Installation guide

Chapter 10.

Network Configuration

This page provides an introduction to the common networking configurations used by libvirt based

applications. For additional information consult the libvirt network architecture documentation: http://

libvirt.org/intro.html.

Red Hat Enterprise Linux 6 supports the following networking setups for virtualization:

• virtual networks using Network Address Translation (NAT)

• directly allocated physical devices using PCI passthrough or SR-IOV.

• bridged networks

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).

Host configuration

Every standard 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 /usr/share/libvirt/networks/default.xml

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

Once the 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