Configuring Static IP Assignments For A libvirt Development Based Development Environment

Reason

Predictable IP placement of virtual machines is useful when performing repeated test of network software.

Environment:

This post was developed on Fedora Core 29 but should work on other recent Fedora/CentOS/RHEL OS releases.

Pre-reqs

A non-root user with sudo access was used to query and configure libvirt

In this example, four virtual machines are used and connected to the default libvirt network. The virtual machines are configured for DHCP.

Network Configuration Diagram

   baseOS<->|   
            |<->vmos1  
    libvirt |<->vmos2  
    default |<->vmos3  
    network |<->vmos4  

Network Configuration Command Line

 $ sudo virsh net-dumpxml default  
 <network connections='4'>  
  <name>default</name>  
  <uuid>e418d7f8-b770-47e6-9cb0-3d013568b761</uuid>  
  <forward mode='nat'>  
   <nat>  
    <port start='1024' end='65535'/>  
   </nat>  
  </forward>  
  <bridge name='virbr0' stp='on' delay='0'/>  
  <mac address='52:54:00:7a:96:4d'/>  
  <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>  

Gather the MAC addresses of each VM

The example hosts have only one network interface. If there are multiple interfaces, gather the MAC address attached to the default network. IP address can be defined for other networks by adjusting the below command lines as needed.

 $ sudo virsh domiflist vmos4  
 Interface Type    Source   Model    MAC  
 -------------------------------------------------------  
 vnet3   network  default  virtio   52:54:00:d3:3e:e7  

Set the mac IP reservation for each MAC address.

Ensure the assigned IP address are available.

 sudo virsh net-update default add ip-dhcp-host '<host mac="52:54:00:87:c4:d1" ip="192.168.122.3"/>' --live --config  
 sudo virsh net-update default add ip-dhcp-host '<host mac="52:54:00:57:b0:a6" ip="192.168.122.4"/>' --live --config  
 sudo virsh net-update default add ip-dhcp-host '<host mac="52:54:00:37:aa:4f" ip="192.168.122.5"/>' --live --config  
 sudo virsh net-update default add ip-dhcp-host '<host mac="52:54:00:d3:3e:e7" ip="192.168.122.6"/>' --live --config  

Display updated network configuration

 $ sudo virsh net-dumpxml default  
 <network connections='4'>  
  <name>default</name>  
  <uuid>e418d7f8-b770-47e6-9cb0-3d013568b761</uuid>  
  <forward mode='nat'>  
   <nat>  
    <port start='1024' end='65535'/>  
   </nat>  
  </forward>  
  <bridge name='virbr0' stp='on' delay='0'/>  
  <mac address='52:54:00:7a:96:4d'/>  
  <ip address='192.168.122.1' netmask='255.255.255.0'>  
   <dhcp>  
    <range start='192.168.122.2' end='192.168.122.254'/>  
    <host mac='52:54:00:87:c4:d1' ip='192.168.122.3'/>  
    <host mac='52:54:00:57:b0:a6' ip='192.168.122.4'/>  
    <host mac='52:54:00:37:aa:4f' ip='192.168.122.5'/>  
    <host mac='52:54:00:d3:3e:e7' ip='192.168.122.6'/>  
   </dhcp>  
  </ip>  
 </network>  

Start/Restart each VM as needed.

The interface can be disconnected/reconnected if a restart is not wanted.

 $ for f in vmos1 vmow2 vmos3 vmos4 ; do sudo virsh destroy $f ; sleep 5 ; sudo virsh start $f ; done  

Update hosts file

The hosts file is updated to ease host access

 $ cat <<EOF | sudo tee -a /etc/hosts  
 192.168.122.3 vmos1  
 192.168.122.4 vmos2  
 192.168.122.5 vmos3  
 192.168.122.6 vmos4  
 EOF  

Test connectivity

 $ ping -c4 vmos1  
 PING vmos1 (192.168.122.3) 56(84) bytes of data.  
 64 bytes from vmos1 (192.168.122.3): icmp_seq=1 ttl=64 time=0.387 ms  
 64 bytes from vmos1 (192.168.122.3): icmp_seq=2 ttl=64 time=0.418 ms  
 64 bytes from vmos1 (192.168.122.3): icmp_seq=3 ttl=64 time=0.396 ms  
 64 bytes from vmos1 (192.168.122.3): icmp_seq=4 ttl=64 time=0.355 ms  
 --- vmos1 ping statistics ---  
 4 packets transmitted, 4 received, 0% packet loss, time 104ms  
 rtt min/avg/max/mdev = 0.355/0.389/0.418/0.022 ms  

References
Libvirt Networking
Red Hat Virtualization Deployment and Administration Guide