How to set up Linux KVM Bridge (br0) On CentOS

Here we show you how to set up a Linux KVM bridge set to (br0) for use in a KVM slave node using a cheap dedicated server. These settings are specific to our network configuration and won’t work with other providers. You should only ever use these settings on a clean OS install, never change these settings in a live environment. If you make a mistake you will need to reinstall the OS on your server before trying again. First2Host offers this guide as a complimentary service, we cannot help you in the setup of 3^rd party software. If you need support, please contact the software developers of the hypervisor you are using or a systems administrator experienced in Linux KVM Bridge setups.

Before you start

1. The IPv4 Gateway is always your server’s main IP address, but the final 3 digits are .254 so if your servers ip address is 167.114.225.255 then your Gateway will be 167.114.225.254
2. Mac addresses for virtual containers will be needed on KVM slaves. Please contact support for these after you have an ip block to use for guest machines
3. This guide is provided as a complementary service for our customers to use, we can not offer support for specific hypervisors , instead, you should contact the vendor for support. Because we use a custom network configuration customers of other hosting providers should not follow this guide. It will likely break your networking.

To set up a bridge your server will need the bridge-utils package to be installed. First check to see if the package is already installed.

rpm -q bridge-utils

If you get a response, then the package is already installed on your server. If there is no output, then continue to install the package

yum install bridge-utils

Before you set up the bridge in your dedicated server the /etc/sysconfig/network-scripts/ifcfg-eth0 file will look like this

DEVICE=eth0
BOOTPROTO=static
BROADCAST=192.168.2.1
HWADDR=00:22:0E:03:0C:E2
IPADDR=192.167.2.2
IPV6INIT=yes
IPV6_AUTOCONF=yes
NETMASK=255.255.255.255
NETWORK=102.100.152.152
ONBOOT=yes

Backup this file in case of any errors

cp /etc/sysconfig/network-scripts/ifcfg-eth0 /etc/sysconfig/network-scripts/backup-ifcfg-eth0

Create a bridge file

nano -w /etc/sysconfig/network-scripts/ifcfg-br0

So we copy the information from the /etc/sysconfig/network-scripts/ifcfg-eth0 file to the bridge file

DEVICE=br0
TYPE=Bridge
BOOTPROTO=static
IPADDR=SERVER-IP
NETMASK=255.255.255.0
ONBOOT=yes
IPV6INIT=yes
IPV6_AUTOCONF=no
IPV6_DEFROUTE=yes
IPV6ADDR="IPv6ADDRESS"
IPV6_DEFAULTGW=IPv6 Gateway
NETBOOT=no
#IPV6_FAILURE_FATAL=no
#GATEWAY=IPv4 Gateway

Copy the bridge file exactly as you see it above swapping the ip information with your ip details. Don’t remove any (#) or “ from the file just swap the information. Save and close the bridge file.

And next, in the /etc/sysconfig/network-scripts/ifcfg-eth0 file add the required bridge into this file and comment out (#) the information we have below. Make sure you leave DEVICE=eth0, BRIDGE=br0, ONBOOT=yes, NETBOOT=no, NM_CONTROLLED=”no” with no (#)

/etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
BRIDGE=br0
ONBOOT=yes
NETBOOT=no
NM_CONTROLLED="no"

Finally, restart the network, you may get disconnected but you should be able to reconnect assuming you followed this guide and used the exact settings and information we have.

/etc/init.d/network restart

You can verify the bridge after restarting the network by

ifconfig

You should see the bridge br0 listed at the top