Bridged Networking on a KVM Hypervisor

We will be adding a bridge vnet0 to interface eth0

[root@otoscope ~]# brctl show  
bridge name bridge id         STP enabled interfaces  
virbr0      8000.000000000000 yes

Now add this to /etc/sysconfig/network-scripts/ifcfg-vnet0

DEVICE=vnet0  
TYPE=Bridge  
BOOTPROTO=dhcp  
ONBOOT=yes

Add BRIDGE=vnet0 to /etc/sysconfig/network-scripts/ifcfg-eth0:

# Intel Corporation 82579LM Gigabit Network Connection  
DEVICE=eth0  
BOOTPROTO=dhcp  
HWADDR=00:25:90:53:A0:43  
ONBOOT=yes  
BRIDGE=vnet0

Restart the network service and add the bridge:

service network restart  
brctl addif vnet0 eth0

Check:

[root@otoscope ~]# brctl show  
bridge name bridge id          STP enabled interfaces  
virbr0      8000.000000000000  yes     
vnet0       8000.00259053a043  no           eth0

Now add STP with:

brctl stp vnet0 on

Firewall Rules

Make sure that you’ve set up the proper forwarding rules with IPTables.
Don’t use a general free-for-all like this, though:

iptables -A FORWARD -m state --state NEW -j ACCEPT

References