How to add bridge interface to eth0 for KVM in CentOS 5

Well, after installed the KVM on CentOS , you may want to have a bridge networking on some of VMs
that you may have created.

Unfortunately, KVM doesn’t set this up automatically like the vmware who set its own device during

Luckily there are a lot of “How To” telling on step to make it happened.

One of the step that I tried is as follows :

1. First , need to install some package from rpmforge repo. (better sort out the yum repository for rpmforge first if you haven’t)

The package is:

yum install tunctl -y
yum install bridge-utils -y

if necessary add the following into the /etc/rc.local

# into /etc/rc.local
chown root:kvm /dev/net/tun
cmod 0660 /dev/net/tun

then edit the network-configuration file to reflect the above ..

then amend the network script to something like the following :

# Broadcom Corporation NetXtreme BCM5755M Gigabit Ethernet PCI Express

then create the following new network config file into the same folder.

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

Assuming the static IP address previously assigned for this device to work. (eth0)

# Realtek Semiconductor Co., Ltd. RTL-8110SC/8169SC Gigabit Ethernet

Then, to use in KVM. Just edit the hardware-config for the VM.

1. Run “virtual-manager.” as the “privileged user ”

2. select which VM to change. and click “Open”. Probably better to notify user before shutting it down for re-configuration.

3. Get to the hardware tab.
Remove the old-network device there.

4. Then “Add Hardware”. Choose “Network”.

5. then the following will appear.. Choose “Physical network interface”.. eth0(bridge) should appear from the dropdown menu.

6. Done.

Then , maybe need to reboot the VM to get the new hardware detected.
And reconfigure the VMs network setting to suit your new “bridge” network IP setting.

Reference :

1. CentOS KVM How To
2. VLAN Bridge

..and special thanks to .sha for the head up .

p/s : this will be very useful for setting up something that requiring bridge network instead of NAT.
Like the “ADAM.NET Utility” to send “UDP / MODBUS” read/write command via network…

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