KVM libvirt assign static guest IP addresses using DHCP on the virtual machine

Fig.01: Libvirt uses a program, dnsmasq for DNS and DHCP for default network.

View the current dnsmasq DHCP configuration

Type the following command to list networks
# virsh net-list
Sample outputs:

 Name                 State      Autostart     Persistent
----------------------------------------------------------
 default              active     yes           yes

To see the default network information, enter:
# virsh net-dumpxml default
Sample outputs:

<network connections='2'>
  <name>default</name>
  <uuid>e346291e-f86b-4f2f-a16e-654136441805</uuid>
  <forward mode='nat'>
    <nat>
      <port start='1024' end='65535'/>
    </nat>
  </forward>
  <bridge name='virbr0' stp='on' delay='0'/>
  <mac address='52:54:00:12:fe:35'/>
  <ip address='192.168.122.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.122.100' end='192.168.122.254'/>
    </dhcp>
  </ip>
</network>

The DHCP range is between 192.168.122.100 and 192.168.122.254.

How to configure static guest IP addresses on the VM host

First find out your guest VM’s MAC addresses, enter:
# virsh dumpxml {VM-NAME-HERE} | grep -i '<mac'
# virsh dumpxml xenial | grep -i '<mac'
Sample outputs:

<mac address='52:54:00:4c:40:1c'/>

Please note down the MAC addresses of the xenial VM that you want to assign static IP addresses.

Edit the default network

Type the following command:
# virsh net-edit default
Find the following section:

 <dhcp>
      <range start='192.168.122.100' end='192.168.122.254'/>

Append the static IP as follows after range:

     <host mac='52:54:00:4c:40:1c' name='xenial' ip='192.168.122.4'/>

Where,

1. mac='52:54:00:4c:40:1c' – VMs mac address
2. name='xenial' – VMs name.
3. ip='192.168.122.4' – VMs static IP.

Here is my complete file with three static DHCP entries for three VMs:

<network>
  <name>default</name>
  <uuid>e346291e-f86b-4f2f-a16e-654136441805</uuid>
  <forward mode='nat'/>
  <bridge name='virbr0' stp='on' delay='0'/>
  <mac address='52:54:00:12:fe:35'/>
  <ip address='192.168.122.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.122.100' end='192.168.122.254'/>
      <host mac='52:54:00:a0:cc:19' name='centos7' ip='192.168.122.2'/>
      <host mac='52:54:00:f7:a1:c8' name='puffy' ip='192.168.122.3'/>
      <host mac='52:54:00:4c:40:1c' name='xenial' ip='192.168.122.4'/>
    </dhcp>
  </ip>
</network>

Restart DHCP service:
# virsh net-destroy default
# virsh net-start default
Sample outputs:

Network default destroyed
Network default started

If you are running the guest/VM called xenial shutdown it:
# virsh shutdown xenial
# /etc/init.d/libvirt-bin restart
# virsh start xenial
# ping -a 192.168.122.4
Sample outputs:

PING 192.168.122.4 (192.168.122.4) 56(84) bytes of data.
64 bytes from 192.168.122.4: icmp_seq=1 ttl=64 time=0.518 ms
64 bytes from 192.168.122.4: icmp_seq=2 ttl=64 time=0.202 ms
64 bytes from 192.168.122.4: icmp_seq=3 ttl=64 time=0.327 ms
^C
--- 192.168.122.4 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 1999ms
rtt min/avg/max/mdev = 0.202/0.349/0.518/0.129 ms

Each time the guest or VM called xenial comes online (or rebooted for the kernel update) it will get 192.168.122.4 as static IP address by dnsmasq DHCP server.