4 tethereal - Dump and analyze network traffic
11 S<[ B<-f> capture filter expression ]>
12 S<[ B<-F> file format ]>
14 S<[ B<-i> interface ]>
17 S<[ B<-N> resolving flags ] ...>
18 S<[ B<-o> preference setting ] ...>
21 S<[ B<-R> display filter expression ]>
23 S<[ B<-t> time stamp format ]>
28 S<[ filter expression ]>
32 B<Tethereal> is a network protocol analyzer. It lets you capture packet
33 data from a live network, or read packets from a previously saved
34 capture file, either printing a decoded form of those packets to the
35 standard output or writing the packets to a file. B<Tethereal> knows
36 how to read B<libpcap> capture files, including those of B<tcpdump>. In
37 addition, B<Tethereal> can read capture files from B<snoop> (including
38 B<Shomiti>) and B<atmsnoop>, B<LanAlyzer>, B<Sniffer> (compressed or
39 uncompressed), Microsoft B<Network Monitor>, AIX's B<iptrace>,
40 B<NetXray>, B<Sniffer Pro>, B<Etherpeek>, B<RADCOM>'s WAN/LAN analyzer,
41 B<Lucent/Ascend> router debug output, HP-UX's B<nettl>, the dump output
42 from B<Toshiba's> ISDN routers, the output from B<i4btrace> from the
43 ISDN4BSD project, the output in B<IPLog> format from the Cisco Secure
44 Intrusion Detection System, B<pppd logs> (pppdump format), the output
45 from VMS's B<TCPIPtrace> utility, and the text output from the
46 B<DBS Etherwatch> VMS utility. There is no need to tell B<Tethereal>
47 what type of file you are reading; it will determine the file type by
48 itself. B<Tethereal> is also capable of reading any of these file
49 formats if they are compressed using gzip. B<Tethereal> recognizes this
50 directly from the file; the '.gz' extension is not required for this
53 If the B<-w> flag is not specified, B<Tethereal> prints a decoded form
54 of the packets it captures or reads; otherwise, it writes those packets
55 to the file specified by that flag.
57 When printing a decoded form of packets, B<Tethereal> prints, by
58 default, a summary line containing the fields specified by the
59 preferences file (which are also the fields displayed in the packet list
60 pane in B<Ethereal>), although if it's printing packets as it captures
61 them, rather than printing packets from a saved capture file, it won't
62 print the "frame number" field. If the B<-V> flag is specified, it
63 prints intead a protocol tree, showing all the fields of all protocols
66 When writing packets to a file, B<Tethereal>, by default, writes the
67 file in B<libpcap> format, and writes all of the packets it sees to the
68 output file. The B<-F> flag can be used to specify the format in which
69 to write the file; it can write the file in B<libpcap> format (standard
70 B<libpcap> format, a modified format used by some patched versions of
71 B<libpcap>, or the format used by Red Hat Linux 6.1), B<snoop> format,
72 uncompressed B<Sniffer> format, Microsoft B<Network Monitor> 1.x format,
73 and the format used by Windows-based versions of the B<Sniffer>
76 Read filters in B<Tethereal>, which allow you to select which packets
77 are to be decoded or written to a file, are very powerful; more fields
78 are filterable in B<Tethereal> than in other protocol analyzers, and the
79 syntax you can use to create your filters is richer. As B<Tethereal>
80 progresses, expect more and more protocol fields to be allowed in read
83 Packet capturing is performed with the pcap library. The capture filter
84 syntax follows the rules of the pcap library. This syntax is different
85 from the read filter syntax. A read filter can also be specified when
86 capturing, and only packets that pass the read filter will be displayed
87 or saved to the output file; note, however, that capture filters are much
88 more efficient than read filters, and it may be more difficult for
89 B<Tethereal> to keep up with a busy network if a read filter is
90 specified for a live capture.
92 Compressed file support uses (and therefore requires) the zlib library.
93 If the zlib library is not present, B<Tethereal> will compile, but will
94 be unable to read compressed files.
96 A capture or read filter can either be specified with the B<-f> or B<-R>
97 option, respectively, in which case the entire filter expression must be
98 specified as a single argument (which means that if it contains spaces,
99 it must be quoted), or can be specified with command-line arguments
100 after the option arguments, in which case all the arguments after the
101 filter arguments are treated as a filter expression. If the filter is
102 specified with command-line arguments after the option arguments, it's a
103 capture filter if a capture is being done (i.e., if no B<-r> flag was
104 specified) and a read filter if a capture file is being read (i.e., if a
105 B<-r> flag was specified).
113 Sets the default number of packets to read when capturing live
118 Prints a list of the interfaces on which B<Tethereal> can capture, and
119 exits. Note that "can capture" means that B<Tethereal> was able to open
120 that device to do a live capture; if, on your system, a program doing a
121 network capture must be run from an account with special privileges (for
122 example, as root), then, if B<Tethereal> is run with the B<-D> flag and
123 is not run from such an account, it will not list any interfaces.
127 Sets the capture filter expression.
131 Sets the file format of the output capture file.
135 Prints the version and options and exits.
139 Sets the name of the network interface to use for live packet capture.
140 It should match one of the names listed in "B<netstat -i>" or
141 "B<ifconfig -a>". If no interface is specified, B<Tethereal> searches
142 the list of interfaces, choosing the first non-loopback interface if
143 there are any non-loopback interfaces, and choosing the first loopback
144 interface if there are no non-loopback interfaces; if there are no
145 interfaces, B<Tethereal> reports an error and doesn't start the capture.
149 Flush the standard output after the information for each packet is
150 printed. (This is not, strictly speaking, line-buffered if B<-V>
151 was specified; however, it is the same as line-buffered if B<-V> wasn't
152 specified, as only one line is printed for each packet, and, as B<-l> is
153 normally used when piping a live capture to a program or script, so that
154 output for a packet shows up as soon as the packet is seen and
155 dissected, it should work just as well as true line-buffering. We do
156 this as a workaround for a deficiency in the Microsoft Visual C++ C
159 This may be useful when piping the output of B<Tethereal> to another
160 program, as it means that the program to which the output is piped will
161 see the dissected data for a packet as soon as B<Tethereal> sees the
162 packet and generates that output, rather than seeing it only when the
163 standard output buffer containing that data fills up.
167 Disables network object name resolution (such as hostname, TCP and UDP port
172 Turns on name resolving for particular types of addresses and port
173 numbers; the argument is a string that may contain the letters B<m> to
174 enable MAC address resolution, B<n> to enable network address
175 resolution, and B<t> to enable transport-layer port number resolution.
176 This overrides B<-n> if both B<-N> and B<-n> are present.
180 Sets a preference value, overriding the default value and any value read
181 from a preference file. The argument to the flag is a string of the
182 form I<prefname>B<:>I<value>, where I<prefname> is the name of the
183 preference (which is the same name that would appear in the preference
184 file), and I<value> is the value to which it should be set.
188 I<Don't> put the interface into promiscuous mode. Note that the
189 interface might be in promiscuous mode for some other reason; hence,
190 B<-p> cannot be used to ensure that the only traffic that is captured is
191 traffic sent to or from the machine on which B<Tethereal> is running,
192 broadcast traffic, and multicast traffic to addresses received by that
197 Reads packet data from I<file>.
201 Causes the specified filter (which uses the syntax of read filters,
202 rather than that of capture filters) to be applied before printing a
203 decoded form of packets or writing packets to a file; packets not
204 matching the filter are discarded rather than being printed or written.
208 Sets the default snapshot length to use when capturing live data.
209 No more than I<snaplen> bytes of each network packet will be read into
210 memory, or saved to disk.
214 Sets the format of the packet timestamp printed in summary lines. The
215 format can be one of 'r' (relative), 'a' (absolute), 'ad' (absolute with
216 date), or 'd' (delta). The relative time is the time elapsed between
217 the first packet and the current packet. The absolute time is the
218 actual time the packet was captured, with no date displayed; the
219 absolute date and time is the actual time and date the packet was
220 captured. The delta time is the time since the previous packet was
221 captured. The default is relative.
225 Prints the version and exits.
229 Causes B<Tethereal> to print a protocol tree for each packet rather than
230 a one-line summary of the packet.
234 Writes packet data to I<savefile>.
238 Causes B<Tethereal> to print a hex and ASCII dump of the packet data
239 after printing the summary or protocol tree.
243 =head1 CAPTURE FILTER SYNTAX
245 See manual page of tcpdump(8).
247 =head1 READ FILTER SYNTAX
249 Read filters help you remove the noise from a packet trace and let you
250 see only the packets that interest you. If a packet meets the
251 requirements expressed in your read filter, then it is printed. Read
252 filters let you compare the fields within a protocol against a specific
253 value, compare fields against fields, and to check the existence of
254 specified fields or protocols.
256 The simplest read filter allows you to check for the existence of a
257 protocol or field. If you want to see all packets which contain the IPX
258 protocol, the filter would be "ipx". (Without the quotation marks) To
259 see all packets that contain a Token-Ring RIF field, use "tr.rif".
261 Fields can also be compared against values. The comparison operators
262 can be expressed either through C-like symbols, or through English-like
269 ge, >= Greater than or Equal to
270 le, <= Less than or Equal to
272 Furthermore, each protocol field is typed. The types are:
274 Unsigned integer (either 8-bit, 16-bit, 24-bit, or 32-bit)
275 Signed integer (either 8-bit, 16-bit, 24-bit, or 32-bit)
277 Ethernet address (6 bytes)
278 Byte string (n-number of bytes)
283 Double-precision floating point number
285 An integer may be expressed in decimal, octal, or hexadecimal notation.
286 The following three read filters are equivalent:
292 Boolean values are either true or false. In a read filter expression
293 testing the value of a Boolean field, "true" is expressed as 1 or any
294 other non-zero value, and "false" is expressed as zero. For example, a
295 token-ring packet's source route field is boolean. To find any
296 source-routed packets, a read filter would be:
300 Non source-routed packets can be found with:
304 Ethernet addresses, as well as a string of bytes, are represented in hex
305 digits. The hex digits may be separated by colons, periods, or hyphens:
307 fddi.dst eq ff:ff:ff:ff:ff:ff
308 ipx.srcnode == 0.0.0.0.0.1
309 eth.src == aa-aa-aa-aa-aa-aa
311 If a string of bytes contains only one byte, then it is represented as
312 an unsigned integer. That is, if you are testing for hex value 'ff' in
313 a one-byte byte-string, you must compare it agains '0xff' and not 'ff'.
315 IPv4 addresses can be represented in either dotted decimal notation, or
316 by using the hostname:
318 ip.dst eq www.mit.edu
319 ip.src == 192.168.1.1
321 IPv4 addresses can be compared with the same logical relations as numbers:
322 eq, ne, gt, ge, lt, and le. The IPv4 address is stored in host order,
323 so you do not have to worry about how the endianness of an IPv4 address
324 when using it in a read filter.
326 Classless InterDomain Routing (CIDR) notation can be used to test if an
327 IPv4 address is in a certain subnet. For example, this display filter
328 will find all packets in the 129.111 Class-B network:
330 ip.addr == 129.111.0.0/16
332 Remember, the number after the slash represents the number of bits used
333 to represent the network. CIDR notation can also be used with
334 hostnames, in this example of finding IP addresses on the same Class C
339 The CIDR notation can only be used on IP addresses or hostnames, not in
340 variable names. So, a display filter like "ip.src/24 == ip.dst/24" is
343 IPX networks are represented by unsigned 32-bit integers. Most likely
344 you will be using hexadecimal when testing for IPX network values:
346 ipx.srcnet == 0xc0a82c00
348 A slice operator also exists. You can check the substring
349 (byte-string) of any protocol or field. For example, you can filter on
350 the vendor portion of an ethernet address (the first three bytes) like
353 eth.src[0:3] == 00:00:83
355 If the length of your byte-slice is only one byte, then it is still
356 represented in hex, but without the preceding "0x":
360 You can use the slice operator on a protocol name, too. And
361 remember, the "frame" protocol encompasses the entire packet, allowing
362 you to look at the nth byte of a packet regardless of its frame type
363 (Ethernet, token-ring, etc.).
365 token[0:5] ne 0.0.0.1.1
369 The following syntax governs slices:
371 [i:j] i = start_offset, j = length
372 [i-j] i = start_offet, j = end_offset, inclusive.
373 [i] i = start_offset, length = 1
374 [:j] start_offset = 0, length = j
375 [i:] start_offset = i, end_offset = end_of_field
377 Offsets and lengths can be negative, in which case they indicate the
378 offset from the B<end> of the field. Here's how to check the last 4
381 frame[-4:4] == 0.1.2.3
385 frame[-4:] == 0.1.2.3
387 You can create complex concatenations of slices using the comma operator:
389 field[1,3-5,9:] == 01:03:04:05:09:0a:0b
391 All the above tests can be combined together with logical expressions.
392 These too are expressable in C-like syntax or with English-like
399 Expressions can be grouped by parentheses as well. The following are
400 all valid read filter expression:
402 tcp.port == 80 and ip.src == 192.168.2.1
404 (ipx.srcnet == 0xbad && ipx.srnode == 0.0.0.0.0.1) || ip
405 tr.dst[0:3] == 0.6.29 xor tr.src[0:3] == 0.6.29
407 A special caveat must be given regarding fields that occur more than
408 once per packet. "ip.addr" occurs twice per IP packet, once for the
409 source address, and once for the destination address. Likewise,
410 tr.rif.ring fields can occur more than once per packet. The following
411 two expressions are not equivalent:
413 ip.addr ne 192.168.4.1
414 not ip.addr eq 192.168.4.1
416 The first filter says "show me all packets where an ip.addr exists that
417 does not equal 192.168.4.1". That is, as long as one ip.addr in the
418 packet does not equal 192.168.44.1, the packet passes the display
419 filter. The second filter "don't show me any packets that have at least
420 one ip.addr field equal to 192.168.4.1". If one ip.addr is 192.168.4.1,
421 the packet does not pass. If B<neither> ip.addr fields is 192.168.4.1,
422 then the packet passes.
424 It is easy to think of the 'ne' and 'eq' operators as having an implict
425 "exists" modifier when dealing with multiply-recurring fields. "ip.addr
426 ne 192.168.4.1" can be thought of as "there exists an ip.addr that does
427 not equal 192.168.4.1".
429 Be careful with multiply-recurring fields; they can be confusing.
431 The following is a table of protocol and protocol fields that are
432 filterable in B<Tethereal>. The abbreviation of the protocol or field is
433 given. This abbreviation is what you use in the read filter. The
434 type of the field is also given.
436 =insert_dfilter_table
440 The F<ethereal.conf> file, which is installed in the F<etc> directory
441 under the main installation directory (for example, F</usr/local/etc>)
442 on UNIX-compatible systems, and in the main installation directory (for
443 example, F<C:\Program Files\Ethereal>) on Windows systems, and the
444 personal preferences file, which is F<$HOME/.ethereal/preferences> on
445 UNIX-compatible systems and F<%APPDATA%\Ethereal\preferences> (or, if
446 %APPDATA% isn't defined,
447 F<%USERPROFILE%\Application Data\Ethereal\preferences>) on
448 Windows systems, contain system-wide and personal preference settings,
449 respectively. The file contains preference settings of the form
450 I<prefname>B<:>I<value>, one per line, where I<prefname> is the name of
451 the preference (which is the same name that would appear in the
452 preference file), and I<value> is the value to which it should be set;
453 white space is allowed between B<:> and I<value>. A preference setting
454 can be continued on subsequent lines by indenting the continuation lines
455 with white space. A B<#> character starts a comment that runs to the
458 The system-wide preference file is read first, if it exists, overriding
459 B<Tethereal>'s default values; the personal preferences file is then
460 read, if it exists, overriding default values and values read from the
461 system-wide preference file.
463 The F<ethers> file, which is found in the F</etc> directory on
464 UNIX-compatible systems, and in the main installation directory (for
465 example, F<C:\Program Files\Ethereal>) on Windows systems, is consulted
466 to correlate 6-byte hardware addresses to names. If an address is not
467 found in the F<ethers> file, the F<$HOME/.ethereal/ethers> file on
468 UNIX-compatible systems, and the F<%APPDATA%\Ethereal\ethers> file (or, if
469 %APPDATA% isn't defined, the
470 F<%USERPROFILE%\Application Data\Ethereal\ethers> file) on Windows
471 systems is consulted next. Each line contains one hardware
472 address and name, separated by whitespace. The digits of the hardware
473 address are separated by either a colon (:), a dash (-), or a period
474 (.). The following three lines are valid lines of an ethers file:
476 ff:ff:ff:ff:ff:ff Broadcast
477 c0-00-ff-ff-ff-ff TR_broadcast
478 00.00.00.00.00.00 Zero_broadcast
480 The F<manuf> file, which is installed in the F<etc> directory under the
481 main installation directory (for example, F</usr/local/etc>) on
482 UNIX-compatible systems, and in the main installation directory (for
483 example, F<C:\Program Files\Ethereal>) on Windows systems, matches the
484 3-byte vendor portion of a 6-byte hardware address with the
485 manufacturer's name. The format of the file is the same as the
486 F<ethers> file, except that each address is three bytes instead of six.
488 The F<ipxnets> file, which is found in the F</etc> directory on
489 UNIX-compatible systems, and in the main installation directory (for
490 example, F<C:\Program Files\Ethereal>) on Windows systems, correlates
491 4-byte IPX network numbers to names. If a network number is not found
492 in the F<ipxnets> file, the F<$HOME/.ethereal/ipxnets> file on
493 UNIX-compatible systems, and the F<%APPDATA%\Ethereal\ipxnets> file (or,
494 if %APPDATA% isn't defined, the
495 F<%USERPROFILE%\Application Data\Ethereal\ipxnets> file)
496 on Windows systems, is consulted next. The format is the same as the
497 F<ethers> file, except that each address if four bytes instead of six.
498 Additionally, the address can be represented a single hexadecimal
499 number, as is more common in the IPX world, rather than four hex octets.
500 For example, these four lines are valid lines of an ipxnets file.
504 00:00:BE:EF IT_Server1
509 L<ethereal(1)>, L<editcap(1)>, L<tcpdump(8)>, L<pcap(3)>
513 B<Tethereal> is part of the B<Ethereal> distribution. The latest version
514 of B<Ethereal> can be found at B<http://www.ethereal.com>.
518 B<Tethereal> uses the same packet dissection code that B<Ethereal> does,
519 as well as using many other modules from B<Ethereal>; see the list of
520 authors in the B<Ethereal> man page for a list of authors of that code.