Bug 1836998

Because of a core OVN bug, virtual machines with floating IP (FIP) addresses cannot route to other networks in an ML2/OVN deployment with distributed virtual routing (DVR) enabled. Core OVN sets a bad next hop when routing SNAT IPv4 traffic from a VM with a floating ip with DVR enabled. Instead of the gateway IP, OVN sets the destination IP. As a result, the router sends an ARP request for an unknown IP instead of routing it to the gateway. + Before deploying a new overcloud with ML2/OVN, disable DVR by setting `NeutronEnableDVR: false` in an environment file. + If you have ML2/OVN in an existing deployment, perform the following steps: + . Set the `enable_distributed_floating_ip parameter` in the [ovs] section of neutron.conf to False. You should also set `NeutronEnableDVR: false` in an environment file used in any re-deployments so that the next re-deployment does not re-enable DVR. . Update the floating IP that requires external SNAT to work through the Neutron API (for example, by changing its description). + NOTE: Disabling DVR causes traffic to be centralized. All L3 traffic goes through the controller/network nodes. This may affect scale, data plane performance, and throughput.