To report a security issue please send an e-mail to security@tcpdump.org.

To report bugs and other problems, contribute patches, request a

feature, provide generic feedback etc please see the file

[CONTRIBUTING](CONTRIBUTING.md) in the libpcap source tree root.

The directory doc/ has README files about specific operating systems and

options.

LIBPCAP 1.x.y

Now maintained by "The Tcpdump Group"

https://www.tcpdump.org

Anonymous Git is available via:

        https://github.com/the-tcpdump-group/libpcap.git

formerly from 	Lawrence Berkeley National Laboratory

		Network Research Group <libpcap@ee.lbl.gov>

		ftp://ftp.ee.lbl.gov/old/libpcap-0.4a7.tar.Z

This directory contains source code for libpcap, a system-independent

interface for user-level packet capture.  libpcap provides a portable

framework for low-level network monitoring.  Applications include

network statistics collection, security monitoring, network debugging,

etc.  Since almost every system vendor provides a different interface

for packet capture, and since we've developed several tools that

require this functionality, we've created this system-independent API

to ease in porting and to alleviate the need for several

system-dependent packet capture modules in each application.

For some platforms there are README.{system} files that discuss issues

with the OS's interface for packet capture on those platforms, such as

how to enable support for that interface in the OS, if it's not built in

by default.

The libpcap interface supports a filtering mechanism based on the

architecture in the BSD packet filter.  BPF is described in the 1993

Winter Usenix paper ``The BSD Packet Filter: A New Architecture for

User-level Packet Capture''.  A compressed PostScript version can be

found at

	ftp://ftp.ee.lbl.gov/papers/bpf-usenix93.ps.Z

or

	https://www.tcpdump.org/papers/bpf-usenix93.ps.Z

and a gzipped version can be found at

	https://www.tcpdump.org/papers/bpf-usenix93.ps.gz

A PDF version can be found at

	https://www.tcpdump.org/papers/bpf-usenix93.pdf

Although most packet capture interfaces support in-kernel filtering,

libpcap utilizes in-kernel filtering only for the BPF interface.

On systems that don't have BPF, all packets are read into user-space

and the BPF filters are evaluated in the libpcap library, incurring

added overhead (especially, for selective filters).  Ideally, libpcap

would translate BPF filters into a filter program that is compatible

with the underlying kernel subsystem, but this is not yet implemented.

BPF is standard in 4.4BSD, BSD/OS, NetBSD, FreeBSD, OpenBSD, DragonFly

BSD, and macOS; an older, modified and undocumented version is standard

in AIX.  {DEC OSF/1, Digital UNIX, Tru64 UNIX} uses the packetfilter

interface but has been extended to accept BPF filters (which libpcap

utilizes).  Also, you can add BPF filter support to Ultrix using the

kernel source and/or object patches available in:

	https://www.tcpdump.org/other/bpfext42.tar.Z

Linux has a number of BPF based systems, and libpcap does not support

any of the eBPF mechanisms as yet, although it supports many of the

memory mapped receive mechanisms.

See the [README.linux](doc/README.linux.md) file for more information.

Note to Linux distributions and *BSD systems that include libpcap:

There's now a rule to make a shared library, which should work on Linux

and *BSD, among other platforms.

It sets the soname of the library to "libpcap.so.1"; this is what it

should be, *NOT* libpcap.so.1.x or libpcap.so.1.x.y or something such as

that.

We've been maintaining binary compatibility between libpcap releases for

quite a while; there's no reason to tie a binary linked with libpcap to

a particular release of libpcap.

Current versions can be found at https://www.tcpdump.org.

 - The TCPdump group