I tried this variant to tell NetworkManager to ignore the virtual devices: [keyfile] unmanaged-devices=mac:xx:xx:xx:xx:xx:xx (using the real MAC address of course) It still does not change anything. But I noticed this in the log, which happen whether or not the unmanaged-devices option is set: Aug 19 18:52:04 n55sf-l NetworkManager[6399]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed Aug 19 18:52:04 n55sf-l NetworkManager[6399]: (vboxnet0): driver 'unknown' does not support carrier detection. Aug 19 18:52:04 n55sf-l NetworkManager[6399]: (vboxnet0): device is virtual, marking as unmanaged Aug 19 18:52:04 n55sf-l NetworkManager[6399]: (vboxnet0): new Ethernet device (driver: 'unknown' ifindex: 4) Aug 19 18:52:04 n55sf-l NetworkManager[6399]: (vboxnet0): exported as /org/freedesktop/NetworkManager/Devices/3 Aug 19 18:52:04 n55sf-l NetworkManager[6399]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed Aug 19 18:52:04 n55sf-l NetworkManager[6399]: (vboxnet1): driver 'unknown' does not support carrier detection. Aug 19 18:52:04 n55sf-l NetworkManager[6399]: (vboxnet1): device is virtual, marking as unmanaged Aug 19 18:52:04 n55sf-l NetworkManager[6399]: (vboxnet1): new Ethernet device (driver: 'unknown' ifindex: 5) Aug 19 18:52:04 n55sf-l NetworkManager[6399]: (vboxnet1): exported as /org/freedesktop/NetworkManager/Devices/4 So, basically it seems that the devices is correctly seen as virtual and unmanaged by Network-Manager but still it finally manages it. More details obtained using command below confirm that NetworkManager does DHCP on vboxnet0 which is definitely wrong. grep -i network.*manag.*vbox /var/log/syslog -C 3 Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (wlan0): device state change: unmanaged -> unavailable (reason 'managed') [10 20 2] Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (wlan0): preparing device Aug 19 18:59:43 n55sf-l NetworkManager[8151]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet0): driver 'unknown' does not support carrier detection. Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet0): device is virtual, marking as unmanaged Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet0): new Ethernet device (driver: 'unknown' ifindex: 4) Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet0): exported as /org/freedesktop/NetworkManager/Devices/3 Aug 19 18:59:43 n55sf-l NetworkManager[8151]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet1): driver 'unknown' does not support carrier detection. Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet1): device is virtual, marking as unmanaged Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet1): new Ethernet device (driver: 'unknown' ifindex: 5) Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet1): exported as /org/freedesktop/NetworkManager/Devices/4 Aug 19 18:59:43 n55sf-l NetworkManager[8151]: urfkill disappeared from the bus Aug 19 18:59:43 n55sf-l NetworkManager[8151]: use BlueZ version 4 Aug 19 18:59:43 n55sf-l wpa_supplicant[893]: dbus: wpa_dbus_get_object_properties: failed to get object properties: (none) none -- Aug 19 18:59:43 n55sf-l wpa_supplicant[893]: wlan0: CTRL-EVENT-SCAN-STARTED Aug 19 18:59:43 n55sf-l NetworkManager[8151]: ModemManager available in the bus Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Auto-activating connection 'Auto SG IP auto'. Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) starting connection 'Auto SG IP auto' Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet0): device state change: unmanaged -> disconnected (reason 'managed') [10 30 2] Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Stage 1 of 5 (Device Prepare) scheduled... Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Stage 1 of 5 (Device Prepare) started... Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet0): device state change: disconnected -> prepare (reason 'none') [30 40 0] Aug 19 18:59:43 n55sf-l NetworkManager[8151]: NetworkManager state is now CONNECTING Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Stage 2 of 5 (Device Configure) scheduled... Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Stage 1 of 5 (Device Prepare) complete. Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Stage 2 of 5 (Device Configure) starting... Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet0): device state change: prepare -> config (reason 'none') [40 50 0] Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Stage 2 of 5 (Device Configure) successful. Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Stage 3 of 5 (IP Configure Start) scheduled. Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Stage 2 of 5 (Device Configure) complete. Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Stage 3 of 5 (IP Configure Start) started... Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet0): device state change: config -> ip-config (reason 'none') [50 70 0] Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Beginning DHCPv4 transaction (timeout in 45 seconds) Aug 19 18:59:43 n55sf-l NetworkManager[8151]: dhclient started with pid 8181 Aug 19 18:59:43 n55sf-l NetworkManager[8151]: Activation (vboxnet0) Stage 3 of 5 (IP Configure Start) complete. Aug 19 18:59:43 n55sf-l NetworkManager[8151]: (vboxnet0): DHCPv4 state changed nbi -> preinit Aug 19 18:59:44 n55sf-l dhclient: DHCPREQUEST of 192.168.56.102 on vboxnet0 to 255.255.255.255 port 67 (xid=0x4b3f5c05) Aug 19 18:59:44 n55sf-l dhclient: DHCPACK of 192.168.56.102 from 192.168.56.100