Comment 1 for bug 1797715

Hi Jürgen,
well lets take a look at your network that is associated to the guest.

Your guest XML representation will have a network definition with a source.
Like this:
  <source network='default' bridge='virbr0'/>
Check `virsh dumpxml <guestname>` to get that.

Once you know the name check the network - in my case "default".
 $ virsh net-info default
Name: default
UUID: 3a360c07-d792-422e-818a-2a61b6ab64d0
Active: yes
Persistent: yes
Autostart: yes
Bridge: virbr0

Is your network active?

If not start checking there what might be different.

If it is active check the definition and share it here.
$ virsh net-dumpxml default
<network connections='2'>
  <name>default</name>
  <uuid>3a360c07-d792-422e-818a-2a61b6ab64d0</uuid>
  <forward mode='nat'>
    <nat>
      <port start='1024' end='65535'/>
    </nat>
  </forward>
  <bridge name='virbr0' stp='on' delay='0'/>
  <mac address='52:54:00:34:06:2f'/>
  <ip address='192.168.122.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.122.2' end='192.168.122.254'/>
    </dhcp>
  </ip>
</network>

What you see above is the "most default" network as installed by the package.
You should see a dnsmasq process running for a config file of that name, like
$ ps axlf | grep dnsmasq
5 111 5607 1 20 0 49964 2424 - S ? 0:00 /usr/sbin/dnsmasq --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro --dhcp-script=/usr/lib/libvirt/libvirt_leaseshelper

The backend storage for all DHCP handling is in /var/lib/libvirt/dnsmasq/.
You'll find config files with the name of the network and lease/mac files with the name of the bridge they are atatched like virbr0.status

Please check the content of these files and if they change when your guest requests access.

Finally while the guest does DHCP the journal should get entries like this:
Oct 15 10:56:23 node-horsea dnsmasq-dhcp[5607]: DHCPDISCOVER(virbr0) 52:54:00:f4:4f:2d
Oct 15 10:56:23 node-horsea dnsmasq-dhcp[5607]: DHCPOFFER(virbr0) 192.168.122.59 52:54:00:f4:4f:2d
Oct 15 10:56:23 node-horsea dnsmasq-dhcp[5607]: DHCPREQUEST(virbr0) 192.168.122.59 52:54:00:f4:4f:2d
Oct 15 10:56:23 node-horsea dnsmasq-dhcp[5607]: DHCPACK(virbr0) 192.168.122.59 52:54:00:f4:4f:2d

Please check if you see those by using "journalctl -f" just before kicking a DHCP in the guest.