<html><head><title>Gavare's eXperimental Emulator: Networking</title>
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<b>GXemul:</b></font>
<font color="#000000" size="6"><b>Networking</b>
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<p><br>
<h2>Networking</h2>
<p>
<ul>
<li><a href="#intro">Introduction</a>
<li><a href="#multihost">Network across multiple hosts</a>
<li><a href="#direct_example_1">Direct-access example 1: udp_snoop</a>
</ul>
<p><br>
<a name="intro"></a>
<h3>Introduction:</h3>
GXemul's current networking layer supports two modes:
<p><ol>
<li>A NAT-like layer, which allows guest OSes to access the outside
internet world (IPv4 only, so far). When only one machine is being
emulated, the following default values apply to the guest OS:<pre>
IPv4 address: 10.0.0.1
Netmask: 255.0.0.0
Gateway / default route: 10.0.0.254
Nameserver: 10.0.0.254
</pre>To the outside world, it will seem as if the host is doing all the
networking, since the emulator is just a normal user process
on the host.
<p>
<li>A direct-access layer, allowing external tools to read/write raw
ethernet packages from/to the emulator.
</ol>
<p><i>NOTE:</i> Both these modes have problems. The NAT-like layer is very
"hackish" and was only meant as a proof-of-concept, to see if networking
like this would work with e.g. NetBSD as a guest OS. (If you are
interested in the technical details, and the reasons why NAT networking is
implemented this way, you might want to read the <a
href="technical.html#net"> networking section in the technical
documentation</a>.) Because of the obvious limitations with the NAT
approach, I have also included support for direct packet access, but this
is not designed for security or anything like that.
<p><font color="#ff0000">Use the networking features at your own risk.
</font>
<p>The emulated machine must have a NIC (network interface card). Not all
machines have this. At the moment, the following NICs are more or less
working:
<ul>
<li><tt><b>dec21143</b></tt>, Digital's 21143 PCI NIC (known as <tt>dc</tt>
in OpenBSD, or <tt>tlp</tt> in NetBSD)
<li><tt><b>ether</b></tt>, the "fake" experimental ethernet device
(documented <a href="experiments.html#expdevices_ether">here</a>)
<li><tt><b>le</b></tt>, <a href="http://en.wikipedia.org/wiki/TURBOchannel">Turbochannel</a>
Lance Ethernet, as used in DECstation 5000/200 ("3max")
<li><tt><b>mec</b></tt>, the SGI O2's ethernet controller
</ul>
<p>It is not possible to simply attach any of the supported NICs into any
of the supported emulated machines. Some machines, for example, have a
specific NIC in them, others may have a PCI bus where a PCI NIC can be
used. This is very much machine-dependent.
<p>If you are impatient, and simply want to try out networking in GXemul,
I would recommend trying out an ftp install of <a
href="guestoses.html#netbsdpmaxinstall">NetBSD/pmax</a>.
<p><br>
<a name="multihost"></a>
<h3>Network across multiple hosts:</h3>
<p>The way to emulate a network of multiple emulated machines, whether
they are actually running on the same physical host, or on multiple hosts,
is to use <a href="configfiles.html">configuration files</a>, and the
"direct-access" method of networking.
<p>Although it <i>is</i> possible to have more than one machine per
configuration file, I strongly recommend against it. Please use one
configuration file for one emulated machine.
<p>Here is a simple example:
<p><table border="0" width="100%"><tr><td width="40"> </td>
<td><pre>
<font color="#2020cf">! Configuration file for a
! "client" machine, netbooting
! of another machine.</font>
<b>net(</b>
<b>local_port(15000)</b>
<b>add_remote(<font color="#ff003f">"localhost:15001"</font>)</b>
<b>)</b>
<b>machine(</b>
<b>name(<font color="#ff003f">"client machine"</font>)</b>
<b>serial_nr(1)</b> <font color="#2020cf">! 10.0.0.1</font>
<b>type(<font color="#ff003f">"sgi"</font>)</b>
<b>subtype(<font color="#ff003f">"o2"</font>)</b>
<b>load(<font color="#ff003f">"netbsd-GENERIC32_IP3x.gz"</font>)</b>
<b>)</b>
</pre></td><td width="20"> </td><td><pre>
<font color="#2020cf">! Configuration file for the
! "server" machine.</font>
<b>net(</b>
<b>local_port(15001)</b>
<b>add_remote(<font color="#ff003f">"localhost:15000"</font>)</b>
<b>)</b>
<b>machine(</b>
<b>name(<font color="#ff003f">"nfs server"</font>)</b>
<b>serial_nr(2)</b> <font color="#2020cf">! 10.0.0.2</font>
<b>type(<font color="#ff003f">"dec"</font>)</b>
<b>subtype(<font color="#ff003f">"3max"</font>)</b>
<b>disk(<font color="#ff003f">"nbsd_pmax.img"</font>)</b>
<b>)</b>
</pre></td><td width="20"> </td></tr></table>
<p>This example creates a network using the default settings (10.0.0.0/8),
but it also uses the direct-access networking mode to allow the network
to be connected to other emulator instances. <tt>local_port(15000)</tt>
means that anything coming in to UDP port 15000 on the host is added to
the network. All ethernet packets on the network are also sent out to all
other connected machines (those added with <tt>add_remote()</tt>).
<p>As you can see in the example, this is a configuration file for
netbooting a NetBSD/sgimips diskless machine, with a NetBSD/pmax machine
acting as the nfs server. Note that the nfs server has ports 15000 and
15001 reversed, compared to the client!
<p>"<tt>localhost</tt>" can be changed to the Internet hostname of a
remote machine, to run the simulation across a physical network.
<p><font color="#ff0000"><b>NOTE:</b> There is no error checking or
security checking of any kind. All UDP packets arriving at the input port
are added to the emulated ethernet. This is not very good of course; use
this feature at your own risk.</font>
<p><br>
<a name="direct_example_1"></a>
<h3>Direct-access example 1: udp_snoop:</h3>
The most basic example of how the simple direct-access system works is a small
program in the <tt>experiments/</tt> directory, <tt>udp_snoop</tt>, which simply
dumps incoming UDP packets to the terminal, in hex and ASCII.
<p>The easiest way to test the example is to download a <a href="ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-3.1/pmax/binary/kernel/netbsd-INSTALL.gz">
NetBSD/pmax INSTALL kernel</a>, and start the emulator with a configuration file
looking something like this:
<pre>
net(
add_remote("localhost:12300")
)
machine(
subtype(3max)
load("netbsd-INSTALL.gz")
)
</pre>
<p>In addition to the machine section, you can see that there is also a
<tt>net()</tt> section. It defaults to emulating a 10.0.0.0/8 IPv4 NATed
network, but there is also an additional "raw output", to UDP port 12300.
<p>Now, do the following:
<ul>
<li>Start the emulator with the configuration file, i.e.
<tt><b>gxemul @testconfig</b></tt>.
<li>Start <tt><b>udp_snoop 12300</b></tt> in another terminal.
<li>Inside emulated NetBSD/pmax, type <tt><b>ifconfig le0 10.0.0.1</b></tt>.
</ul>
<p>This should be enough to see broadcast messages from the guest OS which
are not directed to the gateway. It might look like this:
<pre>
$ ./udp_snoop 12300
ff ff ff ff ff ff 10 20 30 00 00 10 08 06 00 01 ....... 0.......
08 00 06 04 00 01 10 20 30 00 00 10 0a 00 00 02 ....... 0.......
00 00 00 00 00 00 0a 00 00 02 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 ............
33 33 ff 00 00 10 10 20 30 00 00 10 86 dd 60 00 33..... 0.....`.
00 00 00 20 00 01 00 00 00 00 00 00 00 00 00 00 ... ............
00 00 00 00 00 00 ff 02 00 00 00 00 00 00 00 00 ................
00 01 ff 00 00 10 3a 00 01 00 05 02 00 00 83 00 ......:.........
80 83 00 00 00 00 ff 02 00 00 00 00 00 00 00 00 ................
00 01 ff 00 00 10 ......
...
</pre>
</p>
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distrib
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Mandriva
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2010.0
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i586
>
media
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contrib-release
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by-pkgid
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1ac54c475e57234527874d1bc3ad003c
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files
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139
