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Bridge configuration for KVM Slave

Warning: The actions described below are dangerous and can cause loosing of remote access to the server. It is recommended to have direct access to the server in order to revert the changes back in case of emergency.

If the server is in OVH infrastructure, additional configuration steps are required MAC assigning per IP Address

1. Connect to the slave KVM node via SSH

2. Disable Network Manager as it may interfere with the bridge. 

systemctl stop NetworkManager.service
systemctl disable NetworkManager.service
systemctl enable network.service
systemctl start network.service
3. Additionally, it makes sense to review the network configuration file, e.g. /etc/sysconfig/network-scripts/ifcfg-eth0 and verify that it is disabled there as well 
NM_CONTROLLED=no
4. Example of basic network configuration file /etc/sysconfig/network-scripts/ifcfg-eth0 before bridge interface is configured 
TYPE="Ethernet"
PROXY_METHOD="none"
BROWSER_ONLY="no"
BOOTPROTO="none"
NM_CONTROLLED=no
DEFROUTE="yes"
IPV4_FAILURE_FATAL="no"
IPV6INIT="yes"
IPV6_AUTOCONF="yes"
IPV6_DEFROUTE="yes"
IPV6_FAILURE_FATAL="no"
IPV6_ADDR_GEN_MODE="stable-privacy"
NAME="eth0"
UUID="8d6f722c-b945-4083-b50e-9661bf62ae5f"
DEVICE="eth0"
ONBOOT="yes"
IPADDR="203.0.113.2"
GATEWAY="203.0.113.1"
NETMASK="255.255.0.0"
DNS1="8.8.8.8"
IPV6_PRIVACY="no"
5. Install bridge-utils package:

# yum install bridge-utils

6. Create a copy of the network interface to make changes revertible:

cp /etc/sysconfig/network-scripts/ifcfg-eth0 /root/ifcfg-eth0.orig

Note: It is recommended move non-used configuration files out of the network-scripts/ sub-directory. Be aware that configuration files that starts from ifcfg-* files will be applied, including ifcfg-eth0.backup file.

7. Create the bridge file:

vi /etc/sysconfig/network-scripts/ifcfg-br0

8. Copy network configuration settings from ifcfg-eth0 to ifcfg-br0 file to make it look like below: 

DEVICE=br0
TYPE=Bridge
BOOTPROTO=static
ONBOOT=yes
NM_CONTROLLED=no
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
IPADDR=203.0.113.2
NETMASK=255.255.0.0
GATEWAY=203.0.113.1
9. Edit the /etc/sysconfig/network-scripts/ifcfg-eth0 as below: 
NAME=eth0
DEVICE=eth
ONBOOT=yes
NM_CONTROLLED=no
IPV6INIT=yes
IPV6_AUTOCONF=yes
BRIDGE=br0

Warning: All parameters should be written with capitalized characters, e.g. BRIDGE=br0 and NOT Bridge=br0

Warning: In case there is a /etc/sysconfig/network-scripts/route-eth0 file (some Hetzner installation has them), the file should be renamed to /etc/sysconfig/network-scripts/route-br0 accordingly.

10. Restart the network service to apply the changes:

service network restart

11. Check that physical interface eth0 is linked to bridged interface br0 

brctl show
bridge name bridge id STP enabled interfaces
br0 8000.001c42717243 no eth0

If there are any errors while configuring bridge check for known issues on our Support Portal, like below:
Bridge interface does not work on the fresh install
During configuration of bridge interface network fails to restart: bridge support not available: brctl not found

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