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23 .TH TCPDUMP 1 "3 January 2001"
25 tcpdump \- dump traffic on a network
79 \fITcpdump\fP prints out the headers of packets on a network interface
80 that match the boolean \fIexpression\fP.
82 .B Under SunOS with nit or bpf:
85 you must have read access to
89 .B Under Solaris with dlpi:
90 You must have read/write access to the network pseudo device, e.g.
92 .B Under HP-UX with dlpi:
93 You must be root or it must be installed setuid to root.
94 .B Under IRIX with snoop:
95 You must be root or it must be installed setuid to root.
97 You must be root or it must be installed setuid to root.
98 .B Under Ultrix and Digital UNIX:
99 Once the super-user has enabled promiscuous-mode operation using
104 You must have read access to
109 Attempt to convert network and broadcast addresses to names.
112 Exit after receiving \fIcount\fP packets.
115 Dump the compiled packet-matching code in a human readable form to
116 standard output and stop.
119 Dump packet-matching code as a
124 Dump packet-matching code as decimal numbers (preceded with a count).
127 Print the link-level header on each dump line.
130 Use \fIalgo:secret\fP for decrypting IPsec ESP packets.
136 \fBcast128-cbc\fP, or
138 The default is \fBdes-cbc\fP.
139 The ability to decrypt packets is only present if \fItcpdump\fP was compiled
140 with cryptography enabled.
141 \fIsecret\fP the ascii text for ESP secret key.
142 We cannot take arbitrary binary value at this moment.
143 The option assumes RFC2406 ESP, not RFC1827 ESP.
144 The option is only for debugging purposes, and
145 the use of this option with truly `secret' key is discouraged.
146 By presenting IPsec secret key onto command line
147 you make it visible to others, via
152 Print `foreign' internet addresses numerically rather than symbolically
153 (this option is intended to get around serious brain damage in
154 Sun's yp server \(em usually it hangs forever translating non-local
158 Use \fIfile\fP as input for the filter expression.
159 An additional expression given on the command line is ignored.
162 Listen on \fIinterface\fP.
163 If unspecified, \fItcpdump\fP searches the system interface list for the
164 lowest numbered, configured up interface (excluding loopback).
165 Ties are broken by choosing the earliest match.
167 On Linux systems with 2.2 or later kernels, an
169 argument of ``any'' can be used to capture packets from all interfaces.
170 Note that captures on the ``any'' device will not be done in promiscuous
174 Make stdout line buffered.
175 Useful if you want to see the data
179 ``tcpdump\ \ \-l\ \ |\ \ tee dat'' or
180 ``tcpdump\ \ \-l \ \ > dat\ \ &\ \ tail\ \ \-f\ \ dat''.
183 Don't convert addresses (i.e., host addresses, port numbers, etc.) to names.
186 Don't print domain name qualification of host names.
188 if you give this flag then \fItcpdump\fP will print ``nic''
189 instead of ``nic.ddn.mil''.
192 Load SMI MIB module definitions from file \fImodule\fR.
194 can be used several times to load several MIB modules into \fItcpdump\fP.
197 Do not run the packet-matching code optimizer.
199 if you suspect a bug in the optimizer.
202 \fIDon't\fP put the interface
203 into promiscuous mode.
204 Note that the interface might be in promiscuous
205 mode for some other reason; hence, `-p' cannot be used as an abbreviation for
206 `ether host {local-hw-addr} or ether broadcast'.
209 Quick (quiet?) output.
210 Print less protocol information so output
214 Read packets from \fIfile\fR (which was created with the -w option).
215 Standard input is used if \fIfile\fR is ``-''.
218 Snarf \fIsnaplen\fP bytes of data from each packet rather than the
219 default of 68 (with SunOS's NIT, the minimum is actually 96).
220 68 bytes is adequate for IP, ICMP, TCP
221 and UDP but may truncate protocol information from name server and NFS
223 Packets truncated because of a limited snapshot
224 are indicated in the output with ``[|\fIproto\fP]'', where \fIproto\fP
225 is the name of the protocol level at which the truncation has occurred.
226 Note that taking larger snapshots both increases
227 the amount of time it takes to process packets and, effectively,
228 decreases the amount of packet buffering.
229 This may cause packets to be
231 You should limit \fIsnaplen\fP to the smallest number that will
232 capture the protocol information you're interested in.
234 \fIsnaplen\fP to 0 means use the required length to catch whole packets.
237 Force packets selected by "\fIexpression\fP" to be interpreted the
238 specified \fItype\fR.
239 Currently known types are
240 \fBcnfp\fR (Cisco NetFlow protocol),
241 \fBrpc\fR (Remote Procedure Call),
242 \fBrtp\fR (Real-Time Applications protocol),
243 \fBrtcp\fR (Real-Time Applications control protocol),
244 \fBsnmp\fR (Simple Network Management Protocol),
245 \fBvat\fR (Visual Audio Tool),
247 \fBwb\fR (distributed White Board).
250 Assume ESP/AH packets to be based on old specification (RFC1825 to RFC1829).
251 If specified, \fItcpdump\fP will not print replay prevention field.
252 Since there is no protocol version field in ESP/AH specification,
253 \fItcpdump\fP cannot deduce the version of ESP/AH protocol.
256 Print absolute, rather than relative, TCP sequence numbers.
259 \fIDon't\fP print a timestamp on each dump line.
262 Print an unformatted timestamp on each dump line.
265 Print a delta (in micro-seconds) between current and previous line
269 Print a timestamp in default format proceeded by date on each dump line.
272 (Slightly more) verbose output.
273 For example, the time to live,
274 identification, total length and options in an IP packet are printed.
275 Also enables additional packet integrity checks such as verifying the
276 IP and ICMP header checksum.
279 Even more verbose output.
280 For example, additional fields are
281 printed from NFS reply packets, and SMB packets are fully decoded.
284 Even more verbose output.
286 telnet \fBSB\fP ... \fBSE\fP options
290 telnet options are printed in hex as well.
293 Write the raw packets to \fIfile\fR rather than parsing and printing
295 They can later be printed with the \-r option.
296 Standard output is used if \fIfile\fR is ``-''.
299 Print each packet (minus its link level header) in hex.
300 The smaller of the entire packet or
302 bytes will be printed.
305 When printing hex, print ascii too.
308 is also set, the packet is printed in hex/ascii.
309 This is very handy for analysing new protocols.
312 is not also set, some parts of some packets may be printed
314 .IP "\fI expression\fP"
316 selects which packets will be dumped.
317 If no \fIexpression\fP
318 is given, all packets on the net will be dumped.
320 only packets for which \fIexpression\fP is `true' will be dumped.
322 The \fIexpression\fP consists of one or more
324 Primitives usually consist of an
326 (name or number) preceded by one or more qualifiers.
328 different kinds of qualifier:
330 qualifiers say what kind of thing the id name or number refers to.
336 E.g., `host foo', `net 128.3', `port 20'.
342 qualifiers specify a particular transfer direction to and/or from
344 Possible directions are
351 E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'.
353 there is no dir qualifier,
356 For `null' link layers (i.e. point to point protocols such as slip) the
360 qualifiers can be used to specify a desired direction.
362 qualifiers restrict the match to a particular protocol.
376 E.g., `ether src foo', `arp net 128.3', `tcp port 21'.
378 no proto qualifier, all protocols consistent with the type are
380 E.g., `src foo' means `(ip or arp or rarp) src foo'
381 (except the latter is not legal syntax), `net bar' means `(ip or
382 arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'.
384 [`fddi' is actually an alias for `ether'; the parser treats them
385 identically as meaning ``the data link level used on the specified
386 network interface.'' FDDI headers contain Ethernet-like source
387 and destination addresses, and often contain Ethernet-like packet
388 types, so you can filter on these FDDI fields just as with the
389 analogous Ethernet fields.
390 FDDI headers also contain other fields,
391 but you cannot name them explicitly in a filter expression.
393 Similarly, `tr' is an alias for `ether'; the previous paragraph's
394 statements about FDDI headers also apply to Token Ring headers.]
396 In addition to the above, there are some special `primitive' keywords
397 that don't follow the pattern:
402 and arithmetic expressions.
403 All of these are described below.
405 More complex filter expressions are built up by using the words
410 to combine primitives.
411 E.g., `host foo and not port ftp and not port ftp-data'.
412 To save typing, identical qualifier lists can be omitted.
414 `tcp dst port ftp or ftp-data or domain' is exactly the same as
415 `tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
417 Allowable primitives are:
418 .IP "\fBdst host \fIhost\fR"
419 True if the IPv4/v6 destination field of the packet is \fIhost\fP,
420 which may be either an address or a name.
421 .IP "\fBsrc host \fIhost\fR"
422 True if the IPv4/v6 source field of the packet is \fIhost\fP.
423 .IP "\fBhost \fIhost\fP
424 True if either the IPv4/v6 source or destination of the packet is \fIhost\fP.
425 Any of the above host expressions can be prepended with the keywords,
426 \fBip\fP, \fBarp\fP, \fBrarp\fP, or \fBip6\fP as in:
429 \fBip host \fIhost\fR
432 which is equivalent to:
435 \fBether proto \fI\\ip\fB and host \fIhost\fR
438 If \fIhost\fR is a name with multiple IP addresses, each address will
439 be checked for a match.
440 .IP "\fBether dst \fIehost\fP
441 True if the ethernet destination address is \fIehost\fP.
443 may be either a name from /etc/ethers or a number (see
446 .IP "\fBether src \fIehost\fP
447 True if the ethernet source address is \fIehost\fP.
448 .IP "\fBether host \fIehost\fP
449 True if either the ethernet source or destination address is \fIehost\fP.
450 .IP "\fBgateway\fP \fIhost\fP
451 True if the packet used \fIhost\fP as a gateway.
453 source or destination address was \fIhost\fP but neither the IP source
454 nor the IP destination was \fIhost\fP.
455 \fIHost\fP must be a name and
456 must be found both by the machine's host-name-to-IP-address resolution
457 mechanisms (host name file, DNS, NIS, etc.) and by the machine's
458 host-name-to-Ethernet-address resolution mechanism (/etc/ethers, etc.).
459 (An equivalent expression is
462 \fBether host \fIehost \fBand not host \fIhost\fR
465 which can be used with either names or numbers for \fIhost / ehost\fP.)
466 This syntax does not work in IPv6-enabled configuration at this moment.
467 .IP "\fBdst net \fInet\fR"
468 True if the IPv4/v6 destination address of the packet has a network
470 \fINet\fP may be either a name from /etc/networks
471 or a network number (see \fInetworks(4)\fP for details).
472 .IP "\fBsrc net \fInet\fR"
473 True if the IPv4/v6 source address of the packet has a network
475 .IP "\fBnet \fInet\fR"
476 True if either the IPv4/v6 source or destination address of the packet has a network
478 .IP "\fBnet \fInet\fR \fBmask \fImask\fR"
479 True if the IP address matches \fInet\fR with the specific netmask.
480 May be qualified with \fBsrc\fR or \fBdst\fR.
481 Note that this syntax is not valid for IPv6 \fInet\fR.
482 .IP "\fBnet \fInet\fR/\fIlen\fR"
483 True if the IPv4/v6 address matches \fInet\fR a netmask \fIlen\fR bits wide.
484 May be qualified with \fBsrc\fR or \fBdst\fR.
485 .IP "\fBdst port \fIport\fR"
486 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a
487 destination port value of \fIport\fP.
488 The \fIport\fP can be a number or a name used in /etc/services (see
492 If a name is used, both the port
493 number and protocol are checked.
494 If a number or ambiguous name is used,
495 only the port number is checked (e.g., \fBdst port 513\fR will print both
496 tcp/login traffic and udp/who traffic, and \fBport domain\fR will print
497 both tcp/domain and udp/domain traffic).
498 .IP "\fBsrc port \fIport\fR"
499 True if the packet has a source port value of \fIport\fP.
500 .IP "\fBport \fIport\fR"
501 True if either the source or destination port of the packet is \fIport\fP.
502 Any of the above port expressions can be prepended with the keywords,
503 \fBtcp\fP or \fBudp\fP, as in:
506 \fBtcp src port \fIport\fR
509 which matches only tcp packets whose source port is \fIport\fP.
510 .IP "\fBless \fIlength\fR"
511 True if the packet has a length less than or equal to \fIlength\fP.
512 This is equivalent to:
515 \fBlen <= \fIlength\fP.
518 .IP "\fBgreater \fIlength\fR"
519 True if the packet has a length greater than or equal to \fIlength\fP.
520 This is equivalent to:
523 \fBlen >= \fIlength\fP.
526 .IP "\fBip proto \fIprotocol\fR"
527 True if the packet is an IP packet (see
529 of protocol type \fIprotocol\fP.
530 \fIProtocol\fP can be a number or one of the names
531 \fIicmp\fP, \fIicmp6\fP, \fIigmp\fP, \fIigrp\fP, \fIpim\fP, \fIah\fP,
532 \fIesp\fP, \fIvrrp\fP, \fIudp\fP, or \fItcp\fP.
533 Note that the identifiers \fItcp\fP, \fIudp\fP, and \fIicmp\fP are also
534 keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell.
535 Note that this primitive does not chase the protocol header chain.
536 .IP "\fBip6 proto \fIprotocol\fR"
537 True if the packet is an IPv6 packet of protocol type \fIprotocol\fP.
538 Note that this primitive does not chase the protocol header chain.
539 .IP "\fBip6 protochain \fIprotocol\fR"
540 True if the packet is IPv6 packet,
541 and contains protocol header with type \fIprotocol\fR
542 in its protocol header chain.
546 \fBip6 protochain 6\fR
549 matches any IPv6 packet with TCP protocol header in the protocol header chain.
550 The packet may contain, for example,
551 authentication header, routing header, or hop-by-hop option header,
552 between IPv6 header and TCP header.
553 The BPF code emitted by this primitive is complex and
554 cannot be optimized by BPF optimizer code in \fItcpdump\fP,
555 so this can be somewhat slow.
556 .IP "\fBip protochain \fIprotocol\fR"
557 Equivalent to \fBip6 protochain \fIprotocol\fR, but this is for IPv4.
558 .IP "\fBether broadcast\fR"
559 True if the packet is an ethernet broadcast packet.
562 .IP "\fBip broadcast\fR"
563 True if the packet is an IP broadcast packet.
565 the all-zeroes and all-ones broadcast conventions, and looks up
566 the local subnet mask.
567 .IP "\fBether multicast\fR"
568 True if the packet is an ethernet multicast packet.
571 This is shorthand for `\fBether[0] & 1 != 0\fP'.
572 .IP "\fBip multicast\fR"
573 True if the packet is an IP multicast packet.
574 .IP "\fBip6 multicast\fR"
575 True if the packet is an IPv6 multicast packet.
576 .IP "\fBether proto \fIprotocol\fR"
577 True if the packet is of ether type \fIprotocol\fR.
578 \fIProtocol\fP can be a number or one of the names
579 \fIip\fP, \fIip6\fP, \fIarp\fP, \fIrarp\fP, \fIatalk\fP, \fIaarp\fP,
580 \fIdecnet\fP, \fIsca\fP, \fIlat\fP, \fImopdl\fP, \fImoprc\fP,
581 \fIiso\fP, \fIstp\fP, \fIipx\fP, or \fInetbeui\fP.
582 Note these identifiers are also keywords
583 and must be escaped via backslash (\\).
585 [In the case of FDDI (e.g., `\fBfddi protocol arp\fR') and Token Ring
586 (e.g., `\fBtr protocol arp\fR'), for most of those protocols, the
587 protocol identification comes from the 802.2 Logical Link Control (LLC)
588 header, which is usually layered on top of the FDDI or Token Ring
591 When filtering for most protocol identifiers on FDDI or Token Ring,
592 \fBtcpdump\fR checks only the protocol ID field of an LLC header in
593 so-called SNAP format with an Organizational Unit Identifier (OUI) of
594 0x000000, for encapsulated Ethernet; it doesn't check whether the packet
595 is in SNAP format with an OUI of 0x000000.
597 The exceptions are \fIiso\fP, for which it checks the DSAP (Destination
598 Service Access Point) and SSAP (Source Service Access Point) fields of
599 the LLC header, \fIstp\fP and \fInetbeui\fP, where it checks the DSAP of
600 the LLC header, and \fIatalk\fP, where it checks for a SNAP-format
601 packet with an OUI of 0x080007 and the Appletalk etype.
603 In the case of Ethernet, \fBtcpdump\fR checks the Ethernet type field
604 for most of those protocols; the exceptions are \fIiso\fP, \fIsap\fP,
605 and \fInetbeui\fP, for which it checks for an 802.3 frame and then
606 checks the LLC header as it does for FDDI and Token Ring, \fIatalk\fP,
607 where it checks both for the Appletalk etype in an Ethernet frame and
608 for a SNAP-format packet as it does for FDDI and Token Ring, \fIaarp\fP,
609 where it checks for the Appletalk ARP etype in either an Ethernet frame
610 or an 802.2 SNAP frame with an OUI of 0x000000, and \fIipx\fP, where it
611 checks for the IPX etype in an Ethernet frame, the IPX DSAP in the LLC
612 header, the 802.3 with no LLC header encapsulation of IPX, and the IPX
613 etype in a SNAP frame.]
614 .IP "\fBdecnet src \fIhost\fR"
615 True if the DECNET source address is
617 which may be an address of the form ``10.123'', or a DECNET host
619 [DECNET host name support is only available on Ultrix systems
620 that are configured to run DECNET.]
621 .IP "\fBdecnet dst \fIhost\fR"
622 True if the DECNET destination address is
624 .IP "\fBdecnet host \fIhost\fR"
625 True if either the DECNET source or destination address is
627 .IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBatalk\fR, \fBaarp\fR, \fBdecnet\fR, \fBiso\fR, \fBstp\fR, \fBipx\fR, \fInetbeui\fP"
631 \fBether proto \fIp\fR
634 where \fIp\fR is one of the above protocols.
635 .IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR"
639 \fBether proto \fIp\fR
642 where \fIp\fR is one of the above protocols.
644 \fItcpdump\fP does not currently know how to parse these protocols.
645 .IP "\fBvlan \fI[vlan_id]\fR"
646 True if the packet is an IEEE 802.1Q VLAN packet.
647 If \fI[vlan_id]\fR is specified, only true is the packet has the specified
649 Note that the first \fBvlan\fR keyword encountered in \fIexpression\fR
650 changes the decoding offsets for the remainder of \fIexpression\fR
651 on the assumption that the packet is a VLAN packet.
652 .IP "\fBtcp\fR, \fBudp\fR, \fBicmp\fR"
656 \fBip proto \fIp\fR\fB or ip6 proto \fIp\fR
659 where \fIp\fR is one of the above protocols.
660 .IP "\fBiso proto \fIprotocol\fR"
661 True if the packet is an OSI packet of protocol type \fIprotocol\fP.
662 \fIProtocol\fP can be a number or one of the names
663 \fIclnp\fP, \fIesis\fP, or \fIisis\fP.
664 .IP "\fBclnp\fR, \fBesis\fR, \fBisis\fR"
671 where \fIp\fR is one of the above protocols.
672 Note that \fItcpdump\fR does an incomplete job of parsing these protocols.
673 .IP "\fIexpr relop expr\fR"
674 True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =, !=,
675 and \fIexpr\fR is an arithmetic expression composed of integer constants
676 (expressed in standard C syntax), the normal binary operators
677 [+, -, *, /, &, |], a length operator, and special packet data accessors.
679 data inside the packet, use the following syntax:
682 \fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR
685 \fIProto\fR is one of \fBether, fddi, tr,
686 ip, arp, rarp, tcp, udp, icmp\fR or \fBip6\fR, and
687 indicates the protocol layer for the index operation.
688 Note that \fItcp, udp\fR and other upper-layer protocol types only
689 apply to IPv4, not IPv6 (this will be fixed in the future).
690 The byte offset, relative to the indicated protocol layer, is
692 \fISize\fR is optional and indicates the number of bytes in the
693 field of interest; it can be either one, two, or four, and defaults to one.
694 The length operator, indicated by the keyword \fBlen\fP, gives the
695 length of the packet.
697 For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic.
698 The expression `\fBip[0] & 0xf != 5\fP'
699 catches all IP packets with options.
701 `\fBip[6:2] & 0x1fff = 0\fP'
702 catches only unfragmented datagrams and frag zero of fragmented datagrams.
703 This check is implicitly applied to the \fBtcp\fP and \fBudp\fP
705 For instance, \fBtcp[0]\fP always means the first
706 byte of the TCP \fIheader\fP, and never means the first byte of an
707 intervening fragment.
709 Some offsets and field values may be expressed as names rather than
711 The following protocol header field offsets are
712 available: \fBicmptype\fP (ICMP type field), \fBicmpcode\fP (ICMP
713 code field), and \fBtcpflags\fP (TCP flags field).
715 The following ICMP type field values are available: \fBicmp-echoreply\fP,
716 \fBicmp-unreach\fP, \fBicmp-sourcequench\fP, \fBicmp-redirect\fP,
717 \fBicmp-echo\fP, \fBicmp-routeradvert\fP, \fBicmp-routersolicit\fP,
718 \fBicmp-timxceed\fP, \fBicmp-paramprob\fP, \fBicmp-tstamp\fP,
719 \fBicmp-tstampreply\fP, \fBicmp-ireq\fP, \fBicmp-ireqreply\fP,
720 \fBicmp-maskreq\fP, \fBicmp-maskreply\fP.
722 The following TCP flags field values are available: \fBtcp-fin\fP,
723 \fBtcp-syn\fP, \fBtcp-rst\fP, \fBtcp-push\fP, \fBtcp-push\fP,
724 \fBtcp-ack\fP, \fBtcp-urg\fP.
726 Primitives may be combined using:
728 A parenthesized group of primitives and operators
729 (parentheses are special to the Shell and must be escaped).
731 Negation (`\fB!\fP' or `\fBnot\fP').
733 Concatenation (`\fB&&\fP' or `\fBand\fP').
735 Alternation (`\fB||\fP' or `\fBor\fP').
737 Negation has highest precedence.
738 Alternation and concatenation have equal precedence and associate
740 Note that explicit \fBand\fR tokens, not juxtaposition,
741 are now required for concatenation.
743 If an identifier is given without a keyword, the most recent keyword
748 \fBnot host vs and ace\fR
754 \fBnot host vs and host ace\fR
757 which should not be confused with
760 \fBnot ( host vs or ace )\fR
764 Expression arguments can be passed to \fItcpdump\fP as either a single
765 argument or as multiple arguments, whichever is more convenient.
766 Generally, if the expression contains Shell metacharacters, it is
767 easier to pass it as a single, quoted argument.
768 Multiple arguments are concatenated with spaces before being parsed.
771 To print all packets arriving at or departing from \fIsundown\fP:
774 \fBtcpdump host sundown\fP
778 To print traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR:
781 \fBtcpdump host helios and \\( hot or ace \\)\fP
785 To print all IP packets between \fIace\fR and any host except \fIhelios\fR:
788 \fBtcpdump ip host ace and not helios\fP
792 To print all traffic between local hosts and hosts at Berkeley:
796 tcpdump net ucb-ether
800 To print all ftp traffic through internet gateway \fIsnup\fP:
801 (note that the expression is quoted to prevent the shell from
802 (mis-)interpreting the parentheses):
806 tcpdump 'gateway snup and (port ftp or ftp-data)'
810 To print traffic neither sourced from nor destined for local hosts
811 (if you gateway to one other net, this stuff should never make it
812 onto your local net).
816 tcpdump ip and not net \fIlocalnet\fP
820 To print the start and end packets (the SYN and FIN packets) of each
821 TCP conversation that involves a non-local host.
825 tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net \fIlocalnet\fP'
829 To print IP packets longer than 576 bytes sent through gateway \fIsnup\fP:
833 tcpdump 'gateway snup and ip[2:2] > 576'
837 To print IP broadcast or multicast packets that were
839 sent via ethernet broadcast or multicast:
843 tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'
847 To print all ICMP packets that are not echo requests/replies (i.e., not
852 tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'
857 The output of \fItcpdump\fP is protocol dependent.
859 gives a brief description and examples of most of the formats.
867 If the '-e' option is given, the link level header is printed out.
868 On ethernets, the source and destination addresses, protocol,
869 and packet length are printed.
871 On FDDI networks, the '-e' option causes \fItcpdump\fP to print
872 the `frame control' field, the source and destination addresses,
873 and the packet length.
874 (The `frame control' field governs the
875 interpretation of the rest of the packet.
877 as those containing IP datagrams) are `async' packets, with a priority
878 value between 0 and 7; for example, `\fBasync4\fR'.
880 are assumed to contain an 802.2 Logical Link Control (LLC) packet;
881 the LLC header is printed if it is \fInot\fR an ISO datagram or a
882 so-called SNAP packet.
884 On Token Ring networks, the '-e' option causes \fItcpdump\fP to print
885 the `access control' and `frame control' fields, the source and
886 destination addresses, and the packet length.
888 packets are assumed to contain an LLC packet.
889 Regardless of whether
890 the '-e' option is specified or not, the source routing information is
891 printed for source-routed packets.
893 \fI(N.B.: The following description assumes familiarity with
894 the SLIP compression algorithm described in RFC-1144.)\fP
896 On SLIP links, a direction indicator (``I'' for inbound, ``O'' for outbound),
897 packet type, and compression information are printed out.
898 The packet type is printed first.
899 The three types are \fIip\fP, \fIutcp\fP, and \fIctcp\fP.
900 No further link information is printed for \fIip\fR packets.
901 For TCP packets, the connection identifier is printed following the type.
902 If the packet is compressed, its encoded header is printed out.
903 The special cases are printed out as
904 \fB*S+\fIn\fR and \fB*SA+\fIn\fR, where \fIn\fR is the amount by which
905 the sequence number (or sequence number and ack) has changed.
906 If it is not a special case,
907 zero or more changes are printed.
908 A change is indicated by U (urgent pointer), W (window), A (ack),
909 S (sequence number), and I (packet ID), followed by a delta (+n or -n),
911 Finally, the amount of data in the packet and compressed header length
914 For example, the following line shows an outbound compressed TCP packet,
915 with an implicit connection identifier; the ack has changed by 6,
916 the sequence number by 49, and the packet ID by 6; there are 3 bytes of
917 data and 6 bytes of compressed header:
920 \fBO ctcp * A+6 S+49 I+6 3 (6)\fP
926 Arp/rarp output shows the type of request and its arguments.
928 format is intended to be self explanatory.
929 Here is a short sample taken from the start of an `rlogin' from
930 host \fIrtsg\fP to host \fIcsam\fP:
934 \f(CWarp who-has csam tell rtsg
935 arp reply csam is-at CSAM\fR
939 The first line says that rtsg sent an arp packet asking
940 for the ethernet address of internet host csam.
942 replies with its ethernet address (in this example, ethernet addresses
943 are in caps and internet addresses in lower case).
945 This would look less redundant if we had done \fBtcpdump \-n\fP:
949 \f(CWarp who-has 128.3.254.6 tell 128.3.254.68
950 arp reply 128.3.254.6 is-at 02:07:01:00:01:c4\fP
954 If we had done \fBtcpdump \-e\fP, the fact that the first packet is
955 broadcast and the second is point-to-point would be visible:
959 \f(CWRTSG Broadcast 0806 64: arp who-has csam tell rtsg
960 CSAM RTSG 0806 64: arp reply csam is-at CSAM\fR
964 For the first packet this says the ethernet source address is RTSG, the
965 destination is the ethernet broadcast address, the type field
966 contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes.
970 \fI(N.B.:The following description assumes familiarity with
971 the TCP protocol described in RFC-793.
972 If you are not familiar
973 with the protocol, neither this description nor \fItcpdump\fP will
974 be of much use to you.)\fP
976 The general format of a tcp protocol line is:
980 \fIsrc > dst: flags data-seqno ack window urgent options\fP
984 \fISrc\fP and \fIdst\fP are the source and destination IP
986 \fIFlags\fP are some combination of S (SYN),
987 F (FIN), P (PUSH) or R (RST) or a single `.' (no flags).
988 \fIData-seqno\fP describes the portion of sequence space covered
989 by the data in this packet (see example below).
990 \fIAck\fP is sequence number of the next data expected the other
991 direction on this connection.
992 \fIWindow\fP is the number of bytes of receive buffer space available
993 the other direction on this connection.
994 \fIUrg\fP indicates there is `urgent' data in the packet.
995 \fIOptions\fP are tcp options enclosed in angle brackets (e.g., <mss 1024>).
997 \fISrc, dst\fP and \fIflags\fP are always present.
999 depend on the contents of the packet's tcp protocol header and
1000 are output only if appropriate.
1002 Here is the opening portion of an rlogin from host \fIrtsg\fP to
1007 \s-2\f(CWrtsg.1023 > csam.login: S 768512:768512(0) win 4096 <mss 1024>
1008 csam.login > rtsg.1023: S 947648:947648(0) ack 768513 win 4096 <mss 1024>
1009 rtsg.1023 > csam.login: . ack 1 win 4096
1010 rtsg.1023 > csam.login: P 1:2(1) ack 1 win 4096
1011 csam.login > rtsg.1023: . ack 2 win 4096
1012 rtsg.1023 > csam.login: P 2:21(19) ack 1 win 4096
1013 csam.login > rtsg.1023: P 1:2(1) ack 21 win 4077
1014 csam.login > rtsg.1023: P 2:3(1) ack 21 win 4077 urg 1
1015 csam.login > rtsg.1023: P 3:4(1) ack 21 win 4077 urg 1\fR\s+2
1019 The first line says that tcp port 1023 on rtsg sent a packet
1022 The \fBS\fP indicates that the \fISYN\fP flag was set.
1023 The packet sequence number was 768512 and it contained no data.
1024 (The notation is `first:last(nbytes)' which means `sequence
1026 up to but not including \fIlast\fP which is \fInbytes\fP bytes of user data'.)
1027 There was no piggy-backed ack, the available receive window was 4096
1028 bytes and there was a max-segment-size option requesting an mss of
1031 Csam replies with a similar packet except it includes a piggy-backed
1033 Rtsg then acks csam's SYN.
1036 The packet contained no data so there is no data sequence number.
1037 Note that the ack sequence
1038 number is a small integer (1).
1039 The first time \fItcpdump\fP sees a
1040 tcp `conversation', it prints the sequence number from the packet.
1041 On subsequent packets of the conversation, the difference between
1042 the current packet's sequence number and this initial sequence number
1044 This means that sequence numbers after the
1045 first can be interpreted
1046 as relative byte positions in the conversation's data stream (with the
1047 first data byte each direction being `1').
1048 `-S' will override this
1049 feature, causing the original sequence numbers to be output.
1051 On the 6th line, rtsg sends csam 19 bytes of data (bytes 2 through 20
1052 in the rtsg \(-> csam side of the conversation).
1053 The PUSH flag is set in the packet.
1054 On the 7th line, csam says it's received data sent by rtsg up to
1055 but not including byte 21.
1056 Most of this data is apparently sitting in the
1057 socket buffer since csam's receive window has gotten 19 bytes smaller.
1058 Csam also sends one byte of data to rtsg in this packet.
1059 On the 8th and 9th lines,
1060 csam sends two bytes of urgent, pushed data to rtsg.
1062 If the snapshot was small enough that \fItcpdump\fP didn't capture
1063 the full TCP header, it interprets as much of the header as it can
1064 and then reports ``[|\fItcp\fP]'' to indicate the remainder could not
1066 If the header contains a bogus option (one with a length
1067 that's either too small or beyond the end of the header), \fItcpdump\fP
1068 reports it as ``[\fIbad opt\fP]'' and does not interpret any further
1069 options (since it's impossible to tell where they start).
1071 length indicates options are present but the IP datagram length is not
1072 long enough for the options to actually be there, \fItcpdump\fP reports
1073 it as ``[\fIbad hdr length\fP]''.
1075 .B Capturing TCP packets with particular flag combinations (SYN-ACK, URG-ACK, etc.)
1077 There are 6 bits in the control bits section of the TCP header:
1079 .I URG | ACK | PSH | RST | SYN | FIN
1081 Let's assume that we want to watch packets used in establishing
1083 Recall that TCP uses a 3-way handshake protocol
1084 when it initializes a new connection; the connection sequence with
1085 regard to the TCP control bits is
1091 2) Recipient responds with SYN, ACK
1097 Now we're interested in capturing packets that have only the
1098 SYN bit set (Step 1).
1099 Note that we don't want packets from step 2
1100 (SYN-ACK), just a plain initial SYN.
1101 What we need is a correct filter
1102 expression for \fItcpdump\fP.
1104 Recall the structure of a TCP header without options:
1108 -----------------------------------------------------------------
1109 | source port | destination port |
1110 -----------------------------------------------------------------
1112 -----------------------------------------------------------------
1113 | acknowledgment number |
1114 -----------------------------------------------------------------
1115 | HL | reserved |U|A|P|R|S|F| window size |
1116 -----------------------------------------------------------------
1117 | TCP checksum | urgent pointer |
1118 -----------------------------------------------------------------
1121 A TCP header usually holds 20 octets of data, unless options are
1123 The fist line of the graph contains octets 0 - 3, the
1124 second line shows octets 4 - 7 etc.
1126 Starting to count with 0, the relevant TCP control bits are contained
1131 ----------------|---------------|---------------|----------------
1132 | HL | reserved |U|A|P|R|S|F| window size |
1133 ----------------|---------------|---------------|----------------
1134 | | 13th octet | | |
1137 Let's have a closer look at octet no. 13:
1147 We see that this octet contains 2 bytes from the reserved field.
1148 According to RFC 793 this field is reserved for future use and must
1150 The remaining 6 bits are the TCP control bits we are interested
1152 We have numbered the bits in this octet from 0 to 7, right to
1153 left, so the PSH bit is bit number 3, while the URG bit is number 5.
1155 Recall that we want to capture packets with only SYN set.
1156 Let's see what happens to octet 13 if a TCP datagram arrives
1157 with the SYN bit set in its header:
1167 We already mentioned that bits number 7 and 6 belong to the
1168 reserved field, so they must must be 0.
1170 control bits section we see that only bit number 1 (SYN) is set.
1172 Assuming that octet number 13 is an 8-bit unsigned integer in
1173 network byte order, the binary value of this octet is
1177 and its decimal representation is
1181 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 1*2 + 0*2 = 2
1184 We're almost done, because now we know that if only SYN is set,
1185 the value of the 13th octet in the TCP header, when interpreted
1186 as a 8-bit unsigned integer in network byte order, must be exactly 2.
1188 This relationship can be expressed as
1194 We can use this expression as the filter for \fItcpdump\fP in order
1195 to watch packets which have only SYN set:
1198 tcpdump -i xl0 tcp[13] == 2
1201 The expression says "let the 13th octet of a TCP datagram have
1202 the decimal value 2", which is exactly what we want.
1204 Now, let's assume that we need to capture SYN packets, but we
1205 don't care if ACK or any other TCP control bit is set at the
1207 Let's see what happens to octet 13 when a TCP datagram
1208 with SYN-ACK set arrives:
1218 Now bits 1 and 4 are set in the 13th octet.
1224 which translates to decimal
1228 0*2 + 0*2 + 0*2 + 1*2 + 0*2 + 0*2 + 1*2 + 0*2 = 18
1231 Now we can't just use 'tcp[13] == 18' in the \fItcpdump\fP filter
1232 expression, because that would select only those packets that have
1233 SYN-ACK set, but not those with only SYN set.
1234 Remember that we don't care
1235 if ACK or any other control bit is set as long as SYN is set.
1237 In order to achieve our goal, we need to logically AND the
1238 binary value of octet 13 with some other value to preserve
1240 We know that we want SYN to be set in any case,
1241 so we'll logically AND the value in the 13th octet with
1242 the binary value of a SYN:
1246 00010010 SYN-ACK 00000010 SYN
1247 AND 00000010 (we want SYN) AND 00000010 (we want SYN)
1249 = 00000010 = 00000010
1252 We see that this AND operation delivers the same result
1253 regardless whether ACK or another TCP control bit is set.
1254 The decimal representation of the AND value as well as
1255 the result of this operation is 2 (binary 00000010),
1256 so we know that for packets with SYN set the following
1257 relation must hold true:
1259 ( ( value of octet 13 ) AND ( 2 ) ) == ( 2 )
1261 This points us to the \fItcpdump\fP filter expression
1264 tcpdump -i xl0 'tcp[13] & 2 == 2'
1267 Note that you should use single quotes or a backslash
1268 in the expression to hide the AND ('&') special character
1274 UDP format is illustrated by this rwho packet:
1278 \f(CWactinide.who > broadcast.who: udp 84\fP
1282 This says that port \fIwho\fP on host \fIactinide\fP sent a udp
1283 datagram to port \fIwho\fP on host \fIbroadcast\fP, the Internet
1285 The packet contained 84 bytes of user data.
1287 Some UDP services are recognized (from the source or destination
1288 port number) and the higher level protocol information printed.
1289 In particular, Domain Name service requests (RFC-1034/1035) and Sun
1290 RPC calls (RFC-1050) to NFS.
1292 UDP Name Server Requests
1294 \fI(N.B.:The following description assumes familiarity with
1295 the Domain Service protocol described in RFC-1035.
1296 If you are not familiar
1297 with the protocol, the following description will appear to be written
1300 Name server requests are formatted as
1304 \fIsrc > dst: id op? flags qtype qclass name (len)\fP
1306 \f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fR
1310 Host \fIh2opolo\fP asked the domain server on \fIhelios\fP for an
1311 address record (qtype=A) associated with the name \fIucbvax.berkeley.edu.\fP
1312 The query id was `3'.
1313 The `+' indicates the \fIrecursion desired\fP flag
1315 The query length was 37 bytes, not including the UDP and
1316 IP protocol headers.
1317 The query operation was the normal one, \fIQuery\fP,
1318 so the op field was omitted.
1319 If the op had been anything else, it would
1320 have been printed between the `3' and the `+'.
1321 Similarly, the qclass was the normal one,
1322 \fIC_IN\fP, and omitted.
1323 Any other qclass would have been printed
1324 immediately after the `A'.
1326 A few anomalies are checked and may result in extra fields enclosed in
1327 square brackets: If a query contains an answer, name server or
1333 are printed as `[\fIn\fPa]', `[\fIn\fPn]' or `[\fIn\fPau]' where \fIn\fP
1334 is the appropriate count.
1335 If any of the response bits are set (AA, RA or rcode) or any of the
1336 `must be zero' bits are set in bytes two and three, `[b2&3=\fIx\fP]'
1337 is printed, where \fIx\fP is the hex value of header bytes two and three.
1339 UDP Name Server Responses
1341 Name server responses are formatted as
1345 \fIsrc > dst: id op rcode flags a/n/au type class data (len)\fP
1347 \f(CWhelios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273)
1348 helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fR
1352 In the first example, \fIhelios\fP responds to query id 3 from \fIh2opolo\fP
1353 with 3 answer records, 3 name server records and 7 authority records.
1354 The first answer record is type A (address) and its data is internet
1355 address 128.32.137.3.
1356 The total size of the response was 273 bytes,
1357 excluding UDP and IP headers.
1358 The op (Query) and response code
1359 (NoError) were omitted, as was the class (C_IN) of the A record.
1361 In the second example, \fIhelios\fP responds to query 2 with a
1362 response code of non-existent domain (NXDomain) with no answers,
1363 one name server and no authority records.
1364 The `*' indicates that
1365 the \fIauthoritative answer\fP bit was set.
1367 answers, no type, class or data were printed.
1369 Other flag characters that might appear are `\-' (recursion available,
1370 RA, \fInot\fP set) and `|' (truncated message, TC, set).
1372 `question' section doesn't contain exactly one entry, `[\fIn\fPq]'
1375 Note that name server requests and responses tend to be large and the
1376 default \fIsnaplen\fP of 68 bytes may not capture enough of the packet
1378 Use the \fB\-s\fP flag to increase the snaplen if you
1379 need to seriously investigate name server traffic.
1381 has worked well for me.
1386 \fItcpdump\fP now includes fairly extensive SMB/CIFS/NBT decoding for data
1387 on UDP/137, UDP/138 and TCP/139.
1388 Some primitive decoding of IPX and
1389 NetBEUI SMB data is also done.
1391 By default a fairly minimal decode is done, with a much more detailed
1392 decode done if -v is used.
1393 Be warned that with -v a single SMB packet
1394 may take up a page or more, so only use -v if you really want all the
1397 If you are decoding SMB sessions containing unicode strings then you
1398 may wish to set the environment variable USE_UNICODE to 1.
1400 auto-detect unicode srings would be welcome.
1402 For information on SMB packet formats and what all te fields mean see
1403 www.cifs.org or the pub/samba/specs/ directory on your favourite
1404 samba.org mirror site.
1405 The SMB patches were written by Andrew Tridgell
1409 NFS Requests and Replies
1411 Sun NFS (Network File System) requests and replies are printed as:
1415 \fIsrc.xid > dst.nfs: len op args\fP
1416 \fIsrc.nfs > dst.xid: reply stat len op results\fP
1419 sushi.6709 > wrl.nfs: 112 readlink fh 21,24/10.73165
1420 wrl.nfs > sushi.6709: reply ok 40 readlink "../var"
1421 sushi.201b > wrl.nfs:
1422 144 lookup fh 9,74/4096.6878 "xcolors"
1423 wrl.nfs > sushi.201b:
1424 reply ok 128 lookup fh 9,74/4134.3150
1429 In the first line, host \fIsushi\fP sends a transaction with id \fI6709\fP
1430 to \fIwrl\fP (note that the number following the src host is a
1431 transaction id, \fInot\fP the source port).
1432 The request was 112 bytes,
1433 excluding the UDP and IP headers.
1434 The operation was a \fIreadlink\fP
1435 (read symbolic link) on file handle (\fIfh\fP) 21,24/10.731657119.
1436 (If one is lucky, as in this case, the file handle can be interpreted
1437 as a major,minor device number pair, followed by the inode number and
1439 \fIWrl\fP replies `ok' with the contents of the link.
1441 In the third line, \fIsushi\fP asks \fIwrl\fP to lookup the name
1442 `\fIxcolors\fP' in directory file 9,74/4096.6878.
1443 Note that the data printed
1444 depends on the operation type.
1445 The format is intended to be self
1446 explanatory if read in conjunction with
1447 an NFS protocol spec.
1449 If the \-v (verbose) flag is given, additional information is printed.
1455 sushi.1372a > wrl.nfs:
1456 148 read fh 21,11/12.195 8192 bytes @ 24576
1457 wrl.nfs > sushi.1372a:
1458 reply ok 1472 read REG 100664 ids 417/0 sz 29388
1463 (\-v also prints the IP header TTL, ID, length, and fragmentation fields,
1464 which have been omitted from this example.) In the first line,
1465 \fIsushi\fP asks \fIwrl\fP to read 8192 bytes from file 21,11/12.195,
1466 at byte offset 24576.
1467 \fIWrl\fP replies `ok'; the packet shown on the
1468 second line is the first fragment of the reply, and hence is only 1472
1469 bytes long (the other bytes will follow in subsequent fragments, but
1470 these fragments do not have NFS or even UDP headers and so might not be
1471 printed, depending on the filter expression used).
1472 Because the \-v flag
1473 is given, some of the file attributes (which are returned in addition
1474 to the file data) are printed: the file type (``REG'', for regular file),
1475 the file mode (in octal), the uid and gid, and the file size.
1477 If the \-v flag is given more than once, even more details are printed.
1479 Note that NFS requests are very large and much of the detail won't be printed
1480 unless \fIsnaplen\fP is increased.
1481 Try using `\fB\-s 192\fP' to watch
1484 NFS reply packets do not explicitly identify the RPC operation.
1486 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1487 replies using the transaction ID.
1488 If a reply does not closely follow the
1489 corresponding request, it might not be parsable.
1491 AFS Requests and Replies
1493 Transarc AFS (Andrew File System) requests and replies are printed
1499 \fIsrc.sport > dst.dport: rx packet-type\fP
1500 \fIsrc.sport > dst.dport: rx packet-type service call call-name args\fP
1501 \fIsrc.sport > dst.dport: rx packet-type service reply call-name args\fP
1504 elvis.7001 > pike.afsfs:
1505 rx data fs call rename old fid 536876964/1/1 ".newsrc.new"
1506 new fid 536876964/1/1 ".newsrc"
1507 pike.afsfs > elvis.7001: rx data fs reply rename
1512 In the first line, host elvis sends a RX packet to pike.
1514 a RX data packet to the fs (fileserver) service, and is the start of
1516 The RPC call was a rename, with the old directory file id
1517 of 536876964/1/1 and an old filename of `.newsrc.new', and a new directory
1518 file id of 536876964/1/1 and a new filename of `.newsrc'.
1520 responds with a RPC reply to the rename call (which was successful, because
1521 it was a data packet and not an abort packet).
1523 In general, all AFS RPCs are decoded at least by RPC call name.
1525 AFS RPCs have at least some of the arguments decoded (generally only
1526 the `interesting' arguments, for some definition of interesting).
1528 The format is intended to be self-describing, but it will probably
1529 not be useful to people who are not familiar with the workings of
1532 If the -v (verbose) flag is given twice, acknowledgement packets and
1533 additional header information is printed, such as the the RX call ID,
1534 call number, sequence number, serial number, and the RX packet flags.
1536 If the -v flag is given twice, additional information is printed,
1537 such as the the RX call ID, serial number, and the RX packet flags.
1538 The MTU negotiation information is also printed from RX ack packets.
1540 If the -v flag is given three times, the security index and service id
1543 Error codes are printed for abort packets, with the exception of Ubik
1544 beacon packets (because abort packets are used to signify a yes vote
1545 for the Ubik protocol).
1547 Note that AFS requests are very large and many of the arguments won't
1548 be printed unless \fIsnaplen\fP is increased.
1549 Try using `\fB-s 256\fP'
1550 to watch AFS traffic.
1552 AFS reply packets do not explicitly identify the RPC operation.
1554 \fItcpdump\fP keeps track of ``recent'' requests, and matches them to the
1555 replies using the call number and service ID.
1556 If a reply does not closely
1558 corresponding request, it might not be parsable.
1561 KIP Appletalk (DDP in UDP)
1563 Appletalk DDP packets encapsulated in UDP datagrams are de-encapsulated
1564 and dumped as DDP packets (i.e., all the UDP header information is
1568 is used to translate appletalk net and node numbers to names.
1569 Lines in this file have the form
1581 The first two lines give the names of appletalk networks.
1583 line gives the name of a particular host (a host is distinguished
1584 from a net by the 3rd octet in the number \-
1585 a net number \fImust\fP have two octets and a host number \fImust\fP
1586 have three octets.) The number and name should be separated by
1587 whitespace (blanks or tabs).
1590 file may contain blank lines or comment lines (lines starting with
1593 Appletalk addresses are printed in the form
1599 \f(CW144.1.209.2 > icsd-net.112.220
1600 office.2 > icsd-net.112.220
1601 jssmag.149.235 > icsd-net.2\fR
1607 doesn't exist or doesn't contain an entry for some appletalk
1608 host/net number, addresses are printed in numeric form.)
1609 In the first example, NBP (DDP port 2) on net 144.1 node 209
1610 is sending to whatever is listening on port 220 of net icsd node 112.
1611 The second line is the same except the full name of the source node
1612 is known (`office').
1613 The third line is a send from port 235 on
1614 net jssmag node 149 to broadcast on the icsd-net NBP port (note that
1615 the broadcast address (255) is indicated by a net name with no host
1616 number \- for this reason it's a good idea to keep node names and
1617 net names distinct in /etc/atalk.names).
1619 NBP (name binding protocol) and ATP (Appletalk transaction protocol)
1620 packets have their contents interpreted.
1621 Other protocols just dump
1622 the protocol name (or number if no name is registered for the
1623 protocol) and packet size.
1625 \fBNBP packets\fP are formatted like the following examples:
1629 \s-2\f(CWicsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
1630 jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
1631 techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fR\s+2
1635 The first line is a name lookup request for laserwriters sent by net icsd host
1636 112 and broadcast on net jssmag.
1637 The nbp id for the lookup is 190.
1638 The second line shows a reply for this request (note that it has the
1639 same id) from host jssmag.209 saying that it has a laserwriter
1640 resource named "RM1140" registered on port 250.
1642 another reply to the same request saying host techpit has laserwriter
1643 "techpit" registered on port 186.
1645 \fBATP packet\fP formatting is demonstrated by the following example:
1649 \s-2\f(CWjssmag.209.165 > helios.132: atp-req 12266<0-7> 0xae030001
1650 helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
1651 helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
1652 helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
1653 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1654 helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
1655 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1656 helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
1657 helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
1658 jssmag.209.165 > helios.132: atp-req 12266<3,5> 0xae030001
1659 helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
1660 helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
1661 jssmag.209.165 > helios.132: atp-rel 12266<0-7> 0xae030001
1662 jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fR\s+2
1666 Jssmag.209 initiates transaction id 12266 with host helios by requesting
1667 up to 8 packets (the `<0-7>').
1668 The hex number at the end of the line
1669 is the value of the `userdata' field in the request.
1671 Helios responds with 8 512-byte packets.
1672 The `:digit' following the
1673 transaction id gives the packet sequence number in the transaction
1674 and the number in parens is the amount of data in the packet,
1675 excluding the atp header.
1676 The `*' on packet 7 indicates that the
1679 Jssmag.209 then requests that packets 3 & 5 be retransmitted.
1681 resends them then jssmag.209 releases the transaction.
1683 jssmag.209 initiates the next request.
1684 The `*' on the request
1685 indicates that XO (`exactly once') was \fInot\fP set.
1690 Fragmented Internet datagrams are printed as
1694 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR
1695 \fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR
1699 (The first form indicates there are more fragments.
1701 indicates this is the last fragment.)
1703 \fIId\fP is the fragment id.
1704 \fISize\fP is the fragment
1705 size (in bytes) excluding the IP header.
1706 \fIOffset\fP is this
1707 fragment's offset (in bytes) in the original datagram.
1709 The fragment information is output for each fragment.
1711 fragment contains the higher level protocol header and the frag
1712 info is printed after the protocol info.
1714 after the first contain no higher level protocol header and the
1715 frag info is printed after the source and destination addresses.
1716 For example, here is part of an ftp from arizona.edu to lbl-rtsg.arpa
1717 over a CSNET connection that doesn't appear to handle 576 byte datagrams:
1721 \s-2\f(CWarizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+)
1722 arizona > rtsg: (frag 595a:204@328)
1723 rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2
1727 There are a couple of things to note here: First, addresses in the
1728 2nd line don't include port numbers.
1729 This is because the TCP
1730 protocol information is all in the first fragment and we have no idea
1731 what the port or sequence numbers are when we print the later fragments.
1732 Second, the tcp sequence information in the first line is printed as if there
1733 were 308 bytes of user data when, in fact, there are 512 bytes (308 in
1734 the first frag and 204 in the second).
1735 If you are looking for holes
1736 in the sequence space or trying to match up acks
1737 with packets, this can fool you.
1739 A packet with the IP \fIdon't fragment\fP flag is marked with a
1740 trailing \fB(DF)\fP.
1744 By default, all output lines are preceded by a timestamp.
1746 is the current clock time in the form
1752 and is as accurate as the kernel's clock.
1753 The timestamp reflects the time the kernel first saw the packet.
1755 is made to account for the time lag between when the
1756 ethernet interface removed the packet from the wire and when the kernel
1757 serviced the `new packet' interrupt.
1759 traffic(1C), nit(4P), bpf(4), pcap(3)
1761 The original authors are:
1765 Steven McCanne, all of the
1766 Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
1768 It is currently being maintained by tcpdump.org.
1770 The current version is available via http:
1773 .I http://www.tcpdump.org/
1776 The original distribution is available via anonymous ftp:
1779 .I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z
1782 IPv6/IPsec support is added by WIDE/KAME project.
1783 This program uses Eric Young's SSLeay library, under specific configuration.
1785 Please send problems, bugs, questions, desirable enhancements, etc. to:
1788 tcpdump-workers@tcpdump.org
1791 Please send source code contributions, etc. to:
1797 NIT doesn't let you watch your own outbound traffic, BPF will.
1798 We recommend that you use the latter.
1800 On Linux systems with 2.0[.x] kernels:
1802 packets on the loopback device will be seen twice;
1804 packet filtering cannot be done in the kernel, so that all packets must
1805 be copied from the kernel in order to be filtered in user mode;
1807 all of a packet, not just the part that's within the snapshot length,
1808 will be copied from the kernel (the 2.0[.x] packet capture mechanism, if
1809 asked to copy only part of a packet to userland, will not report the
1810 true length of the packet; this would cause most IP packets to get an
1814 We recommend that you upgrade to a 2.2 or later kernel.
1816 Some attempt should be made to reassemble IP fragments or, at least
1817 to compute the right length for the higher level protocol.
1819 Name server inverse queries are not dumped correctly: the (empty)
1820 question section is printed rather than real query in the answer
1822 Some believe that inverse queries are themselves a bug and
1823 prefer to fix the program generating them rather than \fItcpdump\fP.
1825 A packet trace that crosses a daylight savings time change will give
1826 skewed time stamps (the time change is ignored).
1828 Filter expressions that manipulate FDDI or Token Ring headers assume
1829 that all FDDI and Token Ring packets are SNAP-encapsulated Ethernet
1831 This is true for IP, ARP, and DECNET Phase IV, but is not true
1832 for protocols such as ISO CLNS.
1833 Therefore, the filter may inadvertently
1834 accept certain packets that do not properly match the filter expression.
1836 Filter expressions on fields other than those that manipulate Token Ring
1837 headers will not correctly handle source-routed Token Ring packets.
1840 should chase header chain, but at this moment it does not.
1841 .BR "ip6 protochain"
1842 is supplied for this behavior.
1844 Arithmetic expression against transport layer headers, like \fBtcp[0]\fP,
1845 does not work against IPv6 packets.
1846 It only looks at IPv4 packets.
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