Installation guide

# brctl show

bridge name bridge id STP enabled interfaces

virbr0 8000.000000000000 yes

l i bvi rt adds i ptabl es rules which allow traffic to and from guest virtual machines attached to

the vi rbr0 device in the INP UT , FO R WAR D , O UT P UT and P O ST R O UT ING chains. l i bvi rt then

attempts to enable the i p_fo rward parameter. Some other applications may disable i p_fo rward ,

so the best option is to add the following to /etc/sysctl . co nf.

net.ipv4.ip_forward = 1

G u est virt ual mach in e co n f ig u rat io n

Once the host configuration is complete, a guest virtual machine 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/l i bvi rtd /q emu/myg uest. xml ) for the guest:

</interface>

Note

Defining a MAC address is optional. If you do not define one, a MAC address is automatically

generated and used as the MAC address of the bridge device used by the network. 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.

</interface>

11.2. Disabling vhost -net

The vho st-net module is a kernel-level backend for virtio networking that reduces virtualization

overhead by moving virtio packet processing tasks out of user space (the qemu process) and into

the kernel (the vho st-net driver). vhost-net is only available for virtio network interfaces. If the

vhost-net kernel module is loaded, it is enabled by default for all virtio interfaces, but can be disabled

in the interface configuration in the case that a particular workload experiences a degradation in

performance when vhost-net is in use.

Specifically, when UDP traffic is sent from a host machine to a guest virtual machine on that host,

performance degradation can occur if the guest virtual machine processes incoming data at a rate

slower than the host machine sends it. In this situation, enabling vho st-net causes the UD P

socket's receive buffer to overflow more quickly, which results in greater packet loss. It is therefore

better to disable vho st-net in this situation to slow the traffic, and improve overall performance.

To disable vho st-net, edit the <i nterface> sub-element in the guest virtual machine's XML

configuration file and define the network as follows:

Red Hat Ent erp rise Linux 6 Virt ualiz at ion Host Configurat ion and G uest Inst allat ion G uide