2003-10-01 14:59:41 +00:00
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=head1 NAME
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2003-10-15 02:13:33 +00:00
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ethereal-filter - Ethereal filter syntax and reference
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2003-10-01 14:59:41 +00:00
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=head1 SYNOPSYS
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B<ethereal> [other options]
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S<[ B<-R> "filter expression" ]>
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B<tethereal> [other options]
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S<[ B<-R> "filter expression" ]>
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=head1 DESCRIPTION
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2003-12-08 22:24:36 +00:00
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B<Ethereal> and B<Tethereal> share a powerful filter engine that help remove
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2003-12-07 18:32:59 +00:00
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the noise from a packet trace and let you see only the packets that interest
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you. If a packet meets the requirements expressed in your filter, then it
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is displayed in the list of packets. Display filters let you compare the
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fields within a protocol against a specific value, compare fields against
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fields, and to check the existence of specified fields or protocols.
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2003-10-01 14:59:41 +00:00
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2003-10-15 02:13:33 +00:00
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Filters are also used by other features such as statistics generation and
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packet list colorization (the latter is only available to B<Ethereal>). This
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manual page describes their syntax and provides a comprehensive reference of
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filter fields.
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2003-10-15 02:13:33 +00:00
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=head1 FILTER SYNTAX
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2003-12-07 18:32:59 +00:00
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=head2 Check whether a field or protocol exists
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2003-10-15 02:13:33 +00:00
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The simplest filter allows you to check for the existence of a protocol or
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field. If you want to see all packets which contain the IPX protocol, the
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filter would be "ipx". (Without the quotation marks) To see all packets
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that contain a Token-Ring RIF field, use "tr.rif".
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2003-12-07 18:32:59 +00:00
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Think of a protocol or field in a filter as implicitly having the "exists"
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operator.
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2003-12-08 22:24:36 +00:00
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Note: all protocol and field names that are available in B<Ethereal> and
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B<Tethereal> filters are listed in the B<FILTER PROTOCOL REFERENCE> (see
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below).
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=head2 Comparison operators
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2003-10-15 02:13:33 +00:00
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Fields can also be compared against values. The comparison operators
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can be expressed either through C-like symbols, or through English-like
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abbreviations:
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eq, == Equal
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ne, != Not equal
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gt, > Greater than
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lt, < Less Than
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ge, >= Greater than or Equal to
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le, <= Less than or Equal to
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2003-12-07 18:32:59 +00:00
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=head2 Search and match operators
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Additional operators exist expressed only in English, not punctuation:
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contains Does the protocol, byte-string, or text string contain a value
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matches Does the text string match the given Perl regular expression
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The "contains" operator allows a filter to search for any sequence of
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characters that may occur in a protocol or field. The "contains"
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operator is only implemented for protocols (in which case the sequence
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of characters is searched for in the data for that protocol), text
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fields, and raw data fields. For example, to search for a given HTTP
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URL in a capture, the following filter can be used:
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http contains "http://www.ethereal.com"
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2003-12-08 22:24:36 +00:00
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The "matches" operator allows a filter to apply to a specified
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2003-12-17 23:24:49 +00:00
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Perl-compatible regular expression (PCRE). The "matches" operator is only
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implemented for protocols, and also for protocol fields with a text string
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representation. For example, to search for a given WAP WSP User-Agent,
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one can write:
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wsp.user_agent matches "(?i)cldc"
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This example shows an interesting PCRE feature: pattern match options have to
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be specified with the B<(?>optionB<)> construct. For instance, B<(?i)> performs
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a case-insensitive pattern match. More information on PCRE can be found in the
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pcrepattern(3) man page (Perl Regular Expressions are explained in
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B<http://www.perldoc.com/perl5.8.0/pod/perlre.html>).
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Note: the "matches" operator is only available if B<Ethereal> or B<Tethereal>
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have been compiled with the PCRE library. This can be checked by running:
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ethereal -v
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tethereal -v
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2003-12-17 23:24:49 +00:00
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or selecting the "About Ethereal" item from the "Help" menu in B<Ethereal>.
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2003-12-07 18:32:59 +00:00
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=head2 Protocol field types
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Furthermore, each protocol field is typed. The types are:
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Unsigned integer (either 8-bit, 16-bit, 24-bit, or 32-bit)
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Signed integer (either 8-bit, 16-bit, 24-bit, or 32-bit)
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Boolean
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Ethernet address (6 bytes)
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Byte string (n-number of bytes)
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IPv4 address
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IPv6 address
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IPX network number
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Text string
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Double-precision floating point number
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An integer may be expressed in decimal, octal, or hexadecimal notation.
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The following three display filters are equivalent:
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frame.pkt_len > 10
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frame.pkt_len > 012
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frame.pkt_len > 0xa
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Boolean values are either true or false. In a display filter expression
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testing the value of a Boolean field, "true" is expressed as 1 or any
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other non-zero value, and "false" is expressed as zero. For example, a
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token-ring packet's source route field is boolean. To find any
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source-routed packets, a display filter would be:
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tr.sr == 1
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Non source-routed packets can be found with:
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tr.sr == 0
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Ethernet addresses, as well as a string of bytes, are represented in hex
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digits. The hex digits may be separated by colons, periods, or hyphens:
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fddi.dst eq ff:ff:ff:ff:ff:ff
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ipx.srcnode == 0.0.0.0.0.1
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eth.src == aa-aa-aa-aa-aa-aa
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If a string of bytes contains only one byte, then it is represented as
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an unsigned integer. That is, if you are testing for hex value 'ff' in
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a one-byte byte-string, you must compare it agains '0xff' and not 'ff'.
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IPv4 addresses can be represented in either dotted decimal notation, or
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by using the hostname:
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ip.dst eq www.mit.edu
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ip.src == 192.168.1.1
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IPv4 addresses can be compared with the same logical relations as numbers:
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eq, ne, gt, ge, lt, and le. The IPv4 address is stored in host order,
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so you do not have to worry about how the endianness of an IPv4 address
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when using it in a display filter.
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Classless InterDomain Routing (CIDR) notation can be used to test if an
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IPv4 address is in a certain subnet. For example, this display filter
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will find all packets in the 129.111 Class-B network:
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ip.addr == 129.111.0.0/16
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Remember, the number after the slash represents the number of bits used
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to represent the network. CIDR notation can also be used with
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hostnames, in this example of finding IP addresses on the same Class C
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network as 'sneezy':
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ip.addr eq sneezy/24
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The CIDR notation can only be used on IP addresses or hostnames, not in
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variable names. So, a display filter like "ip.src/24 == ip.dst/24" is
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not valid. (yet)
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IPX networks are represented by unsigned 32-bit integers. Most likely
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you will be using hexadecimal when testing for IPX network values:
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ipx.srcnet == 0xc0a82c00
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Strings are enclosed in double-quotes:
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http.request.method == "POST"
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Inside double quotes, you may use the backslash to embed a double-quote,
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or an arbitrary byte represented in either octal or hexadecimal.
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2003-12-07 18:32:59 +00:00
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browser.comment == "An embedded \" double-quote"
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Use of hexadecimal to look for "HEAD":
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http.request.method == "\x48EAD"
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Use of octal to look for "HEAD":
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http.request.method == "\x110EAD"
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This means that you must escape backslashes with backslashes inside
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double quotes:
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smb.path contains "\\\\SERVER\\SHARE"
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to look for \\SERVER\SHARE in "smb.path".
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2003-12-07 18:32:59 +00:00
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=head2 The slice operator
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2003-10-15 02:13:33 +00:00
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A slice operator also exists. You can check the substring
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(byte-string) of any protocol or field. For example, you can filter on
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the vendor portion of an ethernet address (the first three bytes) like
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this:
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eth.src[0:3] == 00:00:83
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If the length of your byte-slice is only one byte, then it is still
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represented in hex, but without the preceding "0x":
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llc[3] == aa
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You can use the slice operator on a protocol name, too. And
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remember, the "frame" protocol encompasses the entire packet, allowing
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you to look at the nth byte of a packet regardless of its frame type
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(Ethernet, token-ring, etc.).
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token[0:5] ne 0.0.0.1.1
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ipx[0:2] == ff:ff
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llc[3:1] eq 0xaa
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The following syntax governs slices:
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[i:j] i = start_offset, j = length
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[i-j] i = start_offset, j = end_offset, inclusive.
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[i] i = start_offset, length = 1
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[:j] start_offset = 0, length = j
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[i:] start_offset = i, end_offset = end_of_field
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Offsets and lengths can be negative, in which case they indicate the
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offset from the B<end> of the field. Here's how to check the last 4
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bytes of a frame:
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frame[-4:4] == 0.1.2.3
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or
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frame[-4:] == 0.1.2.3
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You can create complex concatenations of slices using the comma operator:
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field[1,3-5,9:] == 01:03:04:05:09:0a:0b
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2004-03-24 00:38:34 +00:00
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=head2 Bit field operations
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It is also possible to define tests with bit field operations. Currently the
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following bit field operation is supported:
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bitwise_and, & Bitwise AND
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The bitwise AND operation allows testing if one or more bits are set.
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Bitwise AND operates on integer protocol fields and slices.
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When testing for TCP SYN packets, once can write:
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tcp.flags & 0x02
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Similarly, filtering for all WSP GET and extended GET methods is achieved with:
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wsp.pdu_type & 0x40
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When using slices, the bit mask must be specified as byte string, and it must
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have the same number of bytes as the slice itself, as in:
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ip[42:2] & 40:ff
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2003-12-07 18:32:59 +00:00
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=head2 Logical expressions
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2003-10-15 02:13:33 +00:00
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All the above tests can be combined together with logical expressions.
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These too are expressable in C-like syntax or with English-like
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abbreviations:
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and, && Logical AND
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or, || Logical OR
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not, ! Logical NOT
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Expressions can be grouped by parentheses as well. The following are
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all valid display filter expressions:
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tcp.port == 80 and ip.src == 192.168.2.1
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not llc
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(ipx.srcnet == 0xbad && ipx.srnode == 0.0.0.0.0.1) || ip
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tr.dst[0:3] == 0.6.29 xor tr.src[0:3] == 0.6.29
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2003-12-07 18:32:59 +00:00
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Remember that whenever a protocol or field name occurs in an expression, the
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"exists" operator is implicitly called. The "exists" operator has the highest
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priority. This means that the first filter expression must be read as "show me
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the packets for which tcp.port exists and equals 80, and ip.src exists and
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equals 192.168.2.1". The second filter expression means "show me the packets
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where not (llc exists)", or in other words "where llc does not exist" and hence
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will match all packets that do not convey the llc protocol.
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2003-10-15 02:13:33 +00:00
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A special caveat must be given regarding fields that occur more than
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once per packet. "ip.addr" occurs twice per IP packet, once for the
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source address, and once for the destination address. Likewise,
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"tr.rif.ring" fields can occur more than once per packet. The following
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two expressions are not equivalent:
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ip.addr ne 192.168.4.1
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not ip.addr eq 192.168.4.1
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The first filter says "show me IP packets where an ip.addr exists that
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does not equal 192.168.4.1". That is, as long as one ip.addr in the
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packet does not equal 192.168.44.1, the packet passes the display
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filter. The second filter "don't show me any packets that have at least
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one ip.addr field equal to 192.168.4.1". If one ip.addr is 192.168.4.1,
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the packet does not pass. If B<neither> ip.addr fields is 192.168.4.1,
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then the packet passes.
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It is easy to think of the 'ne' and 'eq' operators as having an implict
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"exists" modifier when dealing with multiply-recurring fields. "ip.addr
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ne 192.168.4.1" can be thought of as "there exists an ip.addr that does
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not equal 192.168.4.1".
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Be careful with multiply-recurring fields; they can be confusing.
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Care must also be taken when using the display filter to remove noise
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from the packet trace. If you want to e.g. filter out all IP multicast
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packets to address 224.1.2.3, then using:
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ip.dst ne 224.1.2.3
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may be too restrictive. Filtering with "ip.dst" selects only those
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B<IP> packets that satisfy the rule. Any other packets, including all
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non-IP packets, will not be displayed. For displaying also the non-IP
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packets, you can use one of the following two expressions:
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not ip or ip.dst ne 224.1.2.3
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not ip.addr eq 224.1.2.3
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The first filter uses "not ip" to include all non-IP packets and then
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lets "ip.dst ne 224.1.2.3" to filter out the unwanted IP packets. The
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second filter has already been explained above where filtering with
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multiply occuring fields was discussed.
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=head1 FILTER PROTOCOL REFERENCE
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Each entry below provides an abbreviated protocol or field name. Every
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one of these fields can be used as a display filter. The type of the
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field is also given.
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2003-10-01 14:59:41 +00:00
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=insert_dfilter_table
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=head1 NOTES
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The B<ethereal-filters> manpage is part of the B<Ethereal> distribution.
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The latest version of B<Ethereal> can be found at
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B<http://www.ethereal.com>.
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2003-12-07 18:32:59 +00:00
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Regular expressions in the "matches" operator are provided with B<libpcre>,
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the Perl-Compatible Regular Expressions library, see B<http://www.pcre.org/>.
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2003-10-01 14:59:41 +00:00
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This manpage does not describe the capture filter syntax, which is
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different. See the tcpdump(8) manpage for a description of capture
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filters. Microsoft Windows versions use WinPcap from
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B<http://winpcap.polito.it/> for which the capture filter syntax is described
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in B<http://winpcap.polito.it/docs/man/html/group__language.html>.
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2003-10-01 14:59:41 +00:00
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=head1 SEE ALSO
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I<ethereal(1)>, I<tethereal(1)>, I<editcap(1)>, I<tcpdump(8)>, I<pcap(3)>
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2003-10-02 14:03:57 +00:00
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=head1 AUTHORS
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See the list of authors in the B<Ethereal> man page for a list of authors of
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that code.
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