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50 lines
2.2 KiB
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@(#) $Header: /tcpdump/master/libpcap/README,v 1.18.1.1 1999/10/07 23:46:40 mcr Exp $ (LBL)
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LIBPCAP 0.4
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Lawrence Berkeley National Laboratory
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Network Research Group
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libpcap@ee.lbl.gov
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ftp://ftp.ee.lbl.gov/libpcap.tar.Z
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This directory contains source code for libpcap, a system-independent
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interface for user-level packet capture. libpcap provides a portable
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framework for low-level network monitoring. Applications include
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network statistics collection, security monitoring, network debugging,
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etc. Since almost every system vendor provides a different interface
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for packet capture, and since we've developed several tools that
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require this functionality, we've created this system-independent API
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to ease in porting and to alleviate the need for several
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system-dependent packet capture modules in each application.
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Note well: this interface is new and is likely to change.
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The libpcap interface supports a filtering mechanism based on the
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architecture in the BSD packet filter. BPF is described in the 1993
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Winter Usenix paper ``The BSD Packet Filter: A New Architecture for
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User-level Packet Capture''. A compressed postscript version is in:
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ftp://ftp.ee.lbl.gov/papers/bpf-usenix93.ps.Z.
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Although most packet capture interfaces support in-kernel filtering,
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libpcap utilizes in-kernel filtering only for the BPF interface.
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On systems that don't have BPF, all packets are read into user-space
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and the BPF filters are evaluated in the libpcap library, incurring
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added overhead (especially, for selective filters). Ideally, libpcap
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would translate BPF filters into a filter program that is compatible
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with the underlying kernel subsystem, but this is not yet implemented.
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BPF is standard in 4.4BSD, BSD/386, NetBSD, and FreeBSD. DEC OSF/1
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uses the packetfilter interface but has been extended to accept BPF
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filters (which libpcap utilizes). Also, you can add BPF filter support
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to Ultrix using the kernel source and/or object patches available in:
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ftp://gatekeeper.dec.com/pub/DEC/net/bpfext42.tar.Z.
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Problems, bugs, questions, desirable enhancements, source code
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contributions, etc., should be sent to the email address
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"libpcap@ee.lbl.gov".
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- Steve McCanne
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Craig Leres
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Van Jacobson
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