Provided by: libpcap0.8_1.7.4-2_amd64 bug

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 (\), 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 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 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.

       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 (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 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.

                                           17 May 2013                             PCAP-FILTER(7)