@(#) $Header: README,v 1.18 97/06/12 14:23:56 leres 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