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    The following form allows you to view linux man pages.

    Command:

    pcap-filter

    
    
    

    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
    
           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
                  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.
    
           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, 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  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
                  '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(3PCAP) currently know how to parse these pro-
    
           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
                  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 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.
                  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.
    
           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).
    
           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.  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
    
                  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)
    
    
    

    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.
    
                                    6 January 2008                  PCAP-FILTER(7)
    
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