until it is interrupted by a SIGINT or
115 SIGTERM signal or the specified number of packets have been processed.
119 finishes capturing packets, it will report counts of:
121 packets ``received by filter'' (the meaning of this depends on the OS on
124 and possibly on the way the OS was configured - if a filter was
125 specified on the command line, on some OSes it counts packets regardless
126 of whether they were matched by the filter expression, and on other OSes
127 it counts only packets that were matched by the filter expression and
131 packets ``dropped by kernel'' (this is the number of packets that were
132 dropped, due to a lack of buffer space, by the packet capture mechanism
135 is running, if the OS reports that information to applications; if not,
136 it will be reported as 0).
138 On platforms that support the SIGINFO signal, such as most BSDs, it will
139 report those counts when it receives a SIGINFO signal (generated, for
140 example, by typing your ``status'' character, typically control-T) and
141 will continue capturing packets.
143 Reading packets from a network interface may require that you have
146 .B Under SunOS 3.x or 4.x with NIT or BPF:
147 You must have read access to
152 .B Under Solaris with DLPI:
153 You must have read/write access to the network pseudo device, e.g.
155 On at least some versions of Solaris, however, this is not sufficient to
158 to capture in promiscuous mode; on those versions of Solaris, you must
161 must be installed setuid to root, in order to capture in promiscuous
162 mode. Note that, on many (perhaps all) interfaces, if you don't capture
163 in promiscuous mode, you will not see any outgoing packets, so a capture
164 not done in promiscuous mode may not be very useful.
166 .B Under HP-UX with DLPI:
169 must be installed setuid to root.
171 .B Under IRIX with snoop:
174 must be installed setuid to root.
179 must be installed setuid to root.
181 .B Under Ultrix and Digital UNIX/Tru64 UNIX:
182 Any user may capture network traffic with
184 However, no user (not even the super-user) can capture in promiscuous
185 mode on an interface unless the super-user has enabled promiscuous-mode
186 operation on that interface using
188 and no user (not even the super-user) can capture unicast traffic
189 received by or sent by the machine on an interface unless the super-user
190 has enabled copy-all-mode operation on that interface using
194 packet capture on an interface probably requires that either
195 promiscuous-mode or copy-all-mode operation, or both modes of
196 operation, be enabled on that interface.
199 You must have read access to
202 Reading a saved packet file doesn't require special privileges.
206 Print each packet (minus its link level header) in ASCII. Handy for
210 Attempt to convert network and broadcast addresses to names.
213 Exit after receiving \fIcount\fP packets.
216 Before writing a raw packet to a savefile, check whether the file is
217 currently larger than \fIfile_size\fP and, if so, close the current
218 savefile and open a new one. Savefiles after the first savefile will
219 have the name specified with the
221 flag, with a number after it, starting at 2 and continuing upward.
222 The units of \fIfile_size\fP are millions of bytes (1,000,000 bytes,
223 not 1,048,576 bytes).
226 Dump the compiled packet-matching code in a human readable form to
227 standard output and stop.
230 Dump packet-matching code as a
235 Dump packet-matching code as decimal numbers (preceded with a count).
238 Print the list of the network interfaces available on the system and on
241 can capture packets. For each network interface, a number and an
242 interface name, possibly followed by a text description of the
243 interface, is printed. The interface name or the number can be supplied
246 flag to specify an interface on which to capture.
248 This can be useful on systems that don't have a command to list them
249 (e.g., Windows systems, or UNIX systems lacking
250 .BR "ifconfig \-a" );
251 the number can be useful on Windows 2000 and later systems, where the
252 interface name is a somewhat complex string.
256 flag will not be supported if
258 was built with an older version of
261 .B pcap_findalldevs()
265 Print the link-level header on each dump line.
268 Use \fIspi@ipaddr algo:secret\fP for decrypting IPsec ESP packets that
269 are addressed to \fIaddr\fP and contain Security Parameter Index value
270 \fIspi\fP. This combination may be repeated with comma or newline seperation.
272 Note that setting the secret for IPv4 ESP packets is supported at this time.
279 \fBcast128-cbc\fP, or
281 The default is \fBdes-cbc\fP.
282 The ability to decrypt packets is only present if \fItcpdump\fP was compiled
283 with cryptography enabled.
285 \fIsecret\fP is the ASCII text for ESP secret key.
286 If preceeded by 0x, then a hex value will be read.
288 The option assumes RFC2406 ESP, not RFC1827 ESP.
289 The option is only for debugging purposes, and
290 the use of this option with a true `secret' key is discouraged.
291 By presenting IPsec secret key onto command line
292 you make it visible to others, via
296 In addition to the above syntax, the syntax \fIfile name\fP may be used
297 to have tcpdump read the provided file in. The file is opened upon
298 receiving the first ESP packet, so any special permissions that tcpdump
299 may have been given should already have been given up.
302 Print `foreign' IPv4 addresses numerically rather than symbolically
303 (this option is intended to get around serious brain damage in
304 Sun's NIS server \(em usually it hangs forever translating non-local
307 The test for `foreign' IPv4 addresses is done using the IPv4 address and
308 netmask of the interface on which capture is being done. If that
309 address or netmask are not available, available, either because the
310 interface on which capture is being done has no address or netmask or
311 because the capture is being done on the Linux "any" interface, which
312 can capture on more than one interface, this option will not work
316 Use \fIfile\fP as input for the filter expression.
317 An additional expression given on the command line is ignored.
320 Listen on \fIinterface\fP.
321 If unspecified, \fItcpdump\fP searches the system interface list for the
322 lowest numbered, configured up interface (excluding loopback).
323 Ties are broken by choosing the earliest match.
325 On Linux systems with 2.2 or later kernels, an
327 argument of ``any'' can be used to capture packets from all interfaces.
328 Note that captures on the ``any'' device will not be done in promiscuous
333 flag is supported, an interface number as printed by that flag can be
339 Make stdout line buffered.
340 Useful if you want to see the data
344 ``tcpdump\ \ \-l\ \ |\ \ tee dat'' or
345 ``tcpdump\ \ \-l \ \ > dat\ \ &\ \ tail\ \ \-f\ \ dat''.
348 List the known data link types for the interface and exit.
351 Load SMI MIB module definitions from file \fImodule\fR.
353 can be used several times to load several MIB modules into \fItcpdump\fP.
356 Don't convert addresses (i.e., host addresses, port numbers, etc.) to names.
359 Don't print domain name qualification of host names.
361 if you give this flag then \fItcpdump\fP will print ``nic''
362 instead of ``nic.ddn.mil''.
365 Do not run the packet-matching code optimizer.
367 if you suspect a bug in the optimizer.
370 \fIDon't\fP put the interface
371 into promiscuous mode.
372 Note that the interface might be in promiscuous
373 mode for some other reason; hence, `-p' cannot be used as an abbreviation for
374 `ether host {local-hw-addr} or ether broadcast'.
377 Quick (quiet?) output.
378 Print less protocol information so output
382 Assume ESP/AH packets to be based on old specification (RFC1825 to RFC1829).
383 If specified, \fItcpdump\fP will not print replay prevention field.
384 Since there is no protocol version field in ESP/AH specification,
385 \fItcpdump\fP cannot deduce the version of ESP/AH protocol.
388 Read packets from \fIfile\fR (which was created with the
391 Standard input is used if \fIfile\fR is ``-''.
394 Print absolute, rather than relative, TCP sequence numbers.
397 Snarf \fIsnaplen\fP bytes of data from each packet rather than the
398 default of 68 (with SunOS's NIT, the minimum is actually 96).
399 68 bytes is adequate for IP, ICMP, TCP
400 and UDP but may truncate protocol information from name server and NFS
402 Packets truncated because of a limited snapshot
403 are indicated in the output with ``[|\fIproto\fP]'', where \fIproto\fP
404 is the name of the protocol level at which the truncation has occurred.
405 Note that taking larger snapshots both increases
406 the amount of time it takes to process packets and, effectively,
407 decreases the amount of packet buffering.
408 This may cause packets to be
410 You should limit \fIsnaplen\fP to the smallest number that will
411 capture the protocol information you're interested in.
413 \fIsnaplen\fP to 0 means use the required length to catch whole packets.
416 Force packets selected by "\fIexpression\fP" to be interpreted the
417 specified \fItype\fR.
418 Currently known types are
419 \fBcnfp\fR (Cisco NetFlow protocol),
420 \fBrpc\fR (Remote Procedure Call),
421 \fBrtp\fR (Real-Time Applications protocol),
422 \fBrtcp\fR (Real-Time Applications control protocol),
423 \fBsnmp\fR (Simple Network Management Protocol),
424 \fBtftp\fR (Trivial File Transfer Protocol),
425 \fBvat\fR (Visual Audio Tool),
427 \fBwb\fR (distributed White Board).
430 \fIDon't\fP print a timestamp on each dump line.
433 Print an unformatted timestamp on each dump line.
436 Print a delta (in micro-seconds) between current and previous line
440 Print a timestamp in default format proceeded by date on each dump line.
443 Print undecoded NFS handles.
446 Make output saved via the
448 option ``packet-buffered''; i.e., as each packet is saved, it will be
449 written to the output file, rather than being written only when the
454 flag will not be supported if
456 was built with an older version of
463 (Slightly more) verbose output.
464 For example, the time to live,
465 identification, total length and options in an IP packet are printed.
466 Also enables additional packet integrity checks such as verifying the
467 IP and ICMP header checksum.
470 Even more verbose output.
471 For example, additional fields are
472 printed from NFS reply packets, and SMB packets are fully decoded.
475 Even more verbose output.
477 telnet \fBSB\fP ... \fBSE\fP options
481 Telnet options are printed in hex as well.
484 Write the raw packets to \fIfile\fR rather than parsing and printing
486 They can later be printed with the \-r option.
487 Standard output is used if \fIfile\fR is ``-''.
490 Print each packet (minus its link level header) in hex.
491 The smaller of the entire packet or
493 bytes will be printed. Note that this is the entire link-layer
494 packet, so for link layers that pad (e.g. Ethernet), the padding bytes
495 will also be printed when the higher layer packet is shorter than the
501 its link level header, in hex.
504 Print each packet (minus its link level header) in hex and ASCII.
505 This is very handy for analysing new protocols.
510 its link level header, in hex and ASCII.
513 Set the data link type to use while capturing packets to \fIdatalinktype\fP.
514 .IP "\fI expression\fP"
516 selects which packets will be dumped.
517 If no \fIexpression\fP
518 is given, all packets on the net will be dumped.
520 only packets for which \fIexpression\fP is `true' will be dumped.
522 The \fIexpression\fP consists of one or more
524 Primitives usually consist of an
526 (name or number) preceded by one or more qualifiers.
528 different kinds of qualifier:
530 qualifiers say what kind of thing the id name or number refers to.
536 E.g., `host foo', `net 128.3', `port 20'.
542 qualifiers specify a particular transfer direction to and/or from
544 Possible directions are
551 E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'.
553 there is no dir qualifier,
556 For some link layers, such as SLIP and the ``cooked'' Linux capture mode
557 used for the ``any'' device and for some other device types, the
561 qualifiers can be used to specify a desired direction.
563 qualifiers restrict the match to a particular protocol.
578 E.g., `ether src foo', `arp net 128.3', `tcp port 21'.
580 no proto qualifier, all protocols consistent with the type are
582 E.g., `src foo' means `(ip or arp or rarp) src foo'
583 (except the latter is not legal syntax), `net bar' means `(ip or
584 arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'.
586 [`fddi' is actually an alias for `ether'; the parser treats them
587 identically as meaning ``the data link level used on the specified
588 network interface.'' FDDI headers contain Ethernet-like source
589 and destination addresses, and often contain Ethernet-like packet
590 types, so you can filter on these FDDI fields just as with the
591 analogous Ethernet fields.
592 FDDI headers also contain other fields,
593 but you cannot name them explicitly in a filter expression.
595 Similarly, `tr' and `wlan' are aliases for `ether'; the previous
596 paragraph's statements about FDDI headers also apply to Token Ring
597 and 802.11 wireless LAN headers. For 802.11 headers, the destination
598 address is the DA field and the source address is the SA field; the
599 BSSID, RA, and TA fields aren't tested.]
601 In addition to the above, there are some special `primitive' keywords
602 that don't follow the pattern:
607 and arithmetic expressions.
608 All of these are described below.
610 More complex filter expressions are built up by using the words
615 to combine primitives.
616 E.g., `host foo and not port ftp and not port ftp-data'.
617 To save typing, identical qualifier lists can be omitted.
619 `tcp dst port ftp or ftp-data or domain' is exactly the same as
620 `tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
622 Allowable primitives are:
623 .IP "\fBdst host \fIhost\fR"
624 True if the IPv4/v6 destination field of the packet is \fIhost\fP,
625 which may be either an address or a name.
626 .IP "\fBsrc host \fIhost\fR"
627 True if the IPv4/v6 source field of the packet is \fIhost\fP.
628 .IP "\fBhost \fIhost\fP
629 True if either the IPv4/v6 source or destination of the packet is \fIhost\fP.
630 Any of the above host expressions can be prepended with the keywords,
631 \fBip\fP, \fBarp\fP, \fBrarp\fP, or \fBip6\fP as in:
634 \fBip host \fIhost\fR
637 which is equivalent to:
640 \fBether proto \fI\\ip\fB and host \fIhost\fR
643 If \fIhost\fR is a name with multiple IP addresses, each address will
644 be checked for a match.
645 .IP "\fBether dst \fIehost\fP
646 True if the ethernet destination address is \fIehost\fP.
648 may be either a name from /etc/ethers or a number (see
651 .IP "\fBether src \fIehost\fP
652 True if the ethernet source address is \fIehost\fP.
653 .IP "\fBether host \fIehost\fP
654 True if either the ethernet source or destination address is \fIehost\fP.
655 .IP "\fBgateway\fP \fIhost\fP
656 True if the packet used \fIhost\fP as a gateway.
658 source or destination address was \fIhost\fP but neither the IP source
659 nor the IP destination was \fIhost\fP.
660 \fIHost\fP must be a name and
661 must be found both by the machine's host-name-to-IP-address resolution
662 mechanisms (host name file, DNS, NIS, etc.) and by the machine's
663 host-name-to-Ethernet-address resolution mechanism (/etc/ethers, etc.).
664 (An equivalent expression is
667 \fBether host \fIehost \fBand not host \fIhost\fR
670 which can be used with either names or numbers for \fIhost / ehost\fP.)
671 This syntax does not work in IPv6-enabled configuration at this moment.
672 .IP "\fBdst net \fInet\fR"
673 True if the IPv4/v6 destination address of the packet has a network
675 \fINet\fP may be either a name from /etc/networks
676 or a network number (see \fInetworks(4)\fP for details).
677 .IP "\fBsrc net \fInet\fR"
678 True if the IPv4/v6 source address of the packet has a network
680 .IP "\fBnet \fInet\fR"
681 True if either the IPv4/v6 source or destination address of the packet has a network
683 .IP "\fBnet \fInet\fR \fBmask \fInetmask\fR"
684 True if the IP address matches \fInet\fR with the specific \fInetmask\fR.
685 May be qualified with \fBsrc\fR or \fBdst\fR.
686 Note that this syntax is not valid for IPv6 \fInet\fR.
687 .IP "\fBnet \fInet\fR/\fIlen\fR"
688 True if the IPv4/v6 address matches \fInet\fR with a netmask \fIlen\fR
690 May be qualified with \fBsrc\fR or \fBdst\fR.
691 .IP "\fBdst port \fIport\fR"
692 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a
693 destination port value of \fIport\fP.
694 The \fIport\fP can be a number or a name used in /etc/services (see
698 If a name is used, both the port
699 number and protocol are checked.
700 If a number or ambiguous name is used,
701 only the port number is checked (e.g., \fBdst port 513\fR will print both
702 tcp/login traffic and udp/who traffic, and \fBport domain\fR will print
703 both tcp/domain and udp/domain traffic).
704 .IP "\fBsrc port \fIport\fR"
705 True if the packet has a source port value of \fIport\fP.
706 .IP "\fBport \fIport\fR"
707 True if either the source or destination port of the packet is \fIport\fP.
708 Any of the above port expressions can be prepended with the keywords,
709 \fBtcp\fP or \fBudp\fP, as in:
712 \fBtcp src port \fIport\fR
715 which matches only tcp packets whose source port is \fIport\fP.
716 .IP "\fBless \fIlength\fR"
717 True if the packet has a length less than or equal to \fIlength\fP.
718 This is equivalent to:
721 \fBlen <= \fIlength\fP.
724 .IP "\fBgreater \fIlength\fR"
725 True if the packet has a length greater than or equal to \fIlength\fP.
726 This is equivalent to:
729 \fBlen >= \fIlength\fP.
732 .IP "\fBip proto \fIprotocol\fR"
733 True if the packet is an IP packet (see
735 of protocol type \fIprotocol\fP.
736 \fIProtocol\fP can be a number or one of the names
737 \fIicmp\fP, \fIicmp6\fP, \fIigmp\fP, \fIigrp\fP, \fIpim\fP, \fIah\fP,
738 \fIesp\fP, \fIvrrp\fP, \fIudp\fP, or \fItcp\fP.
739 Note that the identifiers \fItcp\fP, \fIudp\fP, and \fIicmp\fP are also
740 keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell.
741 Note that this primitive does not chase the protocol header chain.
742 .IP "\fBip6 proto \fIprotocol\fR"
743 True if the packet is an IPv6 packet of protocol type \fIprotocol\fP.
744 Note that this primitive does not chase the protocol header chain.
745 .IP "\fBip6 protochain \fIprotocol\fR"
746 True if the packet is IPv6 packet,
747 and contains protocol header with type \fIprotocol\fR
748 in its protocol header chain.
752 \fBip6 protochain 6\fR
755 matches any IPv6 packet with TCP protocol header in the protocol header chain.
756 The packet may contain, for example,
757 authentication header, routing header, or hop-by-hop option header,
758 between IPv6 header and TCP header.
759 The BPF code emitted by this primitive is complex and
760 cannot be optimized by BPF optimizer code in \fItcpdump\fP,
761 so this can be somewhat slow.
762 .IP "\fBip protochain \fIprotocol\fR"
763 Equivalent to \fBip6 protochain \fIprotocol\fR, but this is for IPv4.
764 .IP "\fBether broadcast\fR"
765 True if the packet is an ethernet broadcast packet.
768 .IP "\fBip broadcast\fR"
769 True if the packet is an IPv4 broadcast packet.
770 It checks for both the all-zeroes and all-ones broadcast conventions,
771 and looks up the subnet mask on the interface on which the capture is
774 If the subnet mask of the interface on which the capture is being done
775 is not available, either because the interface on which capture is being
776 done has no netmask or because the capture is being done on the Linux
777 "any" interface, which can capture on more than one interface, this
778 check will not work correctly.
779 .IP "\fBether multicast\fR"
780 True if the packet is an ethernet multicast packet.
783 This is shorthand for `\fBether[0] & 1 != 0\fP'.
784 .IP "\fBip multicast\fR"
785 True if the packet is an IP multicast packet.
786 .IP "\fBip6 multicast\fR"
787 True if the packet is an IPv6 multicast packet.
788 .IP "\fBether proto \fIprotocol\fR"
789 True if the packet is of ether type \fIprotocol\fR.
790 \fIProtocol\fP can be a number or one of the names
791 \fIip\fP, \fIip6\fP, \fIarp\fP, \fIrarp\fP, \fIatalk\fP, \fIaarp\fP,
792 \fIdecnet\fP, \fIsca\fP, \fIlat\fP, \fImopdl\fP, \fImoprc\fP,
793 \fIiso\fP, \fIstp\fP, \fIipx\fP, or \fInetbeui\fP.
794 Note these identifiers are also keywords
795 and must be escaped via backslash (\\).
797 [In the case of FDDI (e.g., `\fBfddi protocol arp\fR'), Token Ring
798 (e.g., `\fBtr protocol arp\fR'), and IEEE 802.11 wireless LANS (e.g.,
799 `\fBwlan protocol arp\fR'), for most of those protocols, the
800 protocol identification comes from the 802.2 Logical Link Control (LLC)
801 header, which is usually layered on top of the FDDI, Token Ring, or
804 When filtering for most protocol identifiers on FDDI, Token Ring, or
805 802.11, \fItcpdump\fR checks only the protocol ID field of an LLC header
806 in so-called SNAP format with an Organizational Unit Identifier (OUI) of
807 0x000000, for encapsulated Ethernet; it doesn't check whether the packet
808 is in SNAP format with an OUI of 0x000000.
813 \fItcpdump\fR checks the DSAP (Destination Service Access Point) and
814 SSAP (Source Service Access Point) fields of the LLC header;
816 \fBstp\fP and \fInetbeui\fP
817 \fItcpdump\fR checks the DSAP of the LLC header;
820 \fItcpdump\fR checks for a SNAP-format packet with an OUI of 0x080007
821 and the AppleTalk etype.
824 In the case of Ethernet, \fItcpdump\fR checks the Ethernet type field
825 for most of those protocols. The exceptions are:
828 \fBiso\fP, \fBsap\fP, and \fBnetbeui\fP
829 \fItcpdump\fR checks for an 802.3 frame and then checks the LLC header as
830 it does for FDDI, Token Ring, and 802.11;
833 \fItcpdump\fR checks both for the AppleTalk etype in an Ethernet frame and
834 for a SNAP-format packet as it does for FDDI, Token Ring, and 802.11;
837 \fItcpdump\fR checks for the AppleTalk ARP etype in either an Ethernet
838 frame or an 802.2 SNAP frame with an OUI of 0x000000;
841 \fItcpdump\fR checks for the IPX etype in an Ethernet frame, the IPX
842 DSAP in the LLC header, the 802.3-with-no-LLC-header encapsulation of
843 IPX, and the IPX etype in a SNAP frame.
845 .IP "\fBdecnet src \fIhost\fR"
846 True if the DECNET source address is
848 which may be an address of the form ``10.123'', or a DECNET host
850 [DECNET host name support is only available on Ultrix systems
851 that are configured to run DECNET.]
852 .IP "\fBdecnet dst \fIhost\fR"
853 True if the DECNET destination address is
855 .IP "\fBdecnet host \fIhost\fR"
856 True if either the DECNET source or destination address is
858 .IP "\fBifname \fIinterface\fR"
859 True if the packet was logged as coming from the specified interface (applies
860 only to packets logged by OpenBSD's
862 .IP "\fBon \fIinterface\fR"
866 .IP "\fBrnr \fInum\fR"
867 True if the packet was logged as matching the specified PF rule number
868 (applies only to packets logged by OpenBSD's
870 .IP "\fBrulenum \fInum\fR"
874 .IP "\fBreason \fIcode\fR"
875 True if the packet was logged with the specified PF reason code. The known
884 (applies only to packets logged by OpenBSD's
886 .IP "\fBaction \fIact\fR"
887 True if PF took the specified action when the packet was logged. Known actions
892 (applies only to packets logged by OpenBSD's
894 .IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBatalk\fR, \fBaarp\fR, \fBdecnet\fR, \fBiso\fR, \fBstp\fR, \fBipx\fR, \fInetbeui\fP"
898 \fBether proto \fIp\fR
901 where \fIp\fR is one of the above protocols.
902 .IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR"
906 \fBether proto \fIp\fR
909 where \fIp\fR is one of the above protocols.
911 \fItcpdump\fP does not currently know how to parse these protocols.
912 .IP "\fBvlan \fI[vlan_id]\fR"
913 True if the packet is an IEEE 802.1Q VLAN packet.
914 If \fI[vlan_id]\fR is specified, only true is the packet has the specified
916 Note that the first \fBvlan\fR keyword encountered in \fIexpression\fR
917 changes the decoding offsets for the remainder of \fIexpression\fR
918 on the assumption that the packet is a VLAN packet.
919 .IP "\fBtcp\fR, \fBudp\fR, \fBicmp\fR"
923 \fBip proto \fIp\fR\fB or ip6 proto \fIp\fR
926 where \fIp\fR is one of the above protocols.
927 .IP "\fBiso proto \fIprotocol\fR"
928 True if the packet is an OSI packet of protocol type \fIprotocol\fP.
929 \fIProtocol\fP can be a number or one of the names
930 \fIclnp\fP, \fIesis\fP, or \fIisis\fP.
931 .IP "\fBclnp\fR, \fBesis\fR, \fBisis\fR"
938 where \fIp\fR is one of the above protocols.
939 .IP "\fBl1\fR, \fBl2\fR, \fBiih\fR, \fBlsp\fR, \fBsnp\fR, \fBcsnp\fR, \fBpsnp\fR"
940 Abbreviations for IS-IS PDU types.
941 .IP "\fBvpi\fP \fIn\fR
942 True if the packet is an ATM packet, for SunATM on Solaris, with a
943 virtual path identifier of
945 .IP "\fBvci\fP \fIn\fR
946 True if the packet is an ATM packet, for SunATM on Solaris, with a
947 virtual channel identifier of
950 True if the packet is an ATM packet, for SunATM on Solaris, and is
952 Note that the first \fBlane\fR keyword encountered in \fIexpression\fR
953 changes the tests done in the remainder of \fIexpression\fR
954 on the assumption that the packet is either a LANE emulated Ethernet
955 packet or a LANE LE Control packet. If \fBlane\fR isn't specified, the
956 tests are done under the assumption that the packet is an
957 LLC-encapsulated packet.
959 True if the packet is an ATM packet, for SunATM on Solaris, and is
960 an LLC-encapsulated packet.
962 True if the packet is an ATM packet, for SunATM on Solaris, and is
963 a segment OAM F4 flow cell (VPI=0 & VCI=3).
965 True if the packet is an ATM packet, for SunATM on Solaris, and is
966 an end-to-end OAM F4 flow cell (VPI=0 & VCI=4).
968 True if the packet is an ATM packet, for SunATM on Solaris, and is
969 a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).
971 True if the packet is an ATM packet, for SunATM on Solaris, and is
972 a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).
974 True if the packet is an ATM packet, for SunATM on Solaris, and is
975 on a meta signaling circuit (VPI=0 & VCI=1).
977 True if the packet is an ATM packet, for SunATM on Solaris, and is
978 on a broadcast signaling circuit (VPI=0 & VCI=2).
980 True if the packet is an ATM packet, for SunATM on Solaris, and is
981 on a signaling circuit (VPI=0 & VCI=5).
983 True if the packet is an ATM packet, for SunATM on Solaris, and is
984 on an ILMI circuit (VPI=0 & VCI=16).
986 True if the packet is an ATM packet, for SunATM on Solaris, and is
987 on a signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect,
988 Connect Ack, Release, or Release Done message.
989 .IP \fBmetaconnect\fP
990 True if the packet is an ATM packet, for SunATM on Solaris, and is
991 on a meta signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect,
992 Release, or Release Done message.
993 .IP "\fIexpr relop expr\fR"
994 True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =, !=,
995 and \fIexpr\fR is an arithmetic expression composed of integer constants
996 (expressed in standard C syntax), the normal binary operators
997 [+, -, *, /, &, |], a length operator, and special packet data accessors.
999 data inside the packet, use the following syntax:
1002 \fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR
1005 \fIProto\fR is one of \fBether, fddi, tr, wlan, ppp, slip, link,
1006 ip, arp, rarp, tcp, udp, icmp\fR or \fBip6\fR, and
1007 indicates the protocol layer for the index operation.
1008 (\fBether, fddi, wlan, tr, ppp, slip\fR and \fBlink\fR all refer to the
1010 Note that \fItcp, udp\fR and other upper-layer protocol types only
1011 apply to IPv4, not IPv6 (this will be fixed in the future).
1012 The byte offset, relative to the indicated protocol layer, is
1013 given by \fIexpr\fR.
1014 \fISize\fR is optional and indicates the number of bytes in the
1015 field of interest; it can be either one, two, or four, and defaults to one.
1016 The length operator, indicated by the keyword \fBlen\fP, gives the
1017 length of the packet.
1019 For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic.
1020 The expression `\fBip[0] & 0xf != 5\fP'
1021 catches all IP packets with options.
1023 `\fBip[6:2] & 0x1fff = 0\fP'
1024 catches only unfragmented datagrams and frag zero of fragmented datagrams.
1025 This check is implicitly applied to the \fBtcp\fP and \fBudp\fP
1027 For instance, \fBtcp[0]\fP always means the first
1028 byte of the TCP \fIheader\fP, and never means the first byte of an
1029 intervening fragment.
1031 Some offsets and field values may be expressed as names rather than
1033 The following protocol header field offsets are
1034 available: \fBicmptype\fP (ICMP type field), \fBicmpcode\fP (ICMP
1035 code field), and \fBtcpflags\fP (TCP flags field).
1037 The following ICMP type field values are available: \fBicmp-echoreply\fP,
1038 \fBicmp-unreach\fP, \fBicmp-sourcequench\fP, \fBicmp-redirect\fP,
1039 \fBicmp-echo\fP, \fBicmp-routeradvert\fP, \fBicmp-routersolicit\fP,
1040 \fBicmp-timxceed\fP, \fBicmp-paramprob\fP, \fBicmp-tstamp\fP,
1041 \fBicmp-tstampreply\fP, \fBicmp-ireq\fP, \fBicmp-ireqreply\fP,
1042 \fBicmp-maskreq\fP, \fBicmp-maskreply\fP.
1044 The following TCP flags field values are available: \fBtcp-fin\fP,
1045 \fBtcp-syn\fP, \fBtcp-rst\fP, \fBtcp-push\fP,
1046 \fBtcp-ack\fP, \fBtcp-urg\fP.
1048 Primitives may be combined using:
1050 A parenthesized group of primitives and operators
1051 (parentheses are special to the Shell and must be escaped).
1053 Negation (`\fB!\fP' or `\fBnot\fP').
1055 Concatenation (`\fB&&\fP' or `\fBand\fP').
1057 Alternation (`\fB||\fP' or `\fBor\fP').
1059 Negation has highest precedence.
1060 Alternation and concatenation have equal precedence and associate
1062 Note that explicit \fBand\fR tokens, not juxtaposition,
1063 are now required for concatenation.
1065 If an identifier is given without a keyword, the most recent keyword
1070 \fBnot host vs and ace\fR
1076 \fBnot host vs and host ace\fR
1079 which should not be confused with
1082 \fBnot ( host vs or ace )\fR
1086 Expression arguments can be passed to \fItcpdump\fP as either a single
1087 argument or as multiple arguments, whichever is more convenient.
1088 Generally, if the expression contains Shell metacharacters, it is
1089 easier to pass it as a single, quoted argument.
1090 Multiple arguments are concatenated with spaces before being parsed.
1093 To print all packets arriving at or departing from \fIsundown\fP:
1096 \fBtcpdump host sundown\fP
1100 To print traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR:
1103 \fBtcpdump host helios and \\( hot or ace \\)\fP
1107 To print all IP packets between \fIace\fR and any host except \fIhelios\fR:
1110 \fBtcpdump ip host ace and not helios\fP
1114 To print all traffic between local hosts and hosts at Berkeley:
1118 tcpdump net ucb-ether
1122 To print all ftp traffic through internet gateway \fIsnup\fP:
1123 (note that the expression is quoted to prevent the shell from
1124 (mis-)interpreting the parentheses):
1128 tcpdump 'gateway snup and (port ftp or ftp-data)'
1132 To print traffic neither sourced from nor destined for local hosts
1133 (if you gateway to one other net, this stuff should never make it
1134 onto your local net).
1138 tcpdump ip and not net \fIlocalnet\fP
1142 To print the start and end packets (the SYN and FIN packets) of each
1143 TCP conversation that involves a non-local host.
1147 tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net \fIlocalnet\fP'
1151 To print IP packets longer than 576 bytes sent through gateway \fIsnup\fP:
1155 tcpdump 'gateway snup and ip[2:2] > 576'
1159 To print IP broadcast or multicast packets that were
1161 sent via ethernet broadcast or multicast:
1165 tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'
1169 To print all ICMP packets that are not echo requests/replies (i.e., not
1174 tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'
1179 The output of \fItcpdump\fP is protocol dependent.
1181 gives a brief description and examples of most of the formats.
1189 If the '-e' option is given, the link level header is printed out.
1190 On ethernets, the source and destination addresses, protocol,
1191 and packet length are printed.
1193 On FDDI networks, the '-e' option causes \fItcpdump\fP to print
1194 the `frame control' field, the source and destination addresses,
1195 and the packet length.
1196 (The `frame control' field governs the
1197 interpretation of the rest of the packet.
1198 Normal packets (such
1199 as those containing IP datagrams) are `async' packets, with a priority
1200 value between 0 and 7; for example, `\fBasync4\fR'.
1202 are assumed to contain an 802.2 Logical Link Control (LLC) packet;
1203 the LLC header is printed if it is \fInot\fR an ISO datagram or a
1204 so-called SNAP packet.
1206 On Token Ring networks, the '-e' option causes \fItcpdump\fP to print
1207 the `access control' and `frame control' fields, the source and
1208 destination addresses, and the packet length.
1209 As on FDDI networks,
1210 packets are assumed to contain an LLC packet.
1211 Regardless of whether
1212 the '-e' option is specified or not, the source routing information is
1213 printed for source-routed packets.
1215 On 802.11 networks, the '-e' option causes \fItcpdump\fP to print
1216 the `frame control' fields, all of the addresses in the 802.11 header,
1217 and the packet length.
1218 As on FDDI networks,
1219 packets are assumed to contain an LLC packet.
1221 \fI(N.B.: The following description assumes familiarity with
1222 the SLIP compression algorithm described in RFC-1144.)\fP
1224 On SLIP links, a direction indicator (``I'' for inbound, ``O'' for outbound),
1225 packet type, and compression information are printed out.
1226 The packet type is printed first.
1227 The three types are \fIip\fP, \fIutcp\fP, and \fIctcp\fP.
1228 No further link information is printed for \fIip\fR packets.
1229 For TCP packets, the connection identifier is printed following the type.
1230 If the packet is compressed, its encoded header is printed out.
1231 The special cases are printed out as
1232 \fB*S+\fIn\fR and \fB*SA+\fIn\fR, where \fIn\fR is the amount by which
1233 the sequence number (or sequence number and ack) has changed.
1234 If it is not a special case,
1235 zero or more changes are printed.
1236 A change is indicated by U (urgent pointer), W (window), A (ack),
1237 S (sequence number), and I (packet ID), followed by a delta (+n or -n),
1238 or a new value (=n).
1239 Finally, the amount of data in the packet and compressed header length
1242 For example, the following line shows an outbound compressed TCP packet,
1243 with an implicit connection identifier; the ack has changed by 6,
1244 the sequence number by 49, and the packet ID by 6; there are 3 bytes of
1245 data and 6 bytes of compressed header:
1248 \fBO ctcp * A+6 S+49 I+6 3 (6)\fP
1254 Arp/rarp output shows the type of request and its arguments.
1256 format is intended to be self explanatory.
1257 Here is a short sample taken from the start of an `rlogin' from
1258 host \fIrtsg\fP to host \fIcsam\fP:
1262 \f(CWarp who-has csam tell rtsg
1263 arp reply csam is-at CSAM\fR
1267 The first line says that rtsg sent an arp packet asking
1268 for the ethernet address of internet host csam.
1270 replies with its ethernet address (in this example, ethernet addresses
1271 are in caps and internet addresses in lower case).
1273 This would look less redundant if we had done \fItcpdump \-n\fP:
1277 \f(CWarp who-has 128.3.254.6 tell 128.3.254.68
1278 arp reply 128.3.254.6 is-at 02:07:01:00:01:c4\fP
1282 If we had done \fItcpdump \-e\fP, the fact that the first packet is
1283 broadcast and the second is point-to-point would be visible:
1287 \f(CWRTSG Broadcast 0806 64: arp who-has csam tell rtsg
1288 CSAM RTSG 0806 64: arp reply csam is-at CSAM\fR
1292 For the first packet this says the ethernet source address is RTSG, the
1293 destination is the ethernet broadcast address, the type field
1294 contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes.
1298 \fI(N.B.:The following description assumes familiarity with
1299 the TCP protocol described in RFC-793.
1300 If you are not familiar
1301 with the protocol, neither this description nor \fItcpdump\fP will
1302 be of much use to you.)\fP
1304 The general format of a tcp protocol line is:
1308 \fIsrc > dst: flags data-seqno ack window urgent options\fP
1312 \fISrc\fP and \fIdst\fP are the source and destination IP
1313 addresses and ports.
1314 \fIFlags\fP are some combination of S (SYN),
1315 F (FIN), P (PUSH) or R (RST) or a single `.' (no flags).
1316 \fIData-seqno\fP describes the portion of sequence space covered
1317 by the data in this packet (see example below).
1318 \fIAck\fP is sequence number of the next data expected the other
1319 direction on this connection.
1320 \fIWindow\fP is the number of bytes of receive buffer space available
1321 the other direction on this connection.
1322 \fIUrg\fP indicates there is `urgent' data in the packet.
1323 \fIOptions\fP are tcp options enclosed in angle brackets (e.g., <mss 1024>).
1325 \fISrc, dst\fP and \fIflags\fP are always present.
1327 depend on the contents of the packet's tcp protocol header and
1328 are output only if appropriate.
1330 Here is the opening portion of an rlogin from host \fIrtsg\fP to
1335 \s-2\f(CWrtsg.1023 > csam.login: S 768512:768512(0) win 4096 <mss 1024>
1336 csam.login > rtsg.1023: S 947648:947648(0) ack 768513 win 4096 <mss 1024>
1337 rtsg.1023 > csam.login: . ack 1 win 4096
1338 rtsg.1023 > csam.login: P 1:2(1) ack 1 win 4096
1339 csam.login > rtsg.1023: . ack 2 win 4096
1340 rtsg.1023 > csam.login: P 2:21(19) ack 1 win 4096
1341 csam.login > rtsg.1023: P 1:2(1) ack 21 win 4077
1342 csam.login > rtsg.1023: P 2:3(1) ack 21 win 4077 urg 1
1343 csam.login > rtsg.1023: P 3:4(1) ack 21 win 4077 urg 1\fR\s+2
1347 The first line says that tcp port 1023 on rtsg sent a packet
1350 The \fBS\fP indicates that the \fISYN\fP flag was set.
1351 The packet sequence number was 768512 and it contained no data.
1352 (The notation is `first:last(nbytes)' which means `sequence
1354 up to but not including \fIlast\fP which is \fInbytes\fP bytes of user data'.)
1355 There was no piggy-backed ack, the available receive window was 4096
1356 bytes and there was a max-segment-size option requesting an mss of
1359 Csam replies with a similar packet except it includes a piggy-backed
1361 Rtsg then acks csam's SYN.
1364 The packet contained no data so there is no data sequence number.
1365 Note that the ack sequence
1366 number is a small integer (1).
1367 The first time \fItcpdump\fP sees a
1368 tcp `conversation', it prints the sequence number from the packet.
1369 On subsequent packets of the conversation, the difference between
1370 the current packet's sequence number and this initial sequence number
1372 This means that sequence numbers after the
1373 first can be interpreted
1374 as relative byte positions in the conversation's data stream (with the
1375 first data byte each direction being `1').
1376 `-S' will override this
1377 feature, causing the original sequence numbers to be output.
1379 On the 6th line, rtsg sends csam 19 bytes of data (bytes 2 through 20
1380 in the rtsg \(-> csam side of the conversation).
1381 The PUSH flag is set in the packet.
1382 On the 7th line, csam says it's received data sent by rtsg up to
1383 but not including byte 21.
1384 Most of this data is apparently sitting in the
1385 socket buffer since csam's receive window has gotten 19 bytes smaller.
1386 Csam also sends one byte of data to rtsg in this packet.
1387 On the 8th and 9th lines,
1388 csam sends two bytes of urgent, pushed data to rtsg.
1390 If the snapshot was small enough that \fItcpdump\fP didn't capture
1391 the full TCP header, it interprets as much of the header as it can
1392 and then reports ``[|\fItcp\fP]'' to indicate the remainder could not
1394 If the header contains a bogus option (one with a length
1395 that's either too small or beyond the end of the header), \fItcpdump\fP
1396 reports it as ``[\fIbad opt\fP]'' and does not interpret any further
1397 options (since it's impossible to tell where they start).
1399 length indicates options are present but the IP datagram length is not
1400 long enough for the options to actually be there, \fItcpdump\fP reports
1401 it as ``[\fIbad hdr length\fP]''.
1403 .B Capturing TCP packets with particular flag combinations (SYN-ACK, URG-ACK, etc.)
1405 There are 8 bits in the control bits section of the TCP header:
1407 .I CWR | ECE | URG | ACK | PSH | RST | SYN | FIN
1409 Let's assume that we want to watch packets used in establishing
1411 Recall that TCP uses a 3-way handshake protocol
1412 when it initializes a new connection; the connection sequence with
1413 regard to the TCP control bits is
1419 2) Recipient responds with SYN, ACK
1425 Now we're interested in capturing packets that have only the
1426 SYN bit set (Step 1).
1427 Note that we don't want packets from step 2
1428 (SYN-ACK), just a plain initial SYN.
1429 What we need is a correct filter
1430 expression for \fItcpdump\fP.
1432 Recall the structure of a TCP header without options:
1436 -----------------------------------------------------------------
1437 | source port | destination port |
1438 -----------------------------------------------------------------
1440 -----------------------------------------------------------------
1441 | acknowledgment number |
1442 -----------------------------------------------------------------
1443 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1444 -----------------------------------------------------------------
1445 | TCP checksum | urgent pointer |
1446 -----------------------------------------------------------------
1449 A TCP header usually holds 20 octets of data, unless options are
1451 The first line of the graph contains octets 0 - 3, the
1452 second line shows octets 4 - 7 etc.
1454 Starting to count with 0, the relevant TCP control bits are contained
1459 ----------------|---------------|---------------|----------------
1460 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1461 ----------------|---------------|---------------|----------------
1462 | | 13th octet | | |
1465 Let's have a closer look at octet no. 13:
1475 These are the TCP control bits we are interested
1477 We have numbered the bits in this octet from 0 to 7, right to
1478 left, so the PSH bit is bit number 3, while the URG bit is number 5.
1480 Recall that we want to capture packets with only SYN set.
1481 Let's see what happens to octet 13 if a TCP datagram arrives
1482 with the SYN bit set in its header:
1493 control bits section we see that only bit number 1 (SYN) is set.
1495 Assuming that octet number 13 is an 8-bit unsigned integer in
1496 network byte order, the binary value of this octet is
1500 and its decimal representation is
1504 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 1*2 + 0*2 = 2
1507 We're almost done, because now we know that if only SYN is set,
1508 the value of the 13th octet in the TCP header, when interpreted
1509 as a 8-bit unsigned integer in network byte order, must be exactly 2.
1511 This relationship can be expressed as
1517 We can use this expression as the filter for \fItcpdump\fP in order
1518 to watch packets which have only SYN set:
1521 tcpdump -i xl0 tcp[13] == 2
1524 The expression says "let the 13th octet of a TCP datagram have
1525 the decimal value 2", which is exactly what we want.
1527 Now, let's assume that we need to capture SYN packets, but we
1528 don't care if ACK or any other TCP control bit is set at the
1530 Let's see what happens to octet 13 when a TCP datagram
1531 with SYN-ACK set arrives:
1541 Now bits 1 and 4 are set in the 13th octet.
1547 which translates to decimal
1551 0*2 + 0*2 + 0*2 + 1*2 + 0*2 + 0*2 + 1*2 + 0*2 = 18
1554 Now we can't just use 'tcp[13] == 18' in the \fItcpdump\fP filter
1555 expression, because that would select only those packets that have
1556 SYN-ACK set, but not those with only SYN set.
1557 Remember that we don't care
1558 if ACK or any other control bit is set as long as SYN is set.
1560 In order to achieve our goal, we need to logically AND the
1561 binary value of octet 13 with some other value to preserve
1563 We know that we want SYN to be set in any case,
1564 so we'll logically AND the value in the 13th octet with
1565 the binary value of a SYN:
1569 00010010 SYN-ACK 00000010 SYN
1570 AND 00000010 (we want SYN) AND 00000010 (we want SYN)
1572 = 00000010 = 00000010
1575 We see that this AND operation delivers the same result
1576 regardless whether ACK or another TCP control bit is set.
1577 The decimal representation of the AND value as well as
1578 the result of this operation is 2 (binary 00000010),
1579 so we know that for packets with SYN set the following
1580 relation must hold true:
1582 ( ( value of octet 13 ) AND ( 2 ) ) == ( 2 )
1584 This points us to the \fItcpdump\fP filter expression
1587 tcpdump -i xl0 'tcp[13] & 2 == 2'
1590 Note that you should use single quotes or a backslash
1591 in the expression to hide the AND ('&') special character
1597 UDP format is illustrated by this rwho packet:
1601 \f(CWactinide.who > broadcast.who: udp 84\fP
1605 This says that port \fIwho\fP on host \fIactinide\fP sent a udp
1606 datagram to port \fIwho\fP on host \fIbroadcast\fP, the Internet
1608 The packet contained 84 bytes of user data.
1610 Some UDP services are recognized (from the source or destination
1611 port number) and the higher level protocol information printed.
1612 In particular, Domain Name service requests (RFC-1034/1035) and Sun
1613 RPC calls (RFC-1050) to NFS.
1615 UDP Name Server Requests
1617 \fI(N.B.:The following description assumes familiarity with
1618 the Domain Service protocol described in RFC-1035.
1619 If you are not familiar
1620 with the protocol, the following description will appear to be written
1623 Name server requests are formatted as
1627 \fIsrc > dst: id op? flags qtype qclass name (len)\fP
1629 \f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fR
1633 Host \fIh2opolo\fP asked the domain server on \fIhelios\fP for an
1634 address record (qtype=A) associated with the name \fIucbvax.berkeley.edu.\fP
1635 The query id was `3'.
1636 The `+' indicates the \fIrecursion desired\fP flag
1638 The query length was 37 bytes, not including the UDP and
1639 IP protocol headers.
1640 The query operation was the normal one, \fIQuery\fP,
1641 so the op field was omitted.
1642 If the op had been anything else, it would
1643 have been printed between the `3' and the `+'.
1644 Similarly, the qclass was the normal one,
1645 \fIC_IN\fP, and omitted.
1646 Any other qclass would have been printed
1647 immediately after the `A'.
1649 A few anomalies are checked and may result in extra fields enclosed in
1650 square brackets: If a query contains an answer, authority records or
1651 additional records section,
1656 are printed as `[\fIn\fPa]', `[\fIn\fPn]' or `[\fIn\fPau]' where \fIn\fP
1657 is the appropriate count.
1658 If any of the response bits are set (AA, RA or rcode) or any of the
1659 `must be zero' bits are set in bytes two and three, `[b2&3=\fIx\fP]'
1660 is printed, where \fIx\fP is the hex value of header bytes two and three.
1662 UDP Name Server Responses
1664 Name server responses are formatted as
1668 \fIsrc > dst: id op rcode flags a/n/au type class data (len)\fP
1670 \f(CWhelios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273)
1671 helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fR
1675 In the first example, \fIhelios\fP responds to query id 3 from \fIh2opolo\fP
1676 with 3 answer records, 3 name server records and 7 additional records.
1677 The first answer record is type A (address) and its data is internet
1678 address 128.32.137.3.
1679 The total size of the response was 273 bytes,
1680 excluding UDP and IP headers.
1681 The op (Query) and response code
1682 (NoError) were omitted, as was the class (C_IN) of the A record.
1684 In the second example, \fIhelios\fP responds to query 2 with a
1685 response code of non-existent domain (NXDomain) with no answers,
1686 one name server and no authority records.
1687 The `*' indicates that
1688 the \fIauthoritative answer\fP bit was set.
1690 answers, no type, class or data were printed.
1692 Other flag characters that might appear are `\-' (recursion available,
1693 RA, \fInot\fP set) and `|' (truncated message, TC, set).
1695 `question' section doesn't contain exactly one entry, `[\fIn\fPq]'
1698 Note that name server requests and responses tend to be large and the
1699 default \fIsnaplen\fP of 68 bytes may not capture enough of the packet
1701 Use the \fB\-s\fP flag to increase the snaplen if you
1702 need to seriously investigate name server traffic.
1704 has worked well for me.
1709 \fItcpdump\fP now includes fairly extensive SMB/CIFS/NBT decoding for data
1710 on UDP/137, UDP/138 and TCP/139.
1711 Some primitive decoding of IPX and
1712 NetBEUI SMB data is also done.
1714 By default a fairly minimal decode is done, with a much more detailed
1715 decode done if -v is used.
1716 Be warned that with -v a single SMB packet
1717 may take up a page or more, so only use -v if you really want all the
1720 If you are decoding SMB sessions containing unicode strings then you
1721 may wish to set the environment variable USE_UNICODE to 1.
1723 auto-detect unicode strings would be welcome.
1725 For information on SMB packet formats and what all te fields mean see
1726 www.cifs.org or the pub/samba/specs/ directory on your favorite
1727 samba.org mirror site.
1728 The SMB patches were written by Andrew Tridgell
1732 NFS Requests and Replies
1734 Sun NFS (Network File System) requests and replies are printed as:
1738 \fIsrc.xid > dst.nfs: len op args\fP
1739 \fIsrc.nfs > dst.xid: reply stat len op results\fP
1742 sushi.6709 > wrl.nfs: 112 readlink fh 21,24/10.73165
1743 wrl.nfs > sushi.6709: reply ok 40 readlink "../var"
1744 sushi.201b > wrl.nfs:
1745 144 lookup fh 9,74/4096.6878 "xcolors"
1746 wrl.nfs > sushi.201b:
1747 reply ok 128 lookup fh 9,74/4134.3150
1752 In the first line, host \fIsushi\fP sends a transaction with id \fI6709\fP
1753 to \fIwrl\fP (note that the number following the src host is a
1754 transaction id, \fInot\fP the source port).
1755 The request was 112 bytes,
1756 excluding the UDP and IP headers.
1757 The operation was a \fIreadlink\fP
1758 (read symbolic link) on file handle (\fIfh\fP) 21,24/10.731657119.
1759 (If one is lucky, as in this case, the file handle can be interpreted
1760 as a major,minor device number pair, followed by the inode number and
1762 \fIWrl\fP replies `ok' with the contents of the link.
1764 In the third line, \fIsushi\fP asks \fIwrl\fP to lookup the name
1765 `\fIxcolors\fP' in directory file 9,74/4096.6878.
1766 Note that the data printed
1767 depends on the operation type.
1768 The format is intended to be self
1769 explanatory if read in conjunction with
1770 an NFS protocol spec.
1772 If the \-v (verbose) flag is given, additional information is printed.
1778 sushi.1372a > wrl.nfs:
1779 148 read fh 21,11/12.195 8192 bytes @ 24576
1780 wrl.nfs > sushi.1372a:
1781 reply ok 1472 read REG 100664 ids 417/0 sz 29388
1786 (\-v also prints the IP header TTL, ID, length, and fragmentation fields,
1787 which have been omitted from this example.) In the first line,
1788 \fIsushi\fP asks \fIwrl\fP to read 8192 bytes from file 21,11/12.195,
1789 at byte offset 24576.
1790 \fIWrl\fP replies `ok'; the packet shown on the
1791 second line is the first fragment of the reply, and hence is only 1472
1792 bytes long (the other bytes will follow in subsequent fragments, but
1793 these fragments do not have NFS or even UDP headers and so might not be
1794 printed, depending on the filter expression used).
1795 Because the \-v flag
1796 is given, some of the file attributes (which are returned in addition
1797 to the file data) are printed: the file type (``REG'', for regular file),
1798 the file mode (in octal), the uid and gid, and the file size.
1800 If the \-v flag is given more than once, even more details are printed.
1802 Note that NFS requests are very large and much of the detail won't be printed
1803 unless \fIsnaplen\fP is increased.
1804 Try using `\fB\-s 192\fP' to watch
1807 NFS reply packets do not explicitly identify the RPC operation.
1809 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1810 replies using the transaction ID.
1811 If a reply does not closely follow the
1812 corresponding request, it might not be parsable.
1814 AFS Requests and Replies
1816 Transarc AFS (Andrew File System) requests and replies are printed
1822 \fIsrc.sport > dst.dport: rx packet-type\fP
1823 \fIsrc.sport > dst.dport: rx packet-type service call call-name args\fP
1824 \fIsrc.sport > dst.dport: rx packet-type service reply call-name args\fP
1827 elvis.7001 > pike.afsfs:
1828 rx data fs call rename old fid 536876964/1/1 ".newsrc.new"
1829 new fid 536876964/1/1 ".newsrc"
1830 pike.afsfs > elvis.7001: rx data fs reply rename
1835 In the first line, host elvis sends a RX packet to pike.
1837 a RX data packet to the fs (fileserver) service, and is the start of
1839 The RPC call was a rename, with the old directory file id
1840 of 536876964/1/1 and an old filename of `.newsrc.new', and a new directory
1841 file id of 536876964/1/1 and a new filename of `.newsrc'.
1843 responds with a RPC reply to the rename call (which was successful, because
1844 it was a data packet and not an abort packet).
1846 In general, all AFS RPCs are decoded at least by RPC call name.
1848 AFS RPCs have at least some of the arguments decoded (generally only
1849 the `interesting' arguments, for some definition of interesting).
1851 The format is intended to be self-describing, but it will probably
1852 not be useful to people who are not familiar with the workings of
1855 If the -v (verbose) flag is given twice, acknowledgement packets and
1856 additional header information is printed, such as the the RX call ID,
1857 call number, sequence number, serial number, and the RX packet flags.
1859 If the -v flag is given twice, additional information is printed,
1860 such as the the RX call ID, serial number, and the RX packet flags.
1861 The MTU negotiation information is also printed from RX ack packets.
1863 If the -v flag is given three times, the security index and service id
1866 Error codes are printed for abort packets, with the exception of Ubik
1867 beacon packets (because abort packets are used to signify a yes vote
1868 for the Ubik protocol).
1870 Note that AFS requests are very large and many of the arguments won't
1871 be printed unless \fIsnaplen\fP is increased.
1872 Try using `\fB-s 256\fP'
1873 to watch AFS traffic.
1875 AFS reply packets do not explicitly identify the RPC operation.
1877 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1878 replies using the call number and service ID.
1879 If a reply does not closely
1881 corresponding request, it might not be parsable.
1884 KIP AppleTalk (DDP in UDP)
1886 AppleTalk DDP packets encapsulated in UDP datagrams are de-encapsulated
1887 and dumped as DDP packets (i.e., all the UDP header information is
1891 is used to translate appletalk net and node numbers to names.
1892 Lines in this file have the form
1904 The first two lines give the names of appletalk networks.
1906 line gives the name of a particular host (a host is distinguished
1907 from a net by the 3rd octet in the number \-
1908 a net number \fImust\fP have two octets and a host number \fImust\fP
1909 have three octets.) The number and name should be separated by
1910 whitespace (blanks or tabs).
1913 file may contain blank lines or comment lines (lines starting with
1916 AppleTalk addresses are printed in the form
1922 \f(CW144.1.209.2 > icsd-net.112.220
1923 office.2 > icsd-net.112.220
1924 jssmag.149.235 > icsd-net.2\fR
1930 doesn't exist or doesn't contain an entry for some appletalk
1931 host/net number, addresses are printed in numeric form.)
1932 In the first example, NBP (DDP port 2) on net 144.1 node 209
1933 is sending to whatever is listening on port 220 of net icsd node 112.
1934 The second line is the same except the full name of the source node
1935 is known (`office').
1936 The third line is a send from port 235 on
1937 net jssmag node 149 to broadcast on the icsd-net NBP port (note that
1938 the broadcast address (255) is indicated by a net name with no host
1939 number \- for this reason it's a good idea to keep node names and
1940 net names distinct in /etc/atalk.names).
1942 NBP (name binding protocol) and ATP (AppleTalk transaction protocol)
1943 packets have their contents interpreted.
1944 Other protocols just dump
1945 the protocol name (or number if no name is registered for the
1946 protocol) and packet size.
1948 \fBNBP packets\fP are formatted like the following examples:
1952 \s-2\f(CWicsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
1953 jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
1954 techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fR\s+2
1958 The first line is a name lookup request for laserwriters sent by net icsd host
1959 112 and broadcast on net jssmag.
1960 The nbp id for the lookup is 190.
1961 The second line shows a reply for this request (note that it has the
1962 same id) from host jssmag.209 saying that it has a laserwriter
1963 resource named "RM1140" registered on port 250.
1965 another reply to the same request saying host techpit has laserwriter
1966 "techpit" registered on port 186.
1968 \fBATP packet\fP formatting is demonstrated by the following example:
1972 \s-2\f(CWjssmag.209.165 > helios.132: atp-req 12266<0-7> 0xae030001
1973 helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
1974 helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
1975 helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
1976 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1977 helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
1978 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1979 helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
1980 helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
1981 jssmag.209.165 > helios.132: atp-req 12266<3,5> 0xae030001
1982 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1983 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1984 jssmag.209.165 > helios.132: atp-rel 12266<0-7> 0xae030001
1985 jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fR\s+2
1989 Jssmag.209 initiates transaction id 12266 with host helios by requesting
1990 up to 8 packets (the `<0-7>').
1991 The hex number at the end of the line
1992 is the value of the `userdata' field in the request.
1994 Helios responds with 8 512-byte packets.
1995 The `:digit' following the
1996 transaction id gives the packet sequence number in the transaction
1997 and the number in parens is the amount of data in the packet,
1998 excluding the atp header.
1999 The `*' on packet 7 indicates that the
2002 Jssmag.209 then requests that packets 3 & 5 be retransmitted.
2004 resends them then jssmag.209 releases the transaction.
2006 jssmag.209 initiates the next request.
2007 The `*' on the request
2008 indicates that XO (`exactly once') was \fInot\fP set.
2013 Fragmented Internet datagrams are printed as
2017 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR
2018 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR
2022 (The first form indicates there are more fragments.
2024 indicates this is the last fragment.)
2026 \fIId\fP is the fragment id.
2027 \fISize\fP is the fragment
2028 size (in bytes) excluding the IP header.
2029 \fIOffset\fP is this
2030 fragment's offset (in bytes) in the original datagram.
2032 The fragment information is output for each fragment.
2034 fragment contains the higher level protocol header and the frag
2035 info is printed after the protocol info.
2037 after the first contain no higher level protocol header and the
2038 frag info is printed after the source and destination addresses.
2039 For example, here is part of an ftp from arizona.edu to lbl-rtsg.arpa
2040 over a CSNET connection that doesn't appear to handle 576 byte datagrams:
2044 \s-2\f(CWarizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+)
2045 arizona > rtsg: (frag 595a:204@328)
2046 rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2
2050 There are a couple of things to note here: First, addresses in the
2051 2nd line don't include port numbers.
2052 This is because the TCP
2053 protocol information is all in the first fragment and we have no idea
2054 what the port or sequence numbers are when we print the later fragments.
2055 Second, the tcp sequence information in the first line is printed as if there
2056 were 308 bytes of user data when, in fact, there are 512 bytes (308 in
2057 the first frag and 204 in the second).
2058 If you are looking for holes
2059 in the sequence space or trying to match up acks
2060 with packets, this can fool you.
2062 A packet with the IP \fIdon't fragment\fP flag is marked with a
2063 trailing \fB(DF)\fP.
2067 By default, all output lines are preceded by a timestamp.
2069 is the current clock time in the form
2075 and is as accurate as the kernel's clock.
2076 The timestamp reflects the time the kernel first saw the packet.
2078 is made to account for the time lag between when the
2079 ethernet interface removed the packet from the wire and when the kernel
2080 serviced the `new packet' interrupt.
2082 traffic(1C), nit(4P), bpf(4), pcap(3)
2084 The original authors are:
2088 Steven McCanne, all of the
2089 Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
2091 It is currently being maintained by tcpdump.org.
2093 The current version is available via http:
2096 .I http://www.tcpdump.org/
2099 The original distribution is available via anonymous ftp:
2102 .I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z
2105 IPv6/IPsec support is added by WIDE/KAME project.
2106 This program uses Eric Young's SSLeay library, under specific configuration.
2108 Please send problems, bugs, questions, desirable enhancements, etc. to:
2111 tcpdump-workers@tcpdump.org
2114 Please send source code contributions, etc. to:
2120 NIT doesn't let you watch your own outbound traffic, BPF will.
2121 We recommend that you use the latter.
2123 On Linux systems with 2.0[.x] kernels:
2125 packets on the loopback device will be seen twice;
2127 packet filtering cannot be done in the kernel, so that all packets must
2128 be copied from the kernel in order to be filtered in user mode;
2130 all of a packet, not just the part that's within the snapshot length,
2131 will be copied from the kernel (the 2.0[.x] packet capture mechanism, if
2132 asked to copy only part of a packet to userland, will not report the
2133 true length of the packet; this would cause most IP packets to get an
2137 capturing on some PPP devices won't work correctly.
2139 We recommend that you upgrade to a 2.2 or later kernel.
2141 Some attempt should be made to reassemble IP fragments or, at least
2142 to compute the right length for the higher level protocol.
2144 Name server inverse queries are not dumped correctly: the (empty)
2145 question section is printed rather than real query in the answer
2147 Some believe that inverse queries are themselves a bug and
2148 prefer to fix the program generating them rather than \fItcpdump\fP.
2150 A packet trace that crosses a daylight savings time change will give
2151 skewed time stamps (the time change is ignored).
2153 Filter expressions on fields other than those in Token Ring headers will
2154 not correctly handle source-routed Token Ring packets.
2156 Filter expressions on fields other than those in 802.11 headers will not
2157 correctly handle 802.11 data packets with both To DS and From DS set.
2160 should chase header chain, but at this moment it does not.
2161 .BR "ip6 protochain"
2162 is supplied for this behavior.
2164 Arithmetic expression against transport layer headers, like \fBtcp[0]\fP,
2165 does not work against IPv6 packets.
2166 It only looks at IPv4 packets.
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