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KVM/libvirt: Comment configure static guest IP addresses sur the virtualisation host

ayi

What I’d like to do is to set the guests’ network configuration (IP address, subnet, gateway, broadcast address) from the host system. The used network setup is in <code>bridge</code> mode. How can I configure the network from the host rather than configuring the client itself to a static network configuration?
If I execute:
<pre><code class="lang-auto">virsh edit vm1

</code></pre>
there is a <code><network></code> block as well and I tried to configure the network interface from there, but unfortunately the guest VM doesn’t seem to use it and as such is offline to the network (since it uses automatic network configuration only)… Guest VMs are both, Linux and Windows based. Any help would be highly appreciated.

ayi_2

If you don’t want to do any configuration inside the guest, then the only option is a DHCP server that hands out static IP addresses. If you use <code>bridge</code> mode, that will probably be some external DHCP server. Consult its manual to find out how to serve static leases.
But at least in forward modes <code>nat</code> or <code>route</code>, you could use libvirt’s built-in <code>dnsmasqd</code> (More recent versions of libvirtd support the dnsmasq’s “dhcp-hostsfile” option). Here is how:
First, find out the MAC addresses of the VMs you want to assign static IP addresses:
<pre><code class="lang-auto">virsh dumpxml $VM_NAME | grep 'mac address'

</code></pre>
Then edit the network
<pre><code class="lang-auto">virsh net-list
virsh net-edit $NETWORK_NAME # Probably "default"

</code></pre>
Find the <code><dhcp></code> section, restrict the dynamic range and add host entries for your VMs
<pre><code class="lang-auto"><dhcp>
<range start="192.168.122.100" end="192.168.122.254"/>
<host mac="52:54:00:6c:3c:01" name="vm1" ip="192.168.122.11"/>
<host mac="52:54:00:6c:3c:02" name="vm2" ip="192.168.122.12"/>
<host mac="52:54:00:6c:3c:03" name="vm3" ip="192.168.122.13"/>
</dhcp>

</code></pre>
Then, reboot your VM (or restart its DHCP client, e.g. <code>ifdown eth0; ifup eth0</code>)
Update: I see there are reports that the change might not get into effect after “virsh net-edit”. In that case, try this after the edit:
<pre><code class="lang-auto">virsh net-destroy $NETWORK_NAME
virsh net-start $NETWORK_NAME

</code></pre>
… and restart the VM’s DHCP client.
If that still doesn’t work, you might have to
<ul>
<li>
stop the libvirtd service
</li>
<li>
kill any dnsmasq processes that are still alive
</li>
<li>
start the libvirtd service
</li>
</ul>
Note: There is no way the KVM host could force a VM with unknown OS and unknown config to use a certain network configuration. But if know know that the VM uses a certain network config protocol - say DHCP - you can can use that. This is what this post assumes.
Some OS (e.g. some Linux distros) also allow to pass network config options into the guest e.g. via the kernel command line. But that is very specific to the OS, and i see no advantage over the DHCP method.