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(3PCAP),
12 pcap_dispatch(3PCAP), pcap_next(3PCAP), or pcap_next_ex(3PCAP).
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.
30 proto proto qualifiers restrict the match to a particular protocol.
32 Possible protos are: ether, fddi, tr, wlan, ip, ip6, arp, rarp,
33 decnet, tcp and udp. E.g., `ether src foo', `arp net 128.3',
34 `tcp port 21', `udp portrange 7000-7009', `wlan addr2
35 0:2:3:4:5:6'. If there is no proto qualifier, all protocols
36 consistent with the type are assumed. E.g., `src foo' means
37 `(ip or arp or rarp) src foo' (except the latter is not legal
38 syntax), `net bar' means `(ip or arp or rarp) net bar' and `port
39 53' means `(tcp or udp) port 53'.
40 [fddi is actually an alias for ether; the parser treats them identi‐
42 cally as meaning ``the data link level used on the specified network
43 interface''. FDDI headers contain Ethernet-like source and destination
44 addresses, and often contain Ethernet-like packet types, so you can
45 filter on these FDDI fields just as with the analogous Ethernet fields.
46 FDDI headers also contain other fields, but you cannot name them ex‐
47 plicitly in a filter expression.
48 Similarly, tr and wlan are aliases for ether; the previous paragraph's
50 statements about FDDI headers also apply to Token Ring and 802.11 wire‐
51 less LAN headers. For 802.11 headers, the destination address is the
52 DA field and the source address is the SA field; the BSSID, RA, and TA
53 fields aren't tested.]
54 In addition to the above, there are some special `primitive' keywords
56 that don't follow the pattern: gateway, broadcast, less, greater and
57 arithmetic expressions. All of these are described below.
58 More complex filter expressions are built up by using the words and, or
60 and not (or equivalently: `&&', `||' and `!' respectively) to combine
61 primitives. E.g., `host foo and not port ftp and not port ftp-data'.
62 To save typing, identical qualifier lists can be omitted. E.g., `tcp
63 dst port ftp or ftp-data or domain' is exactly the same as `tcp dst
64 port ftp or tcp dst port ftp-data or tcp dst port domain'.
65 Allowable primitives are:
67 dst host host
69 True if the IPv4/v6 destination field of the packet is host,
70 which may be either an address or a name.
71 src host host
73 True if the IPv4/v6 source field of the packet is host.
74 host host
76 True if either the IPv4/v6 source or destination of the packet
77 is host.
78 Any of the above host expressions can be prepended with the key‐
80 words, ip, arp, rarp, or ip6 as in:
81 ip host host
82 which is equivalent to:
83 ether proto \ip and host host
84 If host is a name with multiple IPv4 addresses, each address
85 will be checked for a match.
86 ether dst ehost
88 True if the Ethernet destination address is ehost. Ehost may be
89 either a name from /etc/ethers or a numerical MAC address of the
90 form "xx:xx:xx:xx:xx:xx", "xx.xx.xx.xx.xx.xx", "xx-xx-xx-xx-xx-
91 xx", "xxxx.xxxx.xxxx", "xxxxxxxxxxxx", or various mixes of ':',
92 '.', and '-', where each "x" is a hex digit (0-9, a-f, or A-F).
93 ether src ehost
95 True if the Ethernet source address is ehost.
96 ether host ehost
98 True if either the Ethernet source or destination address is
99 ehost.
100 gateway host
102 True if the packet used host as a gateway. I.e., the Ethernet
103 source or destination address was host but neither the IP source
104 nor the IP destination was host. Host must be a name and must
105 be found both by the machine's host-name-to-IP-address resolu‐
106 tion mechanisms (host name file, DNS, NIS, etc.) and by the ma‐
107 chine's host-name-to-Ethernet-address resolution mechanism
108 (/etc/ethers, etc.). (An equivalent expression is
109 ether host ehost and not host host
110 which can be used with either names or numbers for host /
111 ehost.) This syntax does not work in IPv6-enabled configuration
112 at this moment.
113 dst net net
115 True if the IPv4/v6 destination address of the packet has a net‐
116 work number of net. Net may be either a name from the networks
117 database (/etc/networks, etc.) or a network number. An IPv4
118 network number can be written as a dotted quad (e.g.,
119 192.168.1.0), dotted triple (e.g., 192.168.1), dotted pair (e.g,
120 172.16), or single number (e.g., 10); the netmask is
121 255.255.255.255 for a dotted quad (which means that it's really
122 a host match), 255.255.255.0 for a dotted triple, 255.255.0.0
123 for a dotted pair, or 255.0.0.0 for a single number. An IPv6
124 network number must be written out fully; the netmask is
125 ff:ff:ff:ff:ff:ff:ff:ff, so IPv6 "network" matches are really
126 always host matches, and a network match requires a netmask
127 length.
128 src net net
130 True if the IPv4/v6 source address of the packet has a network
131 number of net.
132 net net
134 True if either the IPv4/v6 source or destination address of the
135 packet has a network number of net.
136 net net mask netmask
138 True if the IPv4 address matches net with the specific netmask.
139 May be qualified with src or dst. Note that this syntax is not
140 valid for IPv6 net.
141 net net/len
143 True if the IPv4/v6 address matches net with a netmask len bits
144 wide. May be qualified with src or dst.
145 dst port port
147 True if the packet is IPv4 TCP, IPv4 UDP, IPv6 TCP or IPv6 UDP
148 and has a destination port value of port. The port can be a
149 number or a name used in /etc/services (see tcp(4P) and
150 udp(4P)). If a name is used, both the port number and protocol
151 are checked. If a number or ambiguous name is used, only the
152 port number is checked (e.g., `dst port 513' will print both
153 tcp/login traffic and udp/who traffic, and `port domain' will
154 print both tcp/domain and udp/domain traffic).
155 src port port
157 True if the packet has a source port value of port.
158 port port
160 True if either the source or destination port of the packet is
161 port.
162 dst portrange port1-port2
164 True if the packet is IPv4 TCP, IPv4 UDP, IPv6 TCP or IPv6 UDP
165 and has a destination port value between port1 and port2 (both
166 inclusive). port1 and port2 are interpreted in the same fashion
167 as the port parameter for port.
168 src portrange port1-port2
170 True if the packet has a source port value between port1 and
171 port2 (both inclusive).
172 portrange port1-port2
174 True if either the source or destination port of the packet is
175 between port1 and port2 (both inclusive).
176 Any of the above port or port range expressions can be prepended
178 with the keywords, tcp or udp, as in:
179 tcp src port port
180 which matches only TCP packets whose source port is port.
181 less length
183 True if the packet has a length less than or equal to length.
184 This is equivalent to:
185 len <= length
186 greater length
188 True if the packet has a length greater than or equal to length.
189 This is equivalent to:
190 len >= length
191 ip proto protocol
193 True if the packet is an IPv4 packet (see ip(4P)) of protocol
194 type protocol. Protocol can be a number or one of the names
195 icmp, icmp6, igmp, igrp, pim, ah, esp, vrrp, udp, or tcp. Note
196 that the identifiers tcp, udp, and icmp are also keywords and
197 must be escaped via backslash (\). Note that this primitive
198 does not chase the protocol header chain.
199 ip6 proto protocol
201 True if the packet is an IPv6 packet of protocol type protocol.
202 Note that this primitive does not chase the protocol header
203 chain.
204 proto protocol
206 True if the packet is an IPv4 or IPv6 packet of protocol type
207 protocol. Note that this primitive does not chase the protocol
208 header chain.
209 tcp, udp, icmp
211 Abbreviations for:
212 proto \protocol
213 where protocol is one of the above protocols.
214 ip6 protochain protocol
216 True if the packet is IPv6 packet, and contains protocol header
217 with type protocol in its protocol header chain. For example,
218 ip6 protochain 6
219 matches any IPv6 packet with TCP protocol header in the protocol
220 header chain. The packet may contain, for example, authentica‐
221 tion header, routing header, or hop-by-hop option header, be‐
222 tween IPv6 header and TCP header. The BPF code emitted by this
223 primitive is complex and cannot be optimized by the BPF opti‐
224 mizer code, and is not supported by filter engines in the ker‐
225 nel, so this can be somewhat slow, and may cause more packets to
226 be dropped.
227 ip protochain protocol
229 Equivalent to ip6 protochain protocol, but this is for IPv4.
230 protochain protocol
232 True if the packet is an IPv4 or IPv6 packet of protocol type
233 protocol. Note that this primitive chases the protocol header
234 chain.
235 ether broadcast
237 True if the packet is an Ethernet broadcast packet. The ether
238 keyword is optional.
239 ip broadcast
241 True if the packet is an IPv4 broadcast packet. It checks for
242 both the all-zeroes and all-ones broadcast conventions, and
243 looks up the subnet mask on the interface on which the capture
244 is being done.
245 If the subnet mask of the interface on which the capture is be‐
247 ing done is not available, either because the interface on which
248 capture is being done has no netmask or because the capture is
249 being done on the Linux "any" interface, which can capture on
250 more than one interface, this check will not work correctly.
251 ether multicast
253 True if the packet is an Ethernet multicast packet. The ether
254 keyword is optional. This is shorthand for `ether[0] & 1 != 0'.
255 ip multicast
257 True if the packet is an IPv4 multicast packet.
258 ip6 multicast
260 True if the packet is an IPv6 multicast packet.
261 ether proto protocol
263 True if the packet is of ether type protocol. Protocol can be a
264 number or one of the names aarp, arp, atalk, decnet, ip, ip6,
265 ipx, iso, lat, loopback, mopdl, moprc, netbeui, rarp, sca or
266 stp. Note these identifiers (except loopback) are also keywords
267 and must be escaped via backslash (\).
268 [In the case of FDDI (e.g., `fddi proto \arp'), Token Ring
270 (e.g., `tr proto \arp'), and IEEE 802.11 wireless LANs (e.g.,
271 `wlan proto \arp'), for most of those protocols, the protocol
272 identification comes from the 802.2 Logical Link Control (LLC)
273 header, which is usually layered on top of the FDDI, Token Ring,
274 or 802.11 header.
275 When filtering for most protocol identifiers on FDDI, Token
277 Ring, or 802.11, the filter checks only the protocol ID field of
278 an LLC header in so-called SNAP format with an Organizational
279 Unit Identifier (OUI) of 0x000000, for encapsulated Ethernet; it
280 doesn't check whether the packet is in SNAP format with an OUI
281 of 0x000000. The exceptions are:
282 iso the filter checks the DSAP (Destination Service Access
284 Point) and SSAP (Source Service Access Point) fields of
285 the LLC header;
286 stp and netbeui
288 the filter checks the DSAP of the LLC header;
289 atalk the filter checks for a SNAP-format packet with an OUI of
291 0x080007 and the AppleTalk etype.
292 In the case of Ethernet, the filter checks the Ethernet type
294 field for most of those protocols. The exceptions are:
295 iso, stp, and netbeui
297 the filter checks for an 802.3 frame and then checks the
298 LLC header as it does for FDDI, Token Ring, and 802.11;
299 atalk the filter checks both for the AppleTalk etype in an Eth‐
301 ernet frame and for a SNAP-format packet as it does for
302 FDDI, Token Ring, and 802.11;
303 aarp the filter checks for the AppleTalk ARP etype in either
305 an Ethernet frame or an 802.2 SNAP frame with an OUI of
306 0x000000;
307 ipx the filter checks for the IPX etype in an Ethernet frame,
309 the IPX DSAP in the LLC header, the 802.3-with-no-LLC-
310 header encapsulation of IPX, and the IPX etype in a SNAP
311 frame.
312 ip, ip6, arp, rarp, atalk, aarp, decnet, iso, stp, ipx, netbeui
314 Abbreviations for:
315 ether proto \protocol
316 where protocol is one of the above protocols.
317 lat, moprc, mopdl
319 Abbreviations for:
320 ether proto \protocol
321 where protocol is one of the above protocols. Note that not all
322 applications using pcap(3PCAP) currently know how to parse these
323 protocols.
324 decnet src host
326 True if the DECnet source address is host, which may be an ad‐
327 dress of the form ``10.123'', or a DECnet host name. [DECnet
328 host name support is only available on ULTRIX systems that are
329 configured to run DECnet.]
330 decnet dst host
332 True if the DECnet destination address is host.
333 decnet host host
335 True if either the DECnet source or destination address is host.
336 llc True if the packet has an 802.2 LLC header. This includes:
338 Ethernet packets with a length field rather than a type field
340 that aren't raw NetWare-over-802.3 packets;
341 IEEE 802.11 data packets;
343 Token Ring packets (no check is done for LLC frames);
345 FDDI packets (no check is done for LLC frames);
347 LLC-encapsulated ATM packets, for SunATM on Solaris.
349 llc type
351 True if the packet has an 802.2 LLC header and has the specified
352 type. type can be one of:
353 i Information (I) PDUs
355 s Supervisory (S) PDUs
357 u Unnumbered (U) PDUs
359 rr Receiver Ready (RR) S PDUs
361 rnr Receiver Not Ready (RNR) S PDUs
363 rej Reject (REJ) S PDUs
365 ui Unnumbered Information (UI) U PDUs
367 ua Unnumbered Acknowledgment (UA) U PDUs
369 disc Disconnect (DISC) U PDUs
371 sabme Set Asynchronous Balanced Mode Extended (SABME) U PDUs
373 test Test (TEST) U PDUs
375 xid Exchange Identification (XID) U PDUs
377 frmr Frame Reject (FRMR) U PDUs
379 inbound
381 Packet was received by the host performing the capture rather
382 than being sent by that host. This is only supported for cer‐
383 tain link-layer types, such as SLIP and the ``cooked'' Linux
384 capture mode used for the ``any'' device and for some other de‐
385 vice types.
386 outbound
388 Packet was sent by the host performing the capture rather than
389 being received by that host. This is only supported for certain
390 link-layer types, such as SLIP and the ``cooked'' Linux capture
391 mode used for the ``any'' device and for some other device
392 types.
393 ifname interface
395 True if the packet was logged as coming from the specified in‐
396 terface (applies only to packets logged by OpenBSD's or Free‐
397 BSD's pf(4)).
398 on interface
400 Synonymous with the ifname modifier.
401 rnr num
403 True if the packet was logged as matching the specified PF rule
404 number (applies only to packets logged by OpenBSD's or FreeBSD's
405 pf(4)).
406 rulenum num
408 Synonymous with the rnr modifier.
409 reason code
411 True if the packet was logged with the specified PF reason code.
412 The known codes are: match, bad-offset, fragment, short, normal‐
413 ize, and memory (applies only to packets logged by OpenBSD's or
414 FreeBSD's pf(4)).
415 rset name
417 True if the packet was logged as matching the specified PF rule‐
418 set name of an anchored ruleset (applies only to packets logged
419 by OpenBSD's or FreeBSD's pf(4)).
420 ruleset name
422 Synonymous with the rset modifier.
423 srnr num
425 True if the packet was logged as matching the specified PF rule
426 number of an anchored ruleset (applies only to packets logged by
427 OpenBSD's or FreeBSD's pf(4)).
428 subrulenum num
430 Synonymous with the srnr modifier.
431 action act
433 True if PF took the specified action when the packet was logged.
434 Known actions are: pass and block and, with later versions of
435 pf(4), nat, rdr, binat and scrub (applies only to packets logged
436 by OpenBSD's or FreeBSD's pf(4)).
437 wlan ra ehost
439 True if the IEEE 802.11 RA is ehost. The RA field is used in
440 all frames except for management frames.
441 wlan ta ehost
443 True if the IEEE 802.11 TA is ehost. The TA field is used in
444 all frames except for management frames and CTS (Clear To Send)
445 and ACK (Acknowledgment) control frames.
446 wlan addr1 ehost
448 True if the first IEEE 802.11 address is ehost.
449 wlan addr2 ehost
451 True if the second IEEE 802.11 address, if present, is ehost.
452 The second address field is used in all frames except for CTS
453 (Clear To Send) and ACK (Acknowledgment) control frames.
454 wlan addr3 ehost
456 True if the third IEEE 802.11 address, if present, is ehost.
457 The third address field is used in management and data frames,
458 but not in control frames.
459 wlan addr4 ehost
461 True if the fourth IEEE 802.11 address, if present, is ehost.
462 The fourth address field is only used for WDS (Wireless Distri‐
463 bution System) frames.
464 type wlan_type
466 True if the IEEE 802.11 frame type matches the specified
467 wlan_type. Valid wlan_types are: mgt, ctl and data.
468 type wlan_type subtype wlan_subtype
470 True if the IEEE 802.11 frame type matches the specified
471 wlan_type and frame subtype matches the specified wlan_subtype.
472 If the specified wlan_type is mgt, then valid wlan_subtypes are:
474 assoc-req, assoc-resp, reassoc-req, reassoc-resp, probe-req,
475 probe-resp, beacon, atim, disassoc, auth and deauth.
476 If the specified wlan_type is ctl, then valid wlan_subtypes are:
478 ps-poll, rts, cts, ack, cf-end and cf-end-ack.
479 If the specified wlan_type is data, then valid wlan_subtypes
481 are: data, data-cf-ack, data-cf-poll, data-cf-ack-poll, null,
482 cf-ack, cf-poll, cf-ack-poll, qos-data, qos-data-cf-ack, qos-
483 data-cf-poll, qos-data-cf-ack-poll, qos, qos-cf-poll and qos-cf-
484 ack-poll.
485 subtype wlan_subtype
487 True if the IEEE 802.11 frame subtype matches the specified
488 wlan_subtype and frame has the type to which the specified
489 wlan_subtype belongs.
490 dir dir
492 True if the IEEE 802.11 frame direction matches the specified
493 dir. Valid directions are: nods, tods, fromds, dstods, or a nu‐
494 meric value.
495 vlan [vlan_id]
497 True if the packet is an IEEE 802.1Q VLAN packet. If the op‐
498 tional vlan_id is specified, only true if the packet has the
499 specified vlan_id. Note that the first vlan keyword encountered
500 in an expression changes the decoding offsets for the remainder
501 of the expression on the assumption that the packet is a VLAN
502 packet. The `vlan [vlan_id]` keyword may be used more than
503 once, to filter on VLAN hierarchies. Each use of that keyword
504 increments the filter offsets by 4.
505 For example:
507 vlan 100 && vlan 200
508 filters on VLAN 200 encapsulated within VLAN 100, and
509 vlan && vlan 300 && ip
510 filters IPv4 protocol encapsulated in VLAN 300 encapsulated
511 within any higher order VLAN.
512 mpls [label_num]
514 True if the packet is an MPLS packet. If the optional label_num
515 is specified, only true if the packet has the specified la‐
516 bel_num. Note that the first mpls keyword encountered in an ex‐
517 pression changes the decoding offsets for the remainder of the
518 expression on the assumption that the packet is a MPLS-encapsu‐
519 lated IP packet. The `mpls [label_num]` keyword may be used
520 more than once, to filter on MPLS hierarchies. Each use of that
521 keyword increments the filter offsets by 4.
522 For example:
524 mpls 100000 && mpls 1024
525 filters packets with an outer label of 100000 and an inner label
526 of 1024, and
527 mpls && mpls 1024 && host 192.9.200.1
528 filters packets to or from 192.9.200.1 with an inner label of
529 1024 and any outer label.
530 pppoed True if the packet is a PPP-over-Ethernet Discovery packet (Eth‐
532 ernet type 0x8863).
533 pppoes [session_id]
535 True if the packet is a PPP-over-Ethernet Session packet (Ether‐
536 net type 0x8864). If the optional session_id is specified, only
537 true if the packet has the specified session_id. Note that the
538 first pppoes keyword encountered in an expression changes the
539 decoding offsets for the remainder of the expression on the as‐
540 sumption that the packet is a PPPoE session packet.
541 For example:
543 pppoes 0x27 && ip
544 filters IPv4 protocol encapsulated in PPPoE session id 0x27.
545 geneve [vni]
547 True if the packet is a Geneve packet (UDP port 6081). If the
548 optional vni is specified, only true if the packet has the spec‐
549 ified vni. Note that when the geneve keyword is encountered in
550 an expression, it changes the decoding offsets for the remainder
551 of the expression on the assumption that the packet is a Geneve
552 packet.
553 For example:
555 geneve 0xb && ip
556 filters IPv4 protocol encapsulated in Geneve with VNI 0xb. This
557 will match both IPv4 directly encapsulated in Geneve as well as
558 IPv4 contained inside an Ethernet frame.
559 iso proto protocol
561 True if the packet is an OSI packet of protocol type protocol.
562 Protocol can be a number or one of the names clnp, esis, or
563 isis.
564 clnp, esis, isis
566 Abbreviations for:
567 iso proto \protocol
568 where protocol is one of the above protocols.
569 l1, l2, iih, lsp, snp, csnp, psnp
571 Abbreviations for IS-IS PDU types.
572 vpi n True if the packet is an ATM packet, for SunATM on Solaris, with
574 a virtual path identifier of n.
575 vci n True if the packet is an ATM packet, for SunATM on Solaris, with
577 a virtual channel identifier of n.
578 lane True if the packet is an ATM packet, for SunATM on Solaris, and
580 is an ATM LANE packet. Note that the first lane keyword encoun‐
581 tered in an expression changes the tests done in the remainder
582 of the expression on the assumption that the packet is either a
583 LANE emulated Ethernet packet or a LANE LE Control packet. If
584 lane isn't specified, the tests are done under the assumption
585 that the packet is an LLC-encapsulated packet.
586 oamf4s True if the packet is an ATM packet, for SunATM on Solaris, and
588 is a segment OAM F4 flow cell (VPI=0 & VCI=3).
589 oamf4e True if the packet is an ATM packet, for SunATM on Solaris, and
591 is an end-to-end OAM F4 flow cell (VPI=0 & VCI=4).
592 oamf4 True if the packet is an ATM packet, for SunATM on Solaris, and
594 is a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 |
595 VCI=4)).
596 oam True if the packet is an ATM packet, for SunATM on Solaris, and
598 is a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 |
599 VCI=4)).
600 metac True if the packet is an ATM packet, for SunATM on Solaris, and
602 is on a meta signaling circuit (VPI=0 & VCI=1).
603 bcc True if the packet is an ATM packet, for SunATM on Solaris, and
605 is on a broadcast signaling circuit (VPI=0 & VCI=2).
606 sc True if the packet is an ATM packet, for SunATM on Solaris, and
608 is on a signaling circuit (VPI=0 & VCI=5).
609 ilmic True if the packet is an ATM packet, for SunATM on Solaris, and
611 is on an ILMI circuit (VPI=0 & VCI=16).
612 connectmsg
614 True if the packet is an ATM packet, for SunATM on Solaris, and
615 is on a signaling circuit and is a Q.2931 Setup, Call Proceed‐
616 ing, Connect, Connect Ack, Release, or Release Done message.
617 metaconnect
619 True if the packet is an ATM packet, for SunATM on Solaris, and
620 is on a meta signaling circuit and is a Q.2931 Setup, Call Pro‐
621 ceeding, Connect, Release, or Release Done message.
622 expr relop expr
624 True if the relation holds, where relop is one of >, <, >=, <=,
625 =, !=, and expr is an arithmetic expression composed of integer
626 constants (expressed in standard C syntax), the normal binary
627 operators [+, -, *, /, %, &, |, ^, <<, >>], a length operator,
628 and special packet data accessors. Note that all comparisons
629 are unsigned, so that, for example, 0x80000000 and 0xffffffff
630 are > 0.
631 The % and ^ operators are currently only supported for filtering
633 in the kernel on Linux with 3.7 and later kernels; on all other
634 systems, if those operators are used, filtering will be done in
635 user mode, which will increase the overhead of capturing packets
636 and may cause more packets to be dropped.
637 To access data inside the packet, use the following syntax:
639 proto [ expr : size ]
640 Proto is one of ether, fddi, tr, wlan, ppp, slip, link, ip, arp,
641 rarp, tcp, udp, icmp, ip6 or radio, and indicates the protocol
642 layer for the index operation. (ether, fddi, wlan, tr, ppp,
643 slip and link all refer to the link layer. radio refers to the
644 "radio header" added to some 802.11 captures.) Note that tcp,
645 udp and other upper-layer protocol types only apply to IPv4, not
646 IPv6 (this will be fixed in the future). The byte offset, rela‐
647 tive to the indicated protocol layer, is given by expr. Size is
648 optional and indicates the number of bytes in the field of in‐
649 terest; it can be either one, two, or four, and defaults to one.
650 The length operator, indicated by the keyword len, gives the
651 length of the packet.
652 For example, `ether[0] & 1 != 0' catches all multicast traffic.
654 The expression `ip[0] & 0xf != 5' catches all IPv4 packets with
655 options. The expression `ip[6:2] & 0x1fff = 0' catches only un‐
656 fragmented IPv4 datagrams and frag zero of fragmented IPv4 data‐
657 grams. This check is implicitly applied to the tcp and udp in‐
658 dex operations. For instance, tcp[0] always means the first
659 byte of the TCP header, and never means the first byte of an in‐
660 tervening fragment.
661 Some offsets and field values may be expressed as names rather
663 than as numeric values. The following protocol header field
664 offsets are available: icmptype (ICMP type field), icmp6type
665 (ICMPv6 type field), icmpcode (ICMP code field), icmp6code
666 (ICMPv6 code field) and tcpflags (TCP flags field).
667 The following ICMP type field values are available: icmp-echore‐
669 ply, icmp-unreach, icmp-sourcequench, icmp-redirect, icmp-echo,
670 icmp-routeradvert, icmp-routersolicit, icmp-timxceed, icmp-
671 paramprob, icmp-tstamp, icmp-tstampreply, icmp-ireq, icmp-ire‐
672 qreply, icmp-maskreq, icmp-maskreply.
673 The following ICMPv6 type fields are available: icmp6-destina‐
675 tionrunreach, icmp6-packettoobig, icmp6-timeexceeded, icmp6-pa‐
676 rameterproblem, icmp6-echo, icmp6-echoreply, icmp6-multicastlis‐
677 tenerquery, icmp6-multicastlistenerreportv1, icmp6-multicastlis‐
678 tenerdone, icmp6-routersolicit, icmp6-routeradvert, icmp6-neigh‐
679 borsolicit, icmp6-neighboradvert, icmp6-redirect, icmp6-router‐
680 renum, icmp6-nodeinformationquery, icmp6-nodeinformationre‐
681 sponse, icmp6-ineighbordiscoverysolicit, icmp6-ineighbordiscov‐
682 eryadvert, icmp6-multicastlistenerreportv2, icmp6-homeagentdis‐
683 coveryrequest, icmp6-homeagentdiscoveryreply, icmp6-mobilepre‐
684 fixsolicit, icmp6-mobileprefixadvert, icmp6-certpathsolicit,
685 icmp6-certpathadvert, icmp6-multicastrouteradvert, icmp6-multi‐
686 castroutersolicit, icmp6-multicastrouterterm.
687 The following TCP flags field values are available: tcp-fin,
689 tcp-syn, tcp-rst, tcp-push, tcp-ack, tcp-urg, tcp-ece, tcp-cwr.
690 Primitives may be combined using:
692 A parenthesized group of primitives and operators.
694 Negation (`!' or `not').
696 Concatenation (`&&' or `and').
698 Alternation (`||' or `or').
700 Negation has the highest precedence. Alternation and concatenation
702 have equal precedence and associate left to right. Note that explicit
703 and tokens, not juxtaposition, are now required for concatenation.
704 If an identifier is given without a keyword, the most recent keyword is
706 assumed. For example,
707 not host vs and ace
708 is short for
709 not host vs and host ace
710 which should not be confused with
711 not (host vs or ace)
712
714 To select all packets arriving at or departing from `sundown':
715 host sundown
716 To select traffic between `helios' and either `hot' or `ace':
718 host helios and (hot or ace)
719 To select all IPv4 packets between `ace' and any host except `helios':
721 ip host ace and not helios
722 To select all traffic between local hosts and hosts at Berkeley:
724 net ucb-ether
725 To select all FTP traffic through Internet gateway `snup':
727 gateway snup and (port ftp or ftp-data)
728 To select IPv4 traffic neither sourced from nor destined for local
730 hosts (if you gateway to one other net, this stuff should never make it
731 onto your local net).
732 ip and not net localnet
733 To select the start and end packets (the SYN and FIN packets) of each
735 TCP conversation that involves a non-local host.
736 tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net localnet
737 To select the TCP packets with flags RST and ACK both set. (i.e. se‐
739 lect only the RST and ACK flags in the flags field, and if the result
740 is "RST and ACK both set", match)
741 tcp[tcpflags] & (tcp-rst|tcp-ack) == (tcp-rst|tcp-ack)
742 To select all IPv4 HTTP packets to and from port 80, i.e. print only
744 packets that contain data, not, for example, SYN and FIN packets and
745 ACK-only packets. (IPv6 is left as an exercise for the reader.)
746 tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)
747 To select IPv4 packets longer than 576 bytes sent through gateway
749 `snup':
750 gateway snup and ip[2:2] > 576
751 To select IPv4 broadcast or multicast packets that were not sent via
753 Ethernet broadcast or multicast:
754 ether[0] & 1 = 0 and ip[16] >= 224
755 To select all ICMP packets that are not echo requests/replies (i.e.,
757 not ping packets):
758 icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply
759 icmp6[icmp6type] != icmp6-echo and icmp6[icmp6type] != icmp6-echoreply
760
762 pcap(3PCAP)
763
765 To report a security issue please send an e-mail to security@tcp‐
766 dump.org.
767 To report bugs and other problems, contribute patches, request a fea‐
769 ture, provide generic feedback etc please see the file CONTRIBUTING.md
770 in the libpcap source tree root.
771 Filter expressions on fields other than those in Token Ring headers
773 will not correctly handle source-routed Token Ring packets.
774 Filter expressions on fields other than those in 802.11 headers will
776 not correctly handle 802.11 data packets with both To DS and From DS
777 set.
778 `ip6 proto' should chase header chain, but at this moment it does not.
780 `ip6 protochain' is supplied for this behavior. For example, to match
781 IPv6 fragments: `ip6 protochain 44'
782 Arithmetic expression against transport layer headers, like tcp[0],
784 does not work against IPv6 packets. It only looks at IPv4 packets.
785 6 February 2021 PCAP-FILTER(7)