20.16.9.6. Direct attachment to physical interfaces
Using
<interface type='direct'> attaches a virtual machine's NIC to a specified physical interface on the host.
This set up requires the Linux macvtap driver to be available. One of the following modes can be chosen for the operation mode of the macvtap device:
vepa ( 'Virtual Ethernet Port Aggregator'), which is the default mode, bridge or private.
To set up direct attachment to physical interface, use the following parameters in the domain XML:
...
<devices>
...
<interface type='direct'>
<source dev='eth0' mode='vepa'/>
</interface>
</devices>
...Figure 20.41. Devices - network interfaces- direct attachment to physical interfaces
The individual modes cause the delivery of packets to behave as shown in Table 20.17, “Direct attachment to physical interface elements”:
| Element | Description |
|---|---|
vepa | All of the guest virtual machines' packets are sent to the external bridge. Packets whose destination is a guest virtual machine on the same host physical machine as where the packet originates from are sent back to the host physical machine by the VEPA capable bridge (today's bridges are typically not VEPA capable). |
bridge | Packets whose destination is on the same host physical machine as where they originate from are directly delivered to the target macvtap device. Both origin and destination devices need to be in bridge mode for direct delivery. If either one of them is in vepa mode, a VEPA capable bridge is required. |
private | All packets are sent to the external bridge and will only be delivered to a target VM on the same host physical machine if they are sent through an external router or gateway and that device sends them back to the host physical machine. This procedure is followed if either the source or destination device is in private mode. |
passthrough | This feature attaches a virtual function of a SRIOV capable NIC directly to a guest virtual machine without losing the migration capability. All packets are sent to the VF/IF of the configured network device. Depending on the capabilities of the device additional prerequisites or limitations may apply; for example, this requires kernel 2.6.38 or newer. |
The network access of direct attached virtual machines can be managed by the hardware switch to which the physical interface of the host physical machine machine is connected to.
The interface can have additional parameters as shown below, if the switch is conforming to the IEEE 802.1Qbg standard. The parameters of the virtualport element are documented in more detail in the IEEE 802.1Qbg standard. The values are network specific and should be provided by the network administrator. In 802.1Qbg terms, the Virtual Station Interface (VSI) represents the virtual interface of a virtual machine.
Note that IEEE 802.1Qbg requires a non-zero value for the VLAN ID.
Additional elements that can be manipulated are described in Table 20.18, “Direct attachment to physical interface additional elements”:
| Element | Description |
|---|---|
managerid | The VSI Manager ID identifies the database containing the VSI type and instance definitions. This is an integer value and the value 0 is reserved. |
typeid | The VSI Type ID identifies a VSI type characterizing the network access. VSI types are typically managed by network administrator. This is an integer value. |
typeidversion | The VSI Type Version allows multiple versions of a VSI Type. This is an integer value. |
instanceid | The VSI Instance ID Identifier is generated when a VSI instance (that is a virtual interface of a virtual machine) is created. This is a globally unique identifier. |
profileid | The profile ID contains the name of the port profile that is to be applied onto this interface. This name is resolved by the port profile database into the network parameters from the port profile, and those network parameters will be applied to this interface. |
Additional parameters in the domain XML include:
...
<devices>
...
<interface type='direct'>
<source dev='eth0.2' mode='vepa'/>
<virtualport type="802.1Qbg">
<parameters managerid="11" typeid="1193047" typeidversion="2" instanceid="09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f"/>
</virtualport>
</interface>
</devices>
...Figure 20.42. Devices - network interfaces- direct attachment to physical interfaces additional parameters
The interface can have additional parameters as shown below if the switch is conforming to the IEEE 802.1Qbh standard. The values are network specific and should be provided by the network administrator.
Additional parameters in the domain XML include:
...
<devices>
...
<interface type='direct'>
<source dev='eth0' mode='private'/>
<virtualport type='802.1Qbh'>
<parameters profileid='finance'/>
</virtualport>
</interface>
</devices>
...Figure 20.43. Devices - network interfaces- direct attachment to physical interfaces more additional parameters
The
profileid attribute, contains the name of the port profile that is to be applied to this interface. This name is resolved by the port profile database into the network parameters from the port profile, and those network parameters will be applied to this interface.
