71 lines
3.1 KiB
HTML
71 lines
3.1 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>Routing through a Gateway</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="node69.html">Configuring a Gateway</A>
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<B>Up:</B> <A HREF="node65.html">Interface Configuration for IP</A>
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<B> Previous:</B> <A HREF="node67.html">Ethernet Interfaces</A>
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<BR> <P>
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<H2><A NAME="SECTION007730000">Routing through a Gateway</A></H2>
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In the previous section, I covered only the case of setting up a host
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on a single Ethernet. Quite frequently, however, one encounters
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networks connected to one another by gateways. These gateways may
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simply link two or more Ethernets, but may provide a link to the
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outside world, the Internet, as well. In order to use the service of a
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gateway, you have to provide additional routing information to the
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networking layer.
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<P>
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For instance, the Ethernets of the Virtual Brewery and the Virtual
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Winery are linked through such a gateway, namely the host vlager.
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Assuming that vlager has already been configured, we only have to
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add another entry to vstout's routing table that tells the kernel
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it can reach all hosts on the Winery's network through vlager.
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The appropriate incantation of route is shown below; the
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gw keyword tells it that the next argument denotes a gateway.
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<pre>
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# route add wine-net gw vlager
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</pre>
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Of course, any host on the Winery network you wish to talk to must have
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a corresponding routing entry for the Brewery's network, otherwise you
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would only be able to send data from vstout to vbardolino,
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but any response returned by the latter would go into the great bit
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bucket.
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<P>
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This example describes only a gateway that switches packets between two
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isolated Ethernets. Now assume that vlager also has a connection
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to the Internet (say, through an additional SLIP link). Then we would
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want datagrams to <em>any</em> destination network other than the Brewery
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to be handed to vlager. This can be accomplished by making it the
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default gateway for vstout:
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<Pre>
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# route add default gw vlager
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</pre>
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<A NAME="2808"></A>
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<A NAME="2809"></A>
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The network name default is a shorthand for 0.0.0.0,
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which denotes the default route. You do not have to add this name to
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/etc/networks, because it is built into route.
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<P>
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When you see high packet loss rates when pinging a host behind
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one or more gateways, this may hint at a very congested network. Packet
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loss is not so much due to technical deficiencies as due to temporary
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excess loads on forwarding hosts, which makes them delay or even drop
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incoming datagrams.
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<P>
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<HR><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="node69.html">Configuring a Gateway</A>
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<B>Up:</B> <A HREF="node65.html">Interface Configuration for IP</A>
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<B> Previous:</B> <A HREF="node67.html">Ethernet Interfaces</A>
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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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