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<?xml version="1.0" encoding="UTF-8"?>
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<title>GXemul: Networking</title>
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<h1>GXemul: Networking</h1>
<p>
<a href="./">Back to the index.</a>
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<p><br>
<ul>
<li><a href="#intro">Introduction</a>
<li><a href="#tap">Virtual Ethernet switch using a tap device</a>
<li><a href="#multihost">Network across multiple hosts</a>
<li><a href="#direct_example_1">UDP "Direct-access" example: udp_snoop</a>
</ul>
<p><br>
<a name="intro"></a>
<h3>Introduction:</h3>
<p>GXemul's current networking layer supports three modes:
<p><ol>
<li>A virtual Ethernet switch built on top of a <i>tap</i> device.
<p>
<li>A NAT-like emulation 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 UDP mode, allowing external tools to read/write raw
ethernet packages from/to the emulator via UDP.
</ol>
<p><i>NOTES:</i>
<p>The tap device support was contributed by Jason Thorpe.
<p>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>.)
<p>The UDP mode is used to connect multiple instances of GXemul in
an easy way, but it provides no security of any kind.
<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>, Lance Ethernet, as used in <a href="machine_decstation.html">DECstation 5000/200</a> ("3max") and the <a href="machine_luna88k.html">LUNA88K</a> machines
<li><tt><b>mec</b></tt>, the <a href="machine_sgi_o2.html">SGI O2</a>'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, and implemented on a case-by-case basis.
<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="machine_decstation.html#netbsdpmaxinstall">NetBSD/pmax</a>.
<p><br>
<a name="tap"></a>
<h3>Virtual Ethernet switch using a <i>tap</i> device:</h3>
<p>The simplest way to emulate a real Ethernet network is using a <i>tap</i>
device. In this mode, the emulator disables the simulated NAT and
direct-access machinery and internally treats all emulated NICs as if
they are on a single Ethernet switch. In this mode, packets destined for
the guest's specific MAC address as well as Ethernet multicast and broadcast
packets are send to the individual guest instances. Individual NIC
emulations may also apply their own multicast filtering; multicast filtering
is implemented for the DEC 21143 and Lance NICs.
<p>The <i>tap</i> interface on the host can be thought of as an upstream
link on the virtual Ethernet switch. In addition to providing a "port"
for the host, the <i>tap</i> interface can be bridged to a physical Ethernet
port on the host, allowing the guests to access the host's connected LAN.
<p>Networking services such as DHCP and DNS must be provided either by
the host or by the host's connected LAN.
<p>Support for the <i>tap</i> device was developed on NetBSD, but should
also work on FreeBSD, OpenBSD, and Linux hosts.
<p>The easiest way to enable tap device networking is to use the <tt>-L</tt>
command line option, e.g.:
<p><pre>gxemul -e 3max <b>-L /dev/tap0</b> -d nbsd_pmax.img
</pre>
<p>Here is a simple example of how to enable it when using configuration
files:
<p><pre>
<font color="#2020cf">! Configuration file for
! virtual Ethernet switch networking
! using a tap device.</font>
<b>net(</b>
<b>tapdev(</b><font color="#ff003f">"/dev/tap0"</font><b>)</b>
<b>)</b>
<b>machine(</b>
<b>name(<font color="#ff003f">"guest machine"</font>)</b>
<b>type(<font color="#ff003f">"dec"</font>)</b>
<b>subtype(<font color="#ff003f">"5000/200"</font>)</b>
<font color="#2020cf">! Add a disk, etc.</font>
<b>)</b>
</pre>
<p>Before starting the emulator, you will need to create the <i>tap</i>
interface on the host. Here is an example for NetBSD:
<p><pre>
<b># ifconfig tap0 create up</b>
</pre>
<p>If you wish to simply network the host and the guests together, then
simply assign an IP address to the <i>tap</i> interface on the host:
<p><pre>
<b># ifconfig tap0 10.0.0.254</b>
</pre>
<p>You can now run a DHCP server on the host for the guests, or you can
configure the guests manually.
<p>If instead you would like to bridge to the host's connected LAN,
Here is an example for NetBSD:
<p><pre>
<b># ifconfig bridge0 create up</b>
<b># brconfig add tap0 add wm0</b>
</pre>
<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. Each configuration file
must have a unique <i>tap</i> instance, and machines in separate
configuration files must use bridged <i>tap</i> devices if they wish
to communicate with each other as if on the same LAN.
<p><small>(The section above is written by Jason Thorpe.)</small>
<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>UDP "Direct-access" example: udp_snoop:</h3>
<p>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>
</body>
</html>
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