# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.

dummy

# Interfaces fictives pour le bridge
iface dummy0 inet manual
 
# Démarrage non automatique du bridge
#auto lan0
 
# Interface/pont pour le réseau interne
iface lan0 inet static
        address 192.168.200.254/24
        bridge_ports dummy0
        bridge_maxwait 5
        bridge_stp off
        bridge_fd 0
        pre-up    /sbin/ip link  add dummy0 type dummy
        post-down /sbin/ip link  del dummy0

# modprobe dummy

ifup lan0

ifconfig lan0
lan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.200.254  netmask 255.255.255.0  broadcast 192.168.200.255
        inet6 fe80::e0a6:f1ff:fece:ee92  prefixlen 64  scopeid 0x20<link>
        ether e2:a6:f1:ce:ee:92  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 164  bytes 27842 (27.1 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

brctl show
bridge name	bridge id		STP enabled	interfaces
lan0		8000.e2a6f1ceee92	no		dummy0

Le bridge doit être arrêté pour être pris en charge par libvirt

ifdown lan0

virsh net-edit default

<network>
  <name>default</name>
  <uuid>10810229-bede-4ae5-a513-05b5d9c4b47d</uuid>
  <forward mode='nat'/>
  <bridge name='lan0' stp='on' delay='0'/>
  <mac address='52:54:00:c0:21:86'/>
  <ip address='192.168.200.254' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.200.1' end='192.168.200.253'/>
    </dhcp>
  </ip>
</network>

virsh net-start default

virsh net-autostart default

virsh net-list --all
 Nom       État    Démarrage automatique   Persistent
-------------------------------------------------------
 default   actif   Oui                     Oui