Creating Permanent Bridged Network Interface

This is very useful in many cases like if you want to add additional security layer using firewall or if you want to rum KVM virtualizaions with permanent interfaces accessed by the hosts as if the guest is a real machine.

I am using Centos 6.2 64 bit and I am using DHCP for assigning IP addressed and DNS and other configurations

1. Install bridge-utils :yum install bridge-utils
2. Bring down the interfaces eth0 : ifdown eth0
3. Edit the configuration file of the eth0 interface to use the bridge and create a new file for the bridge :

vi /etc/sysconfig/network-scripts/ifcfg-eth0
    DEVICE="eth0"
NM_CONTROLLED="yes"
ONBOOT="yes"
HWADDR=64:31:50:04:93:B9
TYPE=Ethernet
BOOTPROTO=dhcp
DEFROUTE=yes
PEERDNS=yes
PEERROUTES=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth0"
#
BRIDGE=br0

The most important line is BRIDGE=br0 where br0 is the name of the bridge device we shall create.

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

DEVICE=br0
TYPE=Bridge
BOOTPROTO=dhcp
ONBOOT=yes
DELAY=0

Note the line TYPE=Bridge

4. The most important part that peventing the bridge from functioning properly was the line :  UUID=5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03 in the ifcfg-eth0 file so I commented it out.

5 .Bring up the interfaces : ifup eth0 ; ifup br0;

6. Configure the iptables firewall to accept connections from the new bridge interface br0 :

 vi /etc/sysconfig/iptables
 
Add this line : -A INPUT -i br0 -j ACCEPT

7. Restart the iptables and network services

 service network restart
 service iptables restart

That is it !