72 lines
2.8 KiB
HTML
72 lines
2.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
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<!--Converted with LaTeX2HTML 96.1-c (Feb 29, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds -->
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<HTML>
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<HEAD>
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<TITLE>Displaying the Routing Table</TITLE>
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</HEAD>
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<BODY LANG="EN">
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<A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node76.html">Displaying Interface Statistics</A>
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<B>Up:</B> <A HREF="node74.html">Checking with netstat</A>
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<B> Previous:</B> <A HREF="node74.html">Checking with netstat</A>
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<BR> <P>
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<H2><A NAME="SECTION007910000">Displaying the Routing Table</A></H2>
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When invoking netstat with the -r flag, it displays the
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kernel routing table in the way we've been doing this with route
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above. On vstout, it produces:
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<pre>
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# netstat -nr
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Kernel routing table
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Destination Gateway Genmask Flags Metric Ref Use
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127.0.0.1 * 255.255.255.255 UH 1 0
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191.72.1.0 * 255.255.255.0 U 1 0
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191.72.2.0 191.72.1.1 255.255.255.0 UGN 1 0
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</pre>
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The -n option makes netstat print addresses as dotted
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quad IP-numbers rather than the symbolic host and network names. This is
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especially useful when you want to avoid address lookups over the network
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(e.g. to a DNS or NIS server).
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<P>
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The second column of netstat's output shows the gateway the
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routing entry points to. If no gateway is used, an asterisk is printed
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instead. Column three shows the ``generality'' of the route. When given
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an IP-address to find a suitable route for, the kernel goes through all
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routing table entries, taking the bitwise AND of the address and the
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genmask before comparing it to the target of the route.
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<P>
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The fourth column displays various flags that describe the route:
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<dl>
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<dt><b>G</b><dd> The route uses a gateway.
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<dt><b>U</b><dd> The interface to be used is up.
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<dt><b>H</b><dd> Only a single host can be reached through the route. For example, this is the case for the loopback entry 127.0.0.1.
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<dt><b>D</b><dd> This is set if the table entry has been generated by an ICMP
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redirect message (see section 3.5).
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<dt><b>M</b><dd> This is set if the table entry was modified by an ICMP redi-
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rect message.
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</dl>
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The Ref column of netstat's output shows the number of
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references to this route, that is, how many other routes (e.g. through
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gateways) rely on the presence of this route. The last two columns show
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the number of times the routing entry has been used, and the interface
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that datagrams are passed to for delivery.
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<P>
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<BR> <HR>
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<P><ADDRESS>
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<I>Andrew Anderson <BR>
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Thu Mar 7 23:22:06 EST 1996</I>
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</ADDRESS>
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</BODY>
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</HTML>
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