770 lines
20 KiB
Groff
770 lines
20 KiB
Groff
.\" @(#) $Header: /tcpdump/master/libpcap/pcap.3,v 1.31 2001/12/29 21:57:07 guy Exp $
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.\"
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.\" Copyright (c) 1994, 1996, 1997
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that: (1) source code distributions
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.\" retain the above copyright notice and this paragraph in its entirety, (2)
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.\" distributions including binary code include the above copyright notice and
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.\" this paragraph in its entirety in the documentation or other materials
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.\" provided with the distribution, and (3) all advertising materials mentioning
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.\" features or use of this software display the following acknowledgement:
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.\" ``This product includes software developed by the University of California,
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.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
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.\" the University nor the names of its contributors may be used to endorse
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.\" or promote products derived from this software without specific prior
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.\" written permission.
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.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
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.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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.\"
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.\" $FreeBSD$
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.\"
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.TH PCAP 3 "3 January 2001"
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.SH NAME
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pcap \- Packet Capture library
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.SH SYNOPSIS
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.nf
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.ft B
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#include <pcap.h>
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.ft
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.LP
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.nf
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.ft B
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char errbuf[PCAP_ERRBUF_SIZE];
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.ft
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.LP
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.ft B
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pcap_t *pcap_open_live(char *device, int snaplen,
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.ti +8
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int promisc, int to_ms, char *errbuf)
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pcap_t *pcap_open_dead(int linktype, int snaplen)
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pcap_t *pcap_open_offline(char *fname, char *errbuf)
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pcap_dumper_t *pcap_dump_open(pcap_t *p, char *fname)
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.ft
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.LP
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.ft B
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int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
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int pcap_getnonblock(pcap_t *p, char *errbuf);
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.ft
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.LP
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.ft B
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int pcap_findalldevs(pcap_if_t **alldevsp, char *errbuf)
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void pcap_freealldevs(pcap_if_t *)
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char *pcap_lookupdev(char *errbuf)
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int pcap_lookupnet(char *device, bpf_u_int32 *netp,
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.ti +8
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bpf_u_int32 *maskp, char *errbuf)
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.ft
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.LP
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.ft B
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int pcap_dispatch(pcap_t *p, int cnt,
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.ti +8
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pcap_handler callback, u_char *user)
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int pcap_loop(pcap_t *p, int cnt,
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.ti +8
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pcap_handler callback, u_char *user)
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void pcap_dump(u_char *user, struct pcap_pkthdr *h,
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.ti +8
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u_char *sp)
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.ft
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.LP
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.ft B
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int pcap_compile(pcap_t *p, struct bpf_program *fp,
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.ti +8
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char *str, int optimize, bpf_u_int32 netmask)
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int pcap_setfilter(pcap_t *p, struct bpf_program *fp)
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void pcap_freecode(struct bpf_program *);
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.ft
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.LP
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.ft B
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u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h)
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.ft
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.LP
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.ft B
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int pcap_datalink(pcap_t *p)
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int pcap_snapshot(pcap_t *p)
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int pcap_is_swapped(pcap_t *p)
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int pcap_major_version(pcap_t *p)
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int pcap_minor_version(pcap_t *p)
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int pcap_stats(pcap_t *p, struct pcap_stat *ps)
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FILE *pcap_file(pcap_t *p)
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int pcap_fileno(pcap_t *p)
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void pcap_perror(pcap_t *p, char *prefix)
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char *pcap_geterr(pcap_t *p)
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char *pcap_strerror(int error)
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.ft
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.LP
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.ft B
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void pcap_close(pcap_t *p)
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void pcap_dump_close(pcap_dumper_t *p)
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.ft
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.fi
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.SH DESCRIPTION
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The Packet Capture library
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provides a high level interface to packet capture systems. All packets
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on the network, even those destined for other hosts, are accessible
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through this mechanism.
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.PP
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.SH ROUTINES
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NOTE:
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.I errbuf
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in
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.BR pcap_open_live() ,
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.BR pcap_open_dead() ,
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.BR pcap_open_offline() ,
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.BR pcap_setnonblock() ,
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.BR pcap_getnonblock() ,
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.BR pcap_findalldevs() ,
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.BR pcap_lookupdev() ,
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and
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.B pcap_lookupnet()
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is assumed to be able to hold at least
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.B PCAP_ERRBUF_SIZE
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chars.
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.PP
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.B pcap_open_live()
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is used to obtain a packet capture descriptor to look
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at packets on the network.
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.I device
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is a string that specifies the network device to open; on Linux systems
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with 2.2 or later kernels, a
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.I device
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argument of "any" or
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.B NULL
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can be used to capture packets from all interfaces.
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.I snaplen
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specifies the maximum number of bytes to capture.
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.I promisc
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specifies if the interface is to be put into promiscuous mode.
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(Note that even if this parameter is false, the interface
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could well be in promiscuous mode for some other reason.) For now, this
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doesn't work on the "any" device; if an argument of "any" or NULL is
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supplied, the
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.I promisc
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flag is ignored.
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.I to_ms
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specifies the read timeout in milliseconds. The read timeout is used to
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arrange that the read not necessarily return immediately when a packet
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is seen, but that it wait for some amount of time to allow more packets
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to arrive and to read multiple packets from the OS kernel in one
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operation. Not all platforms support a read timeout; on platforms that
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don't, the read timeout is ignored.
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.I errbuf
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is used to return error or warning text. It will be set to error text when
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.B pcap_open_live()
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fails and returns
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.BR NULL .
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.I errbuf
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may also be set to warning text when
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.B pcap_open_live()
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succeds; to detect this case the caller should store a zero-length string in
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.I errbuf
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before calling
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.B pcap_open_live()
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and display the warning to the user if
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.I errbuf
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is no longer a zero-length string.
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.PP
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.B pcap_open_dead()
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is used for creating a
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.B pcap_t
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structure to use when calling the other functions in libpcap. It is
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typically used when just using libpcap for compiling BPF code.
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.PP
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.B pcap_open_offline()
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is called to open a ``savefile'' for reading.
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.I fname
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specifies the name of the file to open. The file has
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the same format as those used by
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.B tcpdump(1)
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and
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.BR tcpslice(1) .
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The name "-" in a synonym for
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.BR stdin .
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.I errbuf
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is used to return error text and is only set when
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.B pcap_open_offline()
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fails and returns
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.BR NULL .
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.PP
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.B pcap_dump_open()
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is called to open a ``savefile'' for writing. The name "-" in a synonym
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for
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.BR stdout .
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.B NULL
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is returned on failure.
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.I p
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is a
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.I pcap
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struct as returned by
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.B pcap_open_offline()
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or
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.BR pcap_open_live() .
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.I fname
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specifies the name of the file to open.
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If
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.B NULL
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is returned,
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.B pcap_geterr()
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can be used to get the error text.
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.PP
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.B pcap_setnonblock()
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puts a capture descriptor, opened with
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.BR pcap_open_live() ,
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into ``non-blocking'' mode, or takes it out of ``non-blocking'' mode,
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depending on whether the
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.I nonblock
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argument is non-zero or zero. It has no effect on ``savefiles''.
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If there is an error, \-1 is returned and
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.I errbuf
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is filled in with an appropriate error message; otherwise, 0 is
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returned.
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In
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``non-blocking'' mode, an attempt to read from the capture descriptor
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with
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.B pcap_dispatch()
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will, if no packets are currently available to be read, return 0
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immediately rather than blocking waiting for packets to arrive.
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.B pcap_loop()
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and
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.B pcap_next()
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will not work in ``non-blocking'' mode.
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.PP
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.B pcap_getnonblock()
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returns the current ``non-blocking'' state of the capture descriptor; it
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always returns 0 on ``savefiles''.
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If there is an error, \-1 is returned and
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.I errbuf
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is filled in with an appropriate error message.
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.PP
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.B pcap_findalldevs()
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constructs a list of network devices that can be opened with
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.BR pcap_open_live() .
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(Note that there may be network devices that cannot be opened with
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.BR pcap_open_live()
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by the
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process calling
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.BR pcap_findalldevs() ,
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because, for example, that process might not have sufficient privileges
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to open them for capturing; if so, those devices will not appear on the
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list.)
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.I alldevsp
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is set to point to the first element of the list; each element of the
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list is of type
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.BR pcap_if_t ,
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and has the following members:
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.RS
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.TP
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.B next
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if not
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.BR NULL ,
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a pointer to the next element in the list;
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.B NULL
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for the last element of the list
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.TP
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.B name
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a pointer to a string giving a name for the device to pass to
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.B pcap_open_live()
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.TP
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.B description
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if not
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.BR NULL ,
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a pointer to a string giving a human-readable description of the device
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.TP
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.B addresses
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a pointer to the first element of a list of addresses for the interface
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.TP
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.B flags
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interface flags:
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.RS
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.TP
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.B PCAP_IF_LOOPBACK
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set if the interface is a loopback interface
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.RE
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.RE
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.PP
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Each element of the list of addresses is of type
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.BR pcap_addr_t ,
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and has the following members:
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.RS
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.TP
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.B next
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if not
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.BR NULL ,
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a pointer to the next element in the list;
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.B NULL
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for the last element of the list
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.TP
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.B addr
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a pointer to a
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.B "struct sockaddr"
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containing an address
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.TP
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.B netmask
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if not
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.BR NULL ,
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a pointer to a
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.B "struct sockaddr"
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that contains the netmask corresponding to the address pointed to by
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.B addr
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.TP
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.B broadaddr
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if not
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.BR NULL ,
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a pointer to a
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.B "struct sockaddr"
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that contains the broadcast address corresponding to the address pointed
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to by
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.BR addr ;
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may be null if the interface doesn't support broadcasts
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.TP
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.B dstaddr
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if not
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.BR NULL ,
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a pointer to a
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.B "struct sockaddr"
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that contains the destination address corresponding to the address pointed
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to by
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.BR addr ;
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may be null if the interface isn't a point-to-point interface
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.RE
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.PP
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.B pcap_freealldevs()
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is used to free a list allocated by
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.BR pcap_findalldevs() .
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.PP
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.B pcap_lookupdev()
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returns a pointer to a network device suitable for use with
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.B pcap_open_live()
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and
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.BR pcap_lookupnet() .
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If there is an error,
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.B NULL
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is returned and
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.I errbuf
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is filled in with an appropriate error message.
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.PP
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.B pcap_lookupnet()
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is used to determine the network number and mask
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associated with the network device
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.BR device .
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Both
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.I netp
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and
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.I maskp
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are
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.I bpf_u_int32
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pointers.
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A return of \-1 indicates an error in which case
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.I errbuf
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is filled in with an appropriate error message.
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.PP
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.B pcap_dispatch()
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is used to collect and process packets.
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.I cnt
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specifies the maximum number of packets to process before returning.
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This is not a minimum number; when reading a live capture, only one
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bufferful of packets is read at a time, so fewer than
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.I cnt
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packets may be processed. A
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.I cnt
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of \-1 processes all the packets received in one buffer when reading a
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live capture, or all the packets in the file when reading a
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``savefile''.
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.I callback
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specifies a routine to be called with three arguments:
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a
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.I u_char
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pointer which is passed in from
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.BR pcap_dispatch() ,
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a pointer to the
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.I pcap_pkthdr
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struct (which precede the actual network headers and data),
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and a
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.I u_char
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pointer to the packet data.
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.PP
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The number of packets read is returned.
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0 is returned if no packets were read from a live capture (if, for
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example, they were discarded because they didn't pass the packet filter,
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or if, on platforms that support a read timeout that starts before any
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packets arrive, the timeout expires before any packets arrive, or if the
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file descriptor for the capture device is in non-blocking mode and no
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packets were available to be read) or if no more packets are available
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in a ``savefile.'' A return of \-1 indicates
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an error in which case
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.B pcap_perror()
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or
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.B pcap_geterr()
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may be used to display the error text.
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.PP
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.BR NOTE :
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when reading a live capture,
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.B pcap_dispatch()
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will not necessarily return when the read times out; on some platforms,
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the read timeout isn't supported, and, on other platforms, the timer
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doesn't start until at least one packet arrives. This means that the
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read timeout should
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.B NOT
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be used in, for example, an interactive application, to allow the packet
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capture loop to ``poll'' for user input periodically, as there's no
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guarantee that
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.B pcap_dispatch()
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will return after the timeout expires.
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.PP
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.B pcap_loop()
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is similar to
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.B pcap_dispatch()
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except it keeps reading packets until
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.I cnt
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packets are processed or an error occurs.
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It does
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.B not
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return when live read timeouts occur.
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Rather, specifying a non-zero read timeout to
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.B pcap_open_live()
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and then calling
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.B pcap_dispatch()
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allows the reception and processing of any packets that arrive when the
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timeout occurs.
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A negative
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.I cnt
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causes
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.B pcap_loop()
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to loop forever (or at least until an error occurs).
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.PP
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.B pcap_next()
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reads the next packet (by calling
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.B pcap_dispatch()
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with a
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.I cnt
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of 1) and returns a
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.I u_char
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pointer to the data in that packet. (The
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.I pcap_pkthdr
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struct for that packet is not supplied.)
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.PP
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.B pcap_dump()
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outputs a packet to the ``savefile'' opened with
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.BR pcap_dump_open() .
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Note that its calling arguments are suitable for use with
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.B pcap_dispatch()
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or
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.BR pcap_loop() .
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If called directly, the
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.I user
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parameter is of type
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.I pcap_dumper_t
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as returned by
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.BR pcap_dump_open() .
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.PP
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.B pcap_compile()
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is used to compile the string
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.I str
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into a filter program.
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.I program
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is a pointer to a
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.I bpf_program
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struct and is filled in by
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.BR pcap_compile() .
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.I optimize
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controls whether optimization on the resulting code is performed.
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.I netmask
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specifies the netmask of the local net.
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A return of \-1 indicates an error in which case
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.BR pcap_geterr()
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may be used to display the error text.
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.PP
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.B pcap_compile_nopcap()
|
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is similar to
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.B pcap_compile()
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except that instead of passing a pcap structure, one passes the
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snaplen and linktype explicitly. It is intended to be used for
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compiling filters for direct BPF usage, without necessarily having
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called
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.BR pcap_open() .
|
|
A return of \-1 indicates an error; the error text is unavailable.
|
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.RB ( pcap_compile_nopcap()
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is a wrapper around
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.BR pcap_open_dead() ,
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.BR pcap_compile() ,
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and
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.BR pcap_close() ;
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the latter three routines can be used directly in order to get the error
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text for a compilation error.)
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.B
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.PP
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.B pcap_setfilter()
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is used to specify a filter program.
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.I fp
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is a pointer to a
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.I bpf_program
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struct, usually the result of a call to
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.BR pcap_compile() .
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.B \-1
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is returned on failure, in which case
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.BR pcap_geterr()
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may be used to display the error text;
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.B 0
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is returned on success.
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.PP
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.B pcap_freecode()
|
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is used to free up allocated memory pointed to by a
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.I bpf_program
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struct generated by
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.B pcap_compile()
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when that BPF program is no longer needed, for example after it
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has been made the filter program for a pcap structure by a call to
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.BR pcap_setfilter() .
|
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.PP
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.B pcap_datalink()
|
|
returns the link layer type; link layer types it can return include:
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.PP
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.RS 5
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.TP 5
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.B DLT_NULL
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|
BSD loopback encapsulation; the link layer header is a 4-byte field, in
|
|
.I host
|
|
byte order, containing a PF_ value from
|
|
.B socket.h
|
|
for the network-layer protocol of the packet
|
|
.IP
|
|
Note that ``host byte order'' is the byte order of the machine on which
|
|
the packets are captured, and the PF_ values are for the OS of the
|
|
machine on which the packets are captured; if a live capture is being
|
|
done, ``host byte order'' is the byte order of the machine capturing the
|
|
packets, and the PF_ values are those of the OS of the machine capturing
|
|
the packets, but if a ``savefile'' is being read, the byte order and PF_
|
|
values are
|
|
.I not
|
|
necessarily those of the machine reading the capture file.
|
|
.TP 5
|
|
.B DLT_EN10MB
|
|
Ethernet (10Mb, 100Mb, 1000Mb, and up)
|
|
.TP 5
|
|
.B DLT_IEEE802
|
|
IEEE 802.5 Token Ring
|
|
.TP 5
|
|
.B DLT_ARCNET
|
|
ARCNET
|
|
.TP 5
|
|
.B DLT_SLIP
|
|
SLIP; the link layer header contains, in order:
|
|
.RS 10
|
|
.LP
|
|
a 1-byte flag, which is 0 for packets received by the machine and 1 for
|
|
packets sent by the machine;
|
|
.LP
|
|
a 1-byte field, the upper 4 bits of which indicate the type of packet,
|
|
as per RFC 1144:
|
|
.RS 5
|
|
.TP 5
|
|
0x40
|
|
an unmodified IP datagram (TYPE_IP);
|
|
.TP 5
|
|
0x70
|
|
an uncompressed-TCP IP datagram (UNCOMPRESSED_TCP), with that byte being
|
|
the first byte of the raw IP header on the wire, containing the
|
|
connection number in the protocol field;
|
|
.TP 5
|
|
0x80
|
|
a compressed-TCP IP datagram (COMPRESSED_TCP), with that byte being the
|
|
first byte of the compressed TCP/IP datagram header;
|
|
.RE
|
|
.LP
|
|
for UNCOMPRESSED_TCP, the rest of the modified IP header, and for
|
|
COMPRESSED_TCP, the compressed TCP/IP datagram header;
|
|
.RE
|
|
.RS 5
|
|
.LP
|
|
for a total of 16 bytes; the uncompressed IP datagram follows the header
|
|
.RE
|
|
.TP 5
|
|
.B DLT_PPP
|
|
PPP; if the first 2 bytes are 0xff and 0x03, it's PPP in HDLC-like
|
|
framing, with the PPP header following those two bytes, otherwise it's
|
|
PPP without framing, and the packet begins with the PPP header
|
|
.TP 5
|
|
.B DLT_FDDI
|
|
FDDI
|
|
.TP 5
|
|
.B DLT_ATM_RFC1483
|
|
RFC 1483 LLC/SNAP-encapsulated ATM; the packet begins with an IEEE 802.2
|
|
LLC header
|
|
.TP 5
|
|
.B DLT_RAW
|
|
raw IP; the packet begins with an IP header
|
|
.TP 5
|
|
.B DLT_PPP_SERIAL
|
|
PPP in HDLC-like framing, as per RFC 1662, or Cisco PPP with HDLC
|
|
framing, as per section 4.3.1 of RFC 1547; the first byte will be 0xFF
|
|
for PPP in HDLC-like framing, and will be 0x0F or 0x8F for Cisco PPP
|
|
with HDLC framing
|
|
.TP 5
|
|
.B DLT_PPP_ETHER
|
|
PPPoE; the packet begins with a PPPoE header, as per RFC 2516
|
|
.TP 5
|
|
.B DLT_C_HDLC
|
|
Cisco PPP with HDLC framing, as per section 4.3.1 of RFC 1547
|
|
.TP 5
|
|
.B DLT_IEEE802_11
|
|
IEEE 802.11 wireless LAN
|
|
.TP 5
|
|
.B DLT_LOOP
|
|
OpenBSD loopback encapsulation; the link layer header is a 4-byte field, in
|
|
.I network
|
|
byte order, containing a PF_ value from OpenBSD's
|
|
.B socket.h
|
|
for the network-layer protocol of the packet
|
|
.IP
|
|
Note that, if a ``savefile'' is being read, those PF_ values are
|
|
.I not
|
|
necessarily those of the machine reading the capture file.
|
|
.TP 5
|
|
.B DLT_LINUX_SLL
|
|
Linux "cooked" capture encapsulation; the link layer header contains, in
|
|
order:
|
|
.RS 10
|
|
.LP
|
|
a 2-byte "packet type", in network byte order, which is one of:
|
|
.RS 5
|
|
.TP 5
|
|
0
|
|
packet was sent to us by somebody else
|
|
.TP 5
|
|
1
|
|
packet was broadcast by somebody else
|
|
.TP 5
|
|
2
|
|
packet was multicast, but not broadcast, by somebody else
|
|
.TP 5
|
|
3
|
|
packet was sent by somebody else to somebody else
|
|
.TP 5
|
|
4
|
|
packet was sent by us
|
|
.RE
|
|
.LP
|
|
a 2-byte field, in network byte order, containing a Linux ARPHRD_ value
|
|
for the link layer device type;
|
|
.LP
|
|
a 2-byte field, in network byte order, containing the length of the
|
|
link layer address of the sender of the packet (which could be 0);
|
|
.LP
|
|
an 8-byte field containing that number of bytes of the link layer header
|
|
(if there are more than 8 bytes, only the first 8 are present);
|
|
.LP
|
|
a 2-byte field containing an Ethernet protocol type, in network byte
|
|
order, or containing 1 for Novell 802.3 frames without an 802.2 LLC
|
|
header or 4 for frames beginning with an 802.2 LLC header.
|
|
.RE
|
|
.TP 5
|
|
.B DLT_LTALK
|
|
Apple LocalTalk; the packet begins with an AppleTalk LLAP header
|
|
.RE
|
|
.PP
|
|
.B pcap_snapshot()
|
|
returns the snapshot length specified when
|
|
.B pcap_open_live
|
|
was called.
|
|
.PP
|
|
.B pcap_is_swapped()
|
|
returns true if the current ``savefile'' uses a different byte order
|
|
than the current system.
|
|
.PP
|
|
.B pcap_major_version()
|
|
returns the major number of the version of the pcap used to write the
|
|
savefile.
|
|
.PP
|
|
.B pcap_minor_version()
|
|
returns the minor number of the version of the pcap used to write the
|
|
savefile.
|
|
.PP
|
|
.B pcap_file()
|
|
returns the standard I/O stream of the ``savefile,'' if a ``savefile''
|
|
was opened with
|
|
.BR pcap_open_offline() ,
|
|
or NULL, if a network device was opened with
|
|
.BR pcap_open_live() .
|
|
.PP
|
|
.B pcap_stats()
|
|
returns 0 and fills in a
|
|
.B pcap_stat
|
|
struct. The values represent packet statistics from the start of the
|
|
run to the time of the call. If there is an error or the underlying
|
|
packet capture doesn't support packet statistics, \-1 is returned and
|
|
the error text can be obtained with
|
|
.B pcap_perror()
|
|
or
|
|
.BR pcap_geterr() .
|
|
.B pcap_stats()
|
|
is supported only on live captures, not on ``savefiles''; no statistics
|
|
are stored in ``savefiles'', so no statistics are available when reading
|
|
from a ``savefile''.
|
|
.PP
|
|
.B pcap_fileno()
|
|
returns the file descriptor number from which captured packets are read,
|
|
if a network device was opened with
|
|
.BR pcap_open_live() ,
|
|
or \-1, if a ``savefile'' was opened with
|
|
.BR pcap_open_offline() .
|
|
.PP
|
|
.B pcap_perror()
|
|
prints the text of the last pcap library error on
|
|
.BR stderr ,
|
|
prefixed by
|
|
.IR prefix .
|
|
.PP
|
|
.B pcap_geterr()
|
|
returns the error text pertaining to the last pcap library error.
|
|
.BR NOTE :
|
|
the pointer it returns will no longer point to a valid error message
|
|
string after the
|
|
.B pcap_t
|
|
passed to it is closed; you must use or copy the string before closing
|
|
the
|
|
.BR pcap_t .
|
|
.PP
|
|
.B pcap_strerror()
|
|
is provided in case
|
|
.BR strerror (1)
|
|
isn't available.
|
|
.PP
|
|
.B pcap_close()
|
|
closes the files associated with
|
|
.I p
|
|
and deallocates resources.
|
|
.PP
|
|
.B pcap_dump_close()
|
|
closes the ``savefile.''
|
|
.PP
|
|
.SH SEE ALSO
|
|
tcpdump(1), tcpslice(1)
|
|
.SH AUTHORS
|
|
The original authors are:
|
|
.LP
|
|
Van Jacobson,
|
|
Craig Leres and
|
|
Steven McCanne, all of the
|
|
Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.
|
|
.LP
|
|
The current version is available from "The Tcpdump Group"'s Web site at
|
|
.LP
|
|
.RS
|
|
.I http://www.tcpdump.org/
|
|
.RE
|
|
.SH BUGS
|
|
Please send problems, bugs, questions, desirable enhancements, etc. to:
|
|
.LP
|
|
.RS
|
|
tcpdump-workers@tcpdump.org
|
|
.RE
|
|
.LP
|
|
Please send source code contributions, etc. to:
|
|
.LP
|
|
.RS
|
|
patches@tcpdump.org
|
|
.RE
|