pcap-filter(7)
NAME
pcap-filter - packet filter syntax
DESCRIPTION
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 pcap_loop(),
pcap_dispatch(), pcap_next(), or pcap_next_ex().
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. 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 inbound and outbound
qualifiers can be used to specify a desired direction.
proto proto qualifiers restrict the match to a particular protocol.
Possible protos are: ether, fddi, tr, wlan, ip, ip6, arp, rarp,
decnet, 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
`(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'.
[`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 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 host
True if the IPv4/v6 destination field of the packet is host,
which may be either an address or a name.
src host host
True if the IPv4/v6 source field of the packet is host.
host host
True if either the IPv4/v6 source or destination of the packet
is host.
Any of the above host expressions can be prepended with the
keywords, ip, arp, rarp, or ip6 as in:
ip host host
which is equivalent to:
ether proto \ip and host host
If host is a name with multiple IP addresses, each address will
be checked for a match.
ether dst ehost
True if the Ethernet destination address is ehost. Ehost may be
either a name from /etc/ethers or a number (see ethers(3N) for
numeric format).
ether src ehost
True if the Ethernet source address is ehost.
ether host ehost
True if either the Ethernet source or destination address is
ehost.
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 ehost and not host host
which can be used with either names or numbers for host /
ehost.) This syntax does not work in IPv6-enabled configuration
at this moment.
dst net net
True if the IPv4/v6 destination address of the packet has a
network number of net. 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
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.
src net net
True if the IPv4/v6 source address of the packet has a network
number of net.
net net
True if either the IPv4/v6 source or destination address of the
packet has a network number of net.
net net mask netmask
True if the IPv4 address matches net with the specific netmask.
May be qualified with src or dst. Note that this syntax is not
valid for IPv6 net.
net net/len
True if the IPv4/v6 address matches net with a netmask len bits
wide. May be qualified with src or dst.
dst port port
True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has
a destination port value of port. The port 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 port
True if the packet has a source port value of port.
port port
True if either the source or destination port of the packet is
port.
dst portrange port1-port2
True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has
a destination port value between port1 and port2. port1 and
port2 are interpreted in the same fashion as the port parameter
for port.
src portrange port1-port2
True if the packet has a source port value between port1 and
port2.
portrange port1-port2
True if either the source or destination port of the packet is
between port1 and port2.
Any of the above port or port range expressions can be prepended
with the keywords, tcp or udp, as in:
tcp src port port
which matches only tcp packets whose source port is port.
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
icmp, icmp6, igmp, igrp, pim, ah, esp, vrrp, udp, or tcp. Note
that the identifiers tcp, udp, and icmp are also keywords and
must be escaped via backslash (\). Note that this primitive
does not chase the protocol header chain.
ip6 proto protocol
True if the packet is an IPv6 packet of protocol type protocol.
Note that this primitive does not chase the protocol header
chain.
proto protocol
True if the packet is an IPv4 or IPv6 packet of protocol type
protocol. Note that this primitive does not chase the protocol
header chain.
tcp, udp, icmp
Abbreviations for:
proto p
where p 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. 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.
protochain protocol
True if the packet is an IPv4 or IPv6 packet of protocol type
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 ip, ip6, arp, rarp, atalk, aarp,
decnet, sca, lat, mopdl, moprc, iso, stp, ipx, or netbeui. Note
these identifiers 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 p
where p is one of the above protocols.
lat, moprc, mopdl
Abbreviations for:
ether proto p
where p is one of the above protocols. Note that not all
applications using pcap(3PCAP) currently know how to parse these
protocols.
decnet src host
True if the DECNET source address is 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.]
decnet dst host
True if the DECNET destination address is host.
decnet host host
True if either the DECNET source or destination address is host.
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
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 dir
True if the IEEE 802.11 frame direction matches the specified
dir. 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 [vlan_id]
is specified, only true if the packet has the specified vlan_id.
Note that the first vlan keyword encountered in expression
changes the decoding offsets for the remainder of expression on
the assumption that the packet is a VLAN packet. The vlan
[vlan_id] expression may be used more than once, to filter on
VLAN hierarchies. Each use of that expression 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 protocols encapsulated in VLAN 300 encapsulated
within any higher order VLAN.
mpls [label_num]
True if the packet is an MPLS packet. If [label_num] is
specified, only true is the packet has the specified label_num.
Note that the first mpls keyword encountered in expression
changes the decoding offsets for the remainder of expression on
the assumption that the packet is a MPLS-encapsulated IP packet.
The mpls [label_num] expression may be used more than once, to
filter on MPLS hierarchies. Each use of that expression
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 [session_id] is specified, only true
if the packet has the specified session_id. Note that the first
pppoes keyword encountered in expression changes the decoding
offsets for the remainder of expression on the assumption that
the packet is a PPPoE session packet.
For example:
pppoes 0x27 && ip
filters IPv4 protocols encapsulated in PPPoE session id 0x27.
geneve [vni]
True if the packet is a Geneve packet (UDP port 6081). If [vni]
is specified, only true if the packet has the specified vni.
Note that when the geneve keyword is encountered in expression,
it changes the decoding offsets for the remainder of expression
on the assumption that the packet is a Geneve packet.
For example:
geneve 0xb && ip
filters IPv4 protocols encapsulated in Geneve with VNI 0xb. This
will match both IP directly encapsulated in Geneve as well as IP
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 p
where p 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 expression changes the tests done in the
remainder of 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.
expr relop expr
True if the relation holds, where relop is one of >, <, >=, <=,
=, !=, and expr 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 Linux with 3.7 and later kernels; on all other
systems, 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.
To access data inside the packet, use the following syntax:
proto [ expr : size ]
Proto is one of ether, fddi, tr, wlan, ppp, slip, link, ip, arp,
rarp, tcp, udp, icmp, ip6 or radio, and indicates the protocol
layer for the index operation. (ether, fddi, wlan, tr, ppp,
slip and link 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. The length operator, indicated by the keyword len, gives
the length of the packet.
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), icmpcode
(ICMP 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 TCP flags field values are available: tcp-fin,
tcp-syn, tcp-rst, tcp-push, tcp-ack, tcp-urg.
Primitives may be combined using:
A parenthesized group of primitives and operators.
Negation (`!' or `not').
Concatenation (`&&' or `and').
Alternation (`||' or `or').
Negation has highest precedence. Alternation and concatenation have
equal precedence and associate left to right. Note that explicit and
tokens, not juxtaposition, are now required for concatenation.
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 IP 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 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 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 IP packets longer than 576 bytes sent through gateway snup:
gateway snup and ip[2:2] > 576
To select IP 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
SEE ALSO
pcap(3PCAP)
BUGS
Please send problems, bugs, questions, desirable enhancements, etc. to:
tcpdump-workers@lists.tcpdump.org
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.
Arithmetic expression against transport layer headers, like tcp[0],
does not work against IPv6 packets. It only looks at IPv4 packets.
3 August 2015 PCAP-FILTER(7)
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
