Trying to configure a network bridge for KVM virtual machines? Here’s how we do it.
Here at Bobcares, we have seen several such KVM related queries as part of our Server Management Services for web hosts and online service providers.
Today we’ll take a look at configuring network bridge for KVM virtual machines.
Know more about KVM virtual machines
When a Linux bridge is used in KVM, it allows a virtual machine to access external networks and services outside of the virtual environment. Bridged networking is a dedicated network card to a virtual machine that provides a communication path to the outside networks. Also, this must be set up before creating a virtual machine using Virtual Manager.
Moreover, there are different ways to configure the Bridge Networking in Linux for use in KVM. By default, the Virtual Machine launched in KVM uses a NAT network.
Once you configure and use Bridged networking, guest operating systems access the external network connected directly to the host machine. Also, you can create a bridge either using Virtual Machine Manager, using virsh command-line tool, by directly editing network-scripts or using Linux Network management tools.
How to configure a network bridge for KVM virtual machines
Now let’s take a look at how to configure the network bridge.
Method 1: Creating Bridge Network using Virtual Machine Manager
Here are the steps to create a Linux bridge from Virtual Machine Manager (GUI). Make sure that you have installed KVM on your system.
1. Firstly, open Virtual Machine Manager, and go to Edit > Connection Details > Virtual Networks. Suppose the device name is virbr.
2. Next, click the + at the bottom of the window to configure a new network interface. Here, give the virtual network a name. For example, br1.
3. Then click the Forward button, in the next window, provide virtual network information.
4. After that, click forward and choose if to enable IPv6.
5. Now select the network type and forwarding policy.
6. Finish the setting and save the configurations. As a result, the new Virtual network must display on the overview page.
7. Finally, a bridge on the host system is automatically created for the network.
$ brctl show virbr bridge name bridge id STP enabled interfaces virbr 8000.525400c2410a yes virbr-nic
Method 2: Create KVM bridge with virsh command
First, create a new bridge XML file.
$ vim br1.xml
Then add the below details in the file.
<network> <name>br10</name> <forward mode=’nat’> <nat> <port start=’1024′ end=’65535’/> </nat> </forward> <bridge name=’br10′ stp=’on’ delay=’0’/> <ip address=’192.168.30.1′ netmask=’255.255.255.0′> <dhcp> <range start=’192.168.30.50′ end=’192.168.30.200’/> </dhcp> </ip> </network>
To define a network from an XML file without starting it. So run the below command.
$ sudo virsh net-define br1.xml Network br1 defined from br1.xml
To start a (previously defined) inactive network, run the below command.
$ sudo virsh net-start br1 Network br1 started
To set network to autostart at service start, run the below command.
$ sudo virsh net-autostart br1 Network br1 marked as autostarted
Then, confirm if the autostart flag is turned to yes. In the result, the Persistent should read yes as well.
$ sudo virsh net-list –all
Also, make sure to confirm bridge creation and IP address.
$ ip addr show dev br1
Method 3: Create a bridge by editing network-scripts (CentOS/RHEL/Fedora)
Here is a script that creates a bridge called br1.
$ sudo vim /etc/sysconfig/network-scripts/ifcfg-br1
DEVICE=br1 STP=no TYPE=Bridge BOOTPROTO=none DEFROUTE=yes NAME=br1 ONBOOT=yes DNS1=188.8.131.52 DNS2=192.168.30.1 IPADDR=192.xxx.xx.x PREFIX=24 GATEWAY=192.xxx.xx.x
Here is the configuration of eth0 interface to which br1 will be bridged:
$ cat /etc/sysconfig/network-scripts/ifcfg-eno1 DEVICE=eth0 TYPE=Ethernet ONBOOT=yes BRIDGE=br1
Finally, restart the network daemon.
$ sudo systemctl disable NetworkManager && sudo systemctl stop NetworkManager $ sudo systemctl restart network.service
Method 4: Create a bridge by editing network-scripts (Debian/Ubuntu)
To configure the bridging interface, run the below command.
$ sudo vim /etc/network/interfaces auto br1 iface br1 inet static address 192.xxx.xx.xx network 192.xxx.x.x netmask 255.255.255.0 broadcast 192.xxx.x.xxx gateway 192.xxx.x.x dns-nameservers 192.xxx.x.x bridge_ports eth0 bridge_stp off
Then disable all the lines on eth0 interface section so that it looks something like below:
auto eth0 iface eth0 inet manual
Finally, restart the networking service.
$ sudo systemctl restart networking.service
[Need any further assistance with KVM queries? – We’re available to help you]
Today, we saw how to configure a network bridge for KVM virtual machines.
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