PCI Passthrough Ethernet Interface Devices

For all purposes, a PCI passthrough interface behaves as if it were physically attached to the virtual machine.

Therefore, any potential throughput limitations coming from the virtualized environment, such as the ones introduced by internal copying of data buffers, are eliminated. However, by bypassing the virtualized environment, the use of PCI passthrough Ethernet devices introduces several restrictions that must be taken into consideration. They include:

  • no support for LAG, QoS, ACL, or host interface monitoring

  • no support for live migration

A passthrough interface is attached directly to the provider network’s access switch. Therefore, proper routing of traffic to connect the passthrough interface to a particular project network depends entirely on the VLAN tagging options configured on both the passthrough interface and the access port on the switch.

The access switch routes incoming traffic based on a VLAN ID, which ultimately determines the project network to which the traffic belongs. The VLAN ID is either explicit, as found in incoming tagged packets, or implicit, as defined by the access port’s default VLAN ID when the incoming packets are untagged. In both cases the access switch must be configured to process the proper VLAN ID, which therefore has to be known in advance.


On cold migration, a PCI passthrough interface receives a new MAC address, and therefore a new eth x interface. The IP address is retained.

In the following example a new virtual machine is launched by user user1 on project project1, with a passthrough interface connected to the project network net0 identified with VLAN ID 10. See Configure PCI Passthrough ethernet Interfaces