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Add KVM Network With Virsh

date: 2021-10-16

Introduction

This is a short and sweet walk-through for how to create a new network for libvirt for kvm, from the command line, using virsh.

Name Resolution

Let's start with name resolution.

  • Install libnss-libvirt: 

    apt install libnss-libvirt

  • In /etc/nsswitch.conf, add libvirt to hosts key. 

    # /etc/nsswitch.conf
# change this
...
hosts:          files dns mymachines
...
# to this
...
hosts:          files libvirt dns mymachines
...

Starter XML

You could dumpxml on the existing default network: 

virsh net-dumpxml default > foonet.xml
Then, edit foonet.xml:

  • remove the network uuid
  • change the network name to taste
  • remove the bridge mac
  • change the bridge name to taste
  • change the bridge ip address and dhcp range to taste
<!-- foonet.xml -->
<network>
  <name>foonet</name>
  <forward mode='nat'>
    <nat>
      <port start='1024' end='65535'/>
    </nat>
  </forward>
  <bridge name='virbr101' stp='on' delay='0'/>
  <ip address='10.55.44.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='10.55.44.2' end='10.55.44.254'/>
    </dhcp>
  </ip>
</network>

Define The Network

With the above xml file: virsh net-define foonet.xml

The network definition can now be found in /etc/libvirt/qemu/networks/foonet.xml 

<!-- /etc/libvirt/qemu/networks/foonet.xml -->
<!--
WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE
OVERWRITTEN AND LOST. Changes to this xml configuration should be made using:
  virsh net-edit foonet
or other application using the libvirt API.
-->

<network>
  <name>foonet</name>
  <uuid>e6e40bfc-d449-4043-924c-ca0f0edf4210</uuid>
  <forward mode='nat'>
    <nat>
      <port start='1024' end='65535'/>
    </nat>
  </forward>
  <bridge name='virbr111' stp='on' delay='0'/>
  <mac address='52:54:00:49:a7:f8'/>
  <ip address='10.55.44.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='10.55.44.2' end='10.55.44.254'/>
    </dhcp>
  </ip>
</network>

You could also start the network without defining it using virsh net-create foonet.xml.

Start/Stop

  • Start the network
    • virsh net-start foonet
  • Stop the network
    • virsh net-destroy foonet
  • Undefine the network
    • virsh net-undefine foonet
  • Autostart the network
    • virsh net-autostart foonet
  • Disable autostart for the network
    • virsh net-autostart foonet --disable

Tab completion is you friend!