README.pcap

Mon Jul 14, 1997

To read tcpdump files, you need to packet capture library from LBL.
If you already have tcpdump, then your probably already have it
installed.  If not, then check out:

	ftp://ftp.ee.lbl.gov/libpcap.tar.Z

These sources have been tested with the 0.4 version of libpcap...

--sdo

----------------------------------------------------------------------

The pcap README file:

@(#) $Header: /usr/local/cvs/tcptrace/README.pcap,v 5.1 1998/12/02 04:38:38 sdo Exp $ (LBL)

LIBPCAP 0.4
Lawrence Berkeley National 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 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
"libpcap@ee.lbl.gov".

 - Steve McCanne
   Craig Leres
   Van Jacobson