Config bridge network in order to using KVM

Question

I want to install and configure KVM and I need to create some virtual machines, As I researched I should create a bridge network and select it in KVM.

I installed bridle-utils before anything This is my interfaces file

### Hetzner Online GmbH installimage


source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback
iface lo inet6 loopback

auto eth0
iface eth0 inet static
  address IP_ADDRESS
  netmask 255.255.255.224
  gateway GATEWAY_ADDRESS
  up route add -net SOME_ADDRESS netmask 255.255.255.224 gw SOME_ADDRESS2 dev eth0

iface eth0 inet6 static
  address 2a01:4f8:160:41e6::2
  netmask 64
  gateway fe80::1

Based on Hertnez article I commented eth0 and added br0 lines as below:

### Hetzner Online GmbH installimage

    source /etc/network/interfaces.d/*

    auto lo
    iface lo inet loopback
#    iface lo inet6 loopback

#    auto eth0
#    iface eth0 inet static
#      address (Main IP)
#      netmask 255.255.255.224
#      gateway (Gateway Address)
#      up route add -net (Some Address) netmask 255.255.255.224 gw (Some Address 2) dev eth0

#    iface eth0 inet6 static
#      address 2a01:4f8:160:41e6::2
#      netmask 64
#      gateway fe80::1

auto  br0
iface br0 inet static
 address (Main IP)
 netmask 255.255.255.224
 gateway (Gateway Address)
 bridge_ports eth0
 bridge_stp off
 bridge_fd 1
 bridge_hello 2
 bridge_maxage 12

And when I trying to restart interface after applying changes, I got the error :

RTNETLINK answers: File exists
Failed to start Raise network interfaces.

which version of Ubuntu are you using? It matters because things changed with 18.04. I don't see what is wrong, but see if this helps. I do not understand source /etc/network/interfaces.d/*, try commenting it out. — Doug Smythies, Oct 23 '18 at 15:50
Thank you to reply, Ubuntu v16.04, /etc/network/interfaces.d/ is an empty folder, I think it is not matter — Chris, Oct 23 '18 at 15:55
did you try a complete re-boot instead of just interface re-start (which should be bridge start/re-start anyhow)? — Doug Smythies, Oct 23 '18 at 16:07

score 1 · Accepted Answer · answered Oct 25 '18 at 07:31

the reason for your issue around

RTNETLINK answers: File exists
Failed to start Raise network interfaces.

is due to the same network configuration the bridge should get still being active on the device.

Your reboot managed the same, but you could also have got it solved by bringing the interface you deconfigured down via ifconfig down

Note: to be aware systemd-networkd (and due to that netplan) in 18.04 and later behave different - they would make all of the network match their config and in this case bring down the no more configured interface.

Config bridge network in order to using KVM

1 Answers1