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PCAP-FILTER(7)                                                                                PCAP-FILTER(7)



NAME
       pcap-filter - packet filter syntax

DESCRIPTION
       pcap_compile()  is  used to compile a string into a filter program.  The resulting filter program can
       then be applied to some stream of packets to determine which packets will be supplied to pcap_loop(),
       pcap_dispatch(), pcap_next(), or pcap_next_ex().

       The  filter expression consists of one or more primitives.  Primitives usually consist of an id (name
       or number) preceded by one or more qualifiers.  There are three different kinds of qualifier:

       type   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    qualifiers specify a particular transfer direction to and/or from id.  Possible directions are
              src,  dst,  src or dst, src and dst, ra, ta, addr1, addr2, addr3, and addr4.  E.g., `src foo',
              `dst net 128.3', `src or dst port ftp-data'.  If there is no dir  qualifier,  src  or  dst  is
              assumed.  The ra, ta, addr1, addr2, addr3, and addr4 qualifiers are only valid for IEEE 802.11
              Wireless LAN link layers.  For some link layers, such as SLIP and the ``cooked'' Linux capture
              mode  used  for  the  ``any'' device and for some other device types, the inbound and outbound
              qualifiers can be used to specify a desired direction.

       proto  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  quali-fier, qualifier,
              fier,  all  protocols consistent with the type are assumed.  E.g., `src foo' means `(ip or arp
              or rarp) src foo' (except the latter is not legal syntax), `net bar'  means  `(ip  or  arp  or
              rarp) net bar' and `port 53' means `(tcp or udp) port 53'.

       [`fddi'  is  actually  an alias for `ether'; the parser treats them identically as meaning ``the data
       link level used on the specified network interface.''  FDDI headers contain Ethernet-like source  and
       destination  addresses, and often contain Ethernet-like packet types, so you can filter on these FDDI
       fields just as with the analogous Ethernet fields.  FDDI headers also contain other fields,  but  you
       cannot name them explicitly in a filter expression.

       Similarly,  `tr'  and  `wlan' are aliases for `ether'; the previous paragraph's statements about FDDI
       headers also apply to Token Ring and 802.11 wireless LAN headers.  For 802.11 headers,  the  destina-tion destination
       tion  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 primi-tives. primitives.
       tives.  E.g., `host foo and not port ftp and not port ftp-data'.  To save typing, identical qualifier
       lists can be omitted.  E.g., `tcp dst port ftp or ftp-data or domain' is exactly the same as `tcp dst
       port ftp or tcp dst port ftp-data or tcp dst port domain'.

       Allowable primitives are:

       dst host host
              True if the IPv4/v6 destination field of the packet is host, which may be either an address or
              a name.

       src host host
              True if the IPv4/v6 source field of the packet is host.

       host host
              True if either the IPv4/v6 source or destination of the packet is host.

              Any of the above host expressions can be prepended with the keywords, ip, arp, rarp, or ip6 as
              in:
                   ip host host
              which is equivalent to:
                   ether proto \ip and host host
              If host is a name with multiple IP addresses, each address will be checked for a match.

       ether dst ehost
              True if the Ethernet  destination  address  is  ehost.   Ehost  may  be  either  a  name  from
              /etc/ethers or a number (see ethers(3N) for numeric format).

       ether src ehost
              True if the Ethernet source address is ehost.

       ether host ehost
              True if either the Ethernet source or destination address is ehost.

       gateway host
              True  if  the packet used host as a gateway.  I.e., the Ethernet source or destination address
              was host but neither the IP source nor the IP destination was host.  Host must be a  name  and
              must  be  found both by the machine's host-name-to-IP-address resolution mechanisms (host name
              file, DNS, NIS, etc.) and by the machine's host-name-to-Ethernet-address resolution  mechanism
              (/etc/ethers, etc.).  (An equivalent expression is
                   ether host ehost and not host host
              which  can  be used with either names or numbers for host / ehost.)  This syntax does not work
              in IPv6-enabled configuration at this moment.

       dst net net
              True if the IPv4/v6 destination address of the packet has a network number of net.  Net may be
              either  a  name from the networks database (/etc/networks, etc.) or a network number.  An IPv4
              network number can be written as a dotted  quad  (e.g.,  192.168.1.0),  dotted  triple  (e.g.,
              192.168.1),  dotted  pair  (e.g,  172.16),  or  single  number  (e.g.,  10);  the  netmask  is
              255.255.255.255 for a dotted quad (which means that it's really a host  match),  255.255.255.0
              for a dotted triple, 255.255.0.0 for a dotted pair, or 255.0.0.0 for a single number.  An IPv6
              network number must be written out fully; the  netmask  is  ff:ff:ff:ff:ff:ff:ff:ff,  so  IPv6
              "network"  matches  are  really  always  host  matches, and a network match requires a netmask
              length.

       src net net
              True if the IPv4/v6 source address of the packet has a network number of net.

       net net
              True if either the IPv4/v6 source or destination address of the packet has a network number of
              net.

       net net mask netmask
              True  if the IPv4 address matches net with the specific netmask.  May be qualified with src or
              dst.  Note that this syntax is not valid for IPv6 net.

       net net/len
              True if the IPv4/v6 address matches net with a netmask len bits wide.  May be  qualified  with
              src or dst.

       dst port port
              True  if  the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a destination port value of
              port.  The port can be a number or a name used in /etc/services (see tcp(4P) and udp(4P)).  If
              a  name is used, both the port number and protocol are checked.  If a number or ambiguous name
              is used, only the port number is checked (e.g., dst port 513 will print both tcp/login traffic
              and udp/who traffic, and port domain will print both tcp/domain and udp/domain traffic).

       src port port
              True if the packet has a source port value of port.

       port port
              True if either the source or destination port of the packet is port.

       dst portrange port1-port2
              True  if  the  packet  is  ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a destination port value
              between port1 and port2.  port1 and port2 are interpreted in the  same  fashion  as  the  port
              parameter for port.

       src portrange port1-port2
              True if the packet has a source port value between port1 and port2.

       portrange port1-port2
              True if either the source or destination port of the packet is between port1 and port2.

              Any  of  the  above  port or port range expressions can be prepended with the keywords, tcp or
              udp, as in:
                   tcp src port port
              which matches only tcp packets whose source port is port.

       less length
              True if the packet has a length less than or equal to length.  This is equivalent to:
                   len <= length.

       greater length
              True if the packet has a length greater than or equal to length.  This is equivalent to:
                   len >= length.

       ip proto protocol
              True if the packet is an IPv4 packet (see ip(4P)) of protocol type protocol.  Protocol can  be
              a  number  or one of the names icmp, icmp6, igmp, igrp, pim, ah, esp, vrrp, udp, or tcp.  Note
              that the identifiers tcp, udp, and icmp are also keywords and must be  escaped  via  backslash
              (\),  which is \\ in the C-shell.  Note that this primitive does not chase the protocol header
              chain.

       ip6 proto protocol
              True if the packet is an IPv6 packet of protocol type protocol.  Note that this primitive does
              not chase the protocol header chain.

       ip6 protochain protocol
              True if the packet is IPv6 packet, and contains protocol header with type protocol in its pro-tocol protocol
              tocol header chain.  For example,
                   ip6 protochain 6
              matches any IPv6 packet with TCP protocol header in the protocol header chain.  The packet may
              contain,  for  example,  authentication  header,  routing header, or hop-by-hop option header,
              between IPv6 header and TCP header.  The BPF code emitted by this  primitive  is  complex  and
              cannot be optimized by the BPF optimizer code, so this can be somewhat slow.

       ip protochain protocol
              Equivalent to ip6 protochain protocol, but this is for IPv4.

       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 allones
              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 capture
              ture is being done on the Linux "any" interface, which can capture on more than one interface,
              this check will not work correctly.

       ether multicast
              True if the packet is an Ethernet multicast packet.  The ether keyword is optional.   This  is
              shorthand for `ether[0] & 1 != 0'.

       ip multicast
              True if the packet is an IPv4 multicast packet.

       ip6 multicast
              True if the packet is an IPv6 multicast packet.

       ether proto protocol
              True  if  the  packet is of ether type protocol.  Protocol can be a number or one of the names
              ip, ip6, arp, rarp, atalk, aarp, decnet, sca, lat, mopdl, moprc, iso, stp,  ipx,  or  netbeui.
              Note these identifiers are also keywords and must be escaped via backslash (\).

              [In  the  case  of FDDI (e.g., `fddi protocol arp'), Token Ring (e.g., `tr protocol arp'), and
              IEEE 802.11 wireless LANS (e.g., `wlan protocol arp'), for most of those protocols, the proto-col protocol
              col  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 proto-cols. protocols.
              cols.  The exceptions are:

              iso, stp, and netbeui
                     the filter checks for an 802.3 frame and then checks the LLC  header  as  it  does  for
                     FDDI, Token Ring, and 802.11;

              atalk  the filter checks both for the AppleTalk etype in an Ethernet frame and for a SNAP-for-mat SNAP-format
                     mat 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.

       decnet src host
              True  if the DECNET source address is host, which may be an address of the form ``10.123'', or
              a DECNET host name.  [DECNET host name support is only available on ULTRIX  systems  that  are
              configured to run DECNET.]

       decnet dst host
              True if the DECNET destination address is host.

       decnet host host
              True if either the DECNET source or destination address is host.

       ifname interface
              True  if the packet was logged as coming from the specified interface (applies only to packets
              logged by OpenBSD's or FreeBSD's pf(4)).

       on interface
              Synonymous with the ifname modifier.

       rnr num
              True if the packet was logged as matching the specified PF rule number (applies only to  pack-ets packets
              ets logged by OpenBSD's or FreeBSD's pf(4)).

       rulenum num
              Synonymous with the rnr modifier.

       reason code
              True  if the packet was logged with the specified PF reason code.  The known codes are: match,
              bad-offset, fragment, short,  normalize,  and  memory  (applies  only  to  packets  logged  by
              OpenBSD's or FreeBSD's pf(4)).

       rset name
              True if the packet was logged as matching the specified PF ruleset name of an anchored ruleset
              (applies only to packets logged by OpenBSD's or FreeBSD's pf(4)).

       ruleset name
              Synonomous with the rset modifier.

       srnr num
              True if the packet was logged as matching the specified PF rule number of an anchored  ruleset
              (applies only to packets logged by OpenBSD's or FreeBSD's pf(4)).

       subrulenum num
              Synonomous with the srnr modifier.

       action act
              True  if PF took the specified action when the packet was logged.  Known actions are: pass and
              block and, with later versions of pf(4)), nat, rdr, binat and scrub (applies only  to  packets
              logged by OpenBSD's or FreeBSD's pf(4)).

       wlan ra ehost
              True if the IEEE 802.11 RA is ehost.  The RA field is used in all frames except for management
              frames.

       wlan ta ehost
              True if the IEEE 802.11 TA is ehost.  The TA field is used in all frames except for management
              frames and CTS (Clear To Send) and ACK (Acknowledgment) control frames.

       wlan addr1 ehost
              True if the first IEEE 802.11 address is ehost.

       wlan addr2 ehost
              True  if  the  second  IEEE 802.11 address, if present, is ehost.  The second address field is
              used in all frames except for CTS (Clear To Send) and ACK (Acknowledgment) control frames.

       wlan addr3 ehost
              True if the third IEEE 802.11 address, if present, is ehost.  The third address field is  used
              in management and data frames, but not in control frames.

       wlan addr4 ehost
              True  if  the  fourth  IEEE 802.11 address, if present, is ehost.  The fourth address field is
              only used for WDS (Wireless Distribution System) frames.

       ip, ip6, arp, rarp, atalk, aarp, decnet, iso, stp, ipx, netbeui
              Abbreviations for:
                   ether proto p
              where p is one of the above protocols.

       lat, moprc, mopdl
              Abbreviations for:
                   ether proto p
              where p is one of the above protocols.  Note that not all applications using pcap(3) currently
              know how to parse these protocols.

       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, reas-soc-req, reassoc-req,
              soc-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 cfend
              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-cfpoll,
              poll, data-cf-ack-poll, null, cf-ack, cf-poll, cf-ack-poll,  qos-data,  qos-data-cf-ack,  qos-data-cf-poll, qosdata-cf-poll,
              data-cf-poll, qos-data-cf-ack-poll, qos, qos-cf-poll and qos-cf-ack-poll.

       subtype wlan_subtype
              True  if  the  IEEE  802.11 frame subtype matches the specified wlan_subtype and frame has the
              type to which the specified wlan_subtype belongs.

       dir dir
              True if the IEEE 802.11 frame direction matches the  specified  dir.   Valid  directions  are:
              nods, tods, fromds, dstods, or a numeric value.

       vlan [vlan_id]
              True if the packet is an IEEE 802.1Q VLAN packet.  If [vlan_id] is specified, only true if the
              packet has the specified vlan_id.  Note that the first vlan keyword encountered in  expression
              changes the decoding offsets for the remainder of expression on the assumption that the packet
              is a VLAN packet.  The vlan [vlan_id] expression may be used more than once, to filter on VLAN
              hierarchies.  Each use of that expression increments the filter offsets by 4.

              For example:
                   vlan 100 && vlan 200
              filters on VLAN 200 encapsulated within VLAN 100, and
                   vlan && vlan 300 && ip
              filters IPv4 protocols encapsulated in VLAN 300 encapsulated within any higher order VLAN.

       mpls [label_num]
              True  if  the  packet is an MPLS packet.  If [label_num] is specified, only true is the packet
              has the specified label_num.  Note that the  first  mpls  keyword  encountered  in  expression
              changes the decoding offsets for the remainder of expression on the assumption that the packet
              is a MPLS-encapsulated IP packet.  The mpls [label_num] expression may be used more than once,
              to  filter  on MPLS hierarchies.  Each use of that expression increments the filter offsets by
              4.

              For example:
                   mpls 100000 && mpls 1024
              filters packets with an outer label of 100000 and an inner label of 1024, and
                   mpls && mpls 1024 && host 192.9.200.1
              filters packets to or from 192.9.200.1 with an inner label of 1024 and any outer label.

       pppoed True if the packet is a PPP-over-Ethernet Discovery packet (Ethernet type 0x8863).

       pppoes True if the packet is a PPP-over-Ethernet Session packet (Ethernet type  0x8864).   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 && ip
              filters IPv4 protocols encapsulated in PPPoE.

       tcp, udp, icmp
              Abbreviations for:
                   ip proto p or ip6 proto p
              where p is one of the above protocols.

       iso proto protocol
              True if the packet is an OSI packet of protocol type protocol.  Protocol can be  a  number  or
              one of the names clnp, esis, or isis.

       clnp, esis, isis
              Abbreviations for:
                   iso proto p
              where p is one of the above protocols.

       l1, l2, iih, lsp, snp, csnp, psnp
              Abbreviations for IS-IS PDU types.

       vpi n  True  if the packet is an ATM packet, for SunATM on Solaris, with a virtual path identifier of
              n.

       vci n  True if the packet is an ATM packet, for SunATM on Solaris, with a virtual channel  identifier
              of n.

       lane   True  if  the packet is an ATM packet, for SunATM on Solaris, and is an ATM LANE packet.  Note
              that the first lane keyword encountered in expression changes the tests done in the  remainder
              of expression on the assumption that the packet is either a LANE emulated Ethernet packet or a
              LANE LE Control packet.  If lane isn't specified, the tests are done under the assumption that
              the packet is an LLC-encapsulated packet.

       llc    True if the packet is an ATM packet, for SunATM on Solaris, and is an LLC-encapsulated packet.

       oamf4s True if the packet is an ATM packet, for SunATM on Solaris, and is a segment OAM F4 flow  cell
              (VPI=0 & VCI=3).

       oamf4e True  if  the packet is an ATM packet, for SunATM on Solaris, and is an end-to-end OAM F4 flow
              cell (VPI=0 & VCI=4).

       oamf4  True if the packet is an ATM packet, for SunATM on Solaris, and is a segment or end-to-end OAM
              F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).

       oam    True if the packet is an ATM packet, for SunATM on Solaris, and is a segment or end-to-end OAM
              F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).

       metac  True if the packet is an ATM packet, for SunATM on Solaris, and is on a meta signaling circuit
              (VPI=0 & VCI=1).

       bcc    True  if  the  packet is an ATM packet, for SunATM on Solaris, and is on a broadcast signaling
              circuit (VPI=0 & VCI=2).

       sc     True if the packet is an ATM packet, for SunATM on Solaris, and  is  on  a  signaling  circuit
              (VPI=0 & VCI=5).

       ilmic  True if the packet is an ATM packet, for SunATM on Solaris, and is on an ILMI circuit (VPI=0 &
              VCI=16).

       connectmsg
              True if the packet is an ATM packet, for SunATM on Solaris, and is on a signaling circuit  and
              is a Q.2931 Setup, Call Proceeding, Connect, Connect Ack, Release, or Release Done message.

       metaconnect
              True if the packet is an ATM packet, for SunATM on Solaris, and is on a meta signaling circuit
              and is a Q.2931 Setup, Call Proceeding, Connect, Release, or Release Done message.

       expr relop expr
              True if the relation holds, where relop is one of >, <, >=, <=, =, !=, and expr is  an  arith-
              metic  expression  composed  of integer constants (expressed in standard C syntax), the normal
              binary operators [+, -, *, /, &, |, <<, >>], a length operator, and special packet data acces-sors. accessors.
              sors.  Note that all comparisons are unsigned, so that, for example, 0x80000000 and 0xffffffff
              are > 0.  To access data inside the packet, use the following syntax:
                   proto [ expr : size ]
              Proto is one of ether, fddi, tr, wlan, ppp, slip, link, ip, arp, rarp, tcp, udp, icmp, ip6  or
              radio, and indicates the protocol layer for the index operation.  (ether, fddi, wlan, tr, ppp,
              slip and link all refer to the link layer. radio refers to the "radio header"  added  to  some
              802.11 captures.)  Note that tcp, udp and other upper-layer protocol types only apply to IPv4,
              not IPv6 (this will be fixed in the future).  The byte offset, relative to the indicated  pro-tocol protocol
              tocol  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 opera-tor, operator,
              tor, indicated by the keyword len, gives the length of the packet.

              For  example,  `ether[0] & 1 != 0' catches all multicast traffic.  The expression `ip[0] & 0xf
              != 5' catches all IPv4 packets with options.  The expression `ip[6:2] & 0x1fff  =  0'  catches
              only  unfragmented  IPv4  datagrams and frag zero of fragmented IPv4 datagrams.  This check is
              implicitly applied to the tcp and udp index operations.  For instance, tcp[0] always means the
              first byte of the TCP header, and never means the first byte of an intervening fragment.

              Some  offsets  and  field values may be expressed as names rather than as numeric values.  The
              following protocol header field offsets are available: icmptype (ICMP  type  field),  icmpcode
              (ICMP code field), and tcpflags (TCP flags field).

              The following ICMP type field values are available: icmp-echoreply, icmp-unreach, icmp-source-quench, icmp-sourcequench,
              quench, icmp-redirect, icmp-echo, icmp-routeradvert, icmp-routersolicit, icmp-timxceed,  icmp-paramprob, icmpparamprob,
              paramprob,  icmp-tstamp,  icmp-tstampreply,  icmp-ireq,  icmp-ireqreply,  icmp-maskreq,  icmp-maskreply. icmpmaskreply.
              maskreply.

              The following TCP flags field values are available: tcp-fin, tcp-syn, tcp-rst, tcp-push,  tcp-ack, tcpack,
              ack, tcp-urg.

       Primitives may be combined using:

              A  parenthesized  group  of primitives and operators (parentheses are special to the Shell and
              must be escaped).

              Negation (`!' or `not').

              Concatenation (`&&' or `and').

              Alternation (`||' or `or').

       Negation has highest precedence.  Alternation and concatenation have equal precedence  and  associate
       left to right.  Note that explicit and tokens, not juxtaposition, are now required for concatenation.

       If an identifier is given without a keyword, the most recent keyword is assumed.  For example,
            not host vs and ace
       is short for
            not host vs and host ace
       which should not be confused with
            not ( host vs or ace )

EXAMPLES
       To select all packets arriving at or departing from sundown:
              host sundown

       To select traffic between helios and either hot or ace:
              host helios and \( hot or ace \)

       To select all IP packets between ace and any host except helios:
              ip host ace and not helios

       To select all traffic between local hosts and hosts at Berkeley:
              net ucb-ether

       To select all ftp traffic through internet gateway snup:
              gateway snup and (port ftp or ftp-data)

       To select traffic neither sourced from nor destined for local hosts (if you gateway to one other net,
       this stuff should never make it onto your local net).
              ip and not net localnet

       To  select the start and end packets (the SYN and FIN packets) of each TCP conversation that involves
       a non-local host.
              tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net localnet

       To select all IPv4 HTTP packets to and from port 80, i.e. print only packets that contain data,  not,
       for example, SYN and FIN packets and ACK-only packets.  (IPv6 is left as an exercise for the reader.)
              tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)

       To select IP packets longer than 576 bytes sent through gateway snup:
              gateway snup and ip[2:2] > 576

       To select IP broadcast or multicast packets that were not sent via Ethernet broadcast or multicast:
              ether[0] & 1 = 0 and ip[16] >= 224

       To select all ICMP packets that are not echo requests/replies (i.e., not ping packets):
              icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply

SEE ALSO
       pcap(3PCAP)

AUTHORS
       The original authors are:

       Van Jacobson, Craig Leres and Steven McCanne, all of the Lawrence Berkeley National Laboratory,  Uni-versity University
       versity of California, Berkeley, CA.

       It is currently being maintained by tcpdump.org.

       The current version of libpcap is available via http:

              http://www.tcpdump.org/

       The original distribution is available via anonymous ftp:

              ftp://ftp.ee.lbl.gov/tcpdump.tar.Z

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 sourcerouted
       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  pack-ets. packets.
       ets.  It only looks at IPv4 packets.



                                               6 January 2008                                 PCAP-FILTER(7)

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