@(#) $Header: README,v 1.7 94/06/20 18:56:55 leres Exp $ (LBL)

LIBPCAP 0.0
Lawrence Berkeley Laboratory
Network Research Group
libpcap@ee.lbl.gov
ftp://ftp.ee.lbl.gov/libpcap-*.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
these interfaces, 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.

THIS IS AN ALPHA-QUALITY RELEASE.  The interface is brand new and is
likely to change.  If you code to this interface, and want to track
future versions, be prepared to update your code.  We admit that this
release is premature, but we're releasing it anyway because the tcpdump-3.0
distribution requires it.

libpcap has been built and tested under SGI Irix 4.x & 5.2, SunOS 4.x,
Solaris 2.3, BSD/386 v1.1, DEC/OSF v1.3 v2.0, and Ultrix 4.x.  SunOS 3.5
4.3BSD Reno/Tahoe and 4.4BSD are supported as well, but we currently
do not have the resources to carry out testing in these environments
(we suspect you'll run into problems under these systems -- please
send us the patches if you fix any porting problems).

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).  We haven't tried
taking advantage of other packet filter models first because they
aren't general enough (i.e., only simple filters can be evaluated),
and second because we don't have the time to modify the code generator
(or write a filter translator) and BPF is more efficient anyway.

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.

Please send bugs and comments to libpcap@ee.lbl.gov.

 - Steve McCanne (mccanne@ee.lbl.gov)
   Craig Leres (leres@ee.lbl.gov)
   Van Jacobson (van@ee.lbl.gov)
