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@(#) $Header: /tcpdump/master/libpcap/README,v 1.18.1.1 1999/10/07 23:46:40 mcr 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
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