CentOS / Redhat: KVM Bridged Network Configuration

With bridged networking you can share actual network device with KVM machines. This is required for servers with multiple network cards and gives you good performance. You can choose to put multiple segments into one bridged network or to divide it into different networks interconnected by routers.

Our Sample Setup

The following describes the networking used by our setup:

		+------+       +-----+
LAN      -->	| eth0 |  <==> | br0 |       -> KVM VMs connected to LAN for SAN/NFS
		+------+       +-----+

		+------+       +-----+
Internet -->	| eth1 |  <==> | br1 |       -> KVM VMs connected to the Inernet
		+------+       +-----+


  • All other clients can reached to all VMs via br1 which is connected to public interface. br1 is our default gateway.
  • br0 is connected to private LAN to access other servers, services and storage devices such as SAN/NAS or NFS servers. br0 route is configured via route-br0 static networking configuration file.

Turn Off NetworkManager

The NetworkManager (GUI) tool can create problems with bridged based networking so disable it as follows, enter:
# chkconfig NetworkManager off
# chkconfig network on
# service NetworkManager stop

Edit /etc/sysconfig/network, enter:
# vi /etc/sysconfig/network
Update file as follows:


Save and close the file.

br0: Configure Bridging for eth0

Edit /etc/sysconfig/network-scripts/ifcfg-eth0, enter:
# vi /etc/sysconfig/network-scripts/ifcfg-eth0
Update it as follows:

ETHTOOL_OPTS="autoneg off speed 100 duplex full"

Save and close the file. Create /etc/sysconfig/network-scripts/ifcfg-br0, enter:
# vi /etc/sysconfig/network-scripts/ifcfg-br0
Update it as follows (note options are case sensitive i.e. Bridge and bridge are two different options)


Save and close the file. Finally, create static routing file /etc/sysconfig/network-scripts/route-br0, enter :
# vi /etc/sysconfig/network-scripts/route-br0
Edit it as follows: via dev br0

Save and close the file. Delete old /etc/sysconfig/network-scripts/route-eth0 (if exists):
# rm /etc/sysconfig/network-scripts/route-eth0

br1: Configure Bridging for eth1

Edit /etc/sysconfig/network-scripts/ifcfg-eth1, enter:
# vi /etc/sysconfig/network-scripts/ifcfg-eth1
Update it as follows:

ETHTOOL_OPTS="autoneg off speed 100 duplex full"

Please note that test server is set to 100Mbps full duplex. Save and close the file. Edit /etc/sysconfig/network-scripts/ifcfg-br1, enter:
# vi /etc/sysconfig/network-scripts/ifcfg-br1
Define public IP address including gateway as follows:


Save and close the file.

Restart Network Service

Type the following command:
# service network restart
Make sure everything is working fine:
# brctl show
Sample outputs:

bridge name	bridge id		STP enabled	interfaces
br0		8000.0030488e31ac	no		eth0
br1		8000.0030488e31ad	no		eth1
virbr0		8000.000000000000	yes		

Verify IPs and routing tables:
# ip addr show br0
# ip addr show br1
# ip route
# ping sxi.io
# host google.com

This entry is 2 of 14 in the CentOS / Redhat (RHEL) KVM Virtulization series. Keep reading the rest of the series:

  1. CentOS / Redhat: Install KVM Virtualization Software
  2. CentOS / Redhat: KVM Bridged Network Configuration
  3. KVM virt-manager: Install CentOS As Guest Operating System
  4. KVM virt-install: Install FreeBSD / CentOS As Guest Operating System
  5. KVM: Install CentOS / RHEL Using Kickstart File (Automated Installation)
  6. Troubleshooting KVM Virtualization Problem With Log Files
  7. KVM Virsh: Redirect FreeBSD Console To A Serial Port
  8. KVM: Starting / Stopping Guest Operating Systems With virsh Command
  9. Linux KVM: Disable virbr0 NAT Interface
  10. FreeBSD / OpeBSD Running in KVM Does Not Accept FTP Traffic
  11. KVM: Start a Virtual Machine / Guest At Boot Time
  12. KVM virt-install: Install OpenBSD As Guest Operating System
  13. Linux KVM: OpenBSD Guest Hangs At Starting tty Flags
  14. KVM Virtualization: Start VNC Remote Access For Guest Operating Systems

Posted by: SXI ADMIN

The author is the creator of SXI LLC and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.