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tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html9801" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html">Index</A></B> <BR><BR><!--End of Navigation Panel--><H2><A NAME="SECTION09141000000000000000">39.4.1 Pcap/BPF Network Objects</A></H2><P>These objects provide an extended interface to the LBNL packet capturelibrary (libpcap).(See <TT>ftp://ftp.ee.lbl.gov/libpcap.tar.Z</TT> for more info).This library provides the ability to capture link-layer framesin a promiscuous fashion from network interface drivers(i.e. a copy is made for those programs making use of libpcap).It also provides the ability to read and write packet tracefiles in the ``tcpdump'' format.The extended interface provided by also allows for writingframes out to the network interface driver, provided the driveritself allows this action.Use of the library to capture or create live traffic may be protected;one generally requires at least read access to the system's packet filterfacility which may need to be arranged through a system administrator.<P>The packet capture library works on several UNIX-based platforms.It is optimized for use with theBerkeley Packet Filter (BPF) [<A HREF="node589.html#BPF93" tppabs="http://www.isi.edu/nsnam/ns/doc/node589.html#BPF93">26</A>],and provides a filter compiler for the BPF pseudomachine machine code.On most systems supporting it,a kernel-resident BPF implementation processes the filter code, and applies the resulting pattern matching instructions to received frames.Those frames matching the patterns are received through the BPF machinery;those not matching the pattern are otherwise unaffected.BPF also supports sending link-layer frames.This is generally not suggested, as an entire properly-formatted framemust be created prior to handing it off to BPF.This may be problematic with respect to assigning proper link-layer headersfor next-hop destinations.It is generally preferable to use the raw IP network object for sendingIP packets, as the system's routing function will be used to determineproper link-layer encapsulating headers.<P><BR><HR><!--Table of Child-Links--><A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A><UL><LI><UL><LI><A NAME="tex2html9804" HREF="node547.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node547.html">39.4.1.0.1 Configuration</A></UL></UL><!--End of Table of Child-Links--><HR><!--Navigation Panel--><A NAME="tex2html9802" HREF="node547.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node547.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html9796" HREF="node545.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node545.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html9790" HREF="node545.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node545.html"><IMG WIDTH="63" HEIGHT="24" 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tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html9801" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html">Index</A></B> <!--End of Navigation Panel--><ADDRESS>2003-09-23</ADDRESS></BODY></HTML>⌨️ 快捷键说明
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