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PCAP-FILTER(7)                                                  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 con-
              sistent with the type are assumed.  E.g., 'src foo' means '(ip or arp or rarp) src foo' (except the lat-
              ter  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 (\), which is \\ in the  C-shell.
              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  opti-
              mizer code, so this can be somewhat slow.

       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  broad-
              cast 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  identi-
              fiers are also keywords and must be escaped via backslash (\).

              [In  the case of FDDI (e.g., 'fddi protocol arp'), Token Ring (e.g., 'tr protocol arp'), and IEEE 802.11
              wireless LANS (e.g., 'wlan protocol 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.

       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-off-
              set,  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
              Synonomous 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
              Synonomous 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 manage-
              ment 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 speci-
              fied 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.

       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.

       llc    True if the packet is an ATM packet, for SunATM on Solaris, and 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 expres-
              sion  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:
                   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 (parentheses are special to the Shell and must be
              escaped).

              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 exam-
       ple, 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-workersATlists.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.



                                6 January 2008                  PCAP-FILTER(7)