=head1 NAME

Ethereal - Interactively browse network traffic

=head1 SYNOPSYS

B<ethereal>
S<[ B<-B> byte view height ]>
S<[ B<-b> bold font ]>
S<[ B<-c> count ]>
S<[ B<-f> filter expression ]>
S<[ B<-h> ]>
S<[ B<-i> interface ]> 
S<[ B<-k> ]>
S<[ B<-m> font ]>
S<[ B<-n> ]>
S<[ B<-P> packet list height ]>
S<[ B<-Q> ]>
S<[ B<-r> infile ]>
S<[ B<-R> filter expression ]>
S<[ B<-S> ]>
S<[ B<-s> snaplen ]>
S<[ B<-T> tree view height ]>
S<[ B<-t> time stamp format ]>
S<[ B<-v> ]>
S<[ B<-w> savefile]>

=head1 DESCRIPTION

B<Ethereal> is a GUI network protocol analyzer.  It lets
you interactively browse packet data from a live network or from a previously saved
capture file. Ethereal knows how to read B<libpcap> capture files, including those of
B<tcpdump>. In addition, Ethereal can read capture files from B<snoop> (including
B<Shomiti>), B<LanAlyzer>,
uncompressed B<Sniffer>, Microsoft B<Network Monitor>, AIX's B<iptrace>, B<NetXray>,
B<Sniffer Pro>, B<RADCOM>'s WAN/LAN analyzer, B<Lucent/Ascend> router debug output,
and HP-UX's B<nettl>.
There is no need to tell Ethereal what type of file you
are reading; it will determine the file type by itself. Ethereal is also capable
of reading any of these file formats if they are compressed using gzip. Ethereal
recognizes this directly from the file; the '.gz' extension is not required for 
this purpose.

Like other protocol analyzers, B<Ethereal>'s main window shows 3 views of a packet. It
shows a summary line, briefly describing what the packet is. A protocol tree is shown, allowing
you to drill down to exact protocol or field that you interested in. Finally, a hex dump
shows you exactly what the packet looks like when it goes over the wire.

In addition, B<Ethereal> has some features that make it unique. It can assemble all
the packets in a TCP conversation and show you the ASCII data in that conversation. Display
filters in B<Ethereal> are very powerful; more fields are filterable in Ethereal than in other
protocol analyzers, and the syntax you can use to create your filters is richer. As Ethereal
progresses, expect more and more protocol fields to be allowed in display filters.

Packet capturing is performed with the pcap library. The capture filter syntax follows
the rules of the pcap library. This syntax is different from the display filter syntax.

Compressed file support uses (and therefore requires) the zlib library. If the zlib
library is not present, Ethereal will compile, but will be unable to read compressed files.

=head1 OPTIONS

=over 4

=item -B

Sets the initial height of the byte view (bottom) pane.

=item -b

Sets the name of the bold font used for the data in the byte view
pane that corresponds to the field selected in the protocol tree pane.

=item -c

Sets the default number of packets to read when capturing live
data.

=item -f

Sets the capture filter expression.

=item -h

Prints the version and options and exits.

=item -i

Sets the name of the interface to use for live packet capture.  It
should match one of the names listed in "B<netstat -i>" or "B<ifconfig -a>".

=item -k

Starts the capture session immediately; this option requires 
the B<-i> and B<-w> parameters.

=item -m

Sets the name of the font used by B<Ethereal> for most text.

=item -n

Disables network object name resolution (such as hostname, TCP and UDP port
names).

=item -P

Sets the initial height of the packet list (top) pane.

=item -Q

Causes B<Ethereal> to exit after the end of capture session (useful in
batch mode with B<-c> option for instance); this option requires the
B<-i> and B<-w> parameters.

=item -r

Reads packet data from I<file>.

=item -R

Causes the specified filter (which uses the syntax of display filters,
rather than that of capture filters) to be applied, when a capture file
is read, to all packets read from the capture file; packets not matching
the filter are discarded.

=item -S

Specifies that the live packet capture will be performed in a separate
process, and that the packet display will automatically be updated as
packets are seen.

=item -s

Sets the default snapshot length to use when capturing live data. 
No more than I<snaplen> bytes of each network packet will be read into
memory, or saved to disk.

=item -T

Sets the initial height of the tree view (middle) pane.

=item -t

Sets the format of the packet timestamp displayed in the packet list
window.  The format can be one of 'r' (relative), 'a' (absolute), or 'd'
(delta).  The relative time is the time elapsed between the first packet
and the current packet.  The absolute time is the actual date and time the
packet was captured.  The delta time is the time since the previous packet
was captured.  The default is relative.

=item -v

Prints the version and exits.

=item -w

Sets the default capture file name.

=back

=head1 INTERFACE

=head2 MENU ITEMS

=over 4

=item File:Open, File:Close, File:Reload

Open, close, or reload a capture file.  The I<File:Open> dialog box
allows a filter to be specified; when the capture file is read, the
filter is applied to all packets read from the file, and packets not
matching the filter are discarded.

=item File:Print

Prints, for all the packets in the current capture, the packet number,
followed by  a description of each protocol header found in the packet,
followed by the packet data itself.  Printing options can be set with the
I<Edit:Preferences> menu item, or in the dialog box popped up by this
item.

=item File:Print Packet

Print a description of each protocol header found in the packet, followed
by the packet data itself.  Printing options can be set with the
I<Edit:Preferences> menu item.

=item File:Quit

Exits the application.

=item Edit:Preferences

Sets the packet printing and filter options (see L<"Preferences"> below).

=item Capture:Start

Initiates a live packet capture (see L<"Capture Preferences"> below).
A temporary file will be created to hold the capture. The location of the
file can be chosen by setting your TMPDIR environment variable before
starting ethereal. Otherwise, the default TMPDIR location is system-dependent,
but is likely either /var/tmp or /tmp.

=item Display:Options

Sets the format of the packet timestamp displayed in the packet list
window to relative, absolute, or delta.
Allows you to enable the automatic scrolling of the packet list while a 
live capture is in progress.

=item Display:Match Selected

Creates and applies a display filter based on the data that is currently
highlighted in the protocol tree. The display filter is based on absolute
offset within the packet, so could be unreliable if the packet contains
protocols with variable-length headers, like source-routed token-ring.

=item Display:Colorize Display

Allows you to change the foreground and background colors of the packet
information in the list of packets, based upon display filters.  The list
of display filters is applied to each packet sequentially. After the first
display filter matches a packet, any additional display filters in the list
are ignored. Therefore, if you are filtering on the existence of protocols,
you should list the higher-level protocols first, and the lower-level
protocols last.

=item Display:Collapse All

Collapses the protocol tree branches.

=item Display:Expand All

Expands all branches of the protocol tree.

=item Tools:Follow TCP Stream

If you have a TCP packet selected, it will display the contents of the TCP
data stream in a separate window. This has the side-effect of leaving
the list of packets in a filtered state; only those packets that make up
the TCP stream are shown. You can revert to your old view by pressing
ENTER in the display filter text box, thereby invoking your old
display filter (or resetting it back to no display filter).

=back

=head2 WINDOWS

=over 4

=item Main Window

The main window is split into three panes.  You can resize each pane using
a "thumb" at the right end of each divider line.  Below the panes is a
strip that shows the file load progress, current filter, and informational
text.

The top pane contains the list of network packets that you can scroll
through and select.  The packet number, packet timestamp, source and
destination addresses, protocol, and description are printed for each
packet.  An effort is made to display information as high up the protocol
stack as possible, e.g. IP addresses are displayed for IP packets, but the
MAC layer address is displayed for unknown packet types.

The middle pane contains a I<protocol tree> for the currently-selected
packet.  The tree displays each field and its value in each protocol header
in the stack.

The lowest pane contains a hex dump of the actual packet data. 
Selecting a field in the I<protocol tree> highlights the corresponding
bytes in this section.

A display filter can be entered into the strip at the bottom. 
A filter for HTTP, HTTPS, and DNS traffic might look like this:

  tcp.port == 80 || tcp.port == 443 || tcp.port == 53

Selecting the I<Filter:> button lets you choose from a list of named
filters that you can optionally save.  Pressing the Return or Enter
keys will cause the filter to be applied to the current list of packets.

=item Preferences

The I<Preferences> dialog lets you select the output format of packets
printed using the I<File:Print Packet> menu item and configure
commonly-used filters.

=over 6

=item Printing Preferences

The radio buttons at the top of the I<Printing> page allow you choose
between  printing the packets as text or PostScript, and sending the
output directly to a command or saving it to a file.  The I<Command:> text
entry box is the command to send files to (usually B<lpr>), and the
I<File:> entry box lets you enter the name of the file you wish to save
to.  Additinally, you can select the I<File:> button to browse the file
system for a particular save file.

=item Filter Preferences

The I<Filters> page lets you create and modify filters, and set the
default filter to use when capturing data or opening a capture file.

The I<Filter name> entry specifies a descriptive name for a filter, e.g.
B<Web and DNS traffic>.  The I<Filter string> entry is the text that
actually describes the filtering action to take, as described above.The
dialog buttons perform the following actions:

=over 6

=item New

If there is text in the two entry boxes, it creates a new associated list
item.

=item Change

Modifies the currently selected list item to match what's in the entry
boxes.

=item Copy

Makes a copy of the currently selected list item.

=item Delete

Deletes the currently selected list item.

=item OK

Sets the currently selected list item as the active filter.  If  nothing
is selected, turns filtering off.

=item Save

Saves the current filter list in F<$HOME/.ethereal/filters>.

=item Cancel

Closes the dialog without making any changes.

=back

=item Column Preferences

The I<Columns> page lets you specify the number, title, and format
of each column in the packet list.

The I<Column title> entry is used to specify the title of the column
displayed at the top of the packet list.  The type of data that the column
displays can be specified using the I<Column format> option menu.  The row
of buttons on the left perform the following actions:

=over 6

=item New

Adds a new column to the list.

=item Change

Modifies the currently selected list item.

=item Delete

Deletes the currently selected list item.

=item Up / Down

Moves the selected list item up or down one position.

=item OK

Currently has no effect.

=item Save

Saves the current column format as the default.

=item Cancel

Closes the dialog without making any changes.

=back

=back

=item Capture Preferences

The I<Capture Preferences> dialog lets you specify various parameters for
capturing live packet data.

The I<Interface:> combo box lets you specify the interface from which to
capture packet data.  The I<Count:> entry specifies the number of packets
to capture.  Entering 0 will capture packets indefinitely.  The I<Filter:>
entry lets you specify the capture filter using a tcpdump-style filter
string as described above.  The I<File:> entry specifies the file to save
to, as in the I<Printer Options> dialog above.  You can specify the
maximum number of bytes to capture per packet with the I<Capture length>
entry, and can specify that the display should be updated as packets are
captured with the I<Update list of packets in real time> check box.

=item Display Options

The I<Display Options> dialog lets you specify the format of the time stamp
in the packet list.  You can select "Time of day" for absolute time stamps,
"Seconds since beginning of capture" for relative time stamps, or
"Seconds since previous frame" for delta time stamps.  You can also
specify whether, when the display is updated as packets are captured,
the list should automatically scroll to show the most recently captured
packets or not.

=back

=head1 CAPTURE FILTER SYNTAX

See manual page of tcpdump(8).

=head1 DISPLAY FILTER SYNTAX

Display filters help you remove the noise from a packet trace and let you see only
the packets that interest you. If a packet meets the requirements expressed in your
display filter, then it is displayed in the list of packets. Display filters let
you compare the fields within a protocol against a specific value, compare fields
against fields, and to check the existence of specified fields or protocols.

The simplest display filter allows you to check for the existence of a protocol or
field. If you want to see all packets which contain the IPX protocol, the filter would be
"ipx". (Without the quotation marks) To see all packets that contain a
Token-Ring RIF field, use "tr.rif".

Fields can also be compared against values. The comparison operators can be expressed
either through C-like symbols, or through English-like abbreviations:

    eq, ==    Equal
    ne, !=    Not equal
    gt, >     Greater than
    lt, <     Less Than
    ge, >=    Greater than or Equal to
    le, <=    Less than or Equal to

Furthermore, each protocol field is typed. The types are:

    Unsigned integer (either 8-bit, 16-bit, 24-bit, or 32-bit)
    Signed integer (either 8-bit, 16-bit, 24-bit, or 32-bit)
    Boolean
    Ethernet address (6 bytes)
    Byte string (n-number of bytes)
    IPv4 address
    IPv6 address
    IPX network number
    String (text)
    Double-precision floating point number

An integer may be expressed in decimal, octal, or hexadecimal notation. The following
three display filters are equivalent:

    frame.pkt_len > 10
    frame.pkt_len > 012
    frame.pkt_len > 0xa

Boolean values are either true or false. However, a boolean field is present in a
protocol decode only if its value is true. If the value is false, the field is not presence.
You can therefore check the truth value of a boolean field by simply checking for its
existence, that is, by naming the field.  For example, a token-ring packet's source route
field is boolean. To find any source-routed packets, the display filter is simply:

    tr.sr

Non source-routed packets can be found with the negation of that filter:

    ! tr.sr

Ethernet addresses, as well as a string of bytes, are represented in hex digits. The hex
digits may be separated by colons, periods, or hyphens:

    fddi.dst eq ff:ff:ff:ff:ff:ff
    ipx.srcnode == 0.0.0.0.0.1
    eth.src == aa-aa-aa-aa-aa-aa

If a string of bytes contains only one byte, then it is represented as an unsigned integer.
That is, if you are testing for hex value 'ff' in a one-byte byte-string, you must compare
it agains '0xff' and not 'ff'.

IPv4 addresses can be represented in either dotted decimal notation, or by using the hostname:

    ip.dst eq www.mit.edu
    ip.src == 192.168.1.1

IPX networks are represented by unsigned 32-bit integers. Most likely you will be using
hexadecimal when testing for IPX network values:

    ipx.srcnet == 0xc0a82c00

A substring operator also exists. You can check the substring (byte-string) of any protocol
or field. For example, you can filter on the vendor portion of an ethernet address (the first
three bytes) like this:

    eth.src[0:3] == 00:00:83

Or more simply, since the number of bytes is inherent in the byte-string you provide, you
can provide just the offset. The previous example can be stated like this:

    eth.src[0] == 00:00:83

In fact, the only time you need to explicitly provide a length is when you don't provide
a byte-string, and are comparing fields against fields:

    fddi.src[0:3] == fddi.dst[0:3]

If the length of your byte-string is only one byte, then it must be represented in the
same way as an unsigned 8-bit integer:

    llc[3] == 0xaa

You can use the substring operator on a protocol name, too. And remember, the "frame" protocol
encompasses the entire packet, allowing you to look at the nth byte of a packet regardless
of its frame type (ethernet, token-ring, etc.).

    token[0:5] ne 0.0.0.1.1
    ipx[0:2] == ff:ff
    llc[3:1] eq 0xaa

Offsets for byte-strings can also be negative, in which case the negative number indicates
the number of bytes from the end of the field or protocol that you are testing. Here's how
to check the last 4 bytes of a frame:

    frame[-4] == 0.1.2.3

or

    frame[-4:4] == 0.1.2.3

All the above tests can be combined together with logical expressions. These too are expressable
in C-like syntax or with English-like abbreviations:

    and, &&   Logical AND
    or, ||    Logical OR
    xor, ^^   Logical XOR
    not, !    Logical NOT

Expressions can be grouped by parentheses as well. The following are all valid display filter
expression:

    tcp.port == 80 and ip.src == 192.168.2.1
    not llc
    (ipx.srcnet == 0xbad && ipx.srnode == 0.0.0.0.0.1) || ip
    tr.dst[0:3] == 0.6.29 xor tr.src[0:3] == 0.6.29

A special caveat must be given regarding fields that occur more than once per packet. "ip.addr"
occurs twice per IP packet, once for the source address, and once for the destination address.
Likewise, tr.rif.ring fields can occur more than once per packet. The following two expressions
are not equivalent:

        ip.addr ne 192.168.4.1
    not ip.addr eq 192.168.4.1

The first filter says "show me all packets where an ip.addr exists that does not equal 192.168.4.1".
That is, as long as one ip.addr in the packet does not equal 192.168.44.1, the packet passes
the display filter. The second filter "don't show me any packets that have at least one ip.addr
field equal to 192.168.4.1". If one ip.addr is 192.168.4.1, the packet does not pass. If B<neither>
ip.addr fields is 192.168.4.1, then the packet passes.

It is easy to think of the 'ne' and 'eq' operators as having an implict "exists" modifier
when dealing with multiply-recurring fields. "ip.addr ne 192.168.4.1" can be thought of as
"there exists an ip.addr that does not equal 192.168.4.1".

Be careful with multiply-recurring fields; they can be confusing.

The following is a table of protocol and protocol fields that are filterable in Ethereal.
The abbreviation of the protocol or field is given. This abbreviation is what you use in
the display filter. The type of the field is also given.

=insert_dfilter_table

=head1 SEE ALSO

L<tcpdump(8)>, L<pcap(3)>

=head1 NOTES

The latest version of B<ethereal> can be found at
B<http://ethereal.zing.org>.

=head1 AUTHORS

  Original Author
  -------- ------
  Gerald Combs  <gerald@zing.org>


  Contributors
  ------------
  Gilbert Ramirez          <gramirez@tivoli.com>
  Hannes R. Boehm          <hannes@boehm.org>
  Mike Hall                <mlh@io.com>
  Bobo Rajec               <bobo@bsp-consulting.sk>
  Laurent Deniel           <deniel@worldnet.fr>
  Don Lafontaine           <lafont02@cn.ca>
  Guy Harris               <guy@netapp.com>
  Simon Wilkinson          <sxw@dcs.ed.ac.uk>
  Joerg Mayer              <jmayer@telemation.de>
  Martin Maciaszek         <fastjack@i-s-o.net>
  Didier Jorand            <Didier.Jorand@alcatel.fr>
  Jun-ichiro itojun Hagino <itojun@iijlab.net>
  Richard Sharpe           <sharpe@ns.aus.com>
  John McDermott           <jjm@jkintl.com> 
  Jeff Jahr                <jjahr@shastanets.com>
  Brad Robel-Forrest       <bradr@watchguard.com>
  Ashok Narayanan          <ashokn@cisco.com>
  Aaron Hillegass          <aaron@classmax.com>
  Jason Lango              <jal@netapp.com>
  Johan Feyaerts           <Johan.Feyaerts@siemens.atea.be>
  Olivier Abad             <abad@daba.dhis.org>
  Thierry Andry            <Thierry.Andry@advalvas.be>
  Jeff Foster              <jjfoste@woodward.com>
  Peter Torvals            <petertv@xoommail.com>
  Christophe Tronche       <ch.tronche@computer.org>
  Nathan Neulinger         <nneul@umr.edu>

Alain Magloire <alainm@rcsm.ece.mcgill.ca> was kind enough to give his
permission to use his version of snprintf.c.

Dan Lasley <dlasley@promus.com> gave permission for his dumpit() hex-dump
routine to be used.