Tribblix: manual page: wireshark-filter.4

WIRESHARK-FILTER(4) WIRESHARK-FILTER(4)

NAME

wireshark-filter - Wireshark display filter syntax and reference

SYNOPSIS

wireshark [other options] [ -Y "display filter expression" |
--display-filter "display filter expression" ]

tshark [other options] [ -Y "display filter expression" |
--display-filter "display filter expression" ]

DESCRIPTION

Wireshark and TShark share a powerful filter engine that helps remove
the noise from a packet trace and lets you see only the packets that
interest you. If a packet meets the requirements expressed in your
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 check the existence of
specified fields or protocols.

Filters are also used by other features such as statistics generation
and packet list colorization (the latter is only available to
Wireshark). This manual page describes their syntax. A comprehensive
reference of filter fields can be found within Wireshark and in the
display filter reference at <https://www.wireshark.org/docs/dfref/>.

FILTER SYNTAX

Check whether a field or protocol exists

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

Think of a protocol or field in a filter as implicitly having the
"exists" operator.

Comparison operators

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

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

Search and match operators

Additional operators exist expressed only in English, not C-like
syntax:

contains Does the protocol, field or slice contain a value
matches, ~ Does the protocol or text string match the given
case-insensitive Perl-compatible regular expression

The "contains" operator allows a filter to search for a sequence of
characters, expressed as a string (quoted or unquoted), or bytes,
expressed as a byte array, or for a single character, expressed as a
C-style character constant. For example, to search for a given HTTP
URL in a capture, the following filter can be used:

http contains "https://www.wireshark.org"

The "contains" operator cannot be used on atomic fields, such as
numbers or IP addresses.

The "matches" or "~" operator allows a filter to apply to a
specified Perl-compatible regular expression (PCRE). The "matches"
operator is only implemented for protocols and for protocol fields
with a text string representation. Matches are case-insensitive by
default. For example, to search for a given WAP WSP User-Agent, you
can write:

wsp.header.user_agent matches "cldc"

This would match "cldc", "CLDC", "cLdC" or any other combination of
upper and lower case letters.

You can force case sensitivity using

wsp.header.user_agent matches "(?-i)cldc"

This is an example of PCRE's (?*option)* construct. (?-i) performs a
case-sensitive pattern match but other options can be specified as
well. More information can be found in the
pcrepattern(3)|https://www.pcre.org/original/doc/html/pcrepattern.html
man page.

Functions

The filter language has the following functions:

upper(string-field) - converts a string field to uppercase
lower(string-field) - converts a string field to lowercase
len(field) - returns the byte length of a string or bytes field
count(field) - returns the number of field occurrences in a frame
string(field) - converts a non-string field to string

upper() and lower() are useful for performing case-insensitive string
comparisons. For example:

upper(ncp.nds_stream_name) contains "MACRO"
lower(mount.dump.hostname) == "angel"

string() converts a field value to a string, suitable for use with
operators like "matches" or "contains". Integer fields are converted
to their decimal representation. It can be used with IP/Ethernet
addresses (as well as others), but not with string or byte fields.
For example:

string(frame.number) matches "[13579]$"

gives you all the odd packets.

Protocol field types

Each protocol field is typed. The types are:

ASN.1 object identifier
Boolean
Character string
Compiled Perl-Compatible Regular Expression (GRegex) object
Date and time
Ethernet or other MAC address
EUI64 address
Floating point (double-precision)
Floating point (single-precision)
Frame number
Globally Unique Identifier
IPv4 address
IPv6 address
IPX network number
Label
Protocol
Sequence of bytes
Signed integer, 1, 2, 3, 4, or 8 bytes
Time offset
Unsigned integer, 1, 2, 3, 4, or 8 bytes
1-byte ASCII character

An integer may be expressed in decimal, octal, or hexadecimal
notation, or as a C-style character constant. The following six
display filters are equivalent:

frame.len > 10
frame.len > 012
frame.len > 0xa
frame.len > '\n'
frame.len > '\x0a'
frame.len > '\012'

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 and byte arrays are represented by hex digits.
The hex digits may be separated by colons, periods, or hyphens:

eth.dst eq ff:ff:ff:ff:ff:ff
aim.data == 0.1.0.d
fddi.src == aa-aa-aa-aa-aa-aa
echo.data == 7a

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

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

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 the endianness of an
IPv4 address when using it in a display filter.

Classless Inter-Domain 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 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, as in this example of finding IP addresses on the same
network as 'sneezy' (requires that 'sneezy' resolve to an IP address
for filter to be valid):

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).

Transaction and other IDs are often represented by unsigned 16 or 32
bit integers and formatted as a hexadecimal string with "0x" prefix:

(dhcp.id == 0xfe089c15) || (ip.id == 0x0373)

Strings are enclosed in double quotes:

http.request.method == "POST"

Inside double quotes, you may use a backslash to embed a double quote
or an arbitrary byte represented in either octal or hexadecimal.

browser.comment == "An embedded \" double-quote"

Use of hexadecimal to look for "HEAD":

http.request.method == "\x48EAD"

Use of octal to look for "HEAD":

http.request.method == "\110EAD"

This means that you must escape backslashes with backslashes inside
double quotes.

smb.path contains "\\\\SERVER\\SHARE"

looks for \\SERVER\SHARE in "smb.path". This may be more conveniently
written as

smb.path contains r"\\SERVER\SHARE"

String literals prefixed with 'r' are called "raw strings". Such
strings treat backslash as a literal character. Double quotes may
still be escaped with backslash but note that backslashes are always
preserved in the result.

The slice operator

You can take a slice of a field if the field is a text string or a
byte array. 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

Another example is:

http.content_type[0:4] == "text"

You can use the slice operator on a protocol name, too. The "frame"
protocol can be useful, encompassing all the data captured by
Wireshark or TShark.

token[0:5] ne 0.0.0.1.1
llc[0] eq aa
frame[100-199] contains "wireshark"

The following syntax governs slices:

[i:j] i = start_offset, j = length
[i-j] i = start_offset, 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 can be negative, in which case they indicate the offset from
the end of the field. The last byte of the field is at offset -1,
the last but one byte is at offset -2, and so on. Here's how to
check the last four bytes of a frame:

frame[-4:4] == 0.1.2.3

or

frame[-4:] == 0.1.2.3

A slice is always compared against either a string or a byte
sequence. As a special case, when the slice is only 1 byte wide, you
can compare it against a hex integer that is 0xff or less (which
means it fits inside one byte). This is not allowed for byte
sequences greater than one byte, because then one would need to
specify the endianness of the multi-byte integer. Also, this is not
allowed for decimal numbers, since they would be confused with hex
numbers that are already allowed as byte strings. Nevertheless,
single-byte hex integers can be convenient:

frame[4] == 0xff

Slices can be combined. You can concatenate them using the comma
operator:

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

This concatenates offset 1, offsets 3-5, and offset 9 to the end of
the ftp data.

The membership operator

A field may be checked for matches against a set of values simply
with the membership operator. For instance, you may find traffic on
common HTTP/HTTPS ports with the following filter:

tcp.port in {80, 443, 8080}

as opposed to the more verbose:

tcp.port == 80 or tcp.port == 443 or tcp.port == 8080

To find HTTP requests using the HEAD or GET methods:

http.request.method in {"HEAD", "GET"}

The set of values can also contain ranges:

tcp.port in {443, 4430..4434}
ip.addr in {10.0.0.5 .. 10.0.0.9, 192.168.1.1..192.168.1.9}
frame.time_delta in {10 .. 10.5}

Type conversions

If a field is a text string or a byte array, it can be expressed in
whichever way is most convenient.

So, for instance, the following filters are equivalent:

http.request.method == "GET"
http.request.method == 47.45.54

A range can also be expressed in either way:

frame[60:2] gt 50.51
frame[60:2] gt "PQ"

Bit field operations

It is also possible to define tests with bit field operations.
Currently the following bit field operation is supported:

bitwise_and, & Bitwise AND

The bitwise AND operation allows testing to see if one or more bits
are set. Bitwise AND operates on integer protocol fields and slices.

When testing for TCP SYN packets, you can write:

tcp.flags & 0x02

That expression will match all packets that contain a "tcp.flags"
field with the 0x02 bit, i.e. the SYN bit, set.

Similarly, filtering for all WSP GET and extended GET methods is
achieved with:

wsp.pdu_type & 0x40

When using slices, the bit mask must be specified as a byte string,
and it must have the same number of bytes as the slice itself, as in:

ip[42:2] & 40:ff

Logical expressions

Tests can be combined using logical expressions. These too are
expressible 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 expressions:

tcp.port == 80 and ip.src == 192.168.2.1
not llc
http and frame[100-199] contains "wireshark"
(ipx.src.net == 0xbad && ipx.src.node == 0.0.0.0.0.1) || ip

Remember that whenever a protocol or field name occurs in an
expression, the "exists" operator is implicitly called. The "exists"
operator has the highest priority. This means that the first filter
expression must be read as "show me the packets for which tcp.port
exists and equals 80, and ip.src exists and equals 192.168.2.1". The
second filter expression means "show me the packets where not exists
llc", or in other words "where llc does not exist" and hence will
match all packets that do not contain the llc protocol. The third
filter expression includes the constraint that offset 199 in the
frame exists, in other words the length of the frame is at least 200.

Each comparison has an implicit exists test for any field value. Care
must be taken when using the display filter to remove noise from the
packet trace. If, for example, you want to filter out all IP
multicast packets to address 224.1.2.3, then using:

ip.dst ne 224.1.2.3

may be too restrictive. This is the same as writing:

ip.dst and ip.dst ne 224.1.2.3

The filter selects only frames that have the "ip.dst" field. Any
other frames, including all non-IP packets, will not be displayed. To
display the non-IP packets as well, you can use one of the following
two expressions:

not ip.dst or ip.dst ne 224.1.2.3
not ip.dst eq 224.1.2.3

The first filter uses "not ip.dst" to include all non-IP packets and
then lets "ip.dst ne 224.1.2.3" filter out the unwanted IP packets.
The second filter also negates the implicit existance test and so is
a shorter way to write the first.

FILTER FIELD REFERENCE

The entire list of display filters is too large to list here. You can
can find references and examples at the following locations:

+o The online Display Filter Reference:
<https://www.wireshark.org/docs/dfref/>

+o View:Internals:Supported Protocols in Wireshark

+o tshark -G fields on the command line

+o The Wireshark wiki:
<https://gitlab.com/wireshark/wireshark/-/wikis/DisplayFilters>

NOTES

The wireshark-filter(4) manpage is part of the Wireshark
distribution. The latest version of Wireshark can be found at
<https://www.wireshark.org>.

Regular expressions in the "matches" operator are provided by GRegex
in GLib. See
<https://developer-old.gnome.org/glib/stable/glib-regex-syntax.html>
or <https://www.pcre.org/> for more information.

This manpage does not describe the capture filter syntax, which is
different. See the manual page of pcap-filter(7) or, if that doesn't
exist, tcpdump(8), or, if that doesn't exist,
<https://gitlab.com/wireshark/wireshark/-/wikis/CaptureFilters> for a
description of capture filters.

Display Filters are also described in the User's Guide:
<https://www.wireshark.org/docs/wsug_html_chunked/ChWorkBuildDisplayFilterSection.html>

AUTHORS

See the list of authors in the Wireshark man page for a list of
authors of that code.

2024-03-27 WIRESHARK-FILTER(4)