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<section id="network-emulation">
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<span id="id1"></span><h1>Network emulation<a class="headerlink" href="#network-emulation" title="Link to this heading"></a></h1>
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<p>QEMU can simulate several network cards (e.g. PCI or ISA cards on the PC
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target) and can connect them to a network backend on the host or an
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emulated hub. The various host network backends can either be used to
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connect the NIC of the guest to a real network (e.g. by using a TAP
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devices or the non-privileged user mode network stack), or to other
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guest instances running in another QEMU process (e.g. by using the
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socket host network backend).</p>
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<section id="using-tap-network-interfaces">
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<h2>Using TAP network interfaces<a class="headerlink" href="#using-tap-network-interfaces" title="Link to this heading"></a></h2>
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<p>This is the standard way to connect QEMU to a real network. QEMU adds a
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virtual network device on your host (called <code class="docutils literal notranslate"><span class="pre">tapN</span></code>), and you can then
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configure it as if it was a real ethernet card.</p>
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<section id="linux-host">
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<h3>Linux host<a class="headerlink" href="#linux-host" title="Link to this heading"></a></h3>
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<p>As an example, you can download the <code class="docutils literal notranslate"><span class="pre">linux-test-xxx.tar.gz</span></code> archive
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and copy the script <code class="docutils literal notranslate"><span class="pre">qemu-ifup</span></code> in <code class="docutils literal notranslate"><span class="pre">/etc</span></code> and configure properly
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<code class="docutils literal notranslate"><span class="pre">sudo</span></code> so that the command <code class="docutils literal notranslate"><span class="pre">ifconfig</span></code> contained in <code class="docutils literal notranslate"><span class="pre">qemu-ifup</span></code> can
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be executed as root. You must verify that your host kernel supports the
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TAP network interfaces: the device <code class="docutils literal notranslate"><span class="pre">/dev/net/tun</span></code> must be present.</p>
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<p>See <a class="reference internal" href="../invocation.html#sec-005finvocation"><span class="std std-ref">Invocation</span></a> to have examples of command
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lines using the TAP network interfaces.</p>
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</section>
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<section id="windows-host">
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<h3>Windows host<a class="headerlink" href="#windows-host" title="Link to this heading"></a></h3>
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<p>There is a virtual ethernet driver for Windows 2000/XP systems, called
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TAP-Win32. But it is not included in standard QEMU for Windows, so you
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will need to get it separately. It is part of OpenVPN package, so
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download OpenVPN from : <a class="reference external" href="https://openvpn.net/">https://openvpn.net/</a>.</p>
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</section>
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</section>
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<section id="using-the-user-mode-network-stack">
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<h2>Using the user mode network stack<a class="headerlink" href="#using-the-user-mode-network-stack" title="Link to this heading"></a></h2>
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<p>By using the option <code class="docutils literal notranslate"><span class="pre">-net</span> <span class="pre">user</span></code> (default configuration if no <code class="docutils literal notranslate"><span class="pre">-net</span></code>
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option is specified), QEMU uses a completely user mode network stack
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(you don’t need root privilege to use the virtual network). The virtual
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network configuration is the following:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">guest</span> <span class="p">(</span><span class="mf">10.0.2.15</span><span class="p">)</span> <span class="o"><------></span> <span class="n">Firewall</span><span class="o">/</span><span class="n">DHCP</span> <span class="n">server</span> <span class="o"><-----></span> <span class="n">Internet</span>
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<span class="o">|</span> <span class="p">(</span><span class="mf">10.0.2.2</span><span class="p">)</span>
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<span class="o">|</span>
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<span class="o">----></span> <span class="n">DNS</span> <span class="n">server</span> <span class="p">(</span><span class="mf">10.0.2.3</span><span class="p">)</span>
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<span class="o">|</span>
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<span class="o">----></span> <span class="n">SMB</span> <span class="n">server</span> <span class="p">(</span><span class="mf">10.0.2.4</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>The QEMU VM behaves as if it was behind a firewall which blocks all
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incoming connections. You can use a DHCP client to automatically
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configure the network in the QEMU VM. The DHCP server assign addresses
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to the hosts starting from 10.0.2.15.</p>
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<p>In order to check that the user mode network is working, you can ping
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the address 10.0.2.2 and verify that you got an address in the range
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10.0.2.x from the QEMU virtual DHCP server.</p>
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<p>Note that ICMP traffic in general does not work with user mode
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networking. <code class="docutils literal notranslate"><span class="pre">ping</span></code>, aka. ICMP echo, to the local router (10.0.2.2)
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shall work, however. If you’re using QEMU on Linux >= 3.0, it can use
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unprivileged ICMP ping sockets to allow <code class="docutils literal notranslate"><span class="pre">ping</span></code> to the Internet. The
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host admin has to set the ping_group_range in order to grant access to
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those sockets. To allow ping for GID 100 (usually users group):</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">echo</span> <span class="mi">100</span> <span class="mi">100</span> <span class="o">></span> <span class="o">/</span><span class="n">proc</span><span class="o">/</span><span class="n">sys</span><span class="o">/</span><span class="n">net</span><span class="o">/</span><span class="n">ipv4</span><span class="o">/</span><span class="n">ping_group_range</span>
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</pre></div>
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</div>
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<p>When using the built-in TFTP server, the router is also the TFTP server.</p>
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<p>When using the <code class="docutils literal notranslate"><span class="pre">'-netdev</span> <span class="pre">user,hostfwd=...'</span></code> option, TCP or UDP
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connections can be redirected from the host to the guest. It allows for
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example to redirect X11, telnet or SSH connections.</p>
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</section>
|
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<section id="hubs">
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<h2>Hubs<a class="headerlink" href="#hubs" title="Link to this heading"></a></h2>
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<p>QEMU can simulate several hubs. A hub can be thought of as a virtual
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connection between several network devices. These devices can be for
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example QEMU virtual ethernet cards or virtual Host ethernet devices
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(TAP devices). You can connect guest NICs or host network backends to
|
||
such a hub using the <code class="docutils literal notranslate"><span class="pre">-netdev</span>
|
||
<span class="pre">hubport</span></code> or <code class="docutils literal notranslate"><span class="pre">-nic</span> <span class="pre">hubport</span></code> options. The legacy <code class="docutils literal notranslate"><span class="pre">-net</span></code> option also
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connects the given device to the emulated hub with ID 0 (i.e. the
|
||
default hub) unless you specify a netdev with <code class="docutils literal notranslate"><span class="pre">-net</span> <span class="pre">nic,netdev=xxx</span></code>
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here.</p>
|
||
</section>
|
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<section id="connecting-emulated-networks-between-qemu-instances">
|
||
<h2>Connecting emulated networks between QEMU instances<a class="headerlink" href="#connecting-emulated-networks-between-qemu-instances" title="Link to this heading"></a></h2>
|
||
<p>Using the <code class="docutils literal notranslate"><span class="pre">-netdev</span> <span class="pre">socket</span></code> (or <code class="docutils literal notranslate"><span class="pre">-nic</span> <span class="pre">socket</span></code> or <code class="docutils literal notranslate"><span class="pre">-net</span> <span class="pre">socket</span></code>)
|
||
option, it is possible to create emulated networks that span several
|
||
QEMU instances. See the description of the <code class="docutils literal notranslate"><span class="pre">-netdev</span> <span class="pre">socket</span></code> option in
|
||
<a class="reference internal" href="../invocation.html#sec-005finvocation"><span class="std std-ref">Invocation</span></a> to have a basic
|
||
example.</p>
|
||
</section>
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