@(#) $Header: /tcpdump/master/libpcap/README,v 1.21 2000-06-16 17:50:17 mcr Exp $ (LBL)

LIBPCAP 0.5
Now maintained by "The Tcpdump Group"
See 		www.tcpdump.org

Please send inquiries/comments/reports to 	tcpdump-workers@tcpdump.org

Anonymous CVS is available via:
	cvs -d cvs.tcpdump.org:/tcpdump/master login
	(password "anoncvs")
	cvs -d cvs.tcpdump.org:/tcpdump/master checkout libpcap

Version 0.5 of LIBPCAP can be retrived with the CVS tag "libpcap_0_5":
	cvs -d cvs.tcpdump.org:/tcpdump/master checkout -r libpcap_0_5 libpcap

Please send patches against the master copy to patches@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/OS, NetBSD, FreeBSD, and OpenBSD.  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
"tcpdump-workers@tcpdump.org".