PCAP-FILTER(5) File Formats and Configurations PCAP-FILTER(5)

NAME

pcap-filter - packet filter syntax

DESCRIPTION

pcap_compile(3PCAP) 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
pcap_loop(3PCAP), pcap_dispatch(3PCAP), pcap_next(3PCAP), or
pcap_next_ex(3PCAP).

The filter expression consists of one or more primitives. Primitives
usually consist of an id (name or number) preceded by one or more
qualifiers. There are three different kinds of qualifier:

type type qualifiers say what kind of thing the id name or number
refers to. Possible types are host, net, port and portrange.
E.g., `host foo', `net 128.3', `port 20', `portrange
6000-6008'. If there is no type qualifier, host is assumed.

dir dir qualifiers specify a particular transfer direction to
and/or from id. Possible directions are src, dst, src or dst,
src and dst, ra, ta, addr1, addr2, addr3, and addr4. E.g.,
`src foo', `dst net 128.3', `src or dst port ftp-data'. If
there is no dir qualifier, `src or dst' is assumed. The ra,
ta, addr1, addr2, addr3, and addr4 qualifiers are only valid
for IEEE 802.11 Wireless LAN link layers.

proto proto qualifiers restrict the match to a particular protocol.
Possible protocols are: ether, fddi, tr, wlan, ip, ip6, arp,
rarp, decnet, sctp, tcp and udp. E.g., `ether src foo', `arp
net 128.3', `tcp port 21', `udp portrange 7000-7009', `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 `(ip6 or ip or arp or rarp) src foo', `net bar'
means `(ip or arp or rarp) net bar' and `port 53' means `(tcp
or udp or sctp) port 53' (note that these examples use invalid
syntax to illustrate the principle).

[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.

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.]

In addition to the above, there are some special `primitive' keywords
that don't follow the pattern: gateway, broadcast, less, greater and
arithmetic expressions. All of these are described below.

More complex filter expressions are built up by using the words and,
or and not (or equivalently: `&&', `||' and `!' respectively) 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'.

Allowable primitives are:

dst host hostnameaddr
True if the IPv4/v6 destination field of the packet is
hostnameaddr, which may be either an address or a name.

src host hostnameaddr
True if the IPv4/v6 source field of the packet is
hostnameaddr.

host hostnameaddr
True if either the IPv4/v6 source or destination of the packet
is hostnameaddr.

Any of the above host expressions can be prepended with the
keywords, ip, arp, rarp, or ip6 as in:
ip host hostnameaddr
which is equivalent to:
ether proto \ip and host hostnameaddr
If hostnameaddr is a name with multiple IPv4/v6 addresses,
each address will be checked for a match.

ether dst ethernameaddr
True if the Ethernet destination address is ethernameaddr.
ethernameaddr may be either a name from /etc/ethers or a
numerical MAC address of the form "xx:xx:xx:xx:xx:xx",
"xx.xx.xx.xx.xx.xx", "xx-xx-xx-xx-xx-xx", "xxxx.xxxx.xxxx",
"xxxxxxxxxxxx", or various mixes of ':', '.', and '-', where
each "x" is a hex digit (0-9, a-f, or A-F).

ether src ethernameaddr
True if the Ethernet source address is ethernameaddr.

ether host ethernameaddr
True if either the Ethernet source or destination address is
ethernameaddr.

gateway host
True if the packet used host as a gateway. I.e., the Ethernet
source or destination address was host but neither the IP
source nor the IP destination was host. Host 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
ether host ethernameaddr and not host hostnameaddr
which can be used with either names or numbers for
hostnameaddr / ethernameaddr.) This syntax does not work in
IPv6-enabled configuration at this moment.

dst net netnameaddr
True if the IPv4/v6 destination address of the packet has a
network number of netnameaddr. Net 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 ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff, so IPv6
"network" matches are really always host matches, and a
network match requires a netmask length.

src net netnameaddr
True if the IPv4/v6 source address of the packet has a network
number of netnameaddr.

net netnameaddr
True if either the IPv4/v6 source or destination address of
the packet has a network number of netnameaddr.

net netaddr mask netmask
True if the IPv4 address matches netaddr with the specific
netmask. May be qualified with src or dst. Note that this
syntax is not valid for IPv6 netaddr.

net netaddr/len
True if the IPv4/v6 address matches netaddr with a netmask len
bits wide. May be qualified with src or dst.

dst port portnamenum
True if the packet is IPv4/v6 TCP, UDP or SCTP and has a
destination port value of portnamenum. The portnamenum can be
a number or a name used in /etc/services (see tcp(4P) and
udp(4P)). 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., `dst port 513' will
print both tcp/login traffic and udp/who traffic, and `port
domain' will print both tcp/domain and udp/domain traffic).

src port portnamenum
True if the packet has a source port value of portnamenum.

port portnamenum
True if either the source or destination port of the packet is
portnamenum.

dst portrange portnamenum1-portnamenum2
True if the packet is IPv4/v6 TCP, UDP or SCTP and has a
destination port value between portnamenum1 and portnamenum2
(both inclusive). portnamenum1 and portnamenum2 are
interpreted in the same fashion as the portnamenum parameter
for port.

src portrange portnamenum1-portnamenum2
True if the packet has a source port value between
portnamenum1 and portnamenum2 (both inclusive).

portrange portnamenum1-portnamenum2
True if either the source or destination port of the packet is
between portnamenum1 and portnamenum2 (both inclusive).

Any of the above port or port range expressions can be
prepended with the keywords, tcp, udp or sctp, as in:
tcp src port portnamenum
which matches only TCP packets whose source port is
portnamenum.

less length
True if the packet has a length less than or equal to length.
This is equivalent to:
len <= length

greater length
True if the packet has a length greater than or equal to
length. This is equivalent to:
len >= length

ip proto protocol
True if the packet is an IPv4 packet (see ip(4P)) of protocol
type protocol. Protocol can be a number or one of the names
recognized by getprotobyname(3) (as in e.g. `getent(1)
protocols'), typically from an entry in /etc/protocols, for
example: ah, esp, eigrp (only in Linux, FreeBSD, NetBSD,
DragonFly BSD, and macOS), icmp, igmp, igrp (only in OpenBSD),
pim, sctp, tcp, udp or vrrp. Note that most of these example
identifiers are also keywords and must be escaped via
backslash (\). Note that this primitive does not chase the
protocol header chain.

icmp Abbreviation for:
ip proto 1

ip6 proto protocol
True if the packet is an IPv6 packet of protocol type
protocol. (See `ip proto' above for the meaning of protocol.)
Note that the IPv6 variant of ICMP uses a different protocol
number, named ipv6-icmp in AIX, FreeBSD, illumos, Linux,
macOS, NetBSD, OpenBSD, Solaris and Windows. Note that this
primitive does not chase the protocol header chain.

icmp6 Abbreviation for:
ip6 proto 58

proto protocol
True if the packet is an IPv4 or IPv6 packet of protocol type
protocol. (See `ip proto' above for the meaning of protocol.)
Note that this primitive does not chase the protocol header
chain.

ah, esp, pim, sctp, tcp, udp
Abbreviations for:
proto \protocol
where protocol is one of the above protocols.

ip6 protochain protocol
True if the packet is IPv6 packet, and contains protocol
header with type protocol in its protocol header chain. (See
`ip proto' above for the meaning of protocol.) For example,
ip6 protochain 6
matches any IPv6 packet with TCP protocol header in the
protocol header chain. The packet may contain, for example,
authentication header, routing header, or hop-by-hop option
header, between IPv6 header and TCP header. The BPF code
emitted by this primitive is complex and cannot be optimized
by the BPF optimizer code, and is not supported by filter
engines in the kernel, so this can be somewhat slow, and may
cause more packets to be dropped.

ip protochain protocol
Equivalent to ip6 protochain protocol, but this is for IPv4.
(See `ip proto' above for the meaning of protocol.)

protochain protocol
True if the packet is an IPv4 or IPv6 packet of protocol type
protocol. (See `ip proto' above for the meaning of protocol.)
Note that this primitive chases the protocol header chain.

ether broadcast
True if the packet is an Ethernet broadcast packet. The ether
keyword is optional.

ip broadcast
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.

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 or because the
capture is being done on the Linux "any" interface, which can
capture on more than one interface, this check will not work
correctly.

ether multicast
True if the packet is an Ethernet multicast packet. The ether
keyword is optional. This is shorthand for `ether[0] & 1 !=
0'.

ip multicast
True if the packet is an IPv4 multicast packet.

ip6 multicast
True if the packet is an IPv6 multicast packet.

ether proto protocol
True if the packet is of ether type protocol. Protocol can be
a number or one of the names aarp, arp, atalk, decnet, ip,
ip6, ipx, iso, lat, loopback, mopdl, moprc, netbeui, rarp, sca
or stp. Note these identifiers (except loopback) are also
keywords and must be escaped via backslash (\).

[In the case of FDDI (e.g., `fddi proto \arp'), Token Ring
(e.g., `tr proto \arp'), and IEEE 802.11 wireless LANs (e.g.,
`wlan proto \arp'), 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, Token
Ring, or 802.11 header.

When filtering for most protocol identifiers on FDDI, Token
Ring, 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:

iso the filter checks the DSAP (Destination Service Access
Point) and SSAP (Source Service Access Point) fields of
the LLC header;

stp and netbeui
the filter checks the DSAP of the LLC header;

atalk the filter checks for a SNAP-format packet with an OUI
of 0x080007 and the AppleTalk etype.

In the case of Ethernet, the filter checks the Ethernet type
field for most of those protocols. The exceptions are:

iso, stp, and netbeui
the filter checks for an 802.3 frame and then checks
the LLC header as it does for FDDI, Token Ring, and
802.11;

atalk 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;

aarp the filter checks for the AppleTalk ARP etype in either
an Ethernet frame or an 802.2 SNAP frame with an OUI of
0x000000;

ipx the filter checks for the IPX etype in an Ethernet
frame, the IPX DSAP in the LLC header, the 802.3-with-
no-LLC-header encapsulation of IPX, and the IPX etype
in a SNAP frame.

ip, ip6, arp, rarp, atalk, aarp, decnet, iso, stp, ipx, netbeui
Abbreviations for:
ether proto \protocol
where protocol is one of the above protocols.

lat, moprc, mopdl
Abbreviations for:
ether proto \protocol
where protocol is one of the above protocols. Note that not
all applications using pcap(3PCAP) currently know how to parse
these protocols.

decnet src decnetaddr
True if the DECnet source address is decnetaddr, 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.]

decnet dst decnetaddr
True if the DECnet destination address is decnetaddr.

decnet host decnetaddr
True if either the DECnet source or destination address is
decnetaddr.

llc True if the packet has an 802.2 LLC header. This includes:

Ethernet packets with a length field rather than a type field
that aren't raw NetWare-over-802.3 packets;

IEEE 802.11 data packets;

Token Ring packets (no check is done for LLC frames);

FDDI packets (no check is done for LLC frames);

LLC-encapsulated ATM packets, for SunATM on Solaris.

llc type
True if the packet has an 802.2 LLC header and has the
specified type. type can be one of:

i Information (I) PDUs

s Supervisory (S) PDUs

u Unnumbered (U) PDUs

rr Receiver Ready (RR) S PDUs

rnr Receiver Not Ready (RNR) S PDUs

rej Reject (REJ) S PDUs

ui Unnumbered Information (UI) U PDUs

ua Unnumbered Acknowledgment (UA) U PDUs

disc Disconnect (DISC) U PDUs

sabme Set Asynchronous Balanced Mode Extended (SABME) U PDUs

test Test (TEST) U PDUs

xid Exchange Identification (XID) U PDUs

frmr Frame Reject (FRMR) U PDUs

inbound
Packet was received by the host performing the capture rather
than being sent by that host. This is only supported for
certain link-layer types, such as SLIP and the ``cooked''
Linux capture mode used for the ``any'' device and for some
other device types.

outbound
Packet was sent by the host performing the capture rather than
being received by that host. This is only supported for
certain link-layer types, such as SLIP and the ``cooked''
Linux capture mode used for the ``any'' device and for some
other device types.

ifindex interface_index
True if the packet was logged via the specified interface
(applies only to packets logged by the Linux "any" cooked v2
interface).

ifname interface
True if the packet was logged as coming from the specified
interface (applies only to packets logged by OpenBSD's or
FreeBSD's pf(4)).

on interface
Synonymous with the ifname modifier.

rnr num
True if the packet was logged as matching the specified PF
rule number (applies only to packets logged by OpenBSD's or
FreeBSD's pf(4)).

rulenum num
Synonymous with the rnr modifier.

reason code
True if the packet was logged with the specified PF reason
code. The known codes are: match, bad-offset, fragment,
short, normalize, and memory (applies only to packets logged
by OpenBSD's or FreeBSD's pf(4)).

rset name
True if the packet was logged as matching the specified PF
ruleset name of an anchored ruleset (applies only to packets
logged by OpenBSD's or FreeBSD's pf(4)).

ruleset name
Synonymous with the rset modifier.

srnr num
True if the packet was logged as matching the specified PF
rule number of an anchored ruleset (applies only to packets
logged by OpenBSD's or FreeBSD's pf(4)).

subrulenum num
Synonymous with the srnr modifier.

action act
True if PF took the specified action when the packet was
logged. Known actions are: pass and block and, with later
versions of pf(4), nat, rdr, binat and scrub (applies only to
packets logged by OpenBSD's or FreeBSD's pf(4)).

wlan ra ehost
True if the IEEE 802.11 RA is ehost. The RA field is used in
all frames except for management frames.

wlan ta ehost
True if the IEEE 802.11 TA is ehost. The TA field is used in
all frames except for management frames and CTS (Clear To
Send) and ACK (Acknowledgment) control frames.

wlan addr1 ehost
True if the first IEEE 802.11 address is ehost.

wlan addr2 ehost
True if the second IEEE 802.11 address, if present, is ehost.
The second address field is used in all frames except for CTS
(Clear To Send) and ACK (Acknowledgment) control frames.

wlan addr3 ehost
True if the third IEEE 802.11 address, if present, is ehost.
The third address field is used in management and data frames,
but not in control frames.

wlan addr4 ehost
True if the fourth IEEE 802.11 address, if present, is ehost.
The fourth address field is only used for WDS (Wireless
Distribution System) frames.

type wlan_type
True if the IEEE 802.11 frame type matches the specified
wlan_type. Valid wlan_types are: mgt, ctl and data.

type wlan_type subtype wlan_subtype
True if the IEEE 802.11 frame type matches the specified
wlan_type and frame subtype matches the specified
wlan_subtype.

If the specified wlan_type is mgt, then valid wlan_subtypes
are: assoc-req, assoc-resp, reassoc-req, reassoc-resp, probe-
req, probe-resp, beacon, atim, disassoc, auth and deauth.

If the specified wlan_type is ctl, then valid wlan_subtypes
are: ps-poll, rts, cts, ack, cf-end and cf-end-ack.

If the specified wlan_type is data, then valid wlan_subtypes
are: data, data-cf-ack, data-cf-poll, data-cf-ack-poll, null,
cf-ack, cf-poll, cf-ack-poll, qos-data, qos-data-cf-ack,
qos-data-cf-poll, qos-data-cf-ack-poll, qos, qos-cf-poll and
qos-cf-ack-poll.

subtype wlan_subtype
True if the IEEE 802.11 frame subtype matches the specified
wlan_subtype and frame has the type to which the specified
wlan_subtype belongs.

dir direction
True if the IEEE 802.11 frame direction matches the specified
direction. Valid directions are: nods, tods, fromds, dstods,
or a numeric value.

vlan [vlan_id]
True if the packet is an IEEE 802.1Q VLAN packet. If the
optional vlan_id is specified, only true if the packet has the
specified vlan_id. Note that the first vlan keyword
encountered in an expression changes the decoding offsets for
the remainder of the expression on the assumption that the
packet is a VLAN packet. The `vlan [vlan_id]` keyword may be
used more than once, to filter on VLAN hierarchies. Each use
of that keyword increments the filter offsets by 4.

For example:
vlan 100 && vlan 200
filters on VLAN 200 encapsulated within VLAN 100, and
vlan && vlan 300 && ip
filters IPv4 protocol encapsulated in VLAN 300 encapsulated
within any higher order VLAN.

mpls [label_num]
True if the packet is an MPLS packet. If the optional
label_num is specified, only true if the packet has the
specified label_num. Note that the first mpls keyword
encountered in an expression changes the decoding offsets for
the remainder of the expression on the assumption that the
packet is a MPLS-encapsulated IP packet. The `mpls
[label_num]` keyword may be used more than once, to filter on
MPLS hierarchies. Each use of that keyword increments the
filter offsets by 4.

For example:
mpls 100000 && mpls 1024
filters packets with an outer label of 100000 and an inner
label of 1024, and
mpls && mpls 1024 && host 192.9.200.1
filters packets to or from 192.9.200.1 with an inner label of
1024 and any outer label.

pppoed True if the packet is a PPP-over-Ethernet Discovery packet
(Ethernet type 0x8863).

pppoes [session_id]
True if the packet is a PPP-over-Ethernet Session packet
(Ethernet type 0x8864). If the optional session_id is
specified, only true if the packet has the specified
session_id. Note that the first pppoes keyword encountered in
an expression changes the decoding offsets for the remainder
of the expression on the assumption that the packet is a PPPoE
session packet.

For example:
pppoes 0x27 && ip
filters IPv4 protocol encapsulated in PPPoE session id 0x27.

geneve [vni]
True if the packet is a Geneve packet (UDP port 6081). If the
optional vni is specified, only true if the packet has the
specified vni. Note that when the geneve keyword is
encountered in an expression, it changes the decoding offsets
for the remainder of the expression on the assumption that the
packet is a Geneve packet.

For example:
geneve 0xb && ip
filters IPv4 protocol encapsulated in Geneve with VNI 0xb.
This will match both IPv4 directly encapsulated in Geneve as
well as IPv4 contained inside an Ethernet frame.

iso proto protocol
True if the packet is an OSI packet of protocol type protocol.
Protocol can be a number or one of the names clnp, esis, or
isis.

clnp, esis, isis
Abbreviations for:
iso proto \protocol
where protocol is one of the above protocols.

l1, l2, iih, lsp, snp, csnp, psnp
Abbreviations for IS-IS PDU types.

vpi n True if the packet is an ATM packet, for SunATM on Solaris,
with a virtual path identifier of n.

vci n True if the packet is an ATM packet, for SunATM on Solaris,
with a virtual channel identifier of n.

lane True if the packet is an ATM packet, for SunATM on Solaris,
and is an ATM LANE packet. Note that the first lane keyword
encountered in an expression changes the tests done in the
remainder of the expression on the assumption that the packet
is either a LANE emulated Ethernet packet or a LANE LE Control
packet. If lane isn't specified, the tests are done under the
assumption that the packet is an LLC-encapsulated packet.

oamf4s True if the packet is an ATM packet, for SunATM on Solaris,
and is a segment OAM F4 flow cell (VPI=0 & VCI=3).

oamf4e True if the packet is an ATM packet, for SunATM on Solaris,
and is an end-to-end OAM F4 flow cell (VPI=0 & VCI=4).

oamf4 True if the packet is an ATM packet, for SunATM on Solaris,
and is a segment or end-to-end OAM F4 flow cell (VPI=0 &
(VCI=3 | VCI=4)).

oam True if the packet is an ATM packet, for SunATM on Solaris,
and is a segment or end-to-end OAM F4 flow cell (VPI=0 &
(VCI=3 | VCI=4)).

metac True if the packet is an ATM packet, for SunATM on Solaris,
and is on a meta signaling circuit (VPI=0 & VCI=1).

bcc True if the packet is an ATM packet, for SunATM on Solaris,
and is on a broadcast signaling circuit (VPI=0 & VCI=2).

sc True if the packet is an ATM packet, for SunATM on Solaris,
and is on a signaling circuit (VPI=0 & VCI=5).

ilmic True if the packet is an ATM packet, for SunATM on Solaris,
and is on an ILMI circuit (VPI=0 & VCI=16).

connectmsg
True if the packet is an ATM packet, for SunATM on Solaris,
and is on a signaling circuit and is a Q.2931 Setup, Call
Proceeding, Connect, Connect Ack, Release, or Release Done
message.

metaconnect
True if the packet is an ATM packet, for SunATM on Solaris,
and is on a meta signaling circuit and is a Q.2931 Setup, Call
Proceeding, Connect, Release, or Release Done message.

expr1 relop expr2
True if the relation holds. Relop is one of {>, <, >=, <=, =,
==, !=} (where = means the same as ==). Each of expr1 and
expr2 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.

The % and ^ operators are currently only supported for
filtering in the kernel on particular operating systems (for
example: FreeBSD, Linux with 3.7 and later kernels, NetBSD);
on all other systems (for example: AIX, illumos, Solaris,
OpenBSD), if those operators are used, filtering will be done
in user mode, which will increase the overhead of capturing
packets and may cause more packets to be dropped.

The length operator, indicated by the keyword len, gives the
length of the packet.

To access data inside the packet, use the following syntax:
proto [ expr : size ]
Proto is one of arp, atalk, carp, decnet, ether, fddi, icmp,
icmp6, igmp, igrp, ip, ip6, lat, link, mopdl, moprc, pim, ppp,
radio, rarp, sca, sctp, slip, tcp, tr, udp, vrrp or wlan, and
indicates the protocol layer for the index operation. (ether,
fddi, link, ppp, slip, tr and wlan all refer to the link
layer. radio refers to the "radio header" added to some 802.11
captures.) Note that tcp, udp 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 expr. Size 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.

For example, `ether[0] & 1 != 0' catches all multicast
traffic. The expression `ip[0] & 0xf != 5' catches all IPv4
packets with options. The expression `ip[6:2] & 0x1fff = 0'
catches only unfragmented IPv4 datagrams and frag zero of
fragmented IPv4 datagrams. This check is implicitly applied
to the tcp and udp index operations. For instance, tcp[0]
always means the first byte of the TCP header, 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: icmptype (ICMP type field), icmp6type
(ICMPv6 type field), icmpcode (ICMP code field), icmp6code
(ICMPv6 code field) and tcpflags (TCP flags field).

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

The following ICMPv6 type field values are available:
icmp6-destinationunreach, icmp6-packettoobig,
icmp6-timeexceeded, icmp6-parameterproblem, icmp6-echo,
icmp6-echoreply, icmp6-multicastlistenerquery,
icmp6-multicastlistenerreportv1, icmp6-multicastlistenerdone,
icmp6-routersolicit, icmp6-routeradvert,
icmp6-neighborsolicit, icmp6-neighboradvert, icmp6-redirect,
icmp6-routerrenum, icmp6-nodeinformationquery,
icmp6-nodeinformationresponse,
icmp6-ineighbordiscoverysolicit,
icmp6-ineighbordiscoveryadvert,
icmp6-multicastlistenerreportv2,
icmp6-homeagentdiscoveryrequest,
icmp6-homeagentdiscoveryreply, icmp6-mobileprefixsolicit,
icmp6-mobileprefixadvert, icmp6-certpathsolicit,
icmp6-certpathadvert, icmp6-multicastrouteradvert,
icmp6-multicastroutersolicit, icmp6-multicastrouterterm.

The following TCP flags field values are available: tcp-fin,
tcp-syn, tcp-rst, tcp-push, tcp-ack, tcp-urg, tcp-ece, tcp-
cwr.

Primitives may be combined using:

A parenthesized group of primitives and operators.

Negation (`!' or `not').

Concatenation (`&&' or `and').

Alternation (`||' or `or').

Negation has the highest precedence. Alternation and concatenation
have equal precedence and associate left to right.

If an identifier is given without a keyword, the most recent keyword
is assumed. For example,
not host vs and ace
is short for
not host vs and host ace
which should not be confused with
not (host vs or ace)

EXAMPLES

To select all packets arriving at or departing from `sundown':
host sundown

To select traffic between `helios' and either `hot' or `ace':
host helios and (hot or ace)

To select all IPv4 packets between `ace' and any host except
`helios':
ip host ace and not helios

To select all traffic between local hosts and hosts at Berkeley:
net ucb-ether

To select all FTP traffic through Internet gateway `snup':
gateway snup and (port ftp or ftp-data)

To select IPv4 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).
ip and not net localnet

To select the start and end packets (the SYN and FIN packets) of each
TCP conversation that involves a non-local host.
tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net localnet

To select the TCP packets with flags RST and ACK both set. (i.e.
select only the RST and ACK flags in the flags field, and if the
result is "RST and ACK both set", match)
tcp[tcpflags] & (tcp-rst|tcp-ack) == (tcp-rst|tcp-ack)

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.)
tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)

To select IPv4 packets longer than 576 bytes sent through gateway
`snup':
gateway snup and ip[2:2] > 576

To select IPv4 broadcast or multicast packets that were not sent via
Ethernet broadcast or multicast:
ether[0] & 1 = 0 and ip[16] >= 224

To select all ICMP packets that are not echo requests/replies (i.e.,
not ping packets):
icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply
icmp6[icmp6type] != icmp6-echo and icmp6[icmp6type] != icmp6-echoreply

BACKWARD COMPATIBILITY

The ICMPv6 type code names, as well as the tcp-ece and tcp-cwr TCP
flag names became available in libpcap 1.9.0.

The geneve keyword became available in libpcap 1.8.0.

The ifindex keyword became available in libpcap 1.10.0.

SEE ALSO

pcap(3PCAP)

BUGS

To report a security issue please send an e-mail to
security@tcpdump.org.

To report bugs and other problems, contribute patches, request a
feature, provide generic feedback etc please see the file
CONTRIBUTING.md in the libpcap source tree root.

Filter expressions on fields other than those in Token Ring headers
will not correctly handle source-routed Token Ring packets.

Filter expressions on fields other than those in 802.11 headers will
not correctly handle 802.11 data packets with both To DS and From DS
set.

`ip6 proto' should chase header chain, but at this moment it does
not. `ip6 protochain' is supplied for this behavior. For example,
to match IPv6 fragments: `ip6 protochain 44'

Arithmetic expression against transport layer headers, like tcp[0],
does not work against IPv6 packets. It only looks at IPv4 packets.

13 June 2023 PCAP-FILTER(5)