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
47 explicitly 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
107 machine'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. port1
166 and port2 are interpreted in the same fashion as the port param‐
167 eter for port.
168 src portrange port1-port2
170 True if the packet has a source port value between port1 and
171 port2.
172 portrange port1-port2
174 True if either the source or destination port of the packet is
175 between port1 and port2.
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,
222 between IPv6 header and TCP header. The BPF code emitted by
223 this primitive is complex and cannot be optimized by the BPF
224 optimizer code, and is not supported by filter engines in the
225 kernel, so this can be somewhat slow, and may cause more packets
226 to 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
247 being done is not available, either because the interface on
248 which capture is being done has no netmask or because the cap‐
249 ture is being done on the Linux "any" interface, which can cap‐
250 ture on more than one interface, this check will not work cor‐
251 rectly.
252 ether multicast
254 True if the packet is an Ethernet multicast packet. The ether
255 keyword is optional. This is shorthand for `ether[0] & 1 != 0'.
256 ip multicast
258 True if the packet is an IPv4 multicast packet.
259 ip6 multicast
261 True if the packet is an IPv6 multicast packet.
262 ether proto protocol
264 True if the packet is of ether type protocol. Protocol can be a
265 number or one of the names aarp, arp, atalk, decnet, ip, ip6,
266 ipx, iso, lat, loopback, mopdl, moprc, netbeui, rarp, sca or
267 stp. Note these identifiers (except loopback) are also keywords
268 and must be escaped via backslash (\).
269 [In the case of FDDI (e.g., `fddi proto \arp'), Token Ring
271 (e.g., `tr proto \arp'), and IEEE 802.11 wireless LANs (e.g.,
272 `wlan proto \arp'), for most of those protocols, the protocol
273 identification comes from the 802.2 Logical Link Control (LLC)
274 header, which is usually layered on top of the FDDI, Token Ring,
275 or 802.11 header.
276 When filtering for most protocol identifiers on FDDI, Token
278 Ring, or 802.11, the filter checks only the protocol ID field of
279 an LLC header in so-called SNAP format with an Organizational
280 Unit Identifier (OUI) of 0x000000, for encapsulated Ethernet; it
281 doesn't check whether the packet is in SNAP format with an OUI
282 of 0x000000. The exceptions are:
283 iso the filter checks the DSAP (Destination Service Access
285 Point) and SSAP (Source Service Access Point) fields of
286 the LLC header;
287 stp and netbeui
289 the filter checks the DSAP of the LLC header;
290 atalk the filter checks for a SNAP-format packet with an OUI of
292 0x080007 and the AppleTalk etype.
293 In the case of Ethernet, the filter checks the Ethernet type
295 field for most of those protocols. The exceptions are:
296 iso, stp, and netbeui
298 the filter checks for an 802.3 frame and then checks the
299 LLC header as it does for FDDI, Token Ring, and 802.11;
300 atalk the filter checks both for the AppleTalk etype in an Eth‐
302 ernet frame and for a SNAP-format packet as it does for
303 FDDI, Token Ring, and 802.11;
304 aarp the filter checks for the AppleTalk ARP etype in either
306 an Ethernet frame or an 802.2 SNAP frame with an OUI of
307 0x000000;
308 ipx the filter checks for the IPX etype in an Ethernet frame,
310 the IPX DSAP in the LLC header, the 802.3-with-no-LLC-
311 header encapsulation of IPX, and the IPX etype in a SNAP
312 frame.
313 ip, ip6, arp, rarp, atalk, aarp, decnet, iso, stp, ipx, netbeui
315 Abbreviations for:
316 ether proto \protocol
317 where protocol is one of the above protocols.
318 lat, moprc, mopdl
320 Abbreviations for:
321 ether proto \protocol
322 where protocol is one of the above protocols. Note that not all
323 applications using pcap(3PCAP) currently know how to parse these
324 protocols.
325 decnet src host
327 True if the DECnet source address is host, which may be an
328 address of the form ``10.123'', or a DECnet host name. [DECnet
329 host name support is only available on ULTRIX systems that are
330 configured to run DECnet.]
331 decnet dst host
333 True if the DECnet destination address is host.
334 decnet host host
336 True if either the DECnet source or destination address is host.
337 llc True if the packet has an 802.2 LLC header. This includes:
339 Ethernet packets with a length field rather than a type field
341 that aren't raw NetWare-over-802.3 packets;
342 IEEE 802.11 data packets;
344 Token Ring packets (no check is done for LLC frames);
346 FDDI packets (no check is done for LLC frames);
348 LLC-encapsulated ATM packets, for SunATM on Solaris.
350 llc type
352 True if the packet has an 802.2 LLC header and has the specified
353 type. type can be one of:
354 i Information (I) PDUs
356 s Supervisory (S) PDUs
358 u Unnumbered (U) PDUs
360 rr Receiver Ready (RR) S PDUs
362 rnr Receiver Not Ready (RNR) S PDUs
364 rej Reject (REJ) S PDUs
366 ui Unnumbered Information (UI) U PDUs
368 ua Unnumbered Acknowledgment (UA) U PDUs
370 disc Disconnect (DISC) U PDUs
372 sabme Set Asynchronous Balanced Mode Extended (SABME) U PDUs
374 test Test (TEST) U PDUs
376 xid Exchange Identification (XID) U PDUs
378 frmr Frame Reject (FRMR) U PDUs
380 inbound
382 Packet was received by the host performing the capture rather
383 than being sent by that host. This is only supported for cer‐
384 tain link-layer types, such as SLIP and the ``cooked'' Linux
385 capture mode used for the ``any'' device and for some other
386 device types.
387 outbound
389 Packet was sent by the host performing the capture rather than
390 being received by that host. This is only supported for certain
391 link-layer types, such as SLIP and the ``cooked'' Linux capture
392 mode used for the ``any'' device and for some other device
393 types.
394 ifname interface
396 True if the packet was logged as coming from the specified
397 interface (applies only to packets logged by OpenBSD's or Free‐
398 BSD's pf(4)).
399 on interface
401 Synonymous with the ifname modifier.
402 rnr num
404 True if the packet was logged as matching the specified PF rule
405 number (applies only to packets logged by OpenBSD's or FreeBSD's
406 pf(4)).
407 rulenum num
409 Synonymous with the rnr modifier.
410 reason code
412 True if the packet was logged with the specified PF reason code.
413 The known codes are: match, bad-offset, fragment, short, normal‐
414 ize, and memory (applies only to packets logged by OpenBSD's or
415 FreeBSD's pf(4)).
416 rset name
418 True if the packet was logged as matching the specified PF rule‐
419 set name of an anchored ruleset (applies only to packets logged
420 by OpenBSD's or FreeBSD's pf(4)).
421 ruleset name
423 Synonymous with the rset modifier.
424 srnr num
426 True if the packet was logged as matching the specified PF rule
427 number of an anchored ruleset (applies only to packets logged by
428 OpenBSD's or FreeBSD's pf(4)).
429 subrulenum num
431 Synonymous with the srnr modifier.
432 action act
434 True if PF took the specified action when the packet was logged.
435 Known actions are: pass and block and, with later versions of
436 pf(4), nat, rdr, binat and scrub (applies only to packets logged
437 by OpenBSD's or FreeBSD's pf(4)).
438 wlan ra ehost
440 True if the IEEE 802.11 RA is ehost. The RA field is used in
441 all frames except for management frames.
442 wlan ta ehost
444 True if the IEEE 802.11 TA is ehost. The TA field is used in
445 all frames except for management frames and CTS (Clear To Send)
446 and ACK (Acknowledgment) control frames.
447 wlan addr1 ehost
449 True if the first IEEE 802.11 address is ehost.
450 wlan addr2 ehost
452 True if the second IEEE 802.11 address, if present, is ehost.
453 The second address field is used in all frames except for CTS
454 (Clear To Send) and ACK (Acknowledgment) control frames.
455 wlan addr3 ehost
457 True if the third IEEE 802.11 address, if present, is ehost.
458 The third address field is used in management and data frames,
459 but not in control frames.
460 wlan addr4 ehost
462 True if the fourth IEEE 802.11 address, if present, is ehost.
463 The fourth address field is only used for WDS (Wireless Distri‐
464 bution System) frames.
465 type wlan_type
467 True if the IEEE 802.11 frame type matches the specified
468 wlan_type. Valid wlan_types are: mgt, ctl and data.
469 type wlan_type subtype wlan_subtype
471 True if the IEEE 802.11 frame type matches the specified
472 wlan_type and frame subtype matches the specified wlan_subtype.
473 If the specified wlan_type is mgt, then valid wlan_subtypes are:
475 assoc-req, assoc-resp, reassoc-req, reassoc-resp, probe-req,
476 probe-resp, beacon, atim, disassoc, auth and deauth.
477 If the specified wlan_type is ctl, then valid wlan_subtypes are:
479 ps-poll, rts, cts, ack, cf-end and cf-end-ack.
480 If the specified wlan_type is data, then valid wlan_subtypes
482 are: data, data-cf-ack, data-cf-poll, data-cf-ack-poll, null,
483 cf-ack, cf-poll, cf-ack-poll, qos-data, qos-data-cf-ack, qos-
484 data-cf-poll, qos-data-cf-ack-poll, qos, qos-cf-poll and qos-cf-
485 ack-poll.
486 subtype wlan_subtype
488 True if the IEEE 802.11 frame subtype matches the specified
489 wlan_subtype and frame has the type to which the specified
490 wlan_subtype belongs.
491 dir dir
493 True if the IEEE 802.11 frame direction matches the specified
494 dir. Valid directions are: nods, tods, fromds, dstods, or a
495 numeric value.
496 vlan [vlan_id]
498 True if the packet is an IEEE 802.1Q VLAN packet. If the
499 optional vlan_id is specified, only true if the packet has the
500 specified vlan_id. Note that the first vlan keyword encountered
501 in an expression changes the decoding offsets for the remainder
502 of the expression on the assumption that the packet is a VLAN
503 packet. The `vlan [vlan_id]` keyword may be used more than
504 once, to filter on VLAN hierarchies. Each use of that keyword
505 increments the filter offsets by 4.
506 For example:
508 vlan 100 && vlan 200
509 filters on VLAN 200 encapsulated within VLAN 100, and
510 vlan && vlan 300 && ip
511 filters IPv4 protocol encapsulated in VLAN 300 encapsulated
512 within any higher order VLAN.
513 mpls [label_num]
515 True if the packet is an MPLS packet. If the optional label_num
516 is specified, only true if the packet has the specified
517 label_num. Note that the first mpls keyword encountered in an
518 expression changes the decoding offsets for the remainder of the
519 expression on the assumption that the packet is a MPLS-encapsu‐
520 lated IP packet. The `mpls [label_num]` keyword may be used
521 more than once, to filter on MPLS hierarchies. Each use of that
522 keyword increments the filter offsets by 4.
523 For example:
525 mpls 100000 && mpls 1024
526 filters packets with an outer label of 100000 and an inner label
527 of 1024, and
528 mpls && mpls 1024 && host 192.9.200.1
529 filters packets to or from 192.9.200.1 with an inner label of
530 1024 and any outer label.
531 pppoed True if the packet is a PPP-over-Ethernet Discovery packet (Eth‐
533 ernet type 0x8863).
534 pppoes [session_id]
536 True if the packet is a PPP-over-Ethernet Session packet (Ether‐
537 net type 0x8864). If the optional session_id is specified, only
538 true if the packet has the specified session_id. Note that the
539 first pppoes keyword encountered in an expression changes the
540 decoding offsets for the remainder of the expression on the
541 assumption that the packet is a PPPoE session packet.
542 For example:
544 pppoes 0x27 && ip
545 filters IPv4 protocol encapsulated in PPPoE session id 0x27.
546 geneve [vni]
548 True if the packet is a Geneve packet (UDP port 6081). If the
549 optional vni is specified, only true if the packet has the spec‐
550 ified vni. Note that when the geneve keyword is encountered in
551 an expression, it changes the decoding offsets for the remainder
552 of the expression on the assumption that the packet is a Geneve
553 packet.
554 For example:
556 geneve 0xb && ip
557 filters IPv4 protocol encapsulated in Geneve with VNI 0xb. This
558 will match both IPv4 directly encapsulated in Geneve as well as
559 IPv4 contained inside an Ethernet frame.
560 iso proto protocol
562 True if the packet is an OSI packet of protocol type protocol.
563 Protocol can be a number or one of the names clnp, esis, or
564 isis.
565 clnp, esis, isis
567 Abbreviations for:
568 iso proto \protocol
569 where protocol is one of the above protocols.
570 l1, l2, iih, lsp, snp, csnp, psnp
572 Abbreviations for IS-IS PDU types.
573 vpi n True if the packet is an ATM packet, for SunATM on Solaris, with
575 a virtual path identifier of n.
576 vci n True if the packet is an ATM packet, for SunATM on Solaris, with
578 a virtual channel identifier of n.
579 lane True if the packet is an ATM packet, for SunATM on Solaris, and
581 is an ATM LANE packet. Note that the first lane keyword encoun‐
582 tered in an expression changes the tests done in the remainder
583 of the expression on the assumption that the packet is either a
584 LANE emulated Ethernet packet or a LANE LE Control packet. If
585 lane isn't specified, the tests are done under the assumption
586 that the packet is an LLC-encapsulated packet.
587 oamf4s True if the packet is an ATM packet, for SunATM on Solaris, and
589 is a segment OAM F4 flow cell (VPI=0 & VCI=3).
590 oamf4e True if the packet is an ATM packet, for SunATM on Solaris, and
592 is an end-to-end OAM F4 flow cell (VPI=0 & VCI=4).
593 oamf4 True if the packet is an ATM packet, for SunATM on Solaris, and
595 is a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 |
596 VCI=4)).
597 oam True if the packet is an ATM packet, for SunATM on Solaris, and
599 is a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 |
600 VCI=4)).
601 metac True if the packet is an ATM packet, for SunATM on Solaris, and
603 is on a meta signaling circuit (VPI=0 & VCI=1).
604 bcc True if the packet is an ATM packet, for SunATM on Solaris, and
606 is on a broadcast signaling circuit (VPI=0 & VCI=2).
607 sc True if the packet is an ATM packet, for SunATM on Solaris, and
609 is on a signaling circuit (VPI=0 & VCI=5).
610 ilmic True if the packet is an ATM packet, for SunATM on Solaris, and
612 is on an ILMI circuit (VPI=0 & VCI=16).
613 connectmsg
615 True if the packet is an ATM packet, for SunATM on Solaris, and
616 is on a signaling circuit and is a Q.2931 Setup, Call Proceed‐
617 ing, Connect, Connect Ack, Release, or Release Done message.
618 metaconnect
620 True if the packet is an ATM packet, for SunATM on Solaris, and
621 is on a meta signaling circuit and is a Q.2931 Setup, Call Pro‐
622 ceeding, Connect, Release, or Release Done message.
623 expr relop expr
625 True if the relation holds, where relop is one of >, <, >=, <=,
626 =, !=, and expr is an arithmetic expression composed of integer
627 constants (expressed in standard C syntax), the normal binary
628 operators [+, -, *, /, %, &, |, ^, <<, >>], a length operator,
629 and special packet data accessors. Note that all comparisons
630 are unsigned, so that, for example, 0x80000000 and 0xffffffff
631 are > 0.
632 The % and ^ operators are currently only supported for filtering
634 in the kernel on Linux with 3.7 and later kernels; on all other
635 systems, if those operators are used, filtering will be done in
636 user mode, which will increase the overhead of capturing packets
637 and may cause more packets to be dropped.
638 To access data inside the packet, use the following syntax:
640 proto [ expr : size ]
641 Proto is one of ether, fddi, tr, wlan, ppp, slip, link, ip, arp,
642 rarp, tcp, udp, icmp, ip6 or radio, and indicates the protocol
643 layer for the index operation. (ether, fddi, wlan, tr, ppp,
644 slip and link all refer to the link layer. radio refers to the
645 "radio header" added to some 802.11 captures.) Note that tcp,
646 udp and other upper-layer protocol types only apply to IPv4, not
647 IPv6 (this will be fixed in the future). The byte offset, rela‐
648 tive to the indicated protocol layer, is given by expr. Size is
649 optional and indicates the number of bytes in the field of
650 interest; it can be either one, two, or four, and defaults to
651 one. The length operator, indicated by the keyword len, gives
652 the length of the packet.
653 For example, `ether[0] & 1 != 0' catches all multicast traffic.
655 The expression `ip[0] & 0xf != 5' catches all IPv4 packets with
656 options. The expression `ip[6:2] & 0x1fff = 0' catches only
657 unfragmented IPv4 datagrams and frag zero of fragmented IPv4
658 datagrams. This check is implicitly applied to the tcp and udp
659 index operations. For instance, tcp[0] always means the first
660 byte of the TCP header, and never means the first byte of an
661 intervening fragment.
662 Some offsets and field values may be expressed as names rather
664 than as numeric values. The following protocol header field
665 offsets are available: icmptype (ICMP type field), icmp6type
666 (ICMPv6 type field), icmpcode (ICMP code field), icmp6code
667 (ICMPv6 code field) and tcpflags (TCP flags field).
668 The following ICMP type field values are available: icmp-echore‐
670 ply, icmp-unreach, icmp-sourcequench, icmp-redirect, icmp-echo,
671 icmp-routeradvert, icmp-routersolicit, icmp-timxceed, icmp-
672 paramprob, icmp-tstamp, icmp-tstampreply, icmp-ireq, icmp-ire‐
673 qreply, icmp-maskreq, icmp-maskreply.
674 The following ICMPv6 type fields are available: icmp6-destina‐
676 tionrunreach, icmp6-packettoobig, icmp6-timeexceeded,
677 icmp6-parameterproblem, icmp6-echo, icmp6-echoreply, icmp6-mul‐
678 ticastlistenerquery, icmp6-multicastlistenerreportv1, icmp6-mul‐
679 ticastlistenerdone, icmp6-routersolicit, icmp6-routeradvert,
680 icmp6-neighborsolicit, icmp6-neighboradvert, icmp6-redirect,
681 icmp6-routerrenum, icmp6-nodeinformationquery, icmp6-nodeinfor‐
682 mationresponse, icmp6-ineighbordiscoverysolicit, icmp6-ineigh‐
683 bordiscoveryadvert, icmp6-multicastlistenerreportv2, icmp6-home‐
684 agentdiscoveryrequest, icmp6-homeagentdiscoveryreply,
685 icmp6-mobileprefixsolicit, icmp6-mobileprefixadvert, icmp6-cert‐
686 pathsolicit, icmp6-certpathadvert, icmp6-multicastrouteradvert,
687 icmp6-multicastroutersolicit, icmp6-multicastrouterterm.
688 The following TCP flags field values are available: tcp-fin,
690 tcp-syn, tcp-rst, tcp-push, tcp-ack, tcp-urg, tcp-ece, tcp-cwr.
691 Primitives may be combined using:
693 A parenthesized group of primitives and operators.
695 Negation (`!' or `not').
697 Concatenation (`&&' or `and').
699 Alternation (`||' or `or').
701 Negation has the highest precedence. Alternation and concatenation
703 have equal precedence and associate left to right. Note that explicit
704 and tokens, not juxtaposition, are now required for concatenation.
705 If an identifier is given without a keyword, the most recent keyword is
707 assumed. For example,
708 not host vs and ace
709 is short for
710 not host vs and host ace
711 which should not be confused with
712 not (host vs or ace)
713
715 To select all packets arriving at or departing from `sundown':
716 host sundown
717 To select traffic between `helios' and either `hot' or `ace':
719 host helios and (hot or ace)
720 To select all IPv4 packets between `ace' and any host except `helios':
722 ip host ace and not helios
723 To select all traffic between local hosts and hosts at Berkeley:
725 net ucb-ether
726 To select all FTP traffic through Internet gateway `snup':
728 gateway snup and (port ftp or ftp-data)
729 To select IPv4 traffic neither sourced from nor destined for local
731 hosts (if you gateway to one other net, this stuff should never make it
732 onto your local net).
733 ip and not net localnet
734 To select the start and end packets (the SYN and FIN packets) of each
736 TCP conversation that involves a non-local host.
737 tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net localnet
738 To select the TCP packets with flags RST and ACK both set. (i.e.
740 select only the RST and ACK flags in the flags field, and if the result
741 is "RST and ACK both set", match)
742 tcp[tcpflags] & (tcp-rst|tcp-ack) == (tcp-rst|tcp-ack)
743 To select all IPv4 HTTP packets to and from port 80, i.e. print only
745 packets that contain data, not, for example, SYN and FIN packets and
746 ACK-only packets. (IPv6 is left as an exercise for the reader.)
747 tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)
748 To select IPv4 packets longer than 576 bytes sent through gateway
750 `snup':
751 gateway snup and ip[2:2] > 576
752 To select IPv4 broadcast or multicast packets that were not sent via
754 Ethernet broadcast or multicast:
755 ether[0] & 1 = 0 and ip[16] >= 224
756 To select all ICMP packets that are not echo requests/replies (i.e.,
758 not ping packets):
759 icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply
760 icmp6[icmp6type] != icmp6-echo and icmp6[icmp6type] != icmp6-echoreply
761
763 pcap(3PCAP)
764
766 To report a security issue please send an e-mail to security@tcp‐
767 dump.org.
768 To report bugs and other problems, contribute patches, request a fea‐
770 ture, provide generic feedback etc please see the file CONTRIBUTING.md
771 in the libpcap source tree root.
772 Filter expressions on fields other than those in Token Ring headers
774 will not correctly handle source-routed Token Ring packets.
775 Filter expressions on fields other than those in 802.11 headers will
777 not correctly handle 802.11 data packets with both To DS and From DS
778 set.
779 `ip6 proto' should chase header chain, but at this moment it does not.
781 `ip6 protochain' is supplied for this behavior. For example, to match
782 IPv6 fragments: `ip6 protochain 44'
783 Arithmetic expression against transport layer headers, like tcp[0],
785 does not work against IPv6 packets. It only looks at IPv4 packets.
786 2 September 2020 PCAP-FILTER(7)