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.TH PCAP-FILTER 3 2008-01-06
.SH NAME
pcap-filter \- packet filter syntax
.br
.ad
.SH DESCRIPTION
.LP
.B pcap_compile()
is used to compile a string into a filter program.
The resulting filter program can then be applied to
some stream of packets to determine which packets will be supplied to
.BR pcap_loop() ,
.BR pcap_dispatch() ,
.BR pcap_next() ,
or
.BR pcap_next_ex() .
.LP
The \fIfilter expression\fP consists of one or more
.IR primitives .
Primitives usually consist of an
.I id
(name or number) preceded by one or more qualifiers.
There are three
different kinds of qualifier:
.IP \fItype\fP
qualifiers say what kind of thing the id name or number refers to.
Possible types are
.BR host ,
.B net ,
.B and port .
E.g., `host foo', `net 128.3', `port 20'.
If there is no type
qualifier,
.B host
is assumed.
.IP \fIdir\fP
qualifiers specify a particular transfer direction to and/or from
.IR id .
Possible directions are
.BR src ,
.BR dst ,
.BR "src or dst" ,
.BR "src and dst" ,
.BR ra ,
.BR ta ,
.BR addr1 ,
.BR addr2 ,
.BR addr3 ,
and
.BR addr4 .
E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'.
If
there is no dir qualifier,
.B "src or dst"
is assumed.
The
.BR ra ,
.BR ta ,
.BR addr1 ,
.BR addr2 ,
.BR addr3 ,
and
.B addr4
qualifiers are only valid for IEEE 802.11 Wireless LAN link layers.
For some link layers, such as SLIP and the ``cooked'' Linux capture mode
used for the ``any'' device and for some other device types, the
.B inbound
and
.B outbound
qualifiers can be used to specify a desired direction.
.IP \fIproto\fP
qualifiers restrict the match to a particular protocol.
Possible
protos are:
.BR ether ,
.BR fddi ,
.BR tr ,
.BR wlan ,
.BR ip ,
.BR ip6 ,
.BR arp ,
.BR rarp ,
.BR decnet ,
.B tcp
and
.BR udp .
E.g., `ether src foo', `arp net 128.3', `tcp port 21'
`wlan addr2 0:2:3:4:5:6'.
If there is
no proto qualifier, all protocols consistent with the type are
assumed.
E.g., `src foo' means `(ip or arp or rarp) src foo'
(except the latter is not legal syntax), `net bar' means `(ip or
arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'.
.LP
[`fddi' is actually an alias for `ether'; the parser treats them
identically as meaning ``the data link level used on the specified
network interface.''  FDDI headers contain Ethernet-like source
and destination addresses, and often contain Ethernet-like packet
types, so you can filter on these FDDI fields just as with the
analogous Ethernet fields.
FDDI headers also contain other fields,
but you cannot name them explicitly in a filter expression.
.LP
Similarly, `tr' and `wlan' are aliases for `ether'; the previous
paragraph's statements about FDDI headers also apply to Token Ring
and 802.11 wireless LAN headers.  For 802.11 headers, the destination
address is the DA field and the source address is the SA field; the
BSSID, RA, and TA fields aren't tested.]
.LP
In addition to the above, there are some special `primitive' keywords
that don't follow the pattern:
.BR gateway ,
.BR broadcast ,
.BR less ,
.B greater
and arithmetic expressions.
All of these are described below.
.LP
More complex filter expressions are built up by using the words
.BR and ,
.B or
and
.B not
to combine primitives.
E.g., `host foo and not port ftp and not port ftp-data'.
To save typing, identical qualifier lists can be omitted.
E.g.,
`tcp dst port ftp or ftp-data or domain' is exactly the same as
`tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
.LP
Allowable primitives are:
.IP "\fBdst host \fIhost\fR"
True if the IPv4/v6 destination field of the packet is \fIhost\fP,
which may be either an address or a name.
.IP "\fBsrc host \fIhost\fR"
True if the IPv4/v6 source field of the packet is \fIhost\fP.
.IP "\fBhost \fIhost\fP"
True if either the IPv4/v6 source or destination of the packet is \fIhost\fP.
.IP
Any of the above host expressions can be prepended with the keywords,
\fBip\fP, \fBarp\fP, \fBrarp\fP, or \fBip6\fP as in:
.in +.5i
.nf
\fBip host \fIhost\fR
.fi
.in -.5i
which is equivalent to:
.in +.5i
.nf
\fBether proto \fI\\ip\fB and host \fIhost\fR
.fi
.in -.5i
If \fIhost\fR is a name with multiple IP addresses, each address will
be checked for a match.
.IP "\fBether dst \fIehost\fP"
True if the Ethernet destination address is \fIehost\fP.
\fIEhost\fP
may be either a name from /etc/ethers or a number (see
.IR ethers (3N)
for numeric format).
.IP "\fBether src \fIehost\fP"
True if the Ethernet source address is \fIehost\fP.
.IP "\fBether host \fIehost\fP"
True if either the Ethernet source or destination address is \fIehost\fP.
.IP "\fBgateway\fP \fIhost\fP"
True if the packet used \fIhost\fP as a gateway.
I.e., the Ethernet
source or destination address was \fIhost\fP but neither the IP source
nor the IP destination was \fIhost\fP.
\fIHost\fP must be a name and
must be found both by the machine's host-name-to-IP-address resolution
mechanisms (host name file, DNS, NIS, etc.) and by the machine's
host-name-to-Ethernet-address resolution mechanism (/etc/ethers, etc.).
(An equivalent expression is
.in +.5i
.nf
\fBether host \fIehost \fBand not host \fIhost\fR
.fi
.in -.5i
which can be used with either names or numbers for \fIhost / ehost\fP.)
This syntax does not work in IPv6-enabled configuration at this moment.
.IP "\fBdst net \fInet\fR"
True if the IPv4/v6 destination address of the packet has a network
number of \fInet\fP.
\fINet\fP may be either a name from the networks database
(/etc/networks, etc.) or a network number.
An IPv4 network number can be written as a dotted quad (e.g., 192.168.1.0),
dotted triple (e.g., 192.168.1), dotted pair (e.g, 172.16), or single
number (e.g., 10); the netmask is 255.255.255.255 for a dotted quad
(which means that it's really a host match), 255.255.255.0 for a dotted
triple, 255.255.0.0 for a dotted pair, or 255.0.0.0 for a single number.
An IPv6 network number must be written out fully; the netmask is
ff:ff:ff:ff:ff:ff:ff:ff, so IPv6 "network" matches are really always
host matches, and a network match requires a netmask length.
.IP "\fBsrc net \fInet\fR"
True if the IPv4/v6 source address of the packet has a network
number of \fInet\fP.
.IP "\fBnet \fInet\fR"
True if either the IPv4/v6 source or destination address of the packet has a network
number of \fInet\fP.
.IP "\fBnet \fInet\fR \fBmask \fInetmask\fR"
True if the IPv4 address matches \fInet\fR with the specific \fInetmask\fR.
May be qualified with \fBsrc\fR or \fBdst\fR.
Note that this syntax is not valid for IPv6 \fInet\fR.
.IP "\fBnet \fInet\fR/\fIlen\fR"
True if the IPv4/v6 address matches \fInet\fR with a netmask \fIlen\fR
bits wide.
May be qualified with \fBsrc\fR or \fBdst\fR.
.IP "\fBdst port \fIport\fR"
True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a
destination port value of \fIport\fP.
The \fIport\fP can be a number or a name used in /etc/services (see
.IR tcp (4)
and
.IR udp (4)).
If a name is used, both the port
number and protocol are checked.
If a number or ambiguous name is used,
only the port number is checked (e.g., \fBdst port 513\fR will print both
tcp/login traffic and udp/who traffic, and \fBport domain\fR will print
both tcp/domain and udp/domain traffic).
.IP "\fBsrc port \fIport\fR"
True if the packet has a source port value of \fIport\fP.
.IP "\fBport \fIport\fR"
True if either the source or destination port of the packet is \fIport\fP.
.IP "\fBless \fIlength\fR"
True if the packet has a length less than or equal to \fIlength\fP.
This is equivalent to:
.in +.5i
.nf
\fBlen <= \fIlength\fP.
.fi
.in -.5i
.IP "\fBgreater \fIlength\fR"
True if the packet has a length greater than or equal to \fIlength\fP.
This is equivalent to:
.in +.5i
.nf
\fBlen >= \fIlength\fP.
.fi
.in -.5i
.IP "\fBip proto \fIprotocol\fR"
True if the packet is an IPv4 packet (see
.IR ip (4P))
of protocol type \fIprotocol\fP.
\fIProtocol\fP can be a number or one of the names
\fBicmp\fP, \fBicmp6\fP, \fBigmp\fP, \fBigrp\fP, \fBpim\fP, \fBah\fP,
\fBesp\fP, \fBvrrp\fP, \fBudp\fP, or \fBtcp\fP.
Note that the identifiers \fBtcp\fP, \fBudp\fP, and \fBicmp\fP are also
keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell.
Note that this primitive does not chase the protocol header chain.
.IP "\fBip6 proto \fIprotocol\fR"
True if the packet is an IPv6 packet of protocol type \fIprotocol\fP.
Note that this primitive does not chase the protocol header chain.
.IP "\fBether broadcast\fR"
True if the packet is an Ethernet broadcast packet.
The \fIether\fP
keyword is optional.
.IP "\fBip broadcast\fR"
True if the packet is an IPv4 broadcast packet.
It checks for both the all-zeroes and all-ones broadcast conventions,
and looks up the subnet mask on the interface on which the capture is
being done.
.IP
If the subnet mask of the interface on which the capture is being done
is not available, either because the interface on which capture is being
done has no netmask this check will not work correctly.
.IP "\fBether multicast\fR"
True if the packet is an Ethernet multicast packet.
The \fBether\fP
keyword is optional.
This is shorthand for `\fBether[0] & 1 != 0\fP'.
.IP "\fBip multicast\fR"
True if the packet is an IPv4 multicast packet.
.IP "\fBip6 multicast\fR"
True if the packet is an IPv6 multicast packet.
.IP  "\fBether proto \fIprotocol\fR"
True if the packet is of ether type \fIprotocol\fR.
\fIProtocol\fP can be a number or one of the names
\fBip\fP, \fBip6\fP, \fBarp\fP, \fBrarp\fP, \fBatalk\fP,
\fBdecnet\fP, \fBsca\fP, \fBlat\fP or \fBstp\fP.
Note these identifiers are also keywords
and must be escaped via backslash (\\).
.IP
[In the case of FDDI (e.g., `\fBfddi protocol arp\fR')
and IEEE 802.11 wireless LANS (e.g.,
`\fBwlan protocol arp\fR'), for most of those protocols, the
protocol identification comes from the 802.2 Logical Link Control (LLC)
header, which is usually layered on top of the FDDI or 802.11 header.
.IP
When filtering for most protocol identifiers on FDDI or 802.11,
the filter checks only the protocol ID field of an LLC header
in so-called SNAP format with an Organizational Unit Identifier (OUI) of
0x000000, for encapsulated Ethernet; it doesn't check whether the packet
is in SNAP format with an OUI of 0x000000.
The exceptions are:
.RS
.TP
\fBiso\fP
the filter checks the DSAP (Destination Service Access Point) and
SSAP (Source Service Access Point) fields of the LLC header;
.TP
\fBstp\fP
the filter checks the DSAP of the LLC header;
.TP
\fBatalk\fP
the filter checks for a SNAP-format packet with an OUI of 0x080007
and the AppleTalk etype.
.RE
.IP
In the case of Ethernet, the filter checks the Ethernet type field
for most of those protocols.  The exceptions are:
.RS
.TP
\fBiso\fP and \fBstp\fP
the filter checks for an 802.3 frame and then checks the LLC header as
it does for FDDI and 802.11;
.TP
\fBatalk\fP
the filter checks both for the AppleTalk etype in an Ethernet frame and
for a SNAP-format packet as it does for FDDI, Token Ring, and 802.11;
.TP
.RE
.IP "\fBdecnet src \fIhost\fR"
True if the DECNET source address is
.IR host ,
which may be an address of the form ``10.123'', or a DECNET host
name.
[DECNET host name support is only available on ULTRIX systems
that are configured to run DECNET.]
.IP "\fBdecnet dst \fIhost\fR"
True if the DECNET destination address is
.IR host .
.IP "\fBdecnet host \fIhost\fR"
True if either the DECNET source or destination address is
.IR host .
.IP "\fBifname \fIinterface\fR"
True if the packet was logged as coming from the specified interface (applies
only to packets logged by
.BR pf (4)).
.IP "\fBon \fIinterface\fR"
Synonymous with the
.B ifname
modifier.
.IP "\fBrnr \fInum\fR"
True if the packet was logged as matching the specified PF rule number
(applies only to packets logged by
.BR pf (4)).
.IP "\fBrulenum \fInum\fR"
Synonymous with the
.B rnr
modifier.
.IP "\fBreason \fIcode\fR"
True if the packet was logged with the specified PF reason code.  The known
codes are:
.BR match ,
.BR bad-offset ,
.BR fragment ,
.BR short ,
.BR normalize ,
and
.B memory
(applies only to packets logged by
.BR pf (4)).
.IP "\fBrset \fIname\fR"
True if the packet was logged as matching the specified PF ruleset
name of an anchored ruleset (applies only to packets logged by
.BR pf (4)).
.IP "\fBruleset \fIname\fR"
Synonymous with the
.B rset
modifier.
.IP "\fBsrnr \fInum\fR"
True if the packet was logged as matching the specified PF rule number
of an anchored ruleset (applies only to packets logged by
.BR pf (4)).
.IP "\fBsubrulenum \fInum\fR"
Synonymous with the
.B srnr
modifier.
.IP "\fBaction \fIact\fR"
True if PF took the specified action when the packet was logged.  Known actions
are:
.B pass
and
.B block
and, with later versions of
.BR pf (4)),
.BR nat ,
.BR rdr ,
.B binat
and
.B scrub
(applies only to packets logged by
.BR pf (4)).
.IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBatalk\fR, \fBdecnet\fR, \fBiso\fR, \fBstp\fP"
Abbreviations for:
.in +.5i
.nf
\fBether proto \fIp\fR
.fi
.in -.5i
where \fIp\fR is one of the above protocols.
.IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR"
Abbreviations for:
.in +.5i
.nf
\fBether proto \fIp\fR
.fi
.in -.5i
where \fIp\fR is one of the above protocols.
Note that not all applications using
.BR pcap (3)
currently know how to parse these protocols.
.IP "\fBtype \fIwlan_type\fR"
True if the IEEE 802.11 frame type matches the specified \fIwlan_type\fR.
Valid \fIwlan_type\fRs are:
\fBmgt\fP,
\fBctl\fP
and \fBdata\fP.
.IP "\fBtype \fIwlan_type \fBsubtype \fIwlan_subtype\fR"
True if the IEEE 802.11 frame type matches the specified \fIwlan_type\fR
and frame subtype matches the specified \fIwlan_subtype\fR.
.IP
If the specified \fIwlan_type\fR is \fBmgt\fP,
then valid \fIwlan_subtype\fRs are:
\fBassoc-req\fP,
\fBassoc-resp\fP,
\fBreassoc-req\fP,
\fBreassoc-resp\fP,
\fBprobe-req\fP,
\fBprobe-resp\fP,
\fBbeacon\fP,
\fBatim\fP,
\fBdisassoc\fP,
\fBauth\fP and
\fBdeauth\fP.
.IP
If the specified \fIwlan_type\fR is \fBctl\fP,
then valid \fIwlan_subtype\fRs are:
\fBps-poll\fP,
\fBrts\fP,
\fBcts\fP,
\fBack\fP,
\fBcf-end\fP and
\fBcf-end-ack\fP.
.IP
If the specified \fIwlan_type\fR is \fBdata\fP,
then valid \fIwlan_subtype\fRs are:
\fBdata\fP,
\fBdata-cf-ack\fP,
\fBdata-cf-poll\fP,
\fBdata-cf-ack-poll\fP,
\fBnull\fP,
\fBcf-ack\fP,
\fBcf-poll\fP,
\fBcf-ack-poll\fP,
\fBqos-data\fP,
\fBqos-data-cf-ack\fP,
\fBqos-data-cf-poll\fP,
\fBqos-data-cf-ack-poll\fP,
\fBqos\fP,
\fBqos-cf-poll\fP and
\fBqos-cf-ack-poll\fP.
.IP "\fBsubtype \fIwlan_subtype\fR"
True if the IEEE 802.11 frame subtype matches the specified \fIwlan_subtype\fR
and frame has the type to which the specified \fIwlan_subtype\fR belongs.
.IP "\fBdir \fIdir\fR"
True if the IEEE 802.11 frame direction matches the specified
.IR dir .
Valid directions are:
.BR nods ,
.BR tods ,
.BR fromds ,
.BR dstods ,
or a numeric value.
.IP "\fBvlan \fI[vlan_id]\fR"
True if the packet is an IEEE 802.1Q VLAN packet.
If \fI[vlan_id]\fR is specified, only true if the packet has the specified
\fIvlan_id\fR.
Note that the first \fBvlan\fR keyword encountered in \fIexpression\fR
changes the decoding offsets for the remainder of \fIexpression\fR on
the assumption that the packet is a VLAN packet.  The \fBvlan
\fI[vlan_id]\fR expression may be used more than once, to filter on VLAN
hierarchies.  Each use of that expression increments the filter offsets
by 4.
.IP
For example:
.in +.5i
.nf
\fBvlan 100 && vlan 200\fR
.fi
.in -.5i
filters on VLAN 200 encapsulated within VLAN 100, and
.in +.5i
.nf
\fBvlan && vlan 300 && ip\fR
.fi
.in -.5i
filters IPv4 protocols encapsulated in VLAN 300 encapsulated within any
higher order VLAN.
.IP "\fBmpls \fI[label]\fR"
True if the packet is an MPLS (Multi-Protocol Label Switching) packet.
If \fIlabel\fR is specified, only true if the packet has the specified
\fIlabel\fR.
Note that the first \fBmpls\fR keyword encountered in \fIexpression\fR
changes the decoding offsets for the remainder of \fIexpression\fR on
the assumption that the packet is an MPLS packet.  The \fBmpls
\fI[label]\fR expression may be used more than once, to filter on MPLS
labels stack.  Each use of that expression increments the filter offsets
by 4.
.IP
For example:
.in +.5i
.nf
\fBmpls 42 && mpls 12\fR
.fi
.in -.5i
filters on MPLS label 42 first and requires the next label to be 12 and
.in +.5i
.nf
\fBmpls 42 && net 192.0.2.0/24\fR
.fi
.in -.5i
filters on network 192.0.2.0/24 transported inside packets with label 42.
.IP  "\fBtcp\fR, \fBudp\fR, \fBicmp\fR"
Abbreviations for:
.in +.5i
.nf
\fBip proto \fIp\fR\fB or ip6 proto \fIp\fR
.fi
.in -.5i
where \fIp\fR is one of the above protocols.
.IP  "\fIexpr relop expr\fR"
True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =,
!=, and \fIexpr\fR is an arithmetic expression composed of integer
constants (expressed in standard C syntax), the normal binary operators
[+, -, *, /, &, |, <<, >>], a length operator, and special packet data
accessors.  Note that all comparisons are unsigned, so that, for example,
0x80000000 and 0xffffffff are > 0.
To access
data inside the packet, use the following syntax:
.in +.5i
.nf
\fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR
.fi
.in -.5i
\fIProto\fR is one of \fBether, fddi, tr, wlan, ppp, slip, link,
ip, arp, rarp, tcp, udp, icmp, ip6\fR or \fBradio\fR, and
indicates the protocol layer for the index operation.
(\fBether, fddi, wlan, tr, ppp, slip\fR and \fBlink\fR all refer to the
link layer. \fBradio\fR refers to the "radio header" added to some
802.11 captures.)
Note that \fItcp, udp\fR and other upper-layer protocol types only
apply to IPv4, not IPv6 (this will be fixed in the future).
The byte offset, relative to the indicated protocol layer, is
given by \fIexpr\fR.
\fISize\fR is optional and indicates the number of bytes in the
field of interest; it can be either one, two, or four, and defaults to one.
The length operator, indicated by the keyword \fBlen\fP, gives the
length of the packet.

For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic.
The expression `\fBip[0] & 0xf != 5\fP'
catches all IPv4 packets with options.
The expression
`\fBip[6:2] & 0x1fff = 0\fP'
catches only unfragmented IPv4 datagrams and frag zero of fragmented
IPv4 datagrams.
This check is implicitly applied to the \fBtcp\fP and \fBudp\fP
index operations.
For instance, \fBtcp[0]\fP always means the first
byte of the TCP \fIheader\fP, and never means the first byte of an
intervening fragment.

Some offsets and field values may be expressed as names rather than
as numeric values.
The following protocol header field offsets are
available: \fBicmptype\fP (ICMP type field), \fBicmpcode\fP (ICMP
code field), and \fBtcpflags\fP (TCP flags field).

The following ICMP type field values are available: \fBicmp-echoreply\fP,
\fBicmp-unreach\fP, \fBicmp-sourcequench\fP, \fBicmp-redirect\fP,
\fBicmp-echo\fP, \fBicmp-routeradvert\fP, \fBicmp-routersolicit\fP,
\fBicmp-timxceed\fP, \fBicmp-paramprob\fP, \fBicmp-tstamp\fP,
\fBicmp-tstampreply\fP, \fBicmp-ireq\fP, \fBicmp-ireqreply\fP,
\fBicmp-maskreq\fP, \fBicmp-maskreply\fP.

The following TCP flags field values are available: \fBtcp-fin\fP,
\fBtcp-syn\fP, \fBtcp-rst\fP, \fBtcp-push\fP,
\fBtcp-ack\fP, \fBtcp-urg\fP.
.LP
Primitives may be combined using:
.IP
A parenthesized group of primitives and operators
(parentheses are special to the Shell and must be escaped).
.IP
Negation (`\fB!\fP' or `\fBnot\fP').
.IP
Concatenation (`\fB&&\fP' or `\fBand\fP').
.IP
Alternation (`\fB||\fP' or `\fBor\fP').
.LP
Negation has highest precedence.
Alternation and concatenation have equal precedence and associate
left to right.
Note that explicit \fBand\fR tokens, not juxtaposition,
are now required for concatenation.
.LP
If an identifier is given without a keyword, the most recent keyword
is assumed.
For example,
.in +.5i
.nf
\fBnot host vs and ace\fR
.fi
.in -.5i
is short for
.in +.5i
.nf
\fBnot host vs and host ace\fR
.fi
.in -.5i
which should not be confused with
.in +.5i
.nf
\fBnot ( host vs or ace )\fR
.fi
.in -.5i
.SH EXAMPLES
.LP
To select all packets arriving at or departing from \fIsundown\fP:
.RS
.nf
\fBhost sundown\fP
.fi
.RE
.LP
To select traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR:
.RS
.nf
\fBhost helios and \\( hot or ace \\)\fP
.fi
.RE
.LP
To select all IP packets between \fIace\fR and any host except \fIhelios\fR:
.RS
.nf
\fBip host ace and not helios\fP
.fi
.RE
.LP
To select all traffic between local hosts and hosts at Berkeley:
.RS
.nf
.B
net ucb-ether
.fi
.RE
.LP
To select all ftp traffic through internet gateway \fIsnup\fP:
.RS
.nf
.B
gateway snup and (port ftp or ftp-data)
.fi
.RE
.LP
To select traffic neither sourced from nor destined for local hosts
(if you gateway to one other net, this stuff should never make it
onto your local net).
.RS
.nf
.B
ip and not net \fIlocalnet\fP
.fi
.RE
.LP
To select the start and end packets (the SYN and FIN packets) of each
TCP conversation that involves a non-local host.
.RS
.nf
.B
tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net \fIlocalnet\fP
.fi
.RE
.LP
To select all IPv4 HTTP packets to and from port 80, i.e. print only
packets that contain data, not, for example, SYN and FIN packets and
ACK-only packets.  (IPv6 is left as an exercise for the reader.)
.RS
.nf
.B
tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)
.fi
.RE
.LP
To select IP packets longer than 576 bytes sent through gateway \fIsnup\fP:
.RS
.nf
.B
gateway snup and ip[2:2] > 576
.fi
.RE
.LP
To select IP broadcast or multicast packets that were
.I not
sent via Ethernet broadcast or multicast:
.RS
.nf
.B
ether[0] & 1 = 0 and ip[16] >= 224
.fi
.RE
.LP
To select all ICMP packets that are not echo requests/replies (i.e., not
ping packets):
.RS
.nf
.B
icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply
.fi
.RE
.SH "SEE ALSO"
.BR pcap ( 3 ),
.BR tcpdump ( 8 )
.SH AUTHORS
The original authors are:
.LP
Van Jacobson,
Craig Leres and
Steven McCanne, all of the
Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
.\" Fixes should be submitted to http://sourceforge.net/tracker/?group_id=53067