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23 .TH TCPDUMP 1 "8 August 2002"
25 tcpdump \- dump traffic on a network
30 .B \-aAdDeflnNOpqRStuvxX
85 \fITcpdump\fP prints out the headers of packets on a network interface
86 that match the boolean \fIexpression\fP. It can also be run with the
88 flag, which causes it to save the packet data to a file for later
89 analysis, and/or with the
91 flag, which causes it to read from a saved packet file rather than to
92 read packets from a network interface. In all cases, only packets that
99 will, if not run with the
101 flag, continue capturing packets until it is interrupted by a SIGINT
102 signal (generated, for example, by typing your interrupt character,
103 typically control-C) or a SIGTERM signal (typically generated with the
105 command); if run with the
107 flag, it will capture packets until it is interrupted by a SIGINT or
108 SIGTERM signal or the specified number of packets have been processed.
112 finishes capturing packets, it will report counts of:
114 packets ``received by filter'' (the meaning of this depends on the OS on
117 and possibly on the way the OS was configured - if a filter was
118 specified on the command line, on some OSes it counts packets regardless
119 of whether they were matched by the filter expression, and on other OSes
120 it counts only packets that were matched by the filter expression and
124 packets ``dropped by kernel'' (this is the number of packets that were
125 dropped, due to a lack of buffer space, by the packet capture mechanism
128 is running, if the OS reports that information to applications; if not,
129 it will be reported as 0).
131 On platforms that support the SIGINFO signal, such as most BSDs, it will
132 report those counts when it receives a SIGINFO signal (generated, for
133 example, by typing your ``status'' character, typically control-T) and
134 will continue capturing packets.
136 Reading packets from a network interface may require that you have
139 .B Under SunOS 3.x or 4.x with NIT or BPF:
140 You must have read access to
145 .B Under Solaris with DLPI:
146 You must have read/write access to the network pseudo device, e.g.
148 On at least some versions of Solaris, however, this is not sufficient to
151 to capture in promiscuous mode; on those versions of Solaris, you must
154 must be installed setuid to root, in order to capture in promiscuous
155 mode. Note that, on many (perhaps all) interfaces, if you don't capture
156 in promiscuous mode, you will not see any outgoing packets, so a capture
157 not done in promiscuous mode may not be very useful.
159 .B Under HP-UX with DLPI:
162 must be installed setuid to root.
164 .B Under IRIX with snoop:
167 must be installed setuid to root.
172 must be installed setuid to root.
174 .B Under Ultrix and Digital UNIX/Tru64 UNIX:
175 Any user may capture network traffic with
177 However, no user (not even the super-user) can capture in promiscuous
178 mode on an interface unless the super-user has enabled promiscuous-mode
179 operation on that interface using
181 and no user (not even the super-user) can capture unicast traffic
182 received by or sent by the machine on an interface unless the super-user
183 has enabled copy-all-mode operation on that interface using
187 packet capture on an interface probably requires that either
188 promiscuous-mode or copy-all-mode operation, or both modes of
189 operation, be enabled on that interface.
192 You must have read access to
195 Reading a saved packet file doesn't require special privileges.
200 Print each packet (minus its link level header) in ASCII. Handy for
204 Attempt to convert network and broadcast addresses to names.
207 Exit after receiving \fIcount\fP packets.
210 Before writing a raw packet to a savefile, check whether the file is
211 currently larger than \fIfile_size\fP and, if so, close the current
212 savefile and open a new one. Savefiles after the first savefile will
213 have the name specified with the
215 flag, with a number after it, starting at 2 and continuing upward.
216 The units of \fIfile_size\fP are millions of bytes (1,000,000 bytes,
217 not 1,048,576 bytes).
220 Dump the compiled packet-matching code in a human readable form to
221 standard output and stop.
224 Dump packet-matching code as a
229 Dump packet-matching code as decimal numbers (preceded with a count).
232 Print the list of the network interfaces available on the system and on
235 can capture packets. For each network interface, a number and an
236 interface name, possibly followed by a text description of the
237 interface, is printed. The interface name or the number can be supplied
240 flag to specify an interface on which to capture.
242 This can be useful on systems that don't have a command to list them
243 (e.g., Windows systems, or UNIX systems lacking
244 .BR "ifconfig \-a" );
245 the number can be useful on Windows 2000 and later systems, where the
246 interface name is a somewhat complex string.
250 flag will not be supported if
252 was built with an older version of
255 .B pcap_findalldevs()
259 Print the link-level header on each dump line.
262 Use \fIalgo:secret\fP for decrypting IPsec ESP packets.
268 \fBcast128-cbc\fP, or
270 The default is \fBdes-cbc\fP.
271 The ability to decrypt packets is only present if \fItcpdump\fP was compiled
272 with cryptography enabled.
273 \fIsecret\fP the ASCII text for ESP secret key.
274 We cannot take arbitrary binary value at this moment.
275 The option assumes RFC2406 ESP, not RFC1827 ESP.
276 The option is only for debugging purposes, and
277 the use of this option with truly `secret' key is discouraged.
278 By presenting IPsec secret key onto command line
279 you make it visible to others, via
284 Print `foreign' IPv4 addresses numerically rather than symbolically
285 (this option is intended to get around serious brain damage in
286 Sun's NIS server \(em usually it hangs forever translating non-local
289 The test for `foreign' IPv4 addresses is done using the IPv4 address and
290 netmask of the interface on which capture is being done. If that
291 address or netmask are not available, available, either because the
292 interface on which capture is being done has no address or netmask or
293 because the capture is being done on the Linux "any" interface, which
294 can capture on more than one interface, this option will not work
298 Use \fIfile\fP as input for the filter expression.
299 An additional expression given on the command line is ignored.
302 Listen on \fIinterface\fP.
303 If unspecified, \fItcpdump\fP searches the system interface list for the
304 lowest numbered, configured up interface (excluding loopback).
305 Ties are broken by choosing the earliest match.
307 On Linux systems with 2.2 or later kernels, an
309 argument of ``any'' can be used to capture packets from all interfaces.
310 Note that captures on the ``any'' device will not be done in promiscuous
315 flag is supported, an interface number as printed by that flag can be
321 Make stdout line buffered.
322 Useful if you want to see the data
326 ``tcpdump\ \ \-l\ \ |\ \ tee dat'' or
327 ``tcpdump\ \ \-l \ \ > dat\ \ &\ \ tail\ \ \-f\ \ dat''.
330 Load SMI MIB module definitions from file \fImodule\fR.
332 can be used several times to load several MIB modules into \fItcpdump\fP.
335 Don't convert addresses (i.e., host addresses, port numbers, etc.) to names.
338 Don't print domain name qualification of host names.
340 if you give this flag then \fItcpdump\fP will print ``nic''
341 instead of ``nic.ddn.mil''.
344 Do not run the packet-matching code optimizer.
346 if you suspect a bug in the optimizer.
349 \fIDon't\fP put the interface
350 into promiscuous mode.
351 Note that the interface might be in promiscuous
352 mode for some other reason; hence, `-p' cannot be used as an abbreviation for
353 `ether host {local-hw-addr} or ether broadcast'.
356 Quick (quiet?) output.
357 Print less protocol information so output
361 Assume ESP/AH packets to be based on old specification (RFC1825 to RFC1829).
362 If specified, \fItcpdump\fP will not print replay prevention field.
363 Since there is no protocol version field in ESP/AH specification,
364 \fItcpdump\fP cannot deduce the version of ESP/AH protocol.
367 Read packets from \fIfile\fR (which was created with the -w option).
368 Standard input is used if \fIfile\fR is ``-''.
371 Print absolute, rather than relative, TCP sequence numbers.
374 Snarf \fIsnaplen\fP bytes of data from each packet rather than the
375 default of 68 (with SunOS's NIT, the minimum is actually 96).
376 68 bytes is adequate for IP, ICMP, TCP
377 and UDP but may truncate protocol information from name server and NFS
379 Packets truncated because of a limited snapshot
380 are indicated in the output with ``[|\fIproto\fP]'', where \fIproto\fP
381 is the name of the protocol level at which the truncation has occurred.
382 Note that taking larger snapshots both increases
383 the amount of time it takes to process packets and, effectively,
384 decreases the amount of packet buffering.
385 This may cause packets to be
387 You should limit \fIsnaplen\fP to the smallest number that will
388 capture the protocol information you're interested in.
390 \fIsnaplen\fP to 0 means use the required length to catch whole packets.
393 Force packets selected by "\fIexpression\fP" to be interpreted the
394 specified \fItype\fR.
395 Currently known types are
396 \fBcnfp\fR (Cisco NetFlow protocol),
397 \fBrpc\fR (Remote Procedure Call),
398 \fBrtp\fR (Real-Time Applications protocol),
399 \fBrtcp\fR (Real-Time Applications control protocol),
400 \fBsnmp\fR (Simple Network Management Protocol),
401 \fBvat\fR (Visual Audio Tool),
403 \fBwb\fR (distributed White Board).
406 \fIDon't\fP print a timestamp on each dump line.
409 Print an unformatted timestamp on each dump line.
412 Print a delta (in micro-seconds) between current and previous line
416 Print a timestamp in default format proceeded by date on each dump line.
419 Print undecoded NFS handles.
422 (Slightly more) verbose output.
423 For example, the time to live,
424 identification, total length and options in an IP packet are printed.
425 Also enables additional packet integrity checks such as verifying the
426 IP and ICMP header checksum.
429 Even more verbose output.
430 For example, additional fields are
431 printed from NFS reply packets, and SMB packets are fully decoded.
434 Even more verbose output.
436 telnet \fBSB\fP ... \fBSE\fP options
440 telnet options are printed in hex as well.
443 Write the raw packets to \fIfile\fR rather than parsing and printing
445 They can later be printed with the \-r option.
446 Standard output is used if \fIfile\fR is ``-''.
449 Print each packet (minus its link level header) in hex.
450 The smaller of the entire packet or
452 bytes will be printed. Note that this is the entire link-layer
453 packet, so for link layers that pad (e.g. Ethernet), the padding bytes
454 will also be printed when the higher layer packet is shorter than the
458 When printing hex, print ASCII too.
461 is also set, the packet is printed in hex/ASCII.
462 This is very handy for analysing new protocols.
465 is not also set, some parts of some packets may be printed
467 .IP "\fI expression\fP"
469 selects which packets will be dumped.
470 If no \fIexpression\fP
471 is given, all packets on the net will be dumped.
473 only packets for which \fIexpression\fP is `true' will be dumped.
475 The \fIexpression\fP consists of one or more
477 Primitives usually consist of an
479 (name or number) preceded by one or more qualifiers.
481 different kinds of qualifier:
483 qualifiers say what kind of thing the id name or number refers to.
489 E.g., `host foo', `net 128.3', `port 20'.
495 qualifiers specify a particular transfer direction to and/or from
497 Possible directions are
504 E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'.
506 there is no dir qualifier,
509 For `null' link layers (i.e. point to point protocols such as slip) the
513 qualifiers can be used to specify a desired direction.
515 qualifiers restrict the match to a particular protocol.
530 E.g., `ether src foo', `arp net 128.3', `tcp port 21'.
532 no proto qualifier, all protocols consistent with the type are
534 E.g., `src foo' means `(ip or arp or rarp) src foo'
535 (except the latter is not legal syntax), `net bar' means `(ip or
536 arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'.
538 [`fddi' is actually an alias for `ether'; the parser treats them
539 identically as meaning ``the data link level used on the specified
540 network interface.'' FDDI headers contain Ethernet-like source
541 and destination addresses, and often contain Ethernet-like packet
542 types, so you can filter on these FDDI fields just as with the
543 analogous Ethernet fields.
544 FDDI headers also contain other fields,
545 but you cannot name them explicitly in a filter expression.
547 Similarly, `tr' and `wlan' are aliases for `ether'; the previous
548 paragraph's statements about FDDI headers also apply to Token Ring
549 and 802.11 wireless LAN headers. For 802.11 headers, the destination
550 address is the DA field and the source address is the SA field; the
551 BSSID, RA, and TA fields aren't tested.]
553 In addition to the above, there are some special `primitive' keywords
554 that don't follow the pattern:
559 and arithmetic expressions.
560 All of these are described below.
562 More complex filter expressions are built up by using the words
567 to combine primitives.
568 E.g., `host foo and not port ftp and not port ftp-data'.
569 To save typing, identical qualifier lists can be omitted.
571 `tcp dst port ftp or ftp-data or domain' is exactly the same as
572 `tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
574 Allowable primitives are:
575 .IP "\fBdst host \fIhost\fR"
576 True if the IPv4/v6 destination field of the packet is \fIhost\fP,
577 which may be either an address or a name.
578 .IP "\fBsrc host \fIhost\fR"
579 True if the IPv4/v6 source field of the packet is \fIhost\fP.
580 .IP "\fBhost \fIhost\fP
581 True if either the IPv4/v6 source or destination of the packet is \fIhost\fP.
582 Any of the above host expressions can be prepended with the keywords,
583 \fBip\fP, \fBarp\fP, \fBrarp\fP, or \fBip6\fP as in:
586 \fBip host \fIhost\fR
589 which is equivalent to:
592 \fBether proto \fI\\ip\fB and host \fIhost\fR
595 If \fIhost\fR is a name with multiple IP addresses, each address will
596 be checked for a match.
597 .IP "\fBether dst \fIehost\fP
598 True if the ethernet destination address is \fIehost\fP.
600 may be either a name from /etc/ethers or a number (see
603 .IP "\fBether src \fIehost\fP
604 True if the ethernet source address is \fIehost\fP.
605 .IP "\fBether host \fIehost\fP
606 True if either the ethernet source or destination address is \fIehost\fP.
607 .IP "\fBgateway\fP \fIhost\fP
608 True if the packet used \fIhost\fP as a gateway.
610 source or destination address was \fIhost\fP but neither the IP source
611 nor the IP destination was \fIhost\fP.
612 \fIHost\fP must be a name and
613 must be found both by the machine's host-name-to-IP-address resolution
614 mechanisms (host name file, DNS, NIS, etc.) and by the machine's
615 host-name-to-Ethernet-address resolution mechanism (/etc/ethers, etc.).
616 (An equivalent expression is
619 \fBether host \fIehost \fBand not host \fIhost\fR
622 which can be used with either names or numbers for \fIhost / ehost\fP.)
623 This syntax does not work in IPv6-enabled configuration at this moment.
624 .IP "\fBdst net \fInet\fR"
625 True if the IPv4/v6 destination address of the packet has a network
627 \fINet\fP may be either a name from /etc/networks
628 or a network number (see \fInetworks(4)\fP for details).
629 .IP "\fBsrc net \fInet\fR"
630 True if the IPv4/v6 source address of the packet has a network
632 .IP "\fBnet \fInet\fR"
633 True if either the IPv4/v6 source or destination address of the packet has a network
635 .IP "\fBnet \fInet\fR \fBmask \fInetmask\fR"
636 True if the IP address matches \fInet\fR with the specific \fInetmask\fR.
637 May be qualified with \fBsrc\fR or \fBdst\fR.
638 Note that this syntax is not valid for IPv6 \fInet\fR.
639 .IP "\fBnet \fInet\fR/\fIlen\fR"
640 True if the IPv4/v6 address matches \fInet\fR with a netmask \fIlen\fR
642 May be qualified with \fBsrc\fR or \fBdst\fR.
643 .IP "\fBdst port \fIport\fR"
644 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a
645 destination port value of \fIport\fP.
646 The \fIport\fP can be a number or a name used in /etc/services (see
650 If a name is used, both the port
651 number and protocol are checked.
652 If a number or ambiguous name is used,
653 only the port number is checked (e.g., \fBdst port 513\fR will print both
654 tcp/login traffic and udp/who traffic, and \fBport domain\fR will print
655 both tcp/domain and udp/domain traffic).
656 .IP "\fBsrc port \fIport\fR"
657 True if the packet has a source port value of \fIport\fP.
658 .IP "\fBport \fIport\fR"
659 True if either the source or destination port of the packet is \fIport\fP.
660 Any of the above port expressions can be prepended with the keywords,
661 \fBtcp\fP or \fBudp\fP, as in:
664 \fBtcp src port \fIport\fR
667 which matches only tcp packets whose source port is \fIport\fP.
668 .IP "\fBless \fIlength\fR"
669 True if the packet has a length less than or equal to \fIlength\fP.
670 This is equivalent to:
673 \fBlen <= \fIlength\fP.
676 .IP "\fBgreater \fIlength\fR"
677 True if the packet has a length greater than or equal to \fIlength\fP.
678 This is equivalent to:
681 \fBlen >= \fIlength\fP.
684 .IP "\fBip proto \fIprotocol\fR"
685 True if the packet is an IP packet (see
687 of protocol type \fIprotocol\fP.
688 \fIProtocol\fP can be a number or one of the names
689 \fIicmp\fP, \fIicmp6\fP, \fIigmp\fP, \fIigrp\fP, \fIpim\fP, \fIah\fP,
690 \fIesp\fP, \fIvrrp\fP, \fIudp\fP, or \fItcp\fP.
691 Note that the identifiers \fItcp\fP, \fIudp\fP, and \fIicmp\fP are also
692 keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell.
693 Note that this primitive does not chase the protocol header chain.
694 .IP "\fBip6 proto \fIprotocol\fR"
695 True if the packet is an IPv6 packet of protocol type \fIprotocol\fP.
696 Note that this primitive does not chase the protocol header chain.
697 .IP "\fBip6 protochain \fIprotocol\fR"
698 True if the packet is IPv6 packet,
699 and contains protocol header with type \fIprotocol\fR
700 in its protocol header chain.
704 \fBip6 protochain 6\fR
707 matches any IPv6 packet with TCP protocol header in the protocol header chain.
708 The packet may contain, for example,
709 authentication header, routing header, or hop-by-hop option header,
710 between IPv6 header and TCP header.
711 The BPF code emitted by this primitive is complex and
712 cannot be optimized by BPF optimizer code in \fItcpdump\fP,
713 so this can be somewhat slow.
714 .IP "\fBip protochain \fIprotocol\fR"
715 Equivalent to \fBip6 protochain \fIprotocol\fR, but this is for IPv4.
716 .IP "\fBether broadcast\fR"
717 True if the packet is an ethernet broadcast packet.
720 .IP "\fBip broadcast\fR"
721 True if the packet is an IPv4 broadcast packet.
722 It checks for both the all-zeroes and all-ones broadcast conventions,
723 and looks up the subnet mask on the interface on which the capture is
726 If the subnet mask of the interface on which the capture is being done
727 is not available, either because the interface on which capture is being
728 done has no netmask or because the capture is being done on the Linux
729 "any" interface, which can capture on more than one interface, this
730 check will not work correctly.
731 .IP "\fBether multicast\fR"
732 True if the packet is an ethernet multicast packet.
735 This is shorthand for `\fBether[0] & 1 != 0\fP'.
736 .IP "\fBip multicast\fR"
737 True if the packet is an IP multicast packet.
738 .IP "\fBip6 multicast\fR"
739 True if the packet is an IPv6 multicast packet.
740 .IP "\fBether proto \fIprotocol\fR"
741 True if the packet is of ether type \fIprotocol\fR.
742 \fIProtocol\fP can be a number or one of the names
743 \fIip\fP, \fIip6\fP, \fIarp\fP, \fIrarp\fP, \fIatalk\fP, \fIaarp\fP,
744 \fIdecnet\fP, \fIsca\fP, \fIlat\fP, \fImopdl\fP, \fImoprc\fP,
745 \fIiso\fP, \fIstp\fP, \fIipx\fP, or \fInetbeui\fP.
746 Note these identifiers are also keywords
747 and must be escaped via backslash (\\).
749 [In the case of FDDI (e.g., `\fBfddi protocol arp\fR'), Token Ring
750 (e.g., `\fBtr protocol arp\fR'), and IEEE 802.11 wireless LANS (e.g.,
751 `\fBwlan protocol arp\fR'), for most of those protocols, the
752 protocol identification comes from the 802.2 Logical Link Control (LLC)
753 header, which is usually layered on top of the FDDI, Token Ring, or
756 When filtering for most protocol identifiers on FDDI, Token Ring, or
757 802.11, \fItcpdump\fR checks only the protocol ID field of an LLC header
758 in so-called SNAP format with an Organizational Unit Identifier (OUI) of
759 0x000000, for encapsulated Ethernet; it doesn't check whether the packet
760 is in SNAP format with an OUI of 0x000000.
765 \fItcpdump\fR checks the DSAP (Destination Service Access Point) and
766 SSAP (Source Service Access Point) fields of the LLC header;
768 \fBstp\fP and \fInetbeui\fP
769 \fItcpdump\fR checks the DSAP of the LLC header;
772 \fItcpdump\fR checks for a SNAP-format packet with an OUI of 0x080007
773 and the Appletalk etype.
776 In the case of Ethernet, \fItcpdump\fR checks the Ethernet type field
777 for most of those protocols. The exceptions are:
780 \fBiso\fP, \fBsap\fP, and \fBnetbeui\fP
781 \fItcpdump\fR checks for an 802.3 frame and then checks the LLC header as
782 it does for FDDI, Token Ring, and 802.11;
785 \fItcpdump\fR checks both for the Appletalk etype in an Ethernet frame and
786 for a SNAP-format packet as it does for FDDI, Token Ring, and 802.11;
789 \fItcpdump\fR checks for the Appletalk ARP etype in either an Ethernet
790 frame or an 802.2 SNAP frame with an OUI of 0x000000;
793 \fItcpdump\fR checks for the IPX etype in an Ethernet frame, the IPX
794 DSAP in the LLC header, the 802.3-with-no-LLC-header encapsulation of
795 IPX, and the IPX etype in a SNAP frame.
797 .IP "\fBdecnet src \fIhost\fR"
798 True if the DECNET source address is
800 which may be an address of the form ``10.123'', or a DECNET host
802 [DECNET host name support is only available on Ultrix systems
803 that are configured to run DECNET.]
804 .IP "\fBdecnet dst \fIhost\fR"
805 True if the DECNET destination address is
807 .IP "\fBdecnet host \fIhost\fR"
808 True if either the DECNET source or destination address is
810 .IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBatalk\fR, \fBaarp\fR, \fBdecnet\fR, \fBiso\fR, \fBstp\fR, \fBipx\fR, \fInetbeui\fP"
814 \fBether proto \fIp\fR
817 where \fIp\fR is one of the above protocols.
818 .IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR"
822 \fBether proto \fIp\fR
825 where \fIp\fR is one of the above protocols.
827 \fItcpdump\fP does not currently know how to parse these protocols.
828 .IP "\fBvlan \fI[vlan_id]\fR"
829 True if the packet is an IEEE 802.1Q VLAN packet.
830 If \fI[vlan_id]\fR is specified, only true is the packet has the specified
832 Note that the first \fBvlan\fR keyword encountered in \fIexpression\fR
833 changes the decoding offsets for the remainder of \fIexpression\fR
834 on the assumption that the packet is a VLAN packet.
835 .IP "\fBtcp\fR, \fBudp\fR, \fBicmp\fR"
839 \fBip proto \fIp\fR\fB or ip6 proto \fIp\fR
842 where \fIp\fR is one of the above protocols.
843 .IP "\fBiso proto \fIprotocol\fR"
844 True if the packet is an OSI packet of protocol type \fIprotocol\fP.
845 \fIProtocol\fP can be a number or one of the names
846 \fIclnp\fP, \fIesis\fP, or \fIisis\fP.
847 .IP "\fBclnp\fR, \fBesis\fR, \fBisis\fR"
854 where \fIp\fR is one of the above protocols.
855 Note that \fItcpdump\fR does an incomplete job of parsing these protocols.
856 .IP "\fBvpi\fP \fIn\fR
857 True if the packet is an ATM packet, for SunATM on Solaris, with a
858 virtual path identifier of
860 .IP "\fBvci\fP \fIn\fR
861 True if the packet is an ATM packet, for SunATM on Solaris, with a
862 virtual channel identifier of
865 True if the packet is an ATM packet, for SunATM on Solaris, and is
867 Note that the first \fBlane\fR keyword encountered in \fIexpression\fR
868 changes the tests done in the remainder of \fIexpression\fR
869 on the assumption that the packet is either a LANE emulated Ethernet
870 packet or a LANE LE Control packet. If \fBlane\fR isn't specified, the
871 tests are done under the assumption that the packet is an
872 LLC-encapsulated packet.
874 True if the packet is an ATM packet, for SunATM on Solaris, and is
875 an LLC-encapsulated packet.
877 True if the packet is an ATM packet, for SunATM on Solaris, and is
878 a segment OAM F4 flow cell (VPI=0 & VCI=3).
880 True if the packet is an ATM packet, for SunATM on Solaris, and is
881 an end-to-end OAM F4 flow cell (VPI=0 & VCI=4).
883 True if the packet is an ATM packet, for SunATM on Solaris, and is
884 a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).
886 True if the packet is an ATM packet, for SunATM on Solaris, and is
887 a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).
889 True if the packet is an ATM packet, for SunATM on Solaris, and is
890 on a meta signaling circuit (VPI=0 & VCI=1).
892 True if the packet is an ATM packet, for SunATM on Solaris, and is
893 on a broadcast signaling circuit (VPI=0 & VCI=2).
895 True if the packet is an ATM packet, for SunATM on Solaris, and is
896 on a signaling circuit (VPI=0 & VCI=5).
898 True if the packet is an ATM packet, for SunATM on Solaris, and is
899 on an ILMI circuit (VPI=0 & VCI=16).
901 True if the packet is an ATM packet, for SunATM on Solaris, and is
902 on a signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect,
903 Connect Ack, Release, or Release Done message.
904 .IP \fBmetaconnect\fP
905 True if the packet is an ATM packet, for SunATM on Solaris, and is
906 on a meta signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect,
907 Release, or Release Done message.
908 .IP "\fIexpr relop expr\fR"
909 True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =, !=,
910 and \fIexpr\fR is an arithmetic expression composed of integer constants
911 (expressed in standard C syntax), the normal binary operators
912 [+, -, *, /, &, |], a length operator, and special packet data accessors.
914 data inside the packet, use the following syntax:
917 \fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR
920 \fIProto\fR is one of \fBether, fddi, tr, wlan, ppp, slip, link,
921 ip, arp, rarp, tcp, udp, icmp\fR or \fBip6\fR, and
922 indicates the protocol layer for the index operation.
923 (\fBether, fddi, wlan, tr, ppp, slip\fR and \fBlink\fR all refer to the
925 Note that \fItcp, udp\fR and other upper-layer protocol types only
926 apply to IPv4, not IPv6 (this will be fixed in the future).
927 The byte offset, relative to the indicated protocol layer, is
929 \fISize\fR is optional and indicates the number of bytes in the
930 field of interest; it can be either one, two, or four, and defaults to one.
931 The length operator, indicated by the keyword \fBlen\fP, gives the
932 length of the packet.
934 For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic.
935 The expression `\fBip[0] & 0xf != 5\fP'
936 catches all IP packets with options.
938 `\fBip[6:2] & 0x1fff = 0\fP'
939 catches only unfragmented datagrams and frag zero of fragmented datagrams.
940 This check is implicitly applied to the \fBtcp\fP and \fBudp\fP
942 For instance, \fBtcp[0]\fP always means the first
943 byte of the TCP \fIheader\fP, and never means the first byte of an
944 intervening fragment.
946 Some offsets and field values may be expressed as names rather than
948 The following protocol header field offsets are
949 available: \fBicmptype\fP (ICMP type field), \fBicmpcode\fP (ICMP
950 code field), and \fBtcpflags\fP (TCP flags field).
952 The following ICMP type field values are available: \fBicmp-echoreply\fP,
953 \fBicmp-unreach\fP, \fBicmp-sourcequench\fP, \fBicmp-redirect\fP,
954 \fBicmp-echo\fP, \fBicmp-routeradvert\fP, \fBicmp-routersolicit\fP,
955 \fBicmp-timxceed\fP, \fBicmp-paramprob\fP, \fBicmp-tstamp\fP,
956 \fBicmp-tstampreply\fP, \fBicmp-ireq\fP, \fBicmp-ireqreply\fP,
957 \fBicmp-maskreq\fP, \fBicmp-maskreply\fP.
959 The following TCP flags field values are available: \fBtcp-fin\fP,
960 \fBtcp-syn\fP, \fBtcp-rst\fP, \fBtcp-push\fP, \fBtcp-push\fP,
961 \fBtcp-ack\fP, \fBtcp-urg\fP.
963 Primitives may be combined using:
965 A parenthesized group of primitives and operators
966 (parentheses are special to the Shell and must be escaped).
968 Negation (`\fB!\fP' or `\fBnot\fP').
970 Concatenation (`\fB&&\fP' or `\fBand\fP').
972 Alternation (`\fB||\fP' or `\fBor\fP').
974 Negation has highest precedence.
975 Alternation and concatenation have equal precedence and associate
977 Note that explicit \fBand\fR tokens, not juxtaposition,
978 are now required for concatenation.
980 If an identifier is given without a keyword, the most recent keyword
985 \fBnot host vs and ace\fR
991 \fBnot host vs and host ace\fR
994 which should not be confused with
997 \fBnot ( host vs or ace )\fR
1001 Expression arguments can be passed to \fItcpdump\fP as either a single
1002 argument or as multiple arguments, whichever is more convenient.
1003 Generally, if the expression contains Shell metacharacters, it is
1004 easier to pass it as a single, quoted argument.
1005 Multiple arguments are concatenated with spaces before being parsed.
1008 To print all packets arriving at or departing from \fIsundown\fP:
1011 \fBtcpdump host sundown\fP
1015 To print traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR:
1018 \fBtcpdump host helios and \\( hot or ace \\)\fP
1022 To print all IP packets between \fIace\fR and any host except \fIhelios\fR:
1025 \fBtcpdump ip host ace and not helios\fP
1029 To print all traffic between local hosts and hosts at Berkeley:
1033 tcpdump net ucb-ether
1037 To print all ftp traffic through internet gateway \fIsnup\fP:
1038 (note that the expression is quoted to prevent the shell from
1039 (mis-)interpreting the parentheses):
1043 tcpdump 'gateway snup and (port ftp or ftp-data)'
1047 To print traffic neither sourced from nor destined for local hosts
1048 (if you gateway to one other net, this stuff should never make it
1049 onto your local net).
1053 tcpdump ip and not net \fIlocalnet\fP
1057 To print the start and end packets (the SYN and FIN packets) of each
1058 TCP conversation that involves a non-local host.
1062 tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net \fIlocalnet\fP'
1066 To print IP packets longer than 576 bytes sent through gateway \fIsnup\fP:
1070 tcpdump 'gateway snup and ip[2:2] > 576'
1074 To print IP broadcast or multicast packets that were
1076 sent via ethernet broadcast or multicast:
1080 tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'
1084 To print all ICMP packets that are not echo requests/replies (i.e., not
1089 tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'
1094 The output of \fItcpdump\fP is protocol dependent.
1096 gives a brief description and examples of most of the formats.
1104 If the '-e' option is given, the link level header is printed out.
1105 On ethernets, the source and destination addresses, protocol,
1106 and packet length are printed.
1108 On FDDI networks, the '-e' option causes \fItcpdump\fP to print
1109 the `frame control' field, the source and destination addresses,
1110 and the packet length.
1111 (The `frame control' field governs the
1112 interpretation of the rest of the packet.
1113 Normal packets (such
1114 as those containing IP datagrams) are `async' packets, with a priority
1115 value between 0 and 7; for example, `\fBasync4\fR'.
1117 are assumed to contain an 802.2 Logical Link Control (LLC) packet;
1118 the LLC header is printed if it is \fInot\fR an ISO datagram or a
1119 so-called SNAP packet.
1121 On Token Ring networks, the '-e' option causes \fItcpdump\fP to print
1122 the `access control' and `frame control' fields, the source and
1123 destination addresses, and the packet length.
1124 As on FDDI networks,
1125 packets are assumed to contain an LLC packet.
1126 Regardless of whether
1127 the '-e' option is specified or not, the source routing information is
1128 printed for source-routed packets.
1130 On 802.11 networks, the '-e' option causes \fItcpdump\fP to print
1131 the `frame control' fields, all of the addresses in the 802.11 header,
1132 and the packet length.
1133 As on FDDI networks,
1134 packets are assumed to contain an LLC packet.
1136 \fI(N.B.: The following description assumes familiarity with
1137 the SLIP compression algorithm described in RFC-1144.)\fP
1139 On SLIP links, a direction indicator (``I'' for inbound, ``O'' for outbound),
1140 packet type, and compression information are printed out.
1141 The packet type is printed first.
1142 The three types are \fIip\fP, \fIutcp\fP, and \fIctcp\fP.
1143 No further link information is printed for \fIip\fR packets.
1144 For TCP packets, the connection identifier is printed following the type.
1145 If the packet is compressed, its encoded header is printed out.
1146 The special cases are printed out as
1147 \fB*S+\fIn\fR and \fB*SA+\fIn\fR, where \fIn\fR is the amount by which
1148 the sequence number (or sequence number and ack) has changed.
1149 If it is not a special case,
1150 zero or more changes are printed.
1151 A change is indicated by U (urgent pointer), W (window), A (ack),
1152 S (sequence number), and I (packet ID), followed by a delta (+n or -n),
1153 or a new value (=n).
1154 Finally, the amount of data in the packet and compressed header length
1157 For example, the following line shows an outbound compressed TCP packet,
1158 with an implicit connection identifier; the ack has changed by 6,
1159 the sequence number by 49, and the packet ID by 6; there are 3 bytes of
1160 data and 6 bytes of compressed header:
1163 \fBO ctcp * A+6 S+49 I+6 3 (6)\fP
1169 Arp/rarp output shows the type of request and its arguments.
1171 format is intended to be self explanatory.
1172 Here is a short sample taken from the start of an `rlogin' from
1173 host \fIrtsg\fP to host \fIcsam\fP:
1177 \f(CWarp who-has csam tell rtsg
1178 arp reply csam is-at CSAM\fR
1182 The first line says that rtsg sent an arp packet asking
1183 for the ethernet address of internet host csam.
1185 replies with its ethernet address (in this example, ethernet addresses
1186 are in caps and internet addresses in lower case).
1188 This would look less redundant if we had done \fItcpdump \-n\fP:
1192 \f(CWarp who-has 128.3.254.6 tell 128.3.254.68
1193 arp reply 128.3.254.6 is-at 02:07:01:00:01:c4\fP
1197 If we had done \fItcpdump \-e\fP, the fact that the first packet is
1198 broadcast and the second is point-to-point would be visible:
1202 \f(CWRTSG Broadcast 0806 64: arp who-has csam tell rtsg
1203 CSAM RTSG 0806 64: arp reply csam is-at CSAM\fR
1207 For the first packet this says the ethernet source address is RTSG, the
1208 destination is the ethernet broadcast address, the type field
1209 contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes.
1213 \fI(N.B.:The following description assumes familiarity with
1214 the TCP protocol described in RFC-793.
1215 If you are not familiar
1216 with the protocol, neither this description nor \fItcpdump\fP will
1217 be of much use to you.)\fP
1219 The general format of a tcp protocol line is:
1223 \fIsrc > dst: flags data-seqno ack window urgent options\fP
1227 \fISrc\fP and \fIdst\fP are the source and destination IP
1228 addresses and ports.
1229 \fIFlags\fP are some combination of S (SYN),
1230 F (FIN), P (PUSH) or R (RST) or a single `.' (no flags).
1231 \fIData-seqno\fP describes the portion of sequence space covered
1232 by the data in this packet (see example below).
1233 \fIAck\fP is sequence number of the next data expected the other
1234 direction on this connection.
1235 \fIWindow\fP is the number of bytes of receive buffer space available
1236 the other direction on this connection.
1237 \fIUrg\fP indicates there is `urgent' data in the packet.
1238 \fIOptions\fP are tcp options enclosed in angle brackets (e.g., <mss 1024>).
1240 \fISrc, dst\fP and \fIflags\fP are always present.
1242 depend on the contents of the packet's tcp protocol header and
1243 are output only if appropriate.
1245 Here is the opening portion of an rlogin from host \fIrtsg\fP to
1250 \s-2\f(CWrtsg.1023 > csam.login: S 768512:768512(0) win 4096 <mss 1024>
1251 csam.login > rtsg.1023: S 947648:947648(0) ack 768513 win 4096 <mss 1024>
1252 rtsg.1023 > csam.login: . ack 1 win 4096
1253 rtsg.1023 > csam.login: P 1:2(1) ack 1 win 4096
1254 csam.login > rtsg.1023: . ack 2 win 4096
1255 rtsg.1023 > csam.login: P 2:21(19) ack 1 win 4096
1256 csam.login > rtsg.1023: P 1:2(1) ack 21 win 4077
1257 csam.login > rtsg.1023: P 2:3(1) ack 21 win 4077 urg 1
1258 csam.login > rtsg.1023: P 3:4(1) ack 21 win 4077 urg 1\fR\s+2
1262 The first line says that tcp port 1023 on rtsg sent a packet
1265 The \fBS\fP indicates that the \fISYN\fP flag was set.
1266 The packet sequence number was 768512 and it contained no data.
1267 (The notation is `first:last(nbytes)' which means `sequence
1269 up to but not including \fIlast\fP which is \fInbytes\fP bytes of user data'.)
1270 There was no piggy-backed ack, the available receive window was 4096
1271 bytes and there was a max-segment-size option requesting an mss of
1274 Csam replies with a similar packet except it includes a piggy-backed
1276 Rtsg then acks csam's SYN.
1279 The packet contained no data so there is no data sequence number.
1280 Note that the ack sequence
1281 number is a small integer (1).
1282 The first time \fItcpdump\fP sees a
1283 tcp `conversation', it prints the sequence number from the packet.
1284 On subsequent packets of the conversation, the difference between
1285 the current packet's sequence number and this initial sequence number
1287 This means that sequence numbers after the
1288 first can be interpreted
1289 as relative byte positions in the conversation's data stream (with the
1290 first data byte each direction being `1').
1291 `-S' will override this
1292 feature, causing the original sequence numbers to be output.
1294 On the 6th line, rtsg sends csam 19 bytes of data (bytes 2 through 20
1295 in the rtsg \(-> csam side of the conversation).
1296 The PUSH flag is set in the packet.
1297 On the 7th line, csam says it's received data sent by rtsg up to
1298 but not including byte 21.
1299 Most of this data is apparently sitting in the
1300 socket buffer since csam's receive window has gotten 19 bytes smaller.
1301 Csam also sends one byte of data to rtsg in this packet.
1302 On the 8th and 9th lines,
1303 csam sends two bytes of urgent, pushed data to rtsg.
1305 If the snapshot was small enough that \fItcpdump\fP didn't capture
1306 the full TCP header, it interprets as much of the header as it can
1307 and then reports ``[|\fItcp\fP]'' to indicate the remainder could not
1309 If the header contains a bogus option (one with a length
1310 that's either too small or beyond the end of the header), \fItcpdump\fP
1311 reports it as ``[\fIbad opt\fP]'' and does not interpret any further
1312 options (since it's impossible to tell where they start).
1314 length indicates options are present but the IP datagram length is not
1315 long enough for the options to actually be there, \fItcpdump\fP reports
1316 it as ``[\fIbad hdr length\fP]''.
1318 .B Capturing TCP packets with particular flag combinations (SYN-ACK, URG-ACK, etc.)
1320 There are 8 bits in the control bits section of the TCP header:
1322 .I CWR | ECE | URG | ACK | PSH | RST | SYN | FIN
1324 Let's assume that we want to watch packets used in establishing
1326 Recall that TCP uses a 3-way handshake protocol
1327 when it initializes a new connection; the connection sequence with
1328 regard to the TCP control bits is
1334 2) Recipient responds with SYN, ACK
1340 Now we're interested in capturing packets that have only the
1341 SYN bit set (Step 1).
1342 Note that we don't want packets from step 2
1343 (SYN-ACK), just a plain initial SYN.
1344 What we need is a correct filter
1345 expression for \fItcpdump\fP.
1347 Recall the structure of a TCP header without options:
1351 -----------------------------------------------------------------
1352 | source port | destination port |
1353 -----------------------------------------------------------------
1355 -----------------------------------------------------------------
1356 | acknowledgment number |
1357 -----------------------------------------------------------------
1358 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1359 -----------------------------------------------------------------
1360 | TCP checksum | urgent pointer |
1361 -----------------------------------------------------------------
1364 A TCP header usually holds 20 octets of data, unless options are
1366 The first line of the graph contains octets 0 - 3, the
1367 second line shows octets 4 - 7 etc.
1369 Starting to count with 0, the relevant TCP control bits are contained
1374 ----------------|---------------|---------------|----------------
1375 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1376 ----------------|---------------|---------------|----------------
1377 | | 13th octet | | |
1380 Let's have a closer look at octet no. 13:
1390 These are the TCP control bits we are interested
1392 We have numbered the bits in this octet from 0 to 7, right to
1393 left, so the PSH bit is bit number 3, while the URG bit is number 5.
1395 Recall that we want to capture packets with only SYN set.
1396 Let's see what happens to octet 13 if a TCP datagram arrives
1397 with the SYN bit set in its header:
1408 control bits section we see that only bit number 1 (SYN) is set.
1410 Assuming that octet number 13 is an 8-bit unsigned integer in
1411 network byte order, the binary value of this octet is
1415 and its decimal representation is
1419 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 1*2 + 0*2 = 2
1422 We're almost done, because now we know that if only SYN is set,
1423 the value of the 13th octet in the TCP header, when interpreted
1424 as a 8-bit unsigned integer in network byte order, must be exactly 2.
1426 This relationship can be expressed as
1432 We can use this expression as the filter for \fItcpdump\fP in order
1433 to watch packets which have only SYN set:
1436 tcpdump -i xl0 tcp[13] == 2
1439 The expression says "let the 13th octet of a TCP datagram have
1440 the decimal value 2", which is exactly what we want.
1442 Now, let's assume that we need to capture SYN packets, but we
1443 don't care if ACK or any other TCP control bit is set at the
1445 Let's see what happens to octet 13 when a TCP datagram
1446 with SYN-ACK set arrives:
1456 Now bits 1 and 4 are set in the 13th octet.
1462 which translates to decimal
1466 0*2 + 0*2 + 0*2 + 1*2 + 0*2 + 0*2 + 1*2 + 0*2 = 18
1469 Now we can't just use 'tcp[13] == 18' in the \fItcpdump\fP filter
1470 expression, because that would select only those packets that have
1471 SYN-ACK set, but not those with only SYN set.
1472 Remember that we don't care
1473 if ACK or any other control bit is set as long as SYN is set.
1475 In order to achieve our goal, we need to logically AND the
1476 binary value of octet 13 with some other value to preserve
1478 We know that we want SYN to be set in any case,
1479 so we'll logically AND the value in the 13th octet with
1480 the binary value of a SYN:
1484 00010010 SYN-ACK 00000010 SYN
1485 AND 00000010 (we want SYN) AND 00000010 (we want SYN)
1487 = 00000010 = 00000010
1490 We see that this AND operation delivers the same result
1491 regardless whether ACK or another TCP control bit is set.
1492 The decimal representation of the AND value as well as
1493 the result of this operation is 2 (binary 00000010),
1494 so we know that for packets with SYN set the following
1495 relation must hold true:
1497 ( ( value of octet 13 ) AND ( 2 ) ) == ( 2 )
1499 This points us to the \fItcpdump\fP filter expression
1502 tcpdump -i xl0 'tcp[13] & 2 == 2'
1505 Note that you should use single quotes or a backslash
1506 in the expression to hide the AND ('&') special character
1512 UDP format is illustrated by this rwho packet:
1516 \f(CWactinide.who > broadcast.who: udp 84\fP
1520 This says that port \fIwho\fP on host \fIactinide\fP sent a udp
1521 datagram to port \fIwho\fP on host \fIbroadcast\fP, the Internet
1523 The packet contained 84 bytes of user data.
1525 Some UDP services are recognized (from the source or destination
1526 port number) and the higher level protocol information printed.
1527 In particular, Domain Name service requests (RFC-1034/1035) and Sun
1528 RPC calls (RFC-1050) to NFS.
1530 UDP Name Server Requests
1532 \fI(N.B.:The following description assumes familiarity with
1533 the Domain Service protocol described in RFC-1035.
1534 If you are not familiar
1535 with the protocol, the following description will appear to be written
1538 Name server requests are formatted as
1542 \fIsrc > dst: id op? flags qtype qclass name (len)\fP
1544 \f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fR
1548 Host \fIh2opolo\fP asked the domain server on \fIhelios\fP for an
1549 address record (qtype=A) associated with the name \fIucbvax.berkeley.edu.\fP
1550 The query id was `3'.
1551 The `+' indicates the \fIrecursion desired\fP flag
1553 The query length was 37 bytes, not including the UDP and
1554 IP protocol headers.
1555 The query operation was the normal one, \fIQuery\fP,
1556 so the op field was omitted.
1557 If the op had been anything else, it would
1558 have been printed between the `3' and the `+'.
1559 Similarly, the qclass was the normal one,
1560 \fIC_IN\fP, and omitted.
1561 Any other qclass would have been printed
1562 immediately after the `A'.
1564 A few anomalies are checked and may result in extra fields enclosed in
1565 square brackets: If a query contains an answer, authority records or
1566 additional records section,
1571 are printed as `[\fIn\fPa]', `[\fIn\fPn]' or `[\fIn\fPau]' where \fIn\fP
1572 is the appropriate count.
1573 If any of the response bits are set (AA, RA or rcode) or any of the
1574 `must be zero' bits are set in bytes two and three, `[b2&3=\fIx\fP]'
1575 is printed, where \fIx\fP is the hex value of header bytes two and three.
1577 UDP Name Server Responses
1579 Name server responses are formatted as
1583 \fIsrc > dst: id op rcode flags a/n/au type class data (len)\fP
1585 \f(CWhelios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273)
1586 helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fR
1590 In the first example, \fIhelios\fP responds to query id 3 from \fIh2opolo\fP
1591 with 3 answer records, 3 name server records and 7 additional records.
1592 The first answer record is type A (address) and its data is internet
1593 address 128.32.137.3.
1594 The total size of the response was 273 bytes,
1595 excluding UDP and IP headers.
1596 The op (Query) and response code
1597 (NoError) were omitted, as was the class (C_IN) of the A record.
1599 In the second example, \fIhelios\fP responds to query 2 with a
1600 response code of non-existent domain (NXDomain) with no answers,
1601 one name server and no authority records.
1602 The `*' indicates that
1603 the \fIauthoritative answer\fP bit was set.
1605 answers, no type, class or data were printed.
1607 Other flag characters that might appear are `\-' (recursion available,
1608 RA, \fInot\fP set) and `|' (truncated message, TC, set).
1610 `question' section doesn't contain exactly one entry, `[\fIn\fPq]'
1613 Note that name server requests and responses tend to be large and the
1614 default \fIsnaplen\fP of 68 bytes may not capture enough of the packet
1616 Use the \fB\-s\fP flag to increase the snaplen if you
1617 need to seriously investigate name server traffic.
1619 has worked well for me.
1624 \fItcpdump\fP now includes fairly extensive SMB/CIFS/NBT decoding for data
1625 on UDP/137, UDP/138 and TCP/139.
1626 Some primitive decoding of IPX and
1627 NetBEUI SMB data is also done.
1629 By default a fairly minimal decode is done, with a much more detailed
1630 decode done if -v is used.
1631 Be warned that with -v a single SMB packet
1632 may take up a page or more, so only use -v if you really want all the
1635 If you are decoding SMB sessions containing unicode strings then you
1636 may wish to set the environment variable USE_UNICODE to 1.
1638 auto-detect unicode srings would be welcome.
1640 For information on SMB packet formats and what all te fields mean see
1641 www.cifs.org or the pub/samba/specs/ directory on your favourite
1642 samba.org mirror site.
1643 The SMB patches were written by Andrew Tridgell
1647 NFS Requests and Replies
1649 Sun NFS (Network File System) requests and replies are printed as:
1653 \fIsrc.xid > dst.nfs: len op args\fP
1654 \fIsrc.nfs > dst.xid: reply stat len op results\fP
1657 sushi.6709 > wrl.nfs: 112 readlink fh 21,24/10.73165
1658 wrl.nfs > sushi.6709: reply ok 40 readlink "../var"
1659 sushi.201b > wrl.nfs:
1660 144 lookup fh 9,74/4096.6878 "xcolors"
1661 wrl.nfs > sushi.201b:
1662 reply ok 128 lookup fh 9,74/4134.3150
1667 In the first line, host \fIsushi\fP sends a transaction with id \fI6709\fP
1668 to \fIwrl\fP (note that the number following the src host is a
1669 transaction id, \fInot\fP the source port).
1670 The request was 112 bytes,
1671 excluding the UDP and IP headers.
1672 The operation was a \fIreadlink\fP
1673 (read symbolic link) on file handle (\fIfh\fP) 21,24/10.731657119.
1674 (If one is lucky, as in this case, the file handle can be interpreted
1675 as a major,minor device number pair, followed by the inode number and
1677 \fIWrl\fP replies `ok' with the contents of the link.
1679 In the third line, \fIsushi\fP asks \fIwrl\fP to lookup the name
1680 `\fIxcolors\fP' in directory file 9,74/4096.6878.
1681 Note that the data printed
1682 depends on the operation type.
1683 The format is intended to be self
1684 explanatory if read in conjunction with
1685 an NFS protocol spec.
1687 If the \-v (verbose) flag is given, additional information is printed.
1693 sushi.1372a > wrl.nfs:
1694 148 read fh 21,11/12.195 8192 bytes @ 24576
1695 wrl.nfs > sushi.1372a:
1696 reply ok 1472 read REG 100664 ids 417/0 sz 29388
1701 (\-v also prints the IP header TTL, ID, length, and fragmentation fields,
1702 which have been omitted from this example.) In the first line,
1703 \fIsushi\fP asks \fIwrl\fP to read 8192 bytes from file 21,11/12.195,
1704 at byte offset 24576.
1705 \fIWrl\fP replies `ok'; the packet shown on the
1706 second line is the first fragment of the reply, and hence is only 1472
1707 bytes long (the other bytes will follow in subsequent fragments, but
1708 these fragments do not have NFS or even UDP headers and so might not be
1709 printed, depending on the filter expression used).
1710 Because the \-v flag
1711 is given, some of the file attributes (which are returned in addition
1712 to the file data) are printed: the file type (``REG'', for regular file),
1713 the file mode (in octal), the uid and gid, and the file size.
1715 If the \-v flag is given more than once, even more details are printed.
1717 Note that NFS requests are very large and much of the detail won't be printed
1718 unless \fIsnaplen\fP is increased.
1719 Try using `\fB\-s 192\fP' to watch
1722 NFS reply packets do not explicitly identify the RPC operation.
1724 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1725 replies using the transaction ID.
1726 If a reply does not closely follow the
1727 corresponding request, it might not be parsable.
1729 AFS Requests and Replies
1731 Transarc AFS (Andrew File System) requests and replies are printed
1737 \fIsrc.sport > dst.dport: rx packet-type\fP
1738 \fIsrc.sport > dst.dport: rx packet-type service call call-name args\fP
1739 \fIsrc.sport > dst.dport: rx packet-type service reply call-name args\fP
1742 elvis.7001 > pike.afsfs:
1743 rx data fs call rename old fid 536876964/1/1 ".newsrc.new"
1744 new fid 536876964/1/1 ".newsrc"
1745 pike.afsfs > elvis.7001: rx data fs reply rename
1750 In the first line, host elvis sends a RX packet to pike.
1752 a RX data packet to the fs (fileserver) service, and is the start of
1754 The RPC call was a rename, with the old directory file id
1755 of 536876964/1/1 and an old filename of `.newsrc.new', and a new directory
1756 file id of 536876964/1/1 and a new filename of `.newsrc'.
1758 responds with a RPC reply to the rename call (which was successful, because
1759 it was a data packet and not an abort packet).
1761 In general, all AFS RPCs are decoded at least by RPC call name.
1763 AFS RPCs have at least some of the arguments decoded (generally only
1764 the `interesting' arguments, for some definition of interesting).
1766 The format is intended to be self-describing, but it will probably
1767 not be useful to people who are not familiar with the workings of
1770 If the -v (verbose) flag is given twice, acknowledgement packets and
1771 additional header information is printed, such as the the RX call ID,
1772 call number, sequence number, serial number, and the RX packet flags.
1774 If the -v flag is given twice, additional information is printed,
1775 such as the the RX call ID, serial number, and the RX packet flags.
1776 The MTU negotiation information is also printed from RX ack packets.
1778 If the -v flag is given three times, the security index and service id
1781 Error codes are printed for abort packets, with the exception of Ubik
1782 beacon packets (because abort packets are used to signify a yes vote
1783 for the Ubik protocol).
1785 Note that AFS requests are very large and many of the arguments won't
1786 be printed unless \fIsnaplen\fP is increased.
1787 Try using `\fB-s 256\fP'
1788 to watch AFS traffic.
1790 AFS reply packets do not explicitly identify the RPC operation.
1792 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1793 replies using the call number and service ID.
1794 If a reply does not closely
1796 corresponding request, it might not be parsable.
1799 KIP Appletalk (DDP in UDP)
1801 Appletalk DDP packets encapsulated in UDP datagrams are de-encapsulated
1802 and dumped as DDP packets (i.e., all the UDP header information is
1806 is used to translate appletalk net and node numbers to names.
1807 Lines in this file have the form
1819 The first two lines give the names of appletalk networks.
1821 line gives the name of a particular host (a host is distinguished
1822 from a net by the 3rd octet in the number \-
1823 a net number \fImust\fP have two octets and a host number \fImust\fP
1824 have three octets.) The number and name should be separated by
1825 whitespace (blanks or tabs).
1828 file may contain blank lines or comment lines (lines starting with
1831 Appletalk addresses are printed in the form
1837 \f(CW144.1.209.2 > icsd-net.112.220
1838 office.2 > icsd-net.112.220
1839 jssmag.149.235 > icsd-net.2\fR
1845 doesn't exist or doesn't contain an entry for some appletalk
1846 host/net number, addresses are printed in numeric form.)
1847 In the first example, NBP (DDP port 2) on net 144.1 node 209
1848 is sending to whatever is listening on port 220 of net icsd node 112.
1849 The second line is the same except the full name of the source node
1850 is known (`office').
1851 The third line is a send from port 235 on
1852 net jssmag node 149 to broadcast on the icsd-net NBP port (note that
1853 the broadcast address (255) is indicated by a net name with no host
1854 number \- for this reason it's a good idea to keep node names and
1855 net names distinct in /etc/atalk.names).
1857 NBP (name binding protocol) and ATP (Appletalk transaction protocol)
1858 packets have their contents interpreted.
1859 Other protocols just dump
1860 the protocol name (or number if no name is registered for the
1861 protocol) and packet size.
1863 \fBNBP packets\fP are formatted like the following examples:
1867 \s-2\f(CWicsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
1868 jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
1869 techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fR\s+2
1873 The first line is a name lookup request for laserwriters sent by net icsd host
1874 112 and broadcast on net jssmag.
1875 The nbp id for the lookup is 190.
1876 The second line shows a reply for this request (note that it has the
1877 same id) from host jssmag.209 saying that it has a laserwriter
1878 resource named "RM1140" registered on port 250.
1880 another reply to the same request saying host techpit has laserwriter
1881 "techpit" registered on port 186.
1883 \fBATP packet\fP formatting is demonstrated by the following example:
1887 \s-2\f(CWjssmag.209.165 > helios.132: atp-req 12266<0-7> 0xae030001
1888 helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
1889 helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
1890 helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
1891 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1892 helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
1893 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1894 helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
1895 helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
1896 jssmag.209.165 > helios.132: atp-req 12266<3,5> 0xae030001
1897 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1898 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1899 jssmag.209.165 > helios.132: atp-rel 12266<0-7> 0xae030001
1900 jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fR\s+2
1904 Jssmag.209 initiates transaction id 12266 with host helios by requesting
1905 up to 8 packets (the `<0-7>').
1906 The hex number at the end of the line
1907 is the value of the `userdata' field in the request.
1909 Helios responds with 8 512-byte packets.
1910 The `:digit' following the
1911 transaction id gives the packet sequence number in the transaction
1912 and the number in parens is the amount of data in the packet,
1913 excluding the atp header.
1914 The `*' on packet 7 indicates that the
1917 Jssmag.209 then requests that packets 3 & 5 be retransmitted.
1919 resends them then jssmag.209 releases the transaction.
1921 jssmag.209 initiates the next request.
1922 The `*' on the request
1923 indicates that XO (`exactly once') was \fInot\fP set.
1928 Fragmented Internet datagrams are printed as
1932 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR
1933 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR
1937 (The first form indicates there are more fragments.
1939 indicates this is the last fragment.)
1941 \fIId\fP is the fragment id.
1942 \fISize\fP is the fragment
1943 size (in bytes) excluding the IP header.
1944 \fIOffset\fP is this
1945 fragment's offset (in bytes) in the original datagram.
1947 The fragment information is output for each fragment.
1949 fragment contains the higher level protocol header and the frag
1950 info is printed after the protocol info.
1952 after the first contain no higher level protocol header and the
1953 frag info is printed after the source and destination addresses.
1954 For example, here is part of an ftp from arizona.edu to lbl-rtsg.arpa
1955 over a CSNET connection that doesn't appear to handle 576 byte datagrams:
1959 \s-2\f(CWarizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+)
1960 arizona > rtsg: (frag 595a:204@328)
1961 rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2
1965 There are a couple of things to note here: First, addresses in the
1966 2nd line don't include port numbers.
1967 This is because the TCP
1968 protocol information is all in the first fragment and we have no idea
1969 what the port or sequence numbers are when we print the later fragments.
1970 Second, the tcp sequence information in the first line is printed as if there
1971 were 308 bytes of user data when, in fact, there are 512 bytes (308 in
1972 the first frag and 204 in the second).
1973 If you are looking for holes
1974 in the sequence space or trying to match up acks
1975 with packets, this can fool you.
1977 A packet with the IP \fIdon't fragment\fP flag is marked with a
1978 trailing \fB(DF)\fP.
1982 By default, all output lines are preceded by a timestamp.
1984 is the current clock time in the form
1990 and is as accurate as the kernel's clock.
1991 The timestamp reflects the time the kernel first saw the packet.
1993 is made to account for the time lag between when the
1994 ethernet interface removed the packet from the wire and when the kernel
1995 serviced the `new packet' interrupt.
1997 traffic(1C), nit(4P), bpf(4), pcap(3)
1999 The original authors are:
2003 Steven McCanne, all of the
2004 Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
2006 It is currently being maintained by tcpdump.org.
2008 The current version is available via http:
2011 .I http://www.tcpdump.org/
2014 The original distribution is available via anonymous ftp:
2017 .I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z
2020 IPv6/IPsec support is added by WIDE/KAME project.
2021 This program uses Eric Young's SSLeay library, under specific configuration.
2023 Please send problems, bugs, questions, desirable enhancements, etc. to:
2026 tcpdump-workers@tcpdump.org
2029 Please send source code contributions, etc. to:
2035 NIT doesn't let you watch your own outbound traffic, BPF will.
2036 We recommend that you use the latter.
2038 On Linux systems with 2.0[.x] kernels:
2040 packets on the loopback device will be seen twice;
2042 packet filtering cannot be done in the kernel, so that all packets must
2043 be copied from the kernel in order to be filtered in user mode;
2045 all of a packet, not just the part that's within the snapshot length,
2046 will be copied from the kernel (the 2.0[.x] packet capture mechanism, if
2047 asked to copy only part of a packet to userland, will not report the
2048 true length of the packet; this would cause most IP packets to get an
2052 capturing on some PPP devices won't work correctly.
2054 We recommend that you upgrade to a 2.2 or later kernel.
2056 Some attempt should be made to reassemble IP fragments or, at least
2057 to compute the right length for the higher level protocol.
2059 Name server inverse queries are not dumped correctly: the (empty)
2060 question section is printed rather than real query in the answer
2062 Some believe that inverse queries are themselves a bug and
2063 prefer to fix the program generating them rather than \fItcpdump\fP.
2065 A packet trace that crosses a daylight savings time change will give
2066 skewed time stamps (the time change is ignored).
2068 Filter expressions on fields other than those in Token Ring headers will
2069 not correctly handle source-routed Token Ring packets.
2071 Filter expressions on fields other than those in 802.11 headers will not
2072 correctly handle 802.11 data packets with both To DS and From DS set.
2075 should chase header chain, but at this moment it does not.
2076 .BR "ip6 protochain"
2077 is supplied for this behavior.
2079 Arithmetic expression against transport layer headers, like \fBtcp[0]\fP,
2080 does not work against IPv6 packets.
2081 It only looks at IPv4 packets.
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