$OpenBSD: README,v 1.7 2014/04/11 04:08:58 lteo Exp $

$NetBSD: README,v 1.2 1995/03/06 11:38:07 mycroft Exp $

LIBPCAP 0.5

Now maintained by "The Tcpdump Group"

Send patches to patches@tcpdump.org

See www.tcpdump.org

formerly from Lawrence Berkeley National Laboratory

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

ftp://ftp.ee.lbl.gov/libpcap.tar.Z (0.4)

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.

Note well: this interface is new and is likely to change.

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 is in:

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

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/386, NetBSD, and FreeBSD. DEC OSF/1

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:

ftp://gatekeeper.dec.com/pub/DEC/net/bpfext42.tar.Z.

Problems, bugs, questions, desirable enhancements, source code

contributions, etc., should be sent to the email address

"patches@tcpdump.org".