Why: predictable addressing for allow-lists and audit. Two clean ways: set static IP in the guest (netplan) or pin a DHCP lease in libvirt.

1) In-guest (Ubuntu netplan)

# /etc/netplan/01-static.yaml
network:
  version: 2
  ethernets:
    ens3:
      addresses: [10.0.50.23/24]
      gateway4: 10.0.50.1
      nameservers:
        addresses: [10.0.50.10,1.1.1.1]

sudo netplan apply

2) Libvirt DHCP reservation

virsh net-dumpxml default > /tmp/default.xml
# Add inside <dhcp>:
# <host mac='52:54:00:aa:bb:cc' name='vm1' ip='10.0.50.23'/>
virsh net-define /tmp/default.xml
virsh net-destroy default && virsh net-start default

Notes

• Keep MAC stable (virt-manager or virsh edit).
• Avoid duplicate addressing; document allocations.