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22 .TH PCAP 3 "3 January 2001"
24 pcap \- Packet Capture library
33 char errbuf[PCAP_ERRBUF_SIZE];
37 pcap_t *pcap_open_live(const char *device, int snaplen,
39 int promisc, int to_ms, char *errbuf)
40 pcap_t *pcap_open_dead(int linktype, int snaplen)
41 pcap_t *pcap_open_offline(const char *fname, char *errbuf)
42 pcap_dumper_t *pcap_dump_open(pcap_t *p, const char *fname)
46 int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
47 int pcap_getnonblock(pcap_t *p, char *errbuf);
51 int pcap_findalldevs(pcap_if_t **alldevsp, char *errbuf)
52 void pcap_freealldevs(pcap_if_t *alldevs)
53 char *pcap_lookupdev(char *errbuf)
54 int pcap_lookupnet(const char *device, bpf_u_int32 *netp,
56 bpf_u_int32 *maskp, char *errbuf)
60 int pcap_dispatch(pcap_t *p, int cnt,
62 pcap_handler callback, u_char *user)
63 int pcap_loop(pcap_t *p, int cnt,
65 pcap_handler callback, u_char *user)
66 void pcap_dump(u_char *user, struct pcap_pkthdr *h,
72 int pcap_compile(pcap_t *p, struct bpf_program *fp,
74 char *str, int optimize, bpf_u_int32 netmask)
75 int pcap_setfilter(pcap_t *p, struct bpf_program *fp)
76 void pcap_freecode(struct bpf_program *);
80 const u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h)
84 int pcap_datalink(pcap_t *p)
85 int pcap_list_datalinks(pcap_t *p, int **dlt_buf);
86 int pcap_set_datalink(pcap_t *p, int dlt);
87 int pcap_datalink_name_to_val(const char *name);
88 const char *pcap_datalink_val_to_name(int dlt);
89 int pcap_snapshot(pcap_t *p)
90 int pcap_is_swapped(pcap_t *p)
91 int pcap_major_version(pcap_t *p)
92 int pcap_minor_version(pcap_t *p)
93 int pcap_stats(pcap_t *p, struct pcap_stat *ps)
94 FILE *pcap_file(pcap_t *p)
95 int pcap_fileno(pcap_t *p)
96 void pcap_perror(pcap_t *p, char *prefix)
97 char *pcap_geterr(pcap_t *p)
98 char *pcap_strerror(int error)
99 const char *pcap_lib_version(void)
103 void pcap_close(pcap_t *p)
104 int pcap_dump_flush(pcap_dumper_t *p)
105 void pcap_dump_close(pcap_dumper_t *p)
109 The Packet Capture library
110 provides a high level interface to packet capture systems. All packets
111 on the network, even those destined for other hosts, are accessible
112 through this mechanism.
118 .BR pcap_open_live() ,
119 .BR pcap_open_dead() ,
120 .BR pcap_open_offline() ,
121 .BR pcap_setnonblock() ,
122 .BR pcap_getnonblock() ,
123 .BR pcap_findalldevs() ,
124 .BR pcap_lookupdev() ,
127 is assumed to be able to hold at least
132 is used to obtain a packet capture descriptor to look
133 at packets on the network.
135 is a string that specifies the network device to open; on Linux systems
136 with 2.2 or later kernels, a
140 can be used to capture packets from all interfaces.
142 specifies the maximum number of bytes to capture. If this value is less
143 than the size of a packet that is captured, only the first
145 bytes of that packet will be captured and provided as packet data. A
146 value of 65535 should be sufficient, on most if not all networks, to
147 capture all the data available from the packet.
149 specifies if the interface is to be put into promiscuous mode.
150 (Note that even if this parameter is false, the interface
151 could well be in promiscuous mode for some other reason.) For now, this
152 doesn't work on the "any" device; if an argument of "any" or NULL is
157 specifies the read timeout in milliseconds. The read timeout is used to
158 arrange that the read not necessarily return immediately when a packet
159 is seen, but that it wait for some amount of time to allow more packets
160 to arrive and to read multiple packets from the OS kernel in one
161 operation. Not all platforms support a read timeout; on platforms that
162 don't, the read timeout is ignored. A zero value for
164 on platforms that support a read timeout,
165 will cause a read to wait forever to allow enough packets to
166 arrive, with no timeout.
168 is used to return error or warning text. It will be set to error text when
173 may also be set to warning text when
175 succeds; to detect this case the caller should store a zero-length string in
179 and display the warning to the user if
181 is no longer a zero-length string.
184 is used for creating a
186 structure to use when calling the other functions in libpcap. It is
187 typically used when just using libpcap for compiling BPF code.
189 .B pcap_open_offline()
190 is called to open a ``savefile'' for reading.
192 specifies the name of the file to open. The file has
193 the same format as those used by
197 The name "-" in a synonym for
200 is used to return error text and is only set when
201 .B pcap_open_offline()
206 is called to open a ``savefile'' for writing. The name "-" in a synonym
210 is returned on failure.
214 struct as returned by
215 .B pcap_open_offline()
217 .BR pcap_open_live() .
219 specifies the name of the file to open.
224 can be used to get the error text.
226 .B pcap_setnonblock()
227 puts a capture descriptor, opened with
228 .BR pcap_open_live() ,
229 into ``non-blocking'' mode, or takes it out of ``non-blocking'' mode,
230 depending on whether the
232 argument is non-zero or zero. It has no effect on ``savefiles''.
233 If there is an error, \-1 is returned and
235 is filled in with an appropriate error message; otherwise, 0 is
238 ``non-blocking'' mode, an attempt to read from the capture descriptor
241 will, if no packets are currently available to be read, return 0
242 immediately rather than blocking waiting for packets to arrive.
246 will not work in ``non-blocking'' mode.
248 .B pcap_getnonblock()
249 returns the current ``non-blocking'' state of the capture descriptor; it
250 always returns 0 on ``savefiles''.
251 If there is an error, \-1 is returned and
253 is filled in with an appropriate error message.
255 .B pcap_findalldevs()
256 constructs a list of network devices that can be opened with
257 .BR pcap_open_live() .
258 (Note that there may be network devices that cannot be opened with
262 .BR pcap_findalldevs() ,
263 because, for example, that process might not have sufficient privileges
264 to open them for capturing; if so, those devices will not appear on the
267 is set to point to the first element of the list; each element of the
270 and has the following members:
276 a pointer to the next element in the list;
278 for the last element of the list
281 a pointer to a string giving a name for the device to pass to
287 a pointer to a string giving a human-readable description of the device
290 a pointer to the first element of a list of addresses for the interface
297 set if the interface is a loopback interface
301 Each element of the list of addresses is of type
303 and has the following members:
309 a pointer to the next element in the list;
311 for the last element of the list
316 containing an address
323 that contains the netmask corresponding to the address pointed to by
331 that contains the broadcast address corresponding to the address pointed
334 may be null if the interface doesn't support broadcasts
341 that contains the destination address corresponding to the address pointed
344 may be null if the interface isn't a point-to-point interface
347 .B pcap_freealldevs()
348 is used to free a list allocated by
349 .BR pcap_findalldevs() .
352 returns a pointer to a network device suitable for use with
355 .BR pcap_lookupnet() .
356 If there is an error,
360 is filled in with an appropriate error message.
363 is used to determine the network number and mask
364 associated with the network device
373 A return of \-1 indicates an error in which case
375 is filled in with an appropriate error message.
378 is used to collect and process packets.
380 specifies the maximum number of packets to process before returning.
381 This is not a minimum number; when reading a live capture, only one
382 bufferful of packets is read at a time, so fewer than
384 packets may be processed. A
386 of \-1 processes all the packets received in one buffer when reading a
387 live capture, or all the packets in the file when reading a
390 specifies a routine to be called with three arguments:
393 pointer which is passed in from
394 .BR pcap_dispatch() ,
396 .I const struct pcap_pkthdr
397 pointer to a structure with the following members:
403 containing the time when the packet was captured
408 giving the number of bytes of the packet that are available from the
414 giving the length of the packet, in bytes (which might be more than the
415 number of bytes available from the capture, if the length of the packet
416 is larger than the maximum number of bytes to capture)
424 .I struct pcap_pkthdr
425 a pointer to which is passed to the callback routine)
426 bytes of data from the packet (which won't necessarily be the entire
427 packet; to capture the entire packet, you will have to provide a value
432 that is sufficiently large to get all of the packet's data - a value of
433 65535 should be sufficient on most if not all networks).
435 The number of packets read is returned.
436 0 is returned if no packets were read from a live capture (if, for
437 example, they were discarded because they didn't pass the packet filter,
438 or if, on platforms that support a read timeout that starts before any
439 packets arrive, the timeout expires before any packets arrive, or if the
440 file descriptor for the capture device is in non-blocking mode and no
441 packets were available to be read) or if no more packets are available
442 in a ``savefile.'' A return of \-1 indicates
443 an error in which case
447 may be used to display the error text.
450 when reading a live capture,
452 will not necessarily return when the read times out; on some platforms,
453 the read timeout isn't supported, and, on other platforms, the timer
454 doesn't start until at least one packet arrives. This means that the
457 be used in, for example, an interactive application, to allow the packet
458 capture loop to ``poll'' for user input periodically, as there's no
461 will return after the timeout expires.
466 except it keeps reading packets until
468 packets are processed or an error occurs.
471 return when live read timeouts occur.
472 Rather, specifying a non-zero read timeout to
476 allows the reception and processing of any packets that arrive when the
482 to loop forever (or at least until an error occurs). A negative number
483 is returned on an error; 0 is returned if
488 reads the next packet (by calling
494 pointer to the data in that packet. (The
496 struct for that packet is not supplied.)
498 is returned if an error occured, or if no packets were read from a live
499 capture (if, for example, they were discarded because they didn't pass
500 the packet filter, or if, on platforms that support a read timeout that
501 starts before any packets arrive, the timeout expires before any packets
502 arrive, or if the file descriptor for the capture device is in
503 non-blocking mode and no packets were available to be read), or if no
504 more packets are available in a ``savefile.'' Unfortunately, there is
505 no way to determine whether an error occured or not.
508 outputs a packet to the ``savefile'' opened with
509 .BR pcap_dump_open() .
510 Note that its calling arguments are suitable for use with
514 If called directly, the
519 .BR pcap_dump_open() .
522 is used to compile the string
524 into a filter program.
528 struct and is filled in by
531 controls whether optimization on the resulting code is performed.
533 specifies the IPv4 netmask of the network on which packets are being
534 captured; it is used only when checking for IPv4 broadcast addresses in
535 the filter program. If the netmask of the network on which packets are
536 being captured isn't known to the program, or if packets are being
537 captured on the Linux "any" pseudo-interface that can capture on more
538 than one network, a value of 0 can be supplied; tests for IPv4 broadcast
539 addreses won't be done correctly, but all other tests in the filter
540 program will be OK. A return of \-1 indicates an error in which case
542 may be used to display the error text.
544 .B pcap_compile_nopcap()
547 except that instead of passing a pcap structure, one passes the
548 snaplen and linktype explicitly. It is intended to be used for
549 compiling filters for direct BPF usage, without necessarily having
552 A return of \-1 indicates an error; the error text is unavailable.
553 .RB ( pcap_compile_nopcap()
555 .BR pcap_open_dead() ,
559 the latter three routines can be used directly in order to get the error
560 text for a compilation error.)
564 is used to specify a filter program.
568 struct, usually the result of a call to
571 is returned on failure, in which case
573 may be used to display the error text;
575 is returned on success.
578 is used to free up allocated memory pointed to by a
582 when that BPF program is no longer needed, for example after it
583 has been made the filter program for a pcap structure by a call to
584 .BR pcap_setfilter() .
587 returns the link layer type; link layer types it can return include:
592 BSD loopback encapsulation; the link layer header is a 4-byte field, in
594 byte order, containing a PF_ value from
596 for the network-layer protocol of the packet
598 Note that ``host byte order'' is the byte order of the machine on which
599 the packets are captured, and the PF_ values are for the OS of the
600 machine on which the packets are captured; if a live capture is being
601 done, ``host byte order'' is the byte order of the machine capturing the
602 packets, and the PF_ values are those of the OS of the machine capturing
603 the packets, but if a ``savefile'' is being read, the byte order and PF_
606 necessarily those of the machine reading the capture file.
609 Ethernet (10Mb, 100Mb, 1000Mb, and up)
612 IEEE 802.5 Token Ring
618 SLIP; the link layer header contains, in order:
621 a 1-byte flag, which is 0 for packets received by the machine and 1 for
622 packets sent by the machine;
624 a 1-byte field, the upper 4 bits of which indicate the type of packet,
629 an unmodified IP datagram (TYPE_IP);
632 an uncompressed-TCP IP datagram (UNCOMPRESSED_TCP), with that byte being
633 the first byte of the raw IP header on the wire, containing the
634 connection number in the protocol field;
637 a compressed-TCP IP datagram (COMPRESSED_TCP), with that byte being the
638 first byte of the compressed TCP/IP datagram header;
641 for UNCOMPRESSED_TCP, the rest of the modified IP header, and for
642 COMPRESSED_TCP, the compressed TCP/IP datagram header;
646 for a total of 16 bytes; the uncompressed IP datagram follows the header
650 PPP; if the first 2 bytes are 0xff and 0x03, it's PPP in HDLC-like
651 framing, with the PPP header following those two bytes, otherwise it's
652 PPP without framing, and the packet begins with the PPP header
658 RFC 1483 LLC/SNAP-encapsulated ATM; the packet begins with an IEEE 802.2
662 raw IP; the packet begins with an IP header
665 PPP in HDLC-like framing, as per RFC 1662, or Cisco PPP with HDLC
666 framing, as per section 4.3.1 of RFC 1547; the first byte will be 0xFF
667 for PPP in HDLC-like framing, and will be 0x0F or 0x8F for Cisco PPP
671 PPPoE; the packet begins with a PPPoE header, as per RFC 2516
674 Cisco PPP with HDLC framing, as per section 4.3.1 of RFC 1547
677 IEEE 802.11 wireless LAN
683 OpenBSD loopback encapsulation; the link layer header is a 4-byte field, in
685 byte order, containing a PF_ value from OpenBSD's
687 for the network-layer protocol of the packet
689 Note that, if a ``savefile'' is being read, those PF_ values are
691 necessarily those of the machine reading the capture file.
694 Linux "cooked" capture encapsulation; the link layer header contains, in
698 a 2-byte "packet type", in network byte order, which is one of:
702 packet was sent to us by somebody else
705 packet was broadcast by somebody else
708 packet was multicast, but not broadcast, by somebody else
711 packet was sent by somebody else to somebody else
714 packet was sent by us
717 a 2-byte field, in network byte order, containing a Linux ARPHRD_ value
718 for the link layer device type;
720 a 2-byte field, in network byte order, containing the length of the
721 link layer address of the sender of the packet (which could be 0);
723 an 8-byte field containing that number of bytes of the link layer header
724 (if there are more than 8 bytes, only the first 8 are present);
726 a 2-byte field containing an Ethernet protocol type, in network byte
727 order, or containing 1 for Novell 802.3 frames without an 802.2 LLC
728 header or 4 for frames beginning with an 802.2 LLC header.
732 Apple LocalTalk; the packet begins with an AppleTalk LLAP header
735 SunATM devices; the link layer header contains, in order:
738 a 1-byte flag field, containing a direction flag in the uppermost bit,
739 which is set for packets transmitted by the machine and clear for
740 packets received by the machine, and a 4-byte traffic type in the
741 low-order 4 bits, which is one of:
751 LLC-encapsulated traffic
768 a 2-byte VCI field, in network byte order.
772 RFC 2625 IP-over-Fibre Channel, with the link-layer header being the
773 Network_Header as described in that RFC.
776 .B pcap_list_datalinks()
777 is used to get a list of the supported data link types of the interface
778 associated with the pcap descriptor.
779 .B pcap_list_datalinks()
780 allocates an array to hold the list and sets
782 The caller is responsible for freeing the array.
784 is returned on failure;
785 otherwise, the number of data link types in the array is returned.
787 .B pcap_set_datalink()
788 is used to set the current data link type of the pcap descriptor
789 to the type specified by
792 is returned on failure.
794 .B pcap_datalink_name_to_val()
795 translates a data link type name, which is a
799 removed, to the corresponding data link type value. The translation
801 is used to set the current data link type of the pcap descriptor
802 NULL is returned on failure.
804 .B pcap_datalink_val_to_name()
805 translates a data link type value to the corresponding data link type
808 is returned on failure.
811 returns the snapshot length specified when
816 returns true if the current ``savefile'' uses a different byte order
817 than the current system.
819 .B pcap_major_version()
820 returns the major number of the file format of the savefile;
821 .B pcap_minor_version()
822 returns the minor number of the file format of the savefile. The
823 version number is stored in the header of the savefile.
826 returns the standard I/O stream of the ``savefile,'' if a ``savefile''
828 .BR pcap_open_offline() ,
829 or NULL, if a network device was opened with
830 .BR pcap_open_live() .
833 returns 0 and fills in a
835 struct. The values represent packet statistics from the start of the
836 run to the time of the call. If there is an error or the underlying
837 packet capture doesn't support packet statistics, \-1 is returned and
838 the error text can be obtained with
843 is supported only on live captures, not on ``savefiles''; no statistics
844 are stored in ``savefiles'', so no statistics are available when reading
848 returns the file descriptor number from which captured packets are read,
849 if a network device was opened with
850 .BR pcap_open_live() ,
851 or \-1, if a ``savefile'' was opened with
852 .BR pcap_open_offline() .
855 prints the text of the last pcap library error on
861 returns the error text pertaining to the last pcap library error.
863 the pointer it returns will no longer point to a valid error message
866 passed to it is closed; you must use or copy the string before closing
875 .B pcap_lib_version()
876 returns a pointer to a string giving information about the version of
877 the libpcap library being used; note that it contains more information
878 than just a version number.
881 closes the files associated with
883 and deallocates resources.
886 flushes the output buffer to the ``savefile,'' so that any packets
889 but not yet written to the ``savefile'' will be written.
891 is returned on error, 0 on success.
894 closes the ``savefile.''
897 tcpdump(1), tcpslice(1)
899 The original authors are:
903 Steven McCanne, all of the
904 Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
906 The current version is available from "The Tcpdump Group"'s Web site at
909 .I http://www.tcpdump.org/
912 Please send problems, bugs, questions, desirable enhancements, etc. to:
915 tcpdump-workers@tcpdump.org
918 Please send source code contributions, etc. to:
projects / libpcap / blob