Chapter 10. Network Configuration
Red Hat Enterprise Linux 6 supports the following networking setups for virtualization:
You must enable NAT, network bridging or directly share a physical device to allow external hosts access to network services on virtualized guests.
10.1. Network Address Translation (NAT) with libvirt
One of the most common methods for sharing network connections is to use Network Address Translation (NAT) forwarding (also know as virtual networks).
libvirt installation provides NAT based connectivity to virtual machines out of the box. This is the so called 'default virtual network'. Verify that it is available with the
virsh net-list --all command.
# virsh net-list --all
Name State Autostart
default active yes
If it is missing, the example XML configuration file can be reloaded and activated:
# virsh net-define /usr/share/libvirt/networks/default.xml
The default network is defined from
Mark the default network to automatically start:
# virsh net-autostart default
Network default marked as autostarted
Start the default network:
# virsh net-start default
Network default started
libvirt default network is running, you will see an isolated bridge device. This device does not have any physical interfaces added. The new device uses NAT and IP forwarding to connect to outside world. Do not add new interfaces.
# brctl show
bridge name bridge id STP enabled interfaces
virbr0 8000.000000000000 yes
iptables rules which allow traffic to and from guests attached to the
virbr0 device in the
libvirt then attempts to enable the
ip_forward parameter. Some other applications may disable
ip_forward, so the best option is to add the following to
net.ipv4.ip_forward = 1
Once the host configuration is complete, a guest can be connected to the virtual network based on its name. To connect a guest to the 'default' virtual network, the following could be used in the XML configuration file (such as
/etc/libvirtd/qemu/myguest.xml) for the guest:
Defining a MAC address is optional. A MAC address is automatically generated if omitted. Manually setting the MAC address may be useful to maintain consistency or easy reference throughout your environment, or to avoid the very small chance of a conflict.