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PCAP-FILTER(7)	       Miscellaneous Information Manual		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 Free-
	      BSD'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)

NAME | DESCRIPTION | EXAMPLES | SEE ALSO | BUGS

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