
=head1 NAME

tethereal - Dump and analyze network traffic

=head1 SYNOPSYS

B<tethereal>
S<[ B<-c> count ]>
S<[ B<-D> ]>
S<[ B<-f> capture filter expression ]>
S<[ B<-F> file format ]>
S<[ B<-h> ]>
S<[ B<-i> interface ]> 
S<[ B<-l> ]>
S<[ B<-n> ]>
S<[ B<-N> resolving flags ] ...>
S<[ B<-o> preference setting ] ...>
S<[ B<-p> ]>
S<[ B<-r> infile ]>
S<[ B<-R> display filter expression ]>
S<[ B<-s> snaplen ]>
S<[ B<-t> time stamp format ]>
S<[ B<-v> ]>
S<[ B<-V> ]>
S<[ B<-w> savefile ]>
S<[ B<-x> ]>
S<[ filter expression ]>

=head1 DESCRIPTION

B<Tethereal> is a network protocol analyzer.  It lets you capture packet
data from a live network, or read packets from a previously saved
capture file, either printing a decoded form of those packets to the
standard output or writing the packets to a file.  B<Tethereal> knows
how to read B<libpcap> capture files, including those of B<tcpdump>.  In
addition, B<Tethereal> 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, and output in IPLog format from the Cisco Secure
Intrusion Detection System.  There is no need to tell B<Tethereal> what
type of file you are reading; it will determine the file type by itself. 
B<Tethereal> is also capable of reading any of these file formats if
they are compressed using gzip.  B<Tethereal> recognizes this directly
from the file; the '.gz' extension is not required for this purpose.

If the B<-w> flag is not specified, B<Tethereal> prints a decoded form
of the packets it captures or reads; otherwise, it writes those packets
to the file specified by that flag.

When printing a decoded form of packets, B<Tethereal> prints, by
default, a summary line containing the fields specified by the
preferences file (which are also the fields displayed in the packet list
pane in B<Ethereal>), although if it's printing packets as it captures
them, rather than printing packets from a saved capture file, it won't
print the "frame number" field.  If the B<-V> flag is specified, it
prints intead a protocol tree, showing all the fields of all protocols
in the packet.

When writing packets to a file, B<Tethereal>, by default, writes the
file in B<libpcap> format, and writes all of the packets it sees to the
output file.  The B<-F> flag can be used to specify the format in which
to write the file; it can write the file in B<libpcap> format (standard
B<libpcap> format, a modified format used by some patched versions of
B<libpcap>, or the format used by Red Hat Linux 6.1), B<snoop> format,
uncompressed B<Sniffer> format, Microsoft B<Network Monitor> 1.x format,
and the format used by Windows-based versions of the B<Sniffer>
software.

Read filters in B<Tethereal>, which allow you to select which packets
are to be decoded or written to a file, are very powerful; more fields
are filterable in B<Tethereal> than in other protocol analyzers, and the
syntax you can use to create your filters is richer.  As B<Tethereal>
progresses, expect more and more protocol fields to be allowed in read
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 read filter syntax.  A read filter can also be specified when
capturing, and only packets that pass the read filter will be displayed
or saved to the output file; note, however, that capture filers are much
more efficient than read filters, and it may be more difficult for
B<Tethereal> to keep up with a busy network if a read filter is
specified for a live capture.

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

A capture or read filter can either be specified with the B<-f> or B<-R>
option, respectively, in which case the entire filter expression must be
specified as a single argument (which means that if it contains spaces,
it must be quoted), or can be specified with command-line arguments
after the option arguments, in which case all the arguments after the
filter arguments are treated as a filter expression.  If the filter is
specified with command-line arguments after the option arguments, it's a
capture filter if a capture is being done (i.e., if no B<-r> flag was
specified) and a read filter if a capture file is being read (i.e., if a
B<-r> flag was specified).

=head1 OPTIONS

=over 4

=item -c

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

=item -D

Prints a list of the interfaces on which B<Tethereal> can capture, and
exits.  Note that "can capture" means that B<Tethereal> was able to open
that device to do a live capture; if, on your system, a program doing a
network capture must be run from an account with special privileges (for
example, as root), then, if B<Tethereal> is run with the B<-D> flag and
is not run from such an account, it will not list any interfaces.

=item -f

Sets the capture filter expression.

=item -F

Sets the file format of the output capture file.

=item -h

Prints the version and options and exits.

=item -i

Sets the name of the network interface to use for live packet capture. 
It should match one of the names listed in "B<netstat -i>" or
"B<ifconfig -a>".  If no interface is specified, B<Tethereal> 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<Tethereal> reports an error and doesn't start the capture.

=item -l

Flush the standard output after the information for each packet is
printed.  (This is not, strictly speaking, line-buffered if B<-V>
was specified; however, it is the same as line-buffered if B<-V> wasn't
specified, as only one line is printed for each packet, and, as B<-l> is
normally used when piping a live capture to a program or script, so that
output for a packet shows up as soon as the packet is seen and
dissected, it should work just as well as true line-buffering.  We do
this as a workaround for a deficiency in the Microsoft Visual C++ C
library.)

This may be useful when piping the output of B<Tethereal> to another
program, as it means that the program to which the output is piped will
see the dissected data for a packet as soon as B<Tethereal> sees the
packet and generates that output, rather than seeing it only when the
standard output buffer containing that data fills up.

=item -n

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

=item -N

Turns on name resolving for particular types of addresses and port
numbers; the argument is a string that may contain the letters B<m> to
enable MAC address resolution, B<n> to enable network address
resolution, and B<t> to enable transport-layer port number resolution. 
This overrides B<-n> if both B<-N> and B<-n> are present.

=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<Tethereal> is running,
broadcast traffic, and multicast traffic to addresses received by that
machine.

=item -r

Reads packet data from I<file>.

=item -R

Causes the specified filter (which uses the syntax of read filters,
rather than that of capture filters) to be applied before printing a
decoded form of packets or writing packets to a file; packets not
matching the filter are discarded rather than being printed or written.

=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 format of the packet timestamp printed in summary lines.  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 -V

Causes B<Tethereal> to print a protocol tree for each packet rather than
a one-line summary of the packet.

=item -w

Writes packet data to I<savefile>.

=item -x

Causes B<Tethereal> to print a hex and ASCII dump of the packet data
after printing the summary or protocol tree.

=back

=head1 CAPTURE FILTER SYNTAX

See manual page of tcpdump(8).

=head1 READ FILTER SYNTAX

Read 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 read filter, then it is printed.  Read
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 read 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 read filters are equivalent:

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

Boolean values are either true or false.  In a read 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 read 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 addresses 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 read filter.

Classless InterDomain Routing (CIDR) notation can be used to test if an
IPv4 address is in a certain subnet.  For example, this display filter
will find all packets in the 129.111 Class-B network:

    ip.addr == 129.111.0.0/16

Remember, the number after the slash represents the number of bits used
to represent the network.  CIDR notation can also be used with
hostnames, in this example of finding IP addresses on the same Class C
network as 'sneezy':

    ip.addr eq sneezy/24

The CIDR notation can only be used on IP addresses or hostnames, not in
variable names.  So, a display filter like "ip.src/24 == ip.dst/24" is
not valid.  (yet)

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 B<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 read 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<Tethereal>.  The abbreviation of the protocol or field is
given.  This abbreviation is what you use in the read 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<Tethereal>'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.

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

=head1 NOTES

B<Tethereal> is part of the B<Ethereal> distribution.  The latest version
of B<Ethereal> can be found at B<http://www.ethereal.com>.

=head1 AUTHORS

B<Tethereal> uses the same packet dissection code that B<Ethereal> does,
as well as using many other modules from B<Ethereal>; see the list of
authors in the B<Ethereal> man page for a list of authors of that code.
