The answer is.. OVN replaced OVS as the networking technology. You cannot switch back to legacy, they disabled switching between ovs and legacy in the default (1st) datacenter using the gui. You can however, use Ansible to switch it. Remove the VDSM ovs setting, it will just mess you up, and it's not supported in 4.2 To able to migrate a VM in 4.2, you have use OVN with OVS. I did this a few months back, on a 4.2.2 hosted-engine setup: 0) To setup a node in a cluster, make sure the cluster is in OVS, not legacy. 1) Make sure you have an OVN controller setup somewhere. Default appears to be the ovirt-hosted-engine. a) you should also have the external network provider for OVN configured also; see the web interface. 2) when you install the node, make sure it has openvswitch installed and running - ie: a) 'systemctl status openvswitch' says it's up and running. (be sure it's enable also) b) 'ovs-vsctl show' has vdsm bridges listed, and possibly a br-int bridge. 3) if there is no br-int bridge, do 'vdsm-tool ovn-config ovn-controller-ip host-ip' 4) when you have configured several nodes in the OVN, you should see them listed as geneve devices in 'ovs-vsctl show', ie: This is a 4 node cluster, so the other 3 nodes are expected: [ root at d8-r12-c1-n3 ~]# ovs-vsctl show 42df28ba-ffd6-4e61-b7b2-219576da51ab Bridge br-int fail_mode: secure Port "ovn-27461b-0" Interface "ovn-27461b-0" type: geneve options: {csum="true", key=flow, remote_ip="192.168.85.91"} Port "vnet1" Interface "vnet1" Port "ovn-a1c08f-0" Interface "ovn-a1c08f-0" type: geneve options: {csum="true", key=flow, remote_ip="192.168.85.87"} Port "patch-br-int-to-f7a19c7d-021a-455d-bf3a-c15e212d8831" Interface "patch-br-int-to-f7a19c7d-021a-455d-bf3a-c15e212d8831" type: patch options: {peer="patch-f7a19c7d-021a-455d-bf3a-c15e212d8831-to-br-int"} Port "vnet0" Interface "vnet0" Port "patch-br-int-to-7874ba85-8f6f-4e43-9535-5a1b1353a9ec" Interface "patch-br-int-to-7874ba85-8f6f-4e43-9535-5a1b1353a9ec" type: patch options: {peer="patch-7874ba85-8f6f-4e43-9535-5a1b1353a9ec-to-br-int"} Port "ovn-8da92c-0" Interface "ovn-8da92c-0" type: geneve options: {csum="true", key=flow, remote_ip="192.168.85.95"} Port br-int Interface br-int type: internal Bridge "vdsmbr_LZmj3uJ1" Port "vdsmbr_LZmj3uJ1" Interface "vdsmbr_LZmj3uJ1" type: internal Port "net211" tag: 211 Interface "net211" type: internal Port "eno2" Interface "eno2" Bridge "vdsmbr_e7rcnufp" Port "vdsmbr_e7rcnufp" Interface "vdsmbr_e7rcnufp" type: internal Port ipmi tag: 20 Interface ipmi type: internal Port ovirtmgmt tag: 50 Interface ovirtmgmt type: internal Port "patch-f7a19c7d-021a-455d-bf3a-c15e212d8831-to-br-int" Interface "patch-f7a19c7d-021a-455d-bf3a-c15e212d8831-to-br-int" type: patch options: {peer="patch-br-int-to-f7a19c7d-021a-455d-bf3a-c15e212d8831"} Port "eno1" Interface "eno1" Port "patch-7874ba85-8f6f-4e43-9535-5a1b1353a9ec-to-br-int" Interface "patch-7874ba85-8f6f-4e43-9535-5a1b1353a9ec-to-br-int" type: patch options: {peer="patch-br-int-to-7874ba85-8f6f-4e43-9535-5a1b1353a9ec"} ovs_version: "2.7.3" 5) Create in the cluster the legacy style bridge networks - ie, ovirtmgmt, etc. Do this just like you where creating them for the legacy network. Define the VLAN #, the MTU, etc. 6) Now, create in the network config, the OVN networks - ie, ovn-ovirtmgmt is on an external provider (select OVN), and make sure 'connect to physical network' is checked, and the correct network from step 5 is picked. Save this off. This will connect the two networks together in a bridge, and all services are visible to both ie dhcp, dns.. 7) when you create the VM, select the OVN network interface, not the legacy bridge interface (this is why I decided to prefix with 'ovn-'). 8) Create the vm, start it, migrate, stop, re-start, etc, it all should work now. Lots of reading.. lots of interesting stuff found.. finally figured this out after reading a bunch of bug fixes for the latest RC (released today) The only doc link: https://ovirt.org/develop/release-management/features/network/provider-physi...