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_dis-
       patch(), 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 qual-
       ifiers.  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 Wire-
              less  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 quali-
              fiers 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  iden-
       tically  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  para-
       graph'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 key-
              words, 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 resolu-
              tion 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 net-
              work  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, authentica-
              tion  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 cap-
              ture is being done on the Linux "any" interface, which can  cap-
              ture  on  more than one interface, this check will not work cor-
              rectly.

       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, dec-
              net, 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 Eth-
                     ernet 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 appli-
              cations  using  pcap(3) currently know how to parse these proto-
              cols.

       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, normal-
              ize, 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 rule-
              set 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  Distri-
              bution 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 speci-
              fied, 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 incre-
              ments 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 (Eth-
              ernet type 0x8863).

       pppoes [session_id]
              True if the packet is a PPP-over-Ethernet Session packet (Ether-
              net 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 encoun-
              tered 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 Proceed-
              ing, 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 Pro-
              ceeding, 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, rela-
              tive 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-echore-
              ply, icmp-unreach, icmp-sourcequench, icmp-redirect,  icmp-echo,
              icmp-routeradvert,   icmp-routersolicit,   icmp-timxceed,  icmp-
              paramprob, icmp-tstamp, icmp-tstampreply,  icmp-ireq,  icmp-ire-
              qreply, 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 Eth-
       ernet 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(3)

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)

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