1PCAP-FILTER(7) Miscellaneous Information Manual PCAP-FILTER(7)
2
6 pcap-filter - packet filter syntax
7
9 pcap_compile() is used to compile a string into a filter program. The
10 resulting filter program can then be applied to some stream of packets
11 to determine which packets will be supplied to pcap_loop(), pcap_dis‐
12 patch(), pcap_next(), or pcap_next_ex().
13 The filter expression consists of one or more primitives. Primitives
15 usually consist of an id (name or number) preceded by one or more qual‐
16 ifiers. There are three different kinds of qualifier:
17 type type qualifiers say what kind of thing the id name or number
19 refers to. Possible types are host, net , port and portrange.
20 E.g., `host foo', `net 128.3', `port 20', `portrange 6000-6008'.
21 If there is no type qualifier, host is assumed.
22 dir dir qualifiers specify a particular transfer direction to and/or
24 from id. Possible directions are src, dst, src or dst, src and
25 dst, ra, ta, addr1, addr2, addr3, and addr4. E.g., `src foo',
26 `dst net 128.3', `src or dst port ftp-data'. If there is no dir
27 qualifier, src or dst is assumed. The ra, ta, addr1, addr2,
28 addr3, and addr4 qualifiers are only valid for IEEE 802.11 Wire‐
29 less LAN link layers. For some link layers, such as SLIP and
30 the ``cooked'' Linux capture mode used for the ``any'' device
31 and for some other device types, the inbound and outbound quali‐
32 fiers can be used to specify a desired direction.
33 proto proto qualifiers restrict the match to a particular protocol.
35 Possible protos are: ether, fddi, tr, wlan, ip, ip6, arp, rarp,
36 decnet, tcp and udp. E.g., `ether src foo', `arp net 128.3',
37 `tcp port 21', `udp portrange 7000-7009', `wlan addr2
38 0:2:3:4:5:6'. If there is no proto qualifier, all protocols
39 consistent with the type are assumed. E.g., `src foo' means
40 `(ip or arp or rarp) src foo' (except the latter is not legal
41 syntax), `net bar' means `(ip or arp or rarp) net bar' and `port
42 53' means `(tcp or udp) port 53'.
43 [`fddi' is actually an alias for `ether'; the parser treats them iden‐
45 tically as meaning ``the data link level used on the specified network
46 interface.'' FDDI headers contain Ethernet-like source and destination
47 addresses, and often contain Ethernet-like packet types, so you can
48 filter on these FDDI fields just as with the analogous Ethernet fields.
49 FDDI headers also contain other fields, but you cannot name them
50 explicitly in a filter expression.
51 Similarly, `tr' and `wlan' are aliases for `ether'; the previous para‐
53 graph's statements about FDDI headers also apply to Token Ring and
54 802.11 wireless LAN headers. For 802.11 headers, the destination
55 address is the DA field and the source address is the SA field; the
56 BSSID, RA, and TA fields aren't tested.]
57 In addition to the above, there are some special `primitive' keywords
59 that don't follow the pattern: gateway, broadcast, less, greater and
60 arithmetic expressions. All of these are described below.
61 More complex filter expressions are built up by using the words and, or
63 and not to combine primitives. E.g., `host foo and not port ftp and
64 not port ftp-data'. To save typing, identical qualifier lists can be
65 omitted. E.g., `tcp dst port ftp or ftp-data or domain' is exactly the
66 same as `tcp dst port ftp or tcp dst port ftp-data or tcp dst port
67 domain'.
68 Allowable primitives are:
70 dst host host
72 True if the IPv4/v6 destination field of the packet is host,
73 which may be either an address or a name.
74 src host host
76 True if the IPv4/v6 source field of the packet is host.
77 host host
79 True if either the IPv4/v6 source or destination of the packet
80 is host.
81 Any of the above host expressions can be prepended with the key‐
83 words, ip, arp, rarp, or ip6 as in:
84 ip host host
85 which is equivalent to:
86 ether proto \ip and host host
87 If host is a name with multiple IP addresses, each address will
88 be checked for a match.
89 ether dst ehost
91 True if the Ethernet destination address is ehost. Ehost may be
92 either a name from /etc/ethers or a numerical MAC address of the
93 form "xx:xx:xx:xx:xx:xx", "xx.xx.xx.xx.xx.xx", "xx-xx-xx-xx-xx-
94 xx", "xxxx.xxxx.xxxx", "xxxxxxxxxxxx", or various mixes of ':',
95 '.', and '-', where each "x" is a hex digit (0-9, a-f, or A-F).
96 ether src ehost
98 True if the Ethernet source address is ehost.
99 ether host ehost
101 True if either the Ethernet source or destination address is
102 ehost.
103 gateway host
105 True if the packet used host as a gateway. I.e., the Ethernet
106 source or destination address was host but neither the IP source
107 nor the IP destination was host. Host must be a name and must
108 be found both by the machine's host-name-to-IP-address resolu‐
109 tion mechanisms (host name file, DNS, NIS, etc.) and by the
110 machine's host-name-to-Ethernet-address resolution mechanism
111 (/etc/ethers, etc.). (An equivalent expression is
112 ether host ehost and not host host
113 which can be used with either names or numbers for host /
114 ehost.) This syntax does not work in IPv6-enabled configuration
115 at this moment.
116 dst net net
118 True if the IPv4/v6 destination address of the packet has a net‐
119 work number of net. Net may be either a name from the networks
120 database (/etc/networks, etc.) or a network number. An IPv4
121 network number can be written as a dotted quad (e.g.,
122 192.168.1.0), dotted triple (e.g., 192.168.1), dotted pair (e.g,
123 172.16), or single number (e.g., 10); the netmask is
124 255.255.255.255 for a dotted quad (which means that it's really
125 a host match), 255.255.255.0 for a dotted triple, 255.255.0.0
126 for a dotted pair, or 255.0.0.0 for a single number. An IPv6
127 network number must be written out fully; the netmask is
128 ff:ff:ff:ff:ff:ff:ff:ff, so IPv6 "network" matches are really
129 always host matches, and a network match requires a netmask
130 length.
131 src net net
133 True if the IPv4/v6 source address of the packet has a network
134 number of net.
135 net net
137 True if either the IPv4/v6 source or destination address of the
138 packet has a network number of net.
139 net net mask netmask
141 True if the IPv4 address matches net with the specific netmask.
142 May be qualified with src or dst. Note that this syntax is not
143 valid for IPv6 net.
144 net net/len
146 True if the IPv4/v6 address matches net with a netmask len bits
147 wide. May be qualified with src or dst.
148 dst port port
150 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has
151 a destination port value of port. The port can be a number or a
152 name used in /etc/services (see tcp(4P) and udp(4P)). If a name
153 is used, both the port number and protocol are checked. If a
154 number or ambiguous name is used, only the port number is
155 checked (e.g., dst port 513 will print both tcp/login traffic
156 and udp/who traffic, and port domain will print both tcp/domain
157 and udp/domain traffic).
158 src port port
160 True if the packet has a source port value of port.
161 port port
163 True if either the source or destination port of the packet is
164 port.
165 dst portrange port1-port2
167 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has
168 a destination port value between port1 and port2. port1 and
169 port2 are interpreted in the same fashion as the port parameter
170 for port.
171 src portrange port1-port2
173 True if the packet has a source port value between port1 and
174 port2.
175 portrange port1-port2
177 True if either the source or destination port of the packet is
178 between port1 and port2.
179 Any of the above port or port range expressions can be prepended
181 with the keywords, tcp or udp, as in:
182 tcp src port port
183 which matches only tcp packets whose source port is port.
184 less length
186 True if the packet has a length less than or equal to length.
187 This is equivalent to:
188 len <= length.
189 greater length
191 True if the packet has a length greater than or equal to length.
192 This is equivalent to:
193 len >= length.
194 ip proto protocol
196 True if the packet is an IPv4 packet (see ip(4P)) of protocol
197 type protocol. Protocol can be a number or one of the names
198 icmp, icmp6, igmp, igrp, pim, ah, esp, vrrp, udp, or tcp. Note
199 that the identifiers tcp, udp, and icmp are also keywords and
200 must be escaped via backslash (\). Note that this primitive
201 does not chase the protocol header chain.
202 ip6 proto protocol
204 True if the packet is an IPv6 packet of protocol type protocol.
205 Note that this primitive does not chase the protocol header
206 chain.
207 proto protocol
209 True if the packet is an IPv4 or IPv6 packet of protocol type
210 protocol. Note that this primitive does not chase the protocol
211 header chain.
212 tcp, udp, icmp
214 Abbreviations for:
215 proto p
216 where p is one of the above protocols.
217 ip6 protochain protocol
219 True if the packet is IPv6 packet, and contains protocol header
220 with type protocol in its protocol header chain. For example,
221 ip6 protochain 6
222 matches any IPv6 packet with TCP protocol header in the protocol
223 header chain. The packet may contain, for example, authentica‐
224 tion header, routing header, or hop-by-hop option header,
225 between IPv6 header and TCP header. The BPF code emitted by
226 this primitive is complex and cannot be optimized by the BPF
227 optimizer code, and is not supported by filter engines in the
228 kernel, so this can be somewhat slow, and may cause more packets
229 to be dropped.
230 ip protochain protocol
232 Equivalent to ip6 protochain protocol, but this is for IPv4.
233 protochain protocol
235 True if the packet is an IPv4 or IPv6 packet of protocol type
236 protocol. Note that this primitive chases the protocol header
237 chain.
238 ether broadcast
240 True if the packet is an Ethernet broadcast packet. The ether
241 keyword is optional.
242 ip broadcast
244 True if the packet is an IPv4 broadcast packet. It checks for
245 both the all-zeroes and all-ones broadcast conventions, and
246 looks up the subnet mask on the interface on which the capture
247 is being done.
248 If the subnet mask of the interface on which the capture is
250 being done is not available, either because the interface on
251 which capture is being done has no netmask or because the cap‐
252 ture is being done on the Linux "any" interface, which can cap‐
253 ture on more than one interface, this check will not work cor‐
254 rectly.
255 ether multicast
257 True if the packet is an Ethernet multicast packet. The ether
258 keyword is optional. This is shorthand for `ether[0] & 1 != 0'.
259 ip multicast
261 True if the packet is an IPv4 multicast packet.
262 ip6 multicast
264 True if the packet is an IPv6 multicast packet.
265 ether proto protocol
267 True if the packet is of ether type protocol. Protocol can be a
268 number or one of the names ip, ip6, arp, rarp, atalk, aarp, dec‐
269 net, sca, lat, mopdl, moprc, iso, stp, ipx, or netbeui. Note
270 these identifiers are also keywords and must be escaped via
271 backslash (\).
272 [In the case of FDDI (e.g., `fddi proto arp'), Token Ring (e.g.,
274 `tr proto arp'), and IEEE 802.11 wireless LANS (e.g., `wlan
275 proto arp'), for most of those protocols, the protocol identifi‐
276 cation comes from the 802.2 Logical Link Control (LLC) header,
277 which is usually layered on top of the FDDI, Token Ring, or
278 802.11 header.
279 When filtering for most protocol identifiers on FDDI, Token
281 Ring, or 802.11, the filter checks only the protocol ID field of
282 an LLC header in so-called SNAP format with an Organizational
283 Unit Identifier (OUI) of 0x000000, for encapsulated Ethernet; it
284 doesn't check whether the packet is in SNAP format with an OUI
285 of 0x000000. The exceptions are:
286 iso the filter checks the DSAP (Destination Service Access
288 Point) and SSAP (Source Service Access Point) fields of
289 the LLC header;
290 stp and netbeui
292 the filter checks the DSAP of the LLC header;
293 atalk the filter checks for a SNAP-format packet with an OUI of
295 0x080007 and the AppleTalk etype.
296 In the case of Ethernet, the filter checks the Ethernet type
298 field for most of those protocols. The exceptions are:
299 iso, stp, and netbeui
301 the filter checks for an 802.3 frame and then checks the
302 LLC header as it does for FDDI, Token Ring, and 802.11;
303 atalk the filter checks both for the AppleTalk etype in an Eth‐
305 ernet frame and for a SNAP-format packet as it does for
306 FDDI, Token Ring, and 802.11;
307 aarp the filter checks for the AppleTalk ARP etype in either
309 an Ethernet frame or an 802.2 SNAP frame with an OUI of
310 0x000000;
311 ipx the filter checks for the IPX etype in an Ethernet frame,
313 the IPX DSAP in the LLC header, the 802.3-with-no-LLC-
314 header encapsulation of IPX, and the IPX etype in a SNAP
315 frame.
316 ip, ip6, arp, rarp, atalk, aarp, decnet, iso, stp, ipx, netbeui
318 Abbreviations for:
319 ether proto p
320 where p is one of the above protocols.
321 lat, moprc, mopdl
323 Abbreviations for:
324 ether proto p
325 where p is one of the above protocols. Note that not all appli‐
326 cations using pcap(3PCAP) currently know how to parse these pro‐
327 tocols.
328 decnet src host
330 True if the DECNET source address is host, which may be an
331 address of the form ``10.123'', or a DECNET host name. [DECNET
332 host name support is only available on ULTRIX systems that are
333 configured to run DECNET.]
334 decnet dst host
336 True if the DECNET destination address is host.
337 decnet host host
339 True if either the DECNET source or destination address is host.
340 llc True if the packet has an 802.2 LLC header. This includes:
342 Ethernet packets with a length field rather than a type field
344 that aren't raw NetWare-over-802.3 packets;
345 IEEE 802.11 data packets;
347 Token Ring packets (no check is done for LLC frames);
349 FDDI packets (no check is done for LLC frames);
351 LLC-encapsulated ATM packets, for SunATM on Solaris.
353 llc type
355 True if the packet has an 802.2 LLC header and has the specified
356 type. type can be one of:
357 i Information (I) PDUs
359 s Supervisory (S) PDUs
361 u Unnumbered (U) PDUs
363 rr Receiver Ready (RR) S PDUs
365 rnr Receiver Not Ready (RNR) S PDUs
367 rej Reject (REJ) S PDUs
369 ui Unnumbered Information (UI) U PDUs
371 ua Unnumbered Acknowledgment (UA) U PDUs
373 disc Disconnect (DISC) U PDUs
375 sabme Set Asynchronous Balanced Mode Extended (SABME) U PDUs
377 test Test (TEST) U PDUs
379 xid Exchange Identification (XID) U PDUs
381 frmr Frame Reject (FRMR) U PDUs
383 ifname interface
385 True if the packet was logged as coming from the specified
386 interface (applies only to packets logged by OpenBSD's or Free‐
387 BSD's pf(4)).
388 on interface
390 Synonymous with the ifname modifier.
391 rnr num
393 True if the packet was logged as matching the specified PF rule
394 number (applies only to packets logged by OpenBSD's or FreeBSD's
395 pf(4)).
396 rulenum num
398 Synonymous with the rnr modifier.
399 reason code
401 True if the packet was logged with the specified PF reason code.
402 The known codes are: match, bad-offset, fragment, short, normal‐
403 ize, and memory (applies only to packets logged by OpenBSD's or
404 FreeBSD's pf(4)).
405 rset name
407 True if the packet was logged as matching the specified PF rule‐
408 set name of an anchored ruleset (applies only to packets logged
409 by OpenBSD's or FreeBSD's pf(4)).
410 ruleset name
412 Synonymous with the rset modifier.
413 srnr num
415 True if the packet was logged as matching the specified PF rule
416 number of an anchored ruleset (applies only to packets logged by
417 OpenBSD's or FreeBSD's pf(4)).
418 subrulenum num
420 Synonymous with the srnr modifier.
421 action act
423 True if PF took the specified action when the packet was logged.
424 Known actions are: pass and block and, with later versions of
425 pf(4), nat, rdr, binat and scrub (applies only to packets logged
426 by OpenBSD's or FreeBSD's pf(4)).
427 wlan ra ehost
429 True if the IEEE 802.11 RA is ehost. The RA field is used in
430 all frames except for management frames.
431 wlan ta ehost
433 True if the IEEE 802.11 TA is ehost. The TA field is used in
434 all frames except for management frames and CTS (Clear To Send)
435 and ACK (Acknowledgment) control frames.
436 wlan addr1 ehost
438 True if the first IEEE 802.11 address is ehost.
439 wlan addr2 ehost
441 True if the second IEEE 802.11 address, if present, is ehost.
442 The second address field is used in all frames except for CTS
443 (Clear To Send) and ACK (Acknowledgment) control frames.
444 wlan addr3 ehost
446 True if the third IEEE 802.11 address, if present, is ehost.
447 The third address field is used in management and data frames,
448 but not in control frames.
449 wlan addr4 ehost
451 True if the fourth IEEE 802.11 address, if present, is ehost.
452 The fourth address field is only used for WDS (Wireless Distri‐
453 bution System) frames.
454 type wlan_type
456 True if the IEEE 802.11 frame type matches the specified
457 wlan_type. Valid wlan_types are: mgt, ctl and data.
458 type wlan_type subtype wlan_subtype
460 True if the IEEE 802.11 frame type matches the specified
461 wlan_type and frame subtype matches the specified wlan_subtype.
462 If the specified wlan_type is mgt, then valid wlan_subtypes are:
464 assoc-req, assoc-resp, reassoc-req, reassoc-resp, probe-req,
465 probe-resp, beacon, atim, disassoc, auth and deauth.
466 If the specified wlan_type is ctl, then valid wlan_subtypes are:
468 ps-poll, rts, cts, ack, cf-end and cf-end-ack.
469 If the specified wlan_type is data, then valid wlan_subtypes
471 are: data, data-cf-ack, data-cf-poll, data-cf-ack-poll, null,
472 cf-ack, cf-poll, cf-ack-poll, qos-data, qos-data-cf-ack, qos-
473 data-cf-poll, qos-data-cf-ack-poll, qos, qos-cf-poll and qos-cf-
474 ack-poll.
475 subtype wlan_subtype
477 True if the IEEE 802.11 frame subtype matches the specified
478 wlan_subtype and frame has the type to which the specified
479 wlan_subtype belongs.
480 dir dir
482 True if the IEEE 802.11 frame direction matches the specified
483 dir. Valid directions are: nods, tods, fromds, dstods, or a
484 numeric value.
485 vlan [vlan_id]
487 True if the packet is an IEEE 802.1Q VLAN packet. If [vlan_id]
488 is specified, only true if the packet has the specified vlan_id.
489 Note that the first vlan keyword encountered in expression
490 changes the decoding offsets for the remainder of expression on
491 the assumption that the packet is a VLAN packet. The vlan
492 [vlan_id] expression may be used more than once, to filter on
493 VLAN hierarchies. Each use of that expression increments the
494 filter offsets by 4.
495 For example:
497 vlan 100 && vlan 200
498 filters on VLAN 200 encapsulated within VLAN 100, and
499 vlan && vlan 300 && ip
500 filters IPv4 protocols encapsulated in VLAN 300 encapsulated
501 within any higher order VLAN.
502 mpls [label_num]
504 True if the packet is an MPLS packet. If [label_num] is speci‐
505 fied, only true is the packet has the specified label_num. Note
506 that the first mpls keyword encountered in expression changes
507 the decoding offsets for the remainder of expression on the
508 assumption that the packet is a MPLS-encapsulated IP packet.
509 The mpls [label_num] expression may be used more than once, to
510 filter on MPLS hierarchies. Each use of that expression incre‐
511 ments the filter offsets by 4.
512 For example:
514 mpls 100000 && mpls 1024
515 filters packets with an outer label of 100000 and an inner label
516 of 1024, and
517 mpls && mpls 1024 && host 192.9.200.1
518 filters packets to or from 192.9.200.1 with an inner label of
519 1024 and any outer label.
520 pppoed True if the packet is a PPP-over-Ethernet Discovery packet (Eth‐
522 ernet type 0x8863).
523 pppoes [session_id]
525 True if the packet is a PPP-over-Ethernet Session packet (Ether‐
526 net type 0x8864). If [session_id] is specified, only true if
527 the packet has the specified session_id. Note that the first
528 pppoes keyword encountered in expression changes the decoding
529 offsets for the remainder of expression on the assumption that
530 the packet is a PPPoE session packet.
531 For example:
533 pppoes 0x27 && ip
534 filters IPv4 protocols encapsulated in PPPoE session id 0x27.
535 geneve [vni]
537 True if the packet is a Geneve packet (UDP port 6081). If [vni]
538 is specified, only true if the packet has the specified vni.
539 Note that when the geneve keyword is encountered in expression,
540 it changes the decoding offsets for the remainder of expression
541 on the assumption that the packet is a Geneve packet.
542 For example:
544 geneve 0xb && ip
545 filters IPv4 protocols encapsulated in Geneve with VNI 0xb. This
546 will match both IP directly encapsulated in Geneve as well as IP
547 contained inside an Ethernet frame.
548 iso proto protocol
550 True if the packet is an OSI packet of protocol type protocol.
551 Protocol can be a number or one of the names clnp, esis, or
552 isis.
553 clnp, esis, isis
555 Abbreviations for:
556 iso proto p
557 where p is one of the above protocols.
558 l1, l2, iih, lsp, snp, csnp, psnp
560 Abbreviations for IS-IS PDU types.
561 vpi n True if the packet is an ATM packet, for SunATM on Solaris, with
563 a virtual path identifier of n.
564 vci n True if the packet is an ATM packet, for SunATM on Solaris, with
566 a virtual channel identifier of n.
567 lane True if the packet is an ATM packet, for SunATM on Solaris, and
569 is an ATM LANE packet. Note that the first lane keyword encoun‐
570 tered in expression changes the tests done in the remainder of
571 expression on the assumption that the packet is either a LANE
572 emulated Ethernet packet or a LANE LE Control packet. If lane
573 isn't specified, the tests are done under the assumption that
574 the packet is an LLC-encapsulated packet.
575 oamf4s True if the packet is an ATM packet, for SunATM on Solaris, and
577 is a segment OAM F4 flow cell (VPI=0 & VCI=3).
578 oamf4e True if the packet is an ATM packet, for SunATM on Solaris, and
580 is an end-to-end OAM F4 flow cell (VPI=0 & VCI=4).
581 oamf4 True if the packet is an ATM packet, for SunATM on Solaris, and
583 is a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 |
584 VCI=4)).
585 oam True if the packet is an ATM packet, for SunATM on Solaris, and
587 is a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 |
588 VCI=4)).
589 metac True if the packet is an ATM packet, for SunATM on Solaris, and
591 is on a meta signaling circuit (VPI=0 & VCI=1).
592 bcc True if the packet is an ATM packet, for SunATM on Solaris, and
594 is on a broadcast signaling circuit (VPI=0 & VCI=2).
595 sc True if the packet is an ATM packet, for SunATM on Solaris, and
597 is on a signaling circuit (VPI=0 & VCI=5).
598 ilmic True if the packet is an ATM packet, for SunATM on Solaris, and
600 is on an ILMI circuit (VPI=0 & VCI=16).
601 connectmsg
603 True if the packet is an ATM packet, for SunATM on Solaris, and
604 is on a signaling circuit and is a Q.2931 Setup, Call Proceed‐
605 ing, Connect, Connect Ack, Release, or Release Done message.
606 metaconnect
608 True if the packet is an ATM packet, for SunATM on Solaris, and
609 is on a meta signaling circuit and is a Q.2931 Setup, Call Pro‐
610 ceeding, Connect, Release, or Release Done message.
611 expr relop expr
613 True if the relation holds, where relop is one of >, <, >=, <=,
614 =, !=, and expr is an arithmetic expression composed of integer
615 constants (expressed in standard C syntax), the normal binary
616 operators [+, -, *, /, %, &, |, ^, <<, >>], a length operator,
617 and special packet data accessors. Note that all comparisons
618 are unsigned, so that, for example, 0x80000000 and 0xffffffff
619 are > 0.
620 The % and ^ operators are currently only supported for filtering
622 in the kernel on Linux with 3.7 and later kernels; on all other
623 systems, if those operators are used, filtering will be done in
624 user mode, which will increase the overhead of capturing packets
625 and may cause more packets to be dropped.
626 To access data inside the packet, use the following syntax:
628 proto [ expr : size ]
629 Proto is one of ether, fddi, tr, wlan, ppp, slip, link, ip, arp,
630 rarp, tcp, udp, icmp, ip6 or radio, and indicates the protocol
631 layer for the index operation. (ether, fddi, wlan, tr, ppp,
632 slip and link all refer to the link layer. radio refers to the
633 "radio header" added to some 802.11 captures.) Note that tcp,
634 udp and other upper-layer protocol types only apply to IPv4, not
635 IPv6 (this will be fixed in the future). The byte offset, rela‐
636 tive to the indicated protocol layer, is given by expr. Size is
637 optional and indicates the number of bytes in the field of
638 interest; it can be either one, two, or four, and defaults to
639 one. The length operator, indicated by the keyword len, gives
640 the length of the packet.
641 For example, `ether[0] & 1 != 0' catches all multicast traffic.
643 The expression `ip[0] & 0xf != 5' catches all IPv4 packets with
644 options. The expression `ip[6:2] & 0x1fff = 0' catches only
645 unfragmented IPv4 datagrams and frag zero of fragmented IPv4
646 datagrams. This check is implicitly applied to the tcp and udp
647 index operations. For instance, tcp[0] always means the first
648 byte of the TCP header, and never means the first byte of an
649 intervening fragment.
650 Some offsets and field values may be expressed as names rather
652 than as numeric values. The following protocol header field
653 offsets are available: icmptype (ICMP type field), icmp6type
654 (ICMP v6 type field) icmpcode (ICMP code field), icmp6code (ICMP
655 v6 code field), and tcpflags (TCP flags field).
656 The following ICMP type field values are available: icmp-echore‐
658 ply, icmp-unreach, icmp-sourcequench, icmp-redirect, icmp-echo,
659 icmp-routeradvert, icmp-routersolicit, icmp-timxceed, icmp-
660 paramprob, icmp-tstamp, icmp-tstampreply, icmp-ireq, icmp-ire‐
661 qreply, icmp-maskreq, icmp-maskreply.
662 The following ICMPv6 type fields are available: icmp6-echo,
664 icmp6-echoreply, icmp6-multicastlistenerquery, icmp6-multicas‐
665 tlistenerreportv1, icmp6-multicastlistenerdone, icmp6-routerso‐
666 licit, icmp6-routeradvert, icmp6-neighborsolicit, icmp6-neighbo‐
667 radvert, icmp6-redirect, icmp6-routerrenum, icmp6-nodeinforma‐
668 tionquery, icmp6-nodeinformationresponse, icmp6-ineighbordiscov‐
669 erysolicit, icmp6-ineighbordiscoveryadvert, icmp6-multicastlis‐
670 tenerreportv2, icmp6-homeagentdiscoveryrequest, icmp6-homeagent‐
671 discoveryreply, icmp6-mobileprefixsolicit, icmp6-mobileprefixad‐
672 vert, icmp6-certpathsolicit, icmp6-certpathadvert, icmp6-multi‐
673 castrouteradvert, icmp6-multicastroutersolicit, icmp6-multicas‐
674 trouterterm.
675 The following TCP flags field values are available: tcp-fin,
677 tcp-syn, tcp-rst, tcp-push, tcp-ack, tcp-urg, tcp-ece, tcp-cwr.
678 Primitives may be combined using:
680 A parenthesized group of primitives and operators.
682 Negation (`!' or `not').
684 Concatenation (`&&' or `and').
686 Alternation (`||' or `or').
688 Negation has highest precedence. Alternation and concatenation have
690 equal precedence and associate left to right. Note that explicit and
691 tokens, not juxtaposition, are now required for concatenation.
692 If an identifier is given without a keyword, the most recent keyword is
694 assumed. For example,
695 not host vs and ace
696 is short for
697 not host vs and host ace
698 which should not be confused with
699 not ( host vs or ace )
700
702 To select all packets arriving at or departing from sundown:
703 host sundown
704 To select traffic between helios and either hot or ace:
706 host helios and \( hot or ace \)
707 To select all IP packets between ace and any host except helios:
709 ip host ace and not helios
710 To select all traffic between local hosts and hosts at Berkeley:
712 net ucb-ether
713 To select all ftp traffic through internet gateway snup:
715 gateway snup and (port ftp or ftp-data)
716 To select traffic neither sourced from nor destined for local hosts (if
718 you gateway to one other net, this stuff should never make it onto your
719 local net).
720 ip and not net localnet
721 To select the start and end packets (the SYN and FIN packets) of each
723 TCP conversation that involves a non-local host.
724 tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net localnet
725 To select all IPv4 HTTP packets to and from port 80, i.e. print only
727 packets that contain data, not, for example, SYN and FIN packets and
728 ACK-only packets. (IPv6 is left as an exercise for the reader.)
729 tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)
730 To select IP packets longer than 576 bytes sent through gateway snup:
732 gateway snup and ip[2:2] > 576
733 To select IP broadcast or multicast packets that were not sent via Eth‐
735 ernet broadcast or multicast:
736 ether[0] & 1 = 0 and ip[16] >= 224
737 To select all ICMP packets that are not echo requests/replies (i.e.,
739 not ping packets):
740 icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply
741
743 pcap(3PCAP)
744
746 To report a security issue please send an e-mail to security@tcp‐
747 dump.org.
748 To report bugs and other problems, contribute patches, request a fea‐
750 ture, provide generic feedback etc please see the file CONTRIBUTING in
751 the libpcap source tree root.
752 Filter expressions on fields other than those in Token Ring headers
754 will not correctly handle source-routed Token Ring packets.
755 Filter expressions on fields other than those in 802.11 headers will
757 not correctly handle 802.11 data packets with both To DS and From DS
758 set.
759 ip6 proto should chase header chain, but at this moment it does not.
761 ip6 protochain is supplied for this behavior.
762 Arithmetic expression against transport layer headers, like tcp[0],
764 does not work against IPv6 packets. It only looks at IPv4 packets.
765 5 November 2017 PCAP-FILTER(7)