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23 .TH TCPDUMP 1 "3 January 2001"
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' internet addresses numerically rather than symbolically
285 (this option is intended to get around serious brain damage in
286 Sun's yp server \(em usually it hangs forever translating non-local
290 Use \fIfile\fP as input for the filter expression.
291 An additional expression given on the command line is ignored.
294 Listen on \fIinterface\fP.
295 If unspecified, \fItcpdump\fP searches the system interface list for the
296 lowest numbered, configured up interface (excluding loopback).
297 Ties are broken by choosing the earliest match.
299 On Linux systems with 2.2 or later kernels, an
301 argument of ``any'' can be used to capture packets from all interfaces.
302 Note that captures on the ``any'' device will not be done in promiscuous
307 flag is supported, an interface number as printed by that flag can be
313 Make stdout line buffered.
314 Useful if you want to see the data
318 ``tcpdump\ \ \-l\ \ |\ \ tee dat'' or
319 ``tcpdump\ \ \-l \ \ > dat\ \ &\ \ tail\ \ \-f\ \ dat''.
322 Load SMI MIB module definitions from file \fImodule\fR.
324 can be used several times to load several MIB modules into \fItcpdump\fP.
327 Don't convert addresses (i.e., host addresses, port numbers, etc.) to names.
330 Don't print domain name qualification of host names.
332 if you give this flag then \fItcpdump\fP will print ``nic''
333 instead of ``nic.ddn.mil''.
336 Do not run the packet-matching code optimizer.
338 if you suspect a bug in the optimizer.
341 \fIDon't\fP put the interface
342 into promiscuous mode.
343 Note that the interface might be in promiscuous
344 mode for some other reason; hence, `-p' cannot be used as an abbreviation for
345 `ether host {local-hw-addr} or ether broadcast'.
348 Quick (quiet?) output.
349 Print less protocol information so output
353 Assume ESP/AH packets to be based on old specification (RFC1825 to RFC1829).
354 If specified, \fItcpdump\fP will not print replay prevention field.
355 Since there is no protocol version field in ESP/AH specification,
356 \fItcpdump\fP cannot deduce the version of ESP/AH protocol.
359 Read packets from \fIfile\fR (which was created with the -w option).
360 Standard input is used if \fIfile\fR is ``-''.
363 Print absolute, rather than relative, TCP sequence numbers.
366 Snarf \fIsnaplen\fP bytes of data from each packet rather than the
367 default of 68 (with SunOS's NIT, the minimum is actually 96).
368 68 bytes is adequate for IP, ICMP, TCP
369 and UDP but may truncate protocol information from name server and NFS
371 Packets truncated because of a limited snapshot
372 are indicated in the output with ``[|\fIproto\fP]'', where \fIproto\fP
373 is the name of the protocol level at which the truncation has occurred.
374 Note that taking larger snapshots both increases
375 the amount of time it takes to process packets and, effectively,
376 decreases the amount of packet buffering.
377 This may cause packets to be
379 You should limit \fIsnaplen\fP to the smallest number that will
380 capture the protocol information you're interested in.
382 \fIsnaplen\fP to 0 means use the required length to catch whole packets.
385 Force packets selected by "\fIexpression\fP" to be interpreted the
386 specified \fItype\fR.
387 Currently known types are
388 \fBcnfp\fR (Cisco NetFlow protocol),
389 \fBrpc\fR (Remote Procedure Call),
390 \fBrtp\fR (Real-Time Applications protocol),
391 \fBrtcp\fR (Real-Time Applications control protocol),
392 \fBsnmp\fR (Simple Network Management Protocol),
393 \fBvat\fR (Visual Audio Tool),
395 \fBwb\fR (distributed White Board).
398 \fIDon't\fP print a timestamp on each dump line.
401 Print an unformatted timestamp on each dump line.
404 Print a delta (in micro-seconds) between current and previous line
408 Print a timestamp in default format proceeded by date on each dump line.
411 Print undecoded NFS handles.
414 (Slightly more) verbose output.
415 For example, the time to live,
416 identification, total length and options in an IP packet are printed.
417 Also enables additional packet integrity checks such as verifying the
418 IP and ICMP header checksum.
421 Even more verbose output.
422 For example, additional fields are
423 printed from NFS reply packets, and SMB packets are fully decoded.
426 Even more verbose output.
428 telnet \fBSB\fP ... \fBSE\fP options
432 telnet options are printed in hex as well.
435 Write the raw packets to \fIfile\fR rather than parsing and printing
437 They can later be printed with the \-r option.
438 Standard output is used if \fIfile\fR is ``-''.
441 Print each packet (minus its link level header) in hex.
442 The smaller of the entire packet or
444 bytes will be printed. Note that this is the entire link-layer
445 packet, so for link layers that pad (e.g. Ethernet), the padding bytes
446 will also be printed when the higher layer packet is shorter than the
450 When printing hex, print ASCII too.
453 is also set, the packet is printed in hex/ASCII.
454 This is very handy for analysing new protocols.
457 is not also set, some parts of some packets may be printed
459 .IP "\fI expression\fP"
461 selects which packets will be dumped.
462 If no \fIexpression\fP
463 is given, all packets on the net will be dumped.
465 only packets for which \fIexpression\fP is `true' will be dumped.
467 The \fIexpression\fP consists of one or more
469 Primitives usually consist of an
471 (name or number) preceded by one or more qualifiers.
473 different kinds of qualifier:
475 qualifiers say what kind of thing the id name or number refers to.
481 E.g., `host foo', `net 128.3', `port 20'.
487 qualifiers specify a particular transfer direction to and/or from
489 Possible directions are
496 E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'.
498 there is no dir qualifier,
501 For `null' link layers (i.e. point to point protocols such as slip) the
505 qualifiers can be used to specify a desired direction.
507 qualifiers restrict the match to a particular protocol.
522 E.g., `ether src foo', `arp net 128.3', `tcp port 21'.
524 no proto qualifier, all protocols consistent with the type are
526 E.g., `src foo' means `(ip or arp or rarp) src foo'
527 (except the latter is not legal syntax), `net bar' means `(ip or
528 arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'.
530 [`fddi' is actually an alias for `ether'; the parser treats them
531 identically as meaning ``the data link level used on the specified
532 network interface.'' FDDI headers contain Ethernet-like source
533 and destination addresses, and often contain Ethernet-like packet
534 types, so you can filter on these FDDI fields just as with the
535 analogous Ethernet fields.
536 FDDI headers also contain other fields,
537 but you cannot name them explicitly in a filter expression.
539 Similarly, `tr' and `wlan' are aliases for `ether'; the previous
540 paragraph's statements about FDDI headers also apply to Token Ring
541 and 802.11 wireless LAN headers. For 802.11 headers, the destination
542 address is the DA field and the source address is the SA field; the
543 BSSID, RA, and TA fields aren't tested.]
545 In addition to the above, there are some special `primitive' keywords
546 that don't follow the pattern:
551 and arithmetic expressions.
552 All of these are described below.
554 More complex filter expressions are built up by using the words
559 to combine primitives.
560 E.g., `host foo and not port ftp and not port ftp-data'.
561 To save typing, identical qualifier lists can be omitted.
563 `tcp dst port ftp or ftp-data or domain' is exactly the same as
564 `tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
566 Allowable primitives are:
567 .IP "\fBdst host \fIhost\fR"
568 True if the IPv4/v6 destination field of the packet is \fIhost\fP,
569 which may be either an address or a name.
570 .IP "\fBsrc host \fIhost\fR"
571 True if the IPv4/v6 source field of the packet is \fIhost\fP.
572 .IP "\fBhost \fIhost\fP
573 True if either the IPv4/v6 source or destination of the packet is \fIhost\fP.
574 Any of the above host expressions can be prepended with the keywords,
575 \fBip\fP, \fBarp\fP, \fBrarp\fP, or \fBip6\fP as in:
578 \fBip host \fIhost\fR
581 which is equivalent to:
584 \fBether proto \fI\\ip\fB and host \fIhost\fR
587 If \fIhost\fR is a name with multiple IP addresses, each address will
588 be checked for a match.
589 .IP "\fBether dst \fIehost\fP
590 True if the ethernet destination address is \fIehost\fP.
592 may be either a name from /etc/ethers or a number (see
595 .IP "\fBether src \fIehost\fP
596 True if the ethernet source address is \fIehost\fP.
597 .IP "\fBether host \fIehost\fP
598 True if either the ethernet source or destination address is \fIehost\fP.
599 .IP "\fBgateway\fP \fIhost\fP
600 True if the packet used \fIhost\fP as a gateway.
602 source or destination address was \fIhost\fP but neither the IP source
603 nor the IP destination was \fIhost\fP.
604 \fIHost\fP must be a name and
605 must be found both by the machine's host-name-to-IP-address resolution
606 mechanisms (host name file, DNS, NIS, etc.) and by the machine's
607 host-name-to-Ethernet-address resolution mechanism (/etc/ethers, etc.).
608 (An equivalent expression is
611 \fBether host \fIehost \fBand not host \fIhost\fR
614 which can be used with either names or numbers for \fIhost / ehost\fP.)
615 This syntax does not work in IPv6-enabled configuration at this moment.
616 .IP "\fBdst net \fInet\fR"
617 True if the IPv4/v6 destination address of the packet has a network
619 \fINet\fP may be either a name from /etc/networks
620 or a network number (see \fInetworks(4)\fP for details).
621 .IP "\fBsrc net \fInet\fR"
622 True if the IPv4/v6 source address of the packet has a network
624 .IP "\fBnet \fInet\fR"
625 True if either the IPv4/v6 source or destination address of the packet has a network
627 .IP "\fBnet \fInet\fR \fBmask \fInetmask\fR"
628 True if the IP address matches \fInet\fR with the specific \fInetmask\fR.
629 May be qualified with \fBsrc\fR or \fBdst\fR.
630 Note that this syntax is not valid for IPv6 \fInet\fR.
631 .IP "\fBnet \fInet\fR/\fIlen\fR"
632 True if the IPv4/v6 address matches \fInet\fR with a netmask \fIlen\fR
634 May be qualified with \fBsrc\fR or \fBdst\fR.
635 .IP "\fBdst port \fIport\fR"
636 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a
637 destination port value of \fIport\fP.
638 The \fIport\fP can be a number or a name used in /etc/services (see
642 If a name is used, both the port
643 number and protocol are checked.
644 If a number or ambiguous name is used,
645 only the port number is checked (e.g., \fBdst port 513\fR will print both
646 tcp/login traffic and udp/who traffic, and \fBport domain\fR will print
647 both tcp/domain and udp/domain traffic).
648 .IP "\fBsrc port \fIport\fR"
649 True if the packet has a source port value of \fIport\fP.
650 .IP "\fBport \fIport\fR"
651 True if either the source or destination port of the packet is \fIport\fP.
652 Any of the above port expressions can be prepended with the keywords,
653 \fBtcp\fP or \fBudp\fP, as in:
656 \fBtcp src port \fIport\fR
659 which matches only tcp packets whose source port is \fIport\fP.
660 .IP "\fBless \fIlength\fR"
661 True if the packet has a length less than or equal to \fIlength\fP.
662 This is equivalent to:
665 \fBlen <= \fIlength\fP.
668 .IP "\fBgreater \fIlength\fR"
669 True if the packet has a length greater than or equal to \fIlength\fP.
670 This is equivalent to:
673 \fBlen >= \fIlength\fP.
676 .IP "\fBip proto \fIprotocol\fR"
677 True if the packet is an IP packet (see
679 of protocol type \fIprotocol\fP.
680 \fIProtocol\fP can be a number or one of the names
681 \fIicmp\fP, \fIicmp6\fP, \fIigmp\fP, \fIigrp\fP, \fIpim\fP, \fIah\fP,
682 \fIesp\fP, \fIvrrp\fP, \fIudp\fP, or \fItcp\fP.
683 Note that the identifiers \fItcp\fP, \fIudp\fP, and \fIicmp\fP are also
684 keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell.
685 Note that this primitive does not chase the protocol header chain.
686 .IP "\fBip6 proto \fIprotocol\fR"
687 True if the packet is an IPv6 packet of protocol type \fIprotocol\fP.
688 Note that this primitive does not chase the protocol header chain.
689 .IP "\fBip6 protochain \fIprotocol\fR"
690 True if the packet is IPv6 packet,
691 and contains protocol header with type \fIprotocol\fR
692 in its protocol header chain.
696 \fBip6 protochain 6\fR
699 matches any IPv6 packet with TCP protocol header in the protocol header chain.
700 The packet may contain, for example,
701 authentication header, routing header, or hop-by-hop option header,
702 between IPv6 header and TCP header.
703 The BPF code emitted by this primitive is complex and
704 cannot be optimized by BPF optimizer code in \fItcpdump\fP,
705 so this can be somewhat slow.
706 .IP "\fBip protochain \fIprotocol\fR"
707 Equivalent to \fBip6 protochain \fIprotocol\fR, but this is for IPv4.
708 .IP "\fBether broadcast\fR"
709 True if the packet is an ethernet broadcast packet.
712 .IP "\fBip broadcast\fR"
713 True if the packet is an IP broadcast packet.
715 the all-zeroes and all-ones broadcast conventions, and looks up
716 the local subnet mask.
717 .IP "\fBether multicast\fR"
718 True if the packet is an ethernet multicast packet.
721 This is shorthand for `\fBether[0] & 1 != 0\fP'.
722 .IP "\fBip multicast\fR"
723 True if the packet is an IP multicast packet.
724 .IP "\fBip6 multicast\fR"
725 True if the packet is an IPv6 multicast packet.
726 .IP "\fBether proto \fIprotocol\fR"
727 True if the packet is of ether type \fIprotocol\fR.
728 \fIProtocol\fP can be a number or one of the names
729 \fIip\fP, \fIip6\fP, \fIarp\fP, \fIrarp\fP, \fIatalk\fP, \fIaarp\fP,
730 \fIdecnet\fP, \fIsca\fP, \fIlat\fP, \fImopdl\fP, \fImoprc\fP,
731 \fIiso\fP, \fIstp\fP, \fIipx\fP, or \fInetbeui\fP.
732 Note these identifiers are also keywords
733 and must be escaped via backslash (\\).
735 [In the case of FDDI (e.g., `\fBfddi protocol arp\fR'), Token Ring
736 (e.g., `\fBtr protocol arp\fR'), and IEEE 802.11 wireless LANS (e.g.,
737 `\fBwlan protocol arp\fR'), for most of those protocols, the
738 protocol identification comes from the 802.2 Logical Link Control (LLC)
739 header, which is usually layered on top of the FDDI, Token Ring, or
742 When filtering for most protocol identifiers on FDDI, Token Ring, or
743 802.11, \fItcpdump\fR checks only the protocol ID field of an LLC header
744 in so-called SNAP format with an Organizational Unit Identifier (OUI) of
745 0x000000, for encapsulated Ethernet; it doesn't check whether the packet
746 is in SNAP format with an OUI of 0x000000.
751 \fItcpdump\fR checks the DSAP (Destination Service Access Point) and
752 SSAP (Source Service Access Point) fields of the LLC header;
754 \fBstp\fP and \fInetbeui\fP
755 \fItcpdump\fR checks the DSAP of the LLC header;
758 \fItcpdump\fR checks for a SNAP-format packet with an OUI of 0x080007
759 and the Appletalk etype.
762 In the case of Ethernet, \fItcpdump\fR checks the Ethernet type field
763 for most of those protocols. The exceptions are:
766 \fBiso\fP, \fBsap\fP, and \fBnetbeui\fP
767 \fItcpdump\fR checks for an 802.3 frame and then checks the LLC header as
768 it does for FDDI, Token Ring, and 802.11;
771 \fItcpdump\fR checks both for the Appletalk etype in an Ethernet frame and
772 for a SNAP-format packet as it does for FDDI, Token Ring, and 802.11;
775 \fItcpdump\fR checks for the Appletalk ARP etype in either an Ethernet
776 frame or an 802.2 SNAP frame with an OUI of 0x000000;
779 \fItcpdump\fR checks for the IPX etype in an Ethernet frame, the IPX
780 DSAP in the LLC header, the 802.3-with-no-LLC-header encapsulation of
781 IPX, and the IPX etype in a SNAP frame.
783 .IP "\fBdecnet src \fIhost\fR"
784 True if the DECNET source address is
786 which may be an address of the form ``10.123'', or a DECNET host
788 [DECNET host name support is only available on Ultrix systems
789 that are configured to run DECNET.]
790 .IP "\fBdecnet dst \fIhost\fR"
791 True if the DECNET destination address is
793 .IP "\fBdecnet host \fIhost\fR"
794 True if either the DECNET source or destination address is
796 .IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBatalk\fR, \fBaarp\fR, \fBdecnet\fR, \fBiso\fR, \fBstp\fR, \fBipx\fR, \fInetbeui\fP"
800 \fBether proto \fIp\fR
803 where \fIp\fR is one of the above protocols.
804 .IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR"
808 \fBether proto \fIp\fR
811 where \fIp\fR is one of the above protocols.
813 \fItcpdump\fP does not currently know how to parse these protocols.
814 .IP "\fBvlan \fI[vlan_id]\fR"
815 True if the packet is an IEEE 802.1Q VLAN packet.
816 If \fI[vlan_id]\fR is specified, only true is the packet has the specified
818 Note that the first \fBvlan\fR keyword encountered in \fIexpression\fR
819 changes the decoding offsets for the remainder of \fIexpression\fR
820 on the assumption that the packet is a VLAN packet.
821 .IP "\fBtcp\fR, \fBudp\fR, \fBicmp\fR"
825 \fBip proto \fIp\fR\fB or ip6 proto \fIp\fR
828 where \fIp\fR is one of the above protocols.
829 .IP "\fBiso proto \fIprotocol\fR"
830 True if the packet is an OSI packet of protocol type \fIprotocol\fP.
831 \fIProtocol\fP can be a number or one of the names
832 \fIclnp\fP, \fIesis\fP, or \fIisis\fP.
833 .IP "\fBclnp\fR, \fBesis\fR, \fBisis\fR"
840 where \fIp\fR is one of the above protocols.
841 Note that \fItcpdump\fR does an incomplete job of parsing these protocols.
842 .IP "\fBvpi\fP \fIn\fR
843 True if the packet is an ATM packet, for SunATM on Solaris, with a
844 virtual path identifier of
846 .IP "\fBvci\fP \fIn\fR
847 True if the packet is an ATM packet, for SunATM on Solaris, with a
848 virtual channel identifier of
851 True if the packet is an ATM packet, for SunATM on Solaris, and is
854 True if the packet is an ATM packet, for SunATM on Solaris, and is
855 an LLC-encapsulated packet.
857 True if the packet is an ATM packet, for SunATM on Solaris, and is
858 a segment OAM F4 flow cell (VPI=0 & VCI=3).
860 True if the packet is an ATM packet, for SunATM on Solaris, and is
861 an end-to-end OAM F4 flow cell (VPI=0 & VCI=4).
863 True if the packet is an ATM packet, for SunATM on Solaris, and is
864 a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).
866 True if the packet is an ATM packet, for SunATM on Solaris, and is
867 a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).
869 True if the packet is an ATM packet, for SunATM on Solaris, and is
870 on a meta signaling circuit (VPI=0 & VCI=1).
872 True if the packet is an ATM packet, for SunATM on Solaris, and is
873 on a broadcast signaling circuit (VPI=0 & VCI=2).
875 True if the packet is an ATM packet, for SunATM on Solaris, and is
876 on a signaling circuit (VPI=0 & VCI=5).
878 True if the packet is an ATM packet, for SunATM on Solaris, and is
879 on an ILMI circuit (VPI=0 & VCI=16).
881 True if the packet is an ATM packet, for SunATM on Solaris, and is
882 on a signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect,
883 Connect Ack, Release, or Release Done message.
884 .IP \fBmetaconnect\fP
885 True if the packet is an ATM packet, for SunATM on Solaris, and is
886 on a meta signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect,
887 Release, or Release Done message.
888 .IP "\fIexpr relop expr\fR"
889 True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =, !=,
890 and \fIexpr\fR is an arithmetic expression composed of integer constants
891 (expressed in standard C syntax), the normal binary operators
892 [+, -, *, /, &, |], a length operator, and special packet data accessors.
894 data inside the packet, use the following syntax:
897 \fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR
900 \fIProto\fR is one of \fBether, fddi, tr, wlan, ppp, slip, link,
901 ip, arp, rarp, tcp, udp, icmp\fR or \fBip6\fR, and
902 indicates the protocol layer for the index operation.
903 (\fBether, fddi, wlan, tr, ppp, slip\fR and \fBlink\fR all refer to the
905 Note that \fItcp, udp\fR and other upper-layer protocol types only
906 apply to IPv4, not IPv6 (this will be fixed in the future).
907 The byte offset, relative to the indicated protocol layer, is
909 \fISize\fR is optional and indicates the number of bytes in the
910 field of interest; it can be either one, two, or four, and defaults to one.
911 The length operator, indicated by the keyword \fBlen\fP, gives the
912 length of the packet.
914 For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic.
915 The expression `\fBip[0] & 0xf != 5\fP'
916 catches all IP packets with options.
918 `\fBip[6:2] & 0x1fff = 0\fP'
919 catches only unfragmented datagrams and frag zero of fragmented datagrams.
920 This check is implicitly applied to the \fBtcp\fP and \fBudp\fP
922 For instance, \fBtcp[0]\fP always means the first
923 byte of the TCP \fIheader\fP, and never means the first byte of an
924 intervening fragment.
926 Some offsets and field values may be expressed as names rather than
928 The following protocol header field offsets are
929 available: \fBicmptype\fP (ICMP type field), \fBicmpcode\fP (ICMP
930 code field), and \fBtcpflags\fP (TCP flags field).
932 The following ICMP type field values are available: \fBicmp-echoreply\fP,
933 \fBicmp-unreach\fP, \fBicmp-sourcequench\fP, \fBicmp-redirect\fP,
934 \fBicmp-echo\fP, \fBicmp-routeradvert\fP, \fBicmp-routersolicit\fP,
935 \fBicmp-timxceed\fP, \fBicmp-paramprob\fP, \fBicmp-tstamp\fP,
936 \fBicmp-tstampreply\fP, \fBicmp-ireq\fP, \fBicmp-ireqreply\fP,
937 \fBicmp-maskreq\fP, \fBicmp-maskreply\fP.
939 The following TCP flags field values are available: \fBtcp-fin\fP,
940 \fBtcp-syn\fP, \fBtcp-rst\fP, \fBtcp-push\fP, \fBtcp-push\fP,
941 \fBtcp-ack\fP, \fBtcp-urg\fP.
943 Primitives may be combined using:
945 A parenthesized group of primitives and operators
946 (parentheses are special to the Shell and must be escaped).
948 Negation (`\fB!\fP' or `\fBnot\fP').
950 Concatenation (`\fB&&\fP' or `\fBand\fP').
952 Alternation (`\fB||\fP' or `\fBor\fP').
954 Negation has highest precedence.
955 Alternation and concatenation have equal precedence and associate
957 Note that explicit \fBand\fR tokens, not juxtaposition,
958 are now required for concatenation.
960 If an identifier is given without a keyword, the most recent keyword
965 \fBnot host vs and ace\fR
971 \fBnot host vs and host ace\fR
974 which should not be confused with
977 \fBnot ( host vs or ace )\fR
981 Expression arguments can be passed to \fItcpdump\fP as either a single
982 argument or as multiple arguments, whichever is more convenient.
983 Generally, if the expression contains Shell metacharacters, it is
984 easier to pass it as a single, quoted argument.
985 Multiple arguments are concatenated with spaces before being parsed.
988 To print all packets arriving at or departing from \fIsundown\fP:
991 \fBtcpdump host sundown\fP
995 To print traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR:
998 \fBtcpdump host helios and \\( hot or ace \\)\fP
1002 To print all IP packets between \fIace\fR and any host except \fIhelios\fR:
1005 \fBtcpdump ip host ace and not helios\fP
1009 To print all traffic between local hosts and hosts at Berkeley:
1013 tcpdump net ucb-ether
1017 To print all ftp traffic through internet gateway \fIsnup\fP:
1018 (note that the expression is quoted to prevent the shell from
1019 (mis-)interpreting the parentheses):
1023 tcpdump 'gateway snup and (port ftp or ftp-data)'
1027 To print traffic neither sourced from nor destined for local hosts
1028 (if you gateway to one other net, this stuff should never make it
1029 onto your local net).
1033 tcpdump ip and not net \fIlocalnet\fP
1037 To print the start and end packets (the SYN and FIN packets) of each
1038 TCP conversation that involves a non-local host.
1042 tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net \fIlocalnet\fP'
1046 To print IP packets longer than 576 bytes sent through gateway \fIsnup\fP:
1050 tcpdump 'gateway snup and ip[2:2] > 576'
1054 To print IP broadcast or multicast packets that were
1056 sent via ethernet broadcast or multicast:
1060 tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'
1064 To print all ICMP packets that are not echo requests/replies (i.e., not
1069 tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'
1074 The output of \fItcpdump\fP is protocol dependent.
1076 gives a brief description and examples of most of the formats.
1084 If the '-e' option is given, the link level header is printed out.
1085 On ethernets, the source and destination addresses, protocol,
1086 and packet length are printed.
1088 On FDDI networks, the '-e' option causes \fItcpdump\fP to print
1089 the `frame control' field, the source and destination addresses,
1090 and the packet length.
1091 (The `frame control' field governs the
1092 interpretation of the rest of the packet.
1093 Normal packets (such
1094 as those containing IP datagrams) are `async' packets, with a priority
1095 value between 0 and 7; for example, `\fBasync4\fR'.
1097 are assumed to contain an 802.2 Logical Link Control (LLC) packet;
1098 the LLC header is printed if it is \fInot\fR an ISO datagram or a
1099 so-called SNAP packet.
1101 On Token Ring networks, the '-e' option causes \fItcpdump\fP to print
1102 the `access control' and `frame control' fields, the source and
1103 destination addresses, and the packet length.
1104 As on FDDI networks,
1105 packets are assumed to contain an LLC packet.
1106 Regardless of whether
1107 the '-e' option is specified or not, the source routing information is
1108 printed for source-routed packets.
1110 On 802.11 networks, the '-e' option causes \fItcpdump\fP to print
1111 the `frame control' fields, all of the addresses in the 802.11 header,
1112 and the packet length.
1113 As on FDDI networks,
1114 packets are assumed to contain an LLC packet.
1116 \fI(N.B.: The following description assumes familiarity with
1117 the SLIP compression algorithm described in RFC-1144.)\fP
1119 On SLIP links, a direction indicator (``I'' for inbound, ``O'' for outbound),
1120 packet type, and compression information are printed out.
1121 The packet type is printed first.
1122 The three types are \fIip\fP, \fIutcp\fP, and \fIctcp\fP.
1123 No further link information is printed for \fIip\fR packets.
1124 For TCP packets, the connection identifier is printed following the type.
1125 If the packet is compressed, its encoded header is printed out.
1126 The special cases are printed out as
1127 \fB*S+\fIn\fR and \fB*SA+\fIn\fR, where \fIn\fR is the amount by which
1128 the sequence number (or sequence number and ack) has changed.
1129 If it is not a special case,
1130 zero or more changes are printed.
1131 A change is indicated by U (urgent pointer), W (window), A (ack),
1132 S (sequence number), and I (packet ID), followed by a delta (+n or -n),
1133 or a new value (=n).
1134 Finally, the amount of data in the packet and compressed header length
1137 For example, the following line shows an outbound compressed TCP packet,
1138 with an implicit connection identifier; the ack has changed by 6,
1139 the sequence number by 49, and the packet ID by 6; there are 3 bytes of
1140 data and 6 bytes of compressed header:
1143 \fBO ctcp * A+6 S+49 I+6 3 (6)\fP
1149 Arp/rarp output shows the type of request and its arguments.
1151 format is intended to be self explanatory.
1152 Here is a short sample taken from the start of an `rlogin' from
1153 host \fIrtsg\fP to host \fIcsam\fP:
1157 \f(CWarp who-has csam tell rtsg
1158 arp reply csam is-at CSAM\fR
1162 The first line says that rtsg sent an arp packet asking
1163 for the ethernet address of internet host csam.
1165 replies with its ethernet address (in this example, ethernet addresses
1166 are in caps and internet addresses in lower case).
1168 This would look less redundant if we had done \fItcpdump \-n\fP:
1172 \f(CWarp who-has 128.3.254.6 tell 128.3.254.68
1173 arp reply 128.3.254.6 is-at 02:07:01:00:01:c4\fP
1177 If we had done \fItcpdump \-e\fP, the fact that the first packet is
1178 broadcast and the second is point-to-point would be visible:
1182 \f(CWRTSG Broadcast 0806 64: arp who-has csam tell rtsg
1183 CSAM RTSG 0806 64: arp reply csam is-at CSAM\fR
1187 For the first packet this says the ethernet source address is RTSG, the
1188 destination is the ethernet broadcast address, the type field
1189 contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes.
1193 \fI(N.B.:The following description assumes familiarity with
1194 the TCP protocol described in RFC-793.
1195 If you are not familiar
1196 with the protocol, neither this description nor \fItcpdump\fP will
1197 be of much use to you.)\fP
1199 The general format of a tcp protocol line is:
1203 \fIsrc > dst: flags data-seqno ack window urgent options\fP
1207 \fISrc\fP and \fIdst\fP are the source and destination IP
1208 addresses and ports.
1209 \fIFlags\fP are some combination of S (SYN),
1210 F (FIN), P (PUSH) or R (RST) or a single `.' (no flags).
1211 \fIData-seqno\fP describes the portion of sequence space covered
1212 by the data in this packet (see example below).
1213 \fIAck\fP is sequence number of the next data expected the other
1214 direction on this connection.
1215 \fIWindow\fP is the number of bytes of receive buffer space available
1216 the other direction on this connection.
1217 \fIUrg\fP indicates there is `urgent' data in the packet.
1218 \fIOptions\fP are tcp options enclosed in angle brackets (e.g., <mss 1024>).
1220 \fISrc, dst\fP and \fIflags\fP are always present.
1222 depend on the contents of the packet's tcp protocol header and
1223 are output only if appropriate.
1225 Here is the opening portion of an rlogin from host \fIrtsg\fP to
1230 \s-2\f(CWrtsg.1023 > csam.login: S 768512:768512(0) win 4096 <mss 1024>
1231 csam.login > rtsg.1023: S 947648:947648(0) ack 768513 win 4096 <mss 1024>
1232 rtsg.1023 > csam.login: . ack 1 win 4096
1233 rtsg.1023 > csam.login: P 1:2(1) ack 1 win 4096
1234 csam.login > rtsg.1023: . ack 2 win 4096
1235 rtsg.1023 > csam.login: P 2:21(19) ack 1 win 4096
1236 csam.login > rtsg.1023: P 1:2(1) ack 21 win 4077
1237 csam.login > rtsg.1023: P 2:3(1) ack 21 win 4077 urg 1
1238 csam.login > rtsg.1023: P 3:4(1) ack 21 win 4077 urg 1\fR\s+2
1242 The first line says that tcp port 1023 on rtsg sent a packet
1245 The \fBS\fP indicates that the \fISYN\fP flag was set.
1246 The packet sequence number was 768512 and it contained no data.
1247 (The notation is `first:last(nbytes)' which means `sequence
1249 up to but not including \fIlast\fP which is \fInbytes\fP bytes of user data'.)
1250 There was no piggy-backed ack, the available receive window was 4096
1251 bytes and there was a max-segment-size option requesting an mss of
1254 Csam replies with a similar packet except it includes a piggy-backed
1256 Rtsg then acks csam's SYN.
1259 The packet contained no data so there is no data sequence number.
1260 Note that the ack sequence
1261 number is a small integer (1).
1262 The first time \fItcpdump\fP sees a
1263 tcp `conversation', it prints the sequence number from the packet.
1264 On subsequent packets of the conversation, the difference between
1265 the current packet's sequence number and this initial sequence number
1267 This means that sequence numbers after the
1268 first can be interpreted
1269 as relative byte positions in the conversation's data stream (with the
1270 first data byte each direction being `1').
1271 `-S' will override this
1272 feature, causing the original sequence numbers to be output.
1274 On the 6th line, rtsg sends csam 19 bytes of data (bytes 2 through 20
1275 in the rtsg \(-> csam side of the conversation).
1276 The PUSH flag is set in the packet.
1277 On the 7th line, csam says it's received data sent by rtsg up to
1278 but not including byte 21.
1279 Most of this data is apparently sitting in the
1280 socket buffer since csam's receive window has gotten 19 bytes smaller.
1281 Csam also sends one byte of data to rtsg in this packet.
1282 On the 8th and 9th lines,
1283 csam sends two bytes of urgent, pushed data to rtsg.
1285 If the snapshot was small enough that \fItcpdump\fP didn't capture
1286 the full TCP header, it interprets as much of the header as it can
1287 and then reports ``[|\fItcp\fP]'' to indicate the remainder could not
1289 If the header contains a bogus option (one with a length
1290 that's either too small or beyond the end of the header), \fItcpdump\fP
1291 reports it as ``[\fIbad opt\fP]'' and does not interpret any further
1292 options (since it's impossible to tell where they start).
1294 length indicates options are present but the IP datagram length is not
1295 long enough for the options to actually be there, \fItcpdump\fP reports
1296 it as ``[\fIbad hdr length\fP]''.
1298 .B Capturing TCP packets with particular flag combinations (SYN-ACK, URG-ACK, etc.)
1300 There are 8 bits in the control bits section of the TCP header:
1302 .I CWR | ECE | URG | ACK | PSH | RST | SYN | FIN
1304 Let's assume that we want to watch packets used in establishing
1306 Recall that TCP uses a 3-way handshake protocol
1307 when it initializes a new connection; the connection sequence with
1308 regard to the TCP control bits is
1314 2) Recipient responds with SYN, ACK
1320 Now we're interested in capturing packets that have only the
1321 SYN bit set (Step 1).
1322 Note that we don't want packets from step 2
1323 (SYN-ACK), just a plain initial SYN.
1324 What we need is a correct filter
1325 expression for \fItcpdump\fP.
1327 Recall the structure of a TCP header without options:
1331 -----------------------------------------------------------------
1332 | source port | destination port |
1333 -----------------------------------------------------------------
1335 -----------------------------------------------------------------
1336 | acknowledgment number |
1337 -----------------------------------------------------------------
1338 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1339 -----------------------------------------------------------------
1340 | TCP checksum | urgent pointer |
1341 -----------------------------------------------------------------
1344 A TCP header usually holds 20 octets of data, unless options are
1346 The first line of the graph contains octets 0 - 3, the
1347 second line shows octets 4 - 7 etc.
1349 Starting to count with 0, the relevant TCP control bits are contained
1354 ----------------|---------------|---------------|----------------
1355 | HL | rsvd |C|E|U|A|P|R|S|F| window size |
1356 ----------------|---------------|---------------|----------------
1357 | | 13th octet | | |
1360 Let's have a closer look at octet no. 13:
1370 These are the TCP control bits we are interested
1372 We have numbered the bits in this octet from 0 to 7, right to
1373 left, so the PSH bit is bit number 3, while the URG bit is number 5.
1375 Recall that we want to capture packets with only SYN set.
1376 Let's see what happens to octet 13 if a TCP datagram arrives
1377 with the SYN bit set in its header:
1388 control bits section we see that only bit number 1 (SYN) is set.
1390 Assuming that octet number 13 is an 8-bit unsigned integer in
1391 network byte order, the binary value of this octet is
1395 and its decimal representation is
1399 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 1*2 + 0*2 = 2
1402 We're almost done, because now we know that if only SYN is set,
1403 the value of the 13th octet in the TCP header, when interpreted
1404 as a 8-bit unsigned integer in network byte order, must be exactly 2.
1406 This relationship can be expressed as
1412 We can use this expression as the filter for \fItcpdump\fP in order
1413 to watch packets which have only SYN set:
1416 tcpdump -i xl0 tcp[13] == 2
1419 The expression says "let the 13th octet of a TCP datagram have
1420 the decimal value 2", which is exactly what we want.
1422 Now, let's assume that we need to capture SYN packets, but we
1423 don't care if ACK or any other TCP control bit is set at the
1425 Let's see what happens to octet 13 when a TCP datagram
1426 with SYN-ACK set arrives:
1436 Now bits 1 and 4 are set in the 13th octet.
1442 which translates to decimal
1446 0*2 + 0*2 + 0*2 + 1*2 + 0*2 + 0*2 + 1*2 + 0*2 = 18
1449 Now we can't just use 'tcp[13] == 18' in the \fItcpdump\fP filter
1450 expression, because that would select only those packets that have
1451 SYN-ACK set, but not those with only SYN set.
1452 Remember that we don't care
1453 if ACK or any other control bit is set as long as SYN is set.
1455 In order to achieve our goal, we need to logically AND the
1456 binary value of octet 13 with some other value to preserve
1458 We know that we want SYN to be set in any case,
1459 so we'll logically AND the value in the 13th octet with
1460 the binary value of a SYN:
1464 00010010 SYN-ACK 00000010 SYN
1465 AND 00000010 (we want SYN) AND 00000010 (we want SYN)
1467 = 00000010 = 00000010
1470 We see that this AND operation delivers the same result
1471 regardless whether ACK or another TCP control bit is set.
1472 The decimal representation of the AND value as well as
1473 the result of this operation is 2 (binary 00000010),
1474 so we know that for packets with SYN set the following
1475 relation must hold true:
1477 ( ( value of octet 13 ) AND ( 2 ) ) == ( 2 )
1479 This points us to the \fItcpdump\fP filter expression
1482 tcpdump -i xl0 'tcp[13] & 2 == 2'
1485 Note that you should use single quotes or a backslash
1486 in the expression to hide the AND ('&') special character
1492 UDP format is illustrated by this rwho packet:
1496 \f(CWactinide.who > broadcast.who: udp 84\fP
1500 This says that port \fIwho\fP on host \fIactinide\fP sent a udp
1501 datagram to port \fIwho\fP on host \fIbroadcast\fP, the Internet
1503 The packet contained 84 bytes of user data.
1505 Some UDP services are recognized (from the source or destination
1506 port number) and the higher level protocol information printed.
1507 In particular, Domain Name service requests (RFC-1034/1035) and Sun
1508 RPC calls (RFC-1050) to NFS.
1510 UDP Name Server Requests
1512 \fI(N.B.:The following description assumes familiarity with
1513 the Domain Service protocol described in RFC-1035.
1514 If you are not familiar
1515 with the protocol, the following description will appear to be written
1518 Name server requests are formatted as
1522 \fIsrc > dst: id op? flags qtype qclass name (len)\fP
1524 \f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fR
1528 Host \fIh2opolo\fP asked the domain server on \fIhelios\fP for an
1529 address record (qtype=A) associated with the name \fIucbvax.berkeley.edu.\fP
1530 The query id was `3'.
1531 The `+' indicates the \fIrecursion desired\fP flag
1533 The query length was 37 bytes, not including the UDP and
1534 IP protocol headers.
1535 The query operation was the normal one, \fIQuery\fP,
1536 so the op field was omitted.
1537 If the op had been anything else, it would
1538 have been printed between the `3' and the `+'.
1539 Similarly, the qclass was the normal one,
1540 \fIC_IN\fP, and omitted.
1541 Any other qclass would have been printed
1542 immediately after the `A'.
1544 A few anomalies are checked and may result in extra fields enclosed in
1545 square brackets: If a query contains an answer, authority records or
1546 additional records section,
1551 are printed as `[\fIn\fPa]', `[\fIn\fPn]' or `[\fIn\fPau]' where \fIn\fP
1552 is the appropriate count.
1553 If any of the response bits are set (AA, RA or rcode) or any of the
1554 `must be zero' bits are set in bytes two and three, `[b2&3=\fIx\fP]'
1555 is printed, where \fIx\fP is the hex value of header bytes two and three.
1557 UDP Name Server Responses
1559 Name server responses are formatted as
1563 \fIsrc > dst: id op rcode flags a/n/au type class data (len)\fP
1565 \f(CWhelios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273)
1566 helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fR
1570 In the first example, \fIhelios\fP responds to query id 3 from \fIh2opolo\fP
1571 with 3 answer records, 3 name server records and 7 additional records.
1572 The first answer record is type A (address) and its data is internet
1573 address 128.32.137.3.
1574 The total size of the response was 273 bytes,
1575 excluding UDP and IP headers.
1576 The op (Query) and response code
1577 (NoError) were omitted, as was the class (C_IN) of the A record.
1579 In the second example, \fIhelios\fP responds to query 2 with a
1580 response code of non-existent domain (NXDomain) with no answers,
1581 one name server and no authority records.
1582 The `*' indicates that
1583 the \fIauthoritative answer\fP bit was set.
1585 answers, no type, class or data were printed.
1587 Other flag characters that might appear are `\-' (recursion available,
1588 RA, \fInot\fP set) and `|' (truncated message, TC, set).
1590 `question' section doesn't contain exactly one entry, `[\fIn\fPq]'
1593 Note that name server requests and responses tend to be large and the
1594 default \fIsnaplen\fP of 68 bytes may not capture enough of the packet
1596 Use the \fB\-s\fP flag to increase the snaplen if you
1597 need to seriously investigate name server traffic.
1599 has worked well for me.
1604 \fItcpdump\fP now includes fairly extensive SMB/CIFS/NBT decoding for data
1605 on UDP/137, UDP/138 and TCP/139.
1606 Some primitive decoding of IPX and
1607 NetBEUI SMB data is also done.
1609 By default a fairly minimal decode is done, with a much more detailed
1610 decode done if -v is used.
1611 Be warned that with -v a single SMB packet
1612 may take up a page or more, so only use -v if you really want all the
1615 If you are decoding SMB sessions containing unicode strings then you
1616 may wish to set the environment variable USE_UNICODE to 1.
1618 auto-detect unicode srings would be welcome.
1620 For information on SMB packet formats and what all te fields mean see
1621 www.cifs.org or the pub/samba/specs/ directory on your favourite
1622 samba.org mirror site.
1623 The SMB patches were written by Andrew Tridgell
1627 NFS Requests and Replies
1629 Sun NFS (Network File System) requests and replies are printed as:
1633 \fIsrc.xid > dst.nfs: len op args\fP
1634 \fIsrc.nfs > dst.xid: reply stat len op results\fP
1637 sushi.6709 > wrl.nfs: 112 readlink fh 21,24/10.73165
1638 wrl.nfs > sushi.6709: reply ok 40 readlink "../var"
1639 sushi.201b > wrl.nfs:
1640 144 lookup fh 9,74/4096.6878 "xcolors"
1641 wrl.nfs > sushi.201b:
1642 reply ok 128 lookup fh 9,74/4134.3150
1647 In the first line, host \fIsushi\fP sends a transaction with id \fI6709\fP
1648 to \fIwrl\fP (note that the number following the src host is a
1649 transaction id, \fInot\fP the source port).
1650 The request was 112 bytes,
1651 excluding the UDP and IP headers.
1652 The operation was a \fIreadlink\fP
1653 (read symbolic link) on file handle (\fIfh\fP) 21,24/10.731657119.
1654 (If one is lucky, as in this case, the file handle can be interpreted
1655 as a major,minor device number pair, followed by the inode number and
1657 \fIWrl\fP replies `ok' with the contents of the link.
1659 In the third line, \fIsushi\fP asks \fIwrl\fP to lookup the name
1660 `\fIxcolors\fP' in directory file 9,74/4096.6878.
1661 Note that the data printed
1662 depends on the operation type.
1663 The format is intended to be self
1664 explanatory if read in conjunction with
1665 an NFS protocol spec.
1667 If the \-v (verbose) flag is given, additional information is printed.
1673 sushi.1372a > wrl.nfs:
1674 148 read fh 21,11/12.195 8192 bytes @ 24576
1675 wrl.nfs > sushi.1372a:
1676 reply ok 1472 read REG 100664 ids 417/0 sz 29388
1681 (\-v also prints the IP header TTL, ID, length, and fragmentation fields,
1682 which have been omitted from this example.) In the first line,
1683 \fIsushi\fP asks \fIwrl\fP to read 8192 bytes from file 21,11/12.195,
1684 at byte offset 24576.
1685 \fIWrl\fP replies `ok'; the packet shown on the
1686 second line is the first fragment of the reply, and hence is only 1472
1687 bytes long (the other bytes will follow in subsequent fragments, but
1688 these fragments do not have NFS or even UDP headers and so might not be
1689 printed, depending on the filter expression used).
1690 Because the \-v flag
1691 is given, some of the file attributes (which are returned in addition
1692 to the file data) are printed: the file type (``REG'', for regular file),
1693 the file mode (in octal), the uid and gid, and the file size.
1695 If the \-v flag is given more than once, even more details are printed.
1697 Note that NFS requests are very large and much of the detail won't be printed
1698 unless \fIsnaplen\fP is increased.
1699 Try using `\fB\-s 192\fP' to watch
1702 NFS reply packets do not explicitly identify the RPC operation.
1704 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1705 replies using the transaction ID.
1706 If a reply does not closely follow the
1707 corresponding request, it might not be parsable.
1709 AFS Requests and Replies
1711 Transarc AFS (Andrew File System) requests and replies are printed
1717 \fIsrc.sport > dst.dport: rx packet-type\fP
1718 \fIsrc.sport > dst.dport: rx packet-type service call call-name args\fP
1719 \fIsrc.sport > dst.dport: rx packet-type service reply call-name args\fP
1722 elvis.7001 > pike.afsfs:
1723 rx data fs call rename old fid 536876964/1/1 ".newsrc.new"
1724 new fid 536876964/1/1 ".newsrc"
1725 pike.afsfs > elvis.7001: rx data fs reply rename
1730 In the first line, host elvis sends a RX packet to pike.
1732 a RX data packet to the fs (fileserver) service, and is the start of
1734 The RPC call was a rename, with the old directory file id
1735 of 536876964/1/1 and an old filename of `.newsrc.new', and a new directory
1736 file id of 536876964/1/1 and a new filename of `.newsrc'.
1738 responds with a RPC reply to the rename call (which was successful, because
1739 it was a data packet and not an abort packet).
1741 In general, all AFS RPCs are decoded at least by RPC call name.
1743 AFS RPCs have at least some of the arguments decoded (generally only
1744 the `interesting' arguments, for some definition of interesting).
1746 The format is intended to be self-describing, but it will probably
1747 not be useful to people who are not familiar with the workings of
1750 If the -v (verbose) flag is given twice, acknowledgement packets and
1751 additional header information is printed, such as the the RX call ID,
1752 call number, sequence number, serial number, and the RX packet flags.
1754 If the -v flag is given twice, additional information is printed,
1755 such as the the RX call ID, serial number, and the RX packet flags.
1756 The MTU negotiation information is also printed from RX ack packets.
1758 If the -v flag is given three times, the security index and service id
1761 Error codes are printed for abort packets, with the exception of Ubik
1762 beacon packets (because abort packets are used to signify a yes vote
1763 for the Ubik protocol).
1765 Note that AFS requests are very large and many of the arguments won't
1766 be printed unless \fIsnaplen\fP is increased.
1767 Try using `\fB-s 256\fP'
1768 to watch AFS traffic.
1770 AFS reply packets do not explicitly identify the RPC operation.
1772 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1773 replies using the call number and service ID.
1774 If a reply does not closely
1776 corresponding request, it might not be parsable.
1779 KIP Appletalk (DDP in UDP)
1781 Appletalk DDP packets encapsulated in UDP datagrams are de-encapsulated
1782 and dumped as DDP packets (i.e., all the UDP header information is
1786 is used to translate appletalk net and node numbers to names.
1787 Lines in this file have the form
1799 The first two lines give the names of appletalk networks.
1801 line gives the name of a particular host (a host is distinguished
1802 from a net by the 3rd octet in the number \-
1803 a net number \fImust\fP have two octets and a host number \fImust\fP
1804 have three octets.) The number and name should be separated by
1805 whitespace (blanks or tabs).
1808 file may contain blank lines or comment lines (lines starting with
1811 Appletalk addresses are printed in the form
1817 \f(CW144.1.209.2 > icsd-net.112.220
1818 office.2 > icsd-net.112.220
1819 jssmag.149.235 > icsd-net.2\fR
1825 doesn't exist or doesn't contain an entry for some appletalk
1826 host/net number, addresses are printed in numeric form.)
1827 In the first example, NBP (DDP port 2) on net 144.1 node 209
1828 is sending to whatever is listening on port 220 of net icsd node 112.
1829 The second line is the same except the full name of the source node
1830 is known (`office').
1831 The third line is a send from port 235 on
1832 net jssmag node 149 to broadcast on the icsd-net NBP port (note that
1833 the broadcast address (255) is indicated by a net name with no host
1834 number \- for this reason it's a good idea to keep node names and
1835 net names distinct in /etc/atalk.names).
1837 NBP (name binding protocol) and ATP (Appletalk transaction protocol)
1838 packets have their contents interpreted.
1839 Other protocols just dump
1840 the protocol name (or number if no name is registered for the
1841 protocol) and packet size.
1843 \fBNBP packets\fP are formatted like the following examples:
1847 \s-2\f(CWicsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
1848 jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
1849 techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fR\s+2
1853 The first line is a name lookup request for laserwriters sent by net icsd host
1854 112 and broadcast on net jssmag.
1855 The nbp id for the lookup is 190.
1856 The second line shows a reply for this request (note that it has the
1857 same id) from host jssmag.209 saying that it has a laserwriter
1858 resource named "RM1140" registered on port 250.
1860 another reply to the same request saying host techpit has laserwriter
1861 "techpit" registered on port 186.
1863 \fBATP packet\fP formatting is demonstrated by the following example:
1867 \s-2\f(CWjssmag.209.165 > helios.132: atp-req 12266<0-7> 0xae030001
1868 helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
1869 helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
1870 helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
1871 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1872 helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
1873 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1874 helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
1875 helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
1876 jssmag.209.165 > helios.132: atp-req 12266<3,5> 0xae030001
1877 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1878 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1879 jssmag.209.165 > helios.132: atp-rel 12266<0-7> 0xae030001
1880 jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fR\s+2
1884 Jssmag.209 initiates transaction id 12266 with host helios by requesting
1885 up to 8 packets (the `<0-7>').
1886 The hex number at the end of the line
1887 is the value of the `userdata' field in the request.
1889 Helios responds with 8 512-byte packets.
1890 The `:digit' following the
1891 transaction id gives the packet sequence number in the transaction
1892 and the number in parens is the amount of data in the packet,
1893 excluding the atp header.
1894 The `*' on packet 7 indicates that the
1897 Jssmag.209 then requests that packets 3 & 5 be retransmitted.
1899 resends them then jssmag.209 releases the transaction.
1901 jssmag.209 initiates the next request.
1902 The `*' on the request
1903 indicates that XO (`exactly once') was \fInot\fP set.
1908 Fragmented Internet datagrams are printed as
1912 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR
1913 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR
1917 (The first form indicates there are more fragments.
1919 indicates this is the last fragment.)
1921 \fIId\fP is the fragment id.
1922 \fISize\fP is the fragment
1923 size (in bytes) excluding the IP header.
1924 \fIOffset\fP is this
1925 fragment's offset (in bytes) in the original datagram.
1927 The fragment information is output for each fragment.
1929 fragment contains the higher level protocol header and the frag
1930 info is printed after the protocol info.
1932 after the first contain no higher level protocol header and the
1933 frag info is printed after the source and destination addresses.
1934 For example, here is part of an ftp from arizona.edu to lbl-rtsg.arpa
1935 over a CSNET connection that doesn't appear to handle 576 byte datagrams:
1939 \s-2\f(CWarizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+)
1940 arizona > rtsg: (frag 595a:204@328)
1941 rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2
1945 There are a couple of things to note here: First, addresses in the
1946 2nd line don't include port numbers.
1947 This is because the TCP
1948 protocol information is all in the first fragment and we have no idea
1949 what the port or sequence numbers are when we print the later fragments.
1950 Second, the tcp sequence information in the first line is printed as if there
1951 were 308 bytes of user data when, in fact, there are 512 bytes (308 in
1952 the first frag and 204 in the second).
1953 If you are looking for holes
1954 in the sequence space or trying to match up acks
1955 with packets, this can fool you.
1957 A packet with the IP \fIdon't fragment\fP flag is marked with a
1958 trailing \fB(DF)\fP.
1962 By default, all output lines are preceded by a timestamp.
1964 is the current clock time in the form
1970 and is as accurate as the kernel's clock.
1971 The timestamp reflects the time the kernel first saw the packet.
1973 is made to account for the time lag between when the
1974 ethernet interface removed the packet from the wire and when the kernel
1975 serviced the `new packet' interrupt.
1977 traffic(1C), nit(4P), bpf(4), pcap(3)
1979 The original authors are:
1983 Steven McCanne, all of the
1984 Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
1986 It is currently being maintained by tcpdump.org.
1988 The current version is available via http:
1991 .I http://www.tcpdump.org/
1994 The original distribution is available via anonymous ftp:
1997 .I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z
2000 IPv6/IPsec support is added by WIDE/KAME project.
2001 This program uses Eric Young's SSLeay library, under specific configuration.
2003 Please send problems, bugs, questions, desirable enhancements, etc. to:
2006 tcpdump-workers@tcpdump.org
2009 Please send source code contributions, etc. to:
2015 NIT doesn't let you watch your own outbound traffic, BPF will.
2016 We recommend that you use the latter.
2018 On Linux systems with 2.0[.x] kernels:
2020 packets on the loopback device will be seen twice;
2022 packet filtering cannot be done in the kernel, so that all packets must
2023 be copied from the kernel in order to be filtered in user mode;
2025 all of a packet, not just the part that's within the snapshot length,
2026 will be copied from the kernel (the 2.0[.x] packet capture mechanism, if
2027 asked to copy only part of a packet to userland, will not report the
2028 true length of the packet; this would cause most IP packets to get an
2032 capturing on some PPP devices won't work correctly.
2034 We recommend that you upgrade to a 2.2 or later kernel.
2036 Some attempt should be made to reassemble IP fragments or, at least
2037 to compute the right length for the higher level protocol.
2039 Name server inverse queries are not dumped correctly: the (empty)
2040 question section is printed rather than real query in the answer
2042 Some believe that inverse queries are themselves a bug and
2043 prefer to fix the program generating them rather than \fItcpdump\fP.
2045 A packet trace that crosses a daylight savings time change will give
2046 skewed time stamps (the time change is ignored).
2048 Filter expressions that manipulate FDDI, Token Ring, or 802.11 headers
2049 assume that all FDDI, Token Ring, and 802.11 packets are
2050 SNAP-encapsulated Ethernet packets.
2051 This is true for IP, ARP, and DECNET Phase IV, but is not true
2052 for protocols such as ISO CLNS.
2053 Therefore, the filter may inadvertently
2054 accept certain packets that do not properly match the filter expression.
2056 Filter expressions on fields other than those in Token Ring headers will
2057 not correctly handle source-routed Token Ring packets.
2059 Filter expressions on fields other than those in 802.11 headers will not
2060 correctly handle 802.11 data packets with both To DS and From DS set.
2063 should chase header chain, but at this moment it does not.
2064 .BR "ip6 protochain"
2065 is supplied for this behavior.
2067 Arithmetic expression against transport layer headers, like \fBtcp[0]\fP,
2068 does not work against IPv6 packets.
2069 It only looks at IPv4 packets.
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