OSI network layer over PPP support, fix to P2P ISIS processing, and ISIS

[obnox/wireshark/wip.git] / doc / ethereal.pod.template

=head1 NAME

Ethereal - Interactively browse network traffic

=head1 SYNOPSYS

B<ethereal>
S<[ B<-B> byte view height ]>
S<[ B<-c> count ]>
S<[ B<-f> capture filter expression ]>
S<[ B<-h> ]>
S<[ B<-i> interface ]> 
S<[ B<-k> ]>
S<[ B<-m> font ]>
S<[ B<-n> ]>
S<[ B<-o> preference setting ] ...>
S<[ B<-p> ]>
S<[ B<-P> packet list height ]>
S<[ B<-Q> ]>
S<[ B<-r> infile ]>
S<[ B<-R> display 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.  B<Ethereal> knows how to read B<libpcap>
capture files, including those of B<tcpdump>.  In addition, B<Ethereal>
can read capture files from B<snoop> (including B<Shomiti>) and
B<atmsnoop>, B<LanAlyzer>, B<Sniffer> (compressed or uncompressed),
Microsoft B<Network Monitor>, AIX's B<iptrace>, B<NetXray>, B<Sniffer
Pro>, B<Etherpeek>, B<RADCOM>'s WAN/LAN analyzer, B<Lucent/Ascend>
router debug output, HP-UX's B<nettl>, the dump output from B<Toshiba's>
ISDN routers, the output from B<i4btrace> from the ISDN4BSD project, the
output in B<IPLog> format from the Cisco Secure Intrusion Detection
System, and B<pppd logs> (pppdump format).  There is no need to tell
B<Ethereal> what type of file you are reading; it will determine the
file type by itself.  B<Ethereal> is also capable of reading any of
these file formats if they are compressed using gzip.  B<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
(or EBCDIC, or hex) data in that conversation.  Display filters in
B<Ethereal> are very powerful; more fields are filterable in B<Ethereal>
than in other protocol analyzers, and the syntax you can use to create
your filters is richer.  As B<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, B<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 -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 network interface or pipe to use for live packet capture.
Network interface names should match one of the names listed in "B<netstat -i>"
or "B<ifconfig -a>".
Pipe names should be either the name of a FIFO (named pipe) or ``-'' to read
data from the standard input. Data read from pipes must be in libpcap format.

=item -k

Starts the capture session immediately.  If the B<-i> flag was
specified, the capture uses the specified interface.  Otherwise,
B<Ethereal> searches the list of interfaces, choosing the first
non-loopback interface if there are any non-loopback interfaces, and
choosing the first loopback interface if there are no non-loopback
interfaces; if there are no interfaces, B<Ethereal> reports an error and
doesn't start the capture.

=item -m

Sets the name of the font used by B<Ethereal> for most text. 
B<Ethereal> will construct 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 from the name of the main text font.

=item -n

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

=item -o

Sets a preference value, overriding the default value and any value read
from a preference file.  The argument to the flag is a string of the
form I<prefname>B<:>I<value>, where I<prefname> is the name of the
preference (which is the same name that would appear in the preference
file), and I<value> is the value to which it should be set.

=item -p

I<Don't> put the interface into promiscuous mode.  Note that the
interface might be in promiscuous mode for some other reason; hence,
B<-p> cannot be used to ensure that the only traffic that is captured is
traffic sent to or from the machine on which B<Ethereal> is running,
broadcast traffic, and multicast traffic to addresses received by that
machine.

=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

When reading a capture file specified with the B<-r> flag, causes the
specified filter (which uses the syntax of display filters, rather than
that of capture filters) to be applied 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), 'ad'
(absolute with date), or 'd' (delta).  The relative time is the time
elapsed between the first packet and the current packet.  The absolute
time is the actual time the packet was captured, with no date displayed;
the absolute date and time is the actual time and date 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:Save, File:Save As

Save the current capture, or the packets currently displayed from that
capture, to a file.  Check boxes let you select whether to save all
packets, or just those that have passed the current display filter and/or
those that are currently marked, and an option menu lets you select (from 
a list of file formats in which at particular capture, or the packets 
currently displayed from that capture, can be saved), a file format in 
which to save it.

=item File:Print

Prints, for all the packets in the current capture, either the summary
line for the packet or the protocol tree view of the packet; when
printing the protocol tree view, the hex dump of the packet can be
printed as well.  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 fully-expanded protocol tree view of the currently-selected
packet.  Printing options can be set with the I<Edit:Preferences> menu
item.

=item File:Quit

Exits the application.

=item Edit:Find Frame

Allows you to search forward or backward, starting with the currently
selected packet (or the most recently selected packet, if no packet is
selected), for a packet matching a given display filter.

=item Edit:Go To Frame

Allows you to go to a particular numbered packet.

=item Edit:Mark Frame

Allows you to mark (or unmark if currently marked) the selected packet.

=item Edit:Mark All Frames

Allows you to mark all packets that are currently displayed.

=item Edit:Unmark All Frames

Allows you to unmark all packets that are currently displayed.

=item Edit:Preferences

Sets the packet printing, column display, TCP stream coloring, and GUI
options (see L<"Preferences"> below).

=item Edit:Capture Filters

Edits the saved list of capture filters, allowing filters to be added,
changed, or deleted.

=item Edit:Display Filters

Edits the saved list of display filters, allowing filters to be added,
changed, or deleted.

=item Edit:Protocols

Edits the list of protocols, allowing protocol dissection to be 
enabled or disabled.

=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 B<Ethereal>.  Otherwise, the default TMPDIR location is
system-dependent, but is likely either F</var/tmp> or F</tmp>.

=item Capture:Stop

In a capture that updates the packet display as packets arrive (so that
Ethereal responds to user input other than pressing the "Stop" button in
the capture packet statistics dialog box), stops the capture.

=item Display:Options

Allows you to sets the format of the packet timestamp displayed in the
packet list window to relative, absolute, absolute date and time, or
delta, to enable or disable the automatic scrolling of the packet list
while a live capture is in progress or to enable or disable translation
of addresses to names in the display.

=item Display:Match Selected

Creates and applies a display filter based on the data that is currently
highlighted in the protocol tree.  If that data is a field that can be
tested in a display filter expression, the display filter will test that
field; otherwise, the display filter will be based on absolute offset
within the packet, and so could be unreliable if the packet contains
protocols with variable-length headers, such as a source-routed
token-ring packet.

=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 Display:Expand All

Expands all branches of the protocol tree.

=item Display:Show Packet In New Window

Creates a new window containing a protocol tree view and a hex dump
window of the currently selected packet; this window will continue to
display that packet's protocol tree and data even if another packet is
selected.

=item Display:User Specified Decodes

Creates a new window showing whether any protocol ID to dissector
mappings have been changed by the user.  This window also allows the
user to reset all decodes to their default values.

=item Tools:Plugins

Allows you to see what dynamically loadable dissector plugin modules
have been loaded (see I<"Plugins"> below).

=item Tools:Follow TCP Stream

If you have a TCP packet selected, it will display the contents of the
data stream for the TCP connection to which that packet belongs, as
text, in a separate window, and will leave the list of packets in a
filtered state, with only those packets that are part of that TCP
connection being displayed.  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).

The window in which the data stream is displayed lets you select whether
to display:

=over 4

=item

whether to display the entire conversation, or one or the other side of
it;

=item

whether the data being displayed is to be treated as ASCII or EBCDIC
text or as raw hex data;

=back

=back

=over 4

=item

and lets you print what's currently being displayed, using the same
print options that are used for the I<File:Print Packet> menu item, or
save it as text to a file.

=back

=item Tools:Decode As

If you have a packet selected, this menu item will present a dialog
allowing you to change which dissectors are used to decode this
packet.  The dialog has one panel each for the link layer, network
layer and transport layer protocol/port numbers, and will allow each
of these to be changed independently.  For example, if the selected
packet is a TCP packet to port 12345, using this dialog you can
instruct Ethereal to decode all packets to or from that TCP port as
HTTP packets.

=item Tools:Protocol Hierarchy Statistics

This shows the number of packets, and the number of bytes
in those packets, for each protocol in the trace. It
organizes the protocols in the same hierarchy in which
they were found in the trace. Besides counting the packets
in which the protocol exists, a count is also made
for packets in which the protocol is the last protocol in
the stack. These last-protocol counts show you how many packets
(and the byte count associated with those packets) B<ended> in a particular
protocol. In the table, they are listed under "End Packets" and
"End Bytes".

=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 current filter and informational text.

=over 6

=item Top Pane

The top pane contains the list of network packets that you can scroll
through and select.  By default, the packet number, packet timestamp,
source and destination addresses, protocol, and description are
displayed for each packet; the I<Columns> page in the dialog box popped
up by I<Edit:Preferences> lets you change this (although, unfortunately,
you currently have to save the preferences, and exit and restart
Ethereal, for those changes to take effect).

If you click on the heading for a column, the display will be sorted by
that column; clicking on the heading again will reverse the sort order
for that column.

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 right mouse button can be used to pop up a menu of operations.

The middle mouse button can be used to mark a packet.

=item Middle Pane

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 right mouse button can be used to pop up a
menu of operations.

=item Bottom Pane

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.

The right mouse button can be used to pop up a menu of operations.

=item Current Filter

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.
Selecting the I<Reset> button clears the display filter so that all
packets are displayed.

=back

=item Preferences

The I<Preferences> dialog lets you control various personal preferences
for the behavior of B<Ethereal>.

=over 6

=item Printing Preferences

The radio buttons at the top of the I<Printing> page allow you choose
between printing packets with the I<File:Print Packet> menu item 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.  Additionally, you can select the
I<File:> button to browse the file system for a particular save file.

=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

=item TCP Stream Preferences

The I<TCP Streams> page can be used to change the color of the text
displayed in the TCP stream window.  To change a color, simply select
an attribute from the "Set:" menu and use the color selector to get the
desired color.  The new text colors are displayed in a sample window.

=item GUI Preferences

The I<GUI> page is used to modify small aspects of the GUI to your own
personal taste:

=over 6

=item Scrollbars

The vertical scrollbars in the three panes can be set to be either on
the left or the right. 

=item Selection Bars

The selection bar in the
packet list and protocol tree can have either a "browse" or "select"
behavior. If the selection bar has a "browse" behavior, the arrow keys
will move an outline of the selection bar, allowing you to browse
the rest of the list or tree without changing the selection
until you press the space bar. If the selection bar has a "select"
behavior, the arrow keys will move the selection bar and change
the selection to the new item in the packet list or protocol tree.
The highlight method in the hex dump display for the selected protocol
item can be set to use either inverse video, or bold characters.

=item Fonts

The "Font..." button lets you select the font to be used for most text.

=item Colors

The "Colors..." button lets you select the colors to be used for instance
for the marked frames.

=back

=item Protocol Preferences

There are also pages for various protocols that Ethereal dissects,
controlling the way Ethereal handles those protocols.

=back

=item Edit Capture Filter List

=item Edit Display Filter List

=item Capture Filter

=item Display Filter

=item Read Filter

=item Search Filter

The I<Edit Capture Filter List> dialog lets you create, modify, and
delete capture filters, and the I<Edit Display Filter List> dialog lets
you create, modify, and delete display filters.

The I<Capture Filter> dialog lets you do all of the editing operations
listed, and also lets you choose or construct a filter to be used when
capturing packets.

The I<Display Filter> dialog lets you do all of the editing operations
listed, and also lets you choose or construct a filter to be used to
filter the current capture being viewed.

The I<Read Filter> dialog lets you do all of the editing operations
listed, and also lets you choose or construct a filter to be used to
as a read filter for a capture file you open.

The I<Search Filter> dialog lets you do all of the editing operations
listed, and also lets you choose or construct a filter expression to be
used in a find operation.

In all of those dialogs, 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, 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 Add Expression...

For display filter expressions, pops up a dialog box to allow you to
construct a filter expression to test a particular field; it offers
lists of field names, and, when appropriate, lists from which to select
tests to perform on the field and values with which to compare it.  In
that dialog box, the OK button will cause the filter expression you
constructed to be entered into the I<Filter string> entry at the current
cursor position.

=item OK

In the I<Capture Filter> dialog, closes the dialog box and makes the
filter in the I<Filter string> entry the filter in the I<Capture
Preferences> dialog.  In the I<Display Filter> dialog, closes the dialog
box and makes the filter in the I<Filter string> entry the current
display filter, and applies it to the current capture.  In the I<Read
Filter> dialog, closes the dialog box and makes the filter in the
I<Filter string> entry the filter in the I<Open Capture File> dialog. 
In the I<Search Filter> dialog, closes the dialog box and makes the
filter in the I<Filter string> entry the filter in the I<Find Frame>
dialog.

=item Apply

Makes the filter in the I<Filter string> entry the current display
filter, and applies it to the current capture.

=item Save

Saves the current filter list in F<$HOME/.ethereal/cfilters> if the list
of filters being edited is the list of capture filters or in
F<$HOME/.ethereal/dfilters> if the list of filters being edited is the
list of display filters.

=item Close

Closes the dialog without doing anything with the filter in the I<Filter
string> entry.

=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, or the name of a FIFO from which to get the 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,
can specify whether the interface is to be put in promiscuous mode or
not with the I<Capture packets in promiscuous mode> check box, can
specify that the display should be updated as packets are captured with
the I<Update list of packets in real time> check box, can specify
whether in such a capture the packet list pane should scroll to show the
most recently captured packets with the I<Automatic scrolling in live
capture> check box, and can specify whether addresses should be
translated to names in the display with the I<Enable name resolution>
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, "Date and time of day" for absolute time stamps with the
date, "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 and whether addresses should be translated to names in
the display.

=item Plugins

The I<Plugins> dialog lets you view the dissector plugin modules
available on your system.

The I<Plugins List> shows the name and version of each dissector plugin
module found on your system.  The plugins are searched in the following
directories: F</usr/share/ethereal/plugins>,
F</usr/local/share/ethereal/plugins> and F<~/.ethereal/plugins>.  Note
that a dissector plugin module may support more than one protocol; there
is not necessarily a one-to-one correspondence between dissector plugin
modules and protocols.  Protocols supported by a dissector plugin module
are enabled and disabled using the I<Edit:Protocols> dialog box, just as
protocols built into Ethereal are.

=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.  In a display filter expression
testing the value of a Boolean field, "true" is expressed as 1 or any
other non-zero value, and "false" is expressed as zero.  For example, a
token-ring packet's source route field is boolean.  To find any
source-routed packets, a display filter would be:

    tr.sr == 1

Non source-routed packets can be found with:

    tr.sr == 0

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

IPv4 address can be compared with the same logical relations as numbers:
eq, ne, gt, ge, lt, and le.  The IPv4 address is stored in host order,
so you do not have to worry about how the endianness of an IPv4 address
when using it in a display filter.

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 slice 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

If the length of your byte-slice is only one byte, then it is still
represented in hex, but without the preceding "0x": 

    llc[3] == aa

You can use the slice 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


The following syntax governs slices:

        [i:j]   i = start_offset, j = length
        [i-j]   i = start_offet, j = end_offset, inclusive.
        [i]     i = start_offset, length = 1
        [:j]    start_offset = 0, length = j
        [i:]    start_offset = i, end_offset = end_of_field


Offsets and lengths can be negative, in which case they indicate the offset from the
*end* of the field.  Here's how to check the last 4 bytes of a frame:

    frame[-4:4] == 0.1.2.3
or
    frame[-4:] == 0.1.2.3


You can create complex concatenations of slices using the comma operator:

        field[1,3-5,9:] == 01:03:04:05:09:0a:0b


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
    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 B<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 FILES

F</usr/local/etc/ethereal.conf> and F<$HOME/.ethereal/preferences>
contain system-wide and personal preference settings, respectively.  The
file contains preference settings of the form I<prefname>B<:>I<value>,
one per line, where I<prefname> is the name of the preference (which is
the same name that would appear in the preference file), and I<value> is
the value to which it should be set; white space is allowed between B<:>
and I<value>.  A preference setting can be continued on subsequent lines
by indenting the continuation lines with white space.  A B<#> character
starts a comment that runs to the end of the line.

The system-wide preference file is read first, if it exists, overriding
B<Ethereal>'s default values; the personal preferences file is then
read, if it exists, overriding default values and values read from the
system-wide preference file.

Note that whenever the preferences are saved by using the I<Save> button
in the I<Edit:Preferences> dialog box, F<$HOME/.ethereal/preferences>
will be overwritten with the new settings, destroying any comments that
were in the file.

F</etc/ethers> is consulted to correlate 6-byte hardware addresses to
names.  If an address is not found in F</etc/ethers>, the
F<$HOME/.ethereal/ethers> file is consulted next.  Each line contains
one hardware address and name, separated by whitespace.  The digits of
the hardware address are separated by either a colon (:), a dash (-), or
a period (.).  The following three lines are valid lines of an ethers
file:

  ff:ff:ff:ff:ff:ff          Broadcast
  c0-00-ff-ff-ff-ff          TR_broadcast
  00.00.00.00.00.00          Zero_broadcast

F</usr/local/etc/manuf> matches the 3-byte vendor portion of a 6-byte
hardware address with the manufacturer's name.  The format of the file
is the same as the F</etc/ethers> file, except that each address is
three bytes instead of six.

F</etc/ipxnets> and F<$HOME/.ethereal/ipxnets> correlate 4-byte IPX
network numbers to names.  The format is the same as the F</etc/ethers>
file, except that each address if four bytes instead of six. 
Additionally, the address can be represented a single hexadecimal
number, as is more common in the IPX world, rather than four hex octets. 
For example, these four lines are valid lines of an ipxnets file.

  C0.A8.2C.00              HR
  c0-a8-1c-00              CEO
  00:00:BE:EF              IT_Server1
  110f                     FileServer3

=head1 SEE ALSO

L<tethereal(1)>, L<editcap(1)>, L<tcpdump(8)>, L<pcap(3)>

=head1 NOTES

The latest version of B<Ethereal> can be found at
B<http://www.ethereal.com>.

=head1 AUTHORS

  Original Author
  -------- ------
  Gerald Combs  <gerald@ethereal.com>


  Contributors
  ------------
  Gilbert Ramirez          <gram@xiexie.org>
  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@alum.mit.edu>
  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             <oabad@cybercable.fr>
  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>
  Tomislav Vujec           <tvujec@carnet.hr>
  Kojak                    <kojak@bigwig.net>
  Uwe Girlich              <Uwe.Girlich@philosys.de>
  Warren Young             <tangent@mail.com>
  Heikki Vatiainen         <hessu@cs.tut.fi>
  Greg Hankins             <gregh@twoguys.org>
  Jerry Talkington         <jerryt@netapp.com>
  Dave Chapeskie           <dchapes@ddm.on.ca>
  James Coe                <jammer@cin.net>
  Bert Driehuis            <driehuis@playbeing.org>
  Stuart Stanley           <stuarts@mxmail.net>
  John Thomes              <john@ensemblecom.com>
  Laurent Cazalet          <laurent.cazalet@mailclub.net>
  Thomas Parvais           <thomas.parvais@advalvas.be>
  Gerrit Gehnen            <G.Gehnen@atrie.de>
  Craig Newell             <craign@cheque.uq.edu.au>
  Ed Meaney                <emeaney@altiga.com>
  Dietmar Petras           <DPetras@ELSA.de> 
  Fred Reimer              <fwr@ga.prestige.net>
  Florian Lohoff           <flo@rfc822.org>
  Jochen Friedrich         <jochen+ethereal@scram.de>
  Paul Welchinski          <paul.welchinski@telusplanet.net>
  Doug Nazar               <nazard@dragoninc.on.ca>
  Andreas Sikkema          <andreas.sikkema@philips.com>
  Mark Muhlestein          <mmm@netapp.com>
  Graham Bloice            <graham.bloice@trihedral.com>
  Ralf Schneider           <ralf.schneider@alcatel.se>
  Yaniv Kaul               <ykaul@netvision.net.il>
  Paul Ionescu             <ipaul@romsys.ro>
  Mark Burton              <markb@ordern.com>
  Stefan Raab              <sraab@cisco.com>
  Mark Clayton             <clayton@shore.net>
  Michael Rozhavsky        <mike@tochna.technion.ac.il>
  Dug Song                 <dugsong@monkey.org>
  Michael Tuexen           <Michael.Tuexen@icn.siemens.de>
  Bruce Korb               <bkorb@sco.com>
  Jose Pedro Oliveira      <jpo@di.uminho.pt>
  David Frascone           <dave@frascone.com>
  Peter Kjellerstedt       <pkj@axis.com>
  Phil Techau              <phil_t@altavista.net>
  Wes Hardaker             <wjhardaker@ucdavis.edu>
  Robert Tsai              <rtsai@netapp.com>
  Craig Metz               <cmetz@inner.net>
  Per Flock                <per.flock@axis.com>
  Jack Keane               <jkeane@OpenReach.com>
  Brian Wellington         <bwelling@xbill.org>
  Santeri Paavolainen      <santtu@ssh.com>
  Ulrich Kiermayr          <uk@ap.univie.ac.at>
  Neil Hunter              <neil.hunter@energis-squared.com>
  Ralf Holzer              <ralf@well.com>
  Craig Rodrigues          <rodrigc@mediaone.net>
  Ed Warnicke              <hagbard@physics.rutgers.edu>
  Johan Jorgensen          <johan.jorgensen@axis.com>
  Frank Singleton          <frank.singleton@ericsson.com>
  Kevin Shi                <techishi@ms22.hinet.net>
  Mike Frisch              <mfrisch@saturn.tlug.org>
  Burke Lau                <burke_lau@agilent.com>
  Martti Kuparinen         <martti.kuparinen@nomadiclab.com>
  David Hampton            <dhampton@mac.com>
  Kent Engström            <kent@unit.liu.se>
  Ronnie Sahlberg          <rsahlber@bigpond.net.au>
  Alexandre P. Ferreira    <alexandref@spliceip.com.br>
  Simharajan Srishylam     <Simharajan.Srishylam@netapp.com>
  Greg Kilfoyle            <gregk@redback.com>
  James E. Flemer          <jflemer@acm.jhu.edu>
  Peter Lei                <peterlei@cisco.com>
  Thomas Gimpel            <thomas.gimpel@ferrari.de>
  Albert Chin              <china@thewrittenword.com>
  Charles Levert           <charles@comm.polymtl.ca>
  Todd Sabin               <tas@webspan.net>
  Eduardo Pérez Ureta      <eperez@dei.inf.uc3m.es>
  Martin Thomas            <martin_a_thomas@yahoo.com>
  Hartmut Mueller          <hartmut@wendolene.ping.de>
  Michal Melerowicz        <Michal.Melerowicz@nokia.com>
  Hannes Gredler           <hannes@juniper.net>

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.