Attaching a Guest Directly to a Virtualization Host Network Interface with a macvtap Driver

Internal

• Linux Virtualization Networking Concepts
• Linux Virtualization Operations

Overview

TODO, move to KVM_Virtual_Networking_Concepts#Directly_Attaching_a_Guest_Virtual_Machine_to_a_Physical_Network_Interface.

After assignment, this new interface shows up on host:

3: em2: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN qlen 1000
    link/ether 18:66:da:9f:96:d7 brd ff:ff:ff:ff:ff:ff
...
11: macvtap0@em2: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state LOWERLAYERDOWN qlen 500
    link/ether 52:54:00:02:72:ed brd ff:ff:ff:ff:ff:ff

Procedure

The simplest method is to leave the network interface unconfigured on the virtualization host and to assign it to the guest in configuration with virsh edit as follows:

...
<interface type='direct'>
    <source dev='eth0' mode='private'/>
</interface>
...

Note that after saving it, libvirt will update the stored configuration as follows:

...
<interface type='direct'>
    <mac address='52:54:00:02:72:ed'/>
    <source dev='em2' mode='private'/>
    <model type='rtl8139'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
</interface>
...

Note that the MAC address declared in the configuration is different from the MAC address declared by ip addr on the virtualization host.

The new network interface shows up on the guest, alongside the default network interface eth1:

ip addr
...
2: ens8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 52:54:00:02:72:ed brd ff:ff:ff:ff:ff:ff
...
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 52:54:00:e4:e6:8a brd ff:ff:ff:ff:ff:ff

After the first boot, figure out the name of the new network interface and add a /etc/sysconfig/network-scripts/ifcfg-<interface-name> configuration file, similar to:

NAME="ens8"
DEVICE="ens8"
TYPE="Ethernet"
ONBOOT="yes"
BOOTPROTO="none"
IPADDR="172.68.30.1"
PREFIX="24"
DEFROUTE="no"
PEERDNS="no"
PEERROUTES="no"
IPV4_FAILURE_FATAL="yes"
IPV6INIT="no"
IPV6_AUTOCONF="no"
IPV6_DEFROUTE="no"
IPV6_PEERDNS="no"
IPV6_PEERROUTES="no"
IPV6_FAILURE_FATAL="no"
UUID="8e9cbe3a-3582-4213-8a6d-73af4d93e3d0"

Make sure UUID is unique, you can generate a new UUID with ?.

For more details on how to configure network interfaces, see

Configuring a Network Interface

Reboot the second time, both interfaces should be operational.