// Module included in the following assemblies:
//
// * networking/advanced_networking/bgp_routing/no-overlay-mode-bgp-routing.adoc

:_mod-docs-content-type: REFERENCE
[id="nw-no-overlay-default-network-config-ref_{context}"]
= Reference for Cluster Network Operator (CNO) settings for default network underlay routing

[role="_abstract"]
Review the Cluster Network Operator (CNO) custom resource (CR) fields that control BGP, route advertisements, and no-overlay mode for the default OVN-Kubernetes cluster network. No-overlay mode for the default network is configured on the CNO CR.

.Example CNO CR with BGP, no-overlay, and managed routing
[source,yaml]
----
apiVersion: operator.openshift.io/v1
kind: Network
metadata:
  name: cluster
spec:
  additionalRoutingCapabilities:
    providers:
    - FRR
  defaultNetwork:
    ovnKubernetesConfig:
      routeAdvertisements: Enabled
      transport: NoOverlay
      noOverlayConfig:
        outboundSNAT: Enabled
        routing: Managed
        bgpTopology: FullMesh
        asNumber: 64512
    type: OVNKubernetes
----
where:

`spec.defaultNetwork.type`::
Must be `OVNKubernetes`.

`spec.additionalRoutingCapabilities.providers`::
Specifies additional routing components on the cluster. For BGP and route advertisements, include `FRR` so FRR-K8s is deployed on nodes.

`spec.defaultNetwork.ovnKubernetesConfig.routeAdvertisements`::
Specifies whether the cluster can import and advertise routes as configured by `RouteAdvertisements` objects and related BGP configuration. Set to `Enabled` so the cluster can import and advertise routes as configured by `RouteAdvertisements` objects and related BGP configuration.

`spec.defaultNetwork.ovnKubernetesConfig.transport`::
Specifies the transport protocol. Set to `NoOverlay` to disable the default encapsulation for the default network and use underlay for routing pod traffic.

`spec.defaultNetwork.ovnKubernetesConfig.noOverlayConfig.outboundSNAT`::
Specifies outbound SNAT for the default network. Set to `Enabled` or `Disabled`. When `Enabled`, outbound pod traffic to networks outside the pod subnet is source NATed to the node IP when required. When `Disabled`, the underlay must route pod IPs directly. Pod-to-pod traffic within the cluster is not SNATed; traffic to node IPs, the Kubernetes API, and cluster DNS is still SNATed where applicable.

`spec.defaultNetwork.ovnKubernetesConfig.noOverlayConfig.routing`::
Specifies the routing mode for the default network. Set to `Managed` for a full-mesh BGP fabric between nodes (intra-cluster), or `Unmanaged` when you provide `FRRConfiguration` and `RouteAdvertisements` CRs for external BGP.

`spec.defaultNetwork.ovnKubernetesConfig.noOverlayConfig.bgpTopology`::
Specifies the BGP topology for the default network. When routing is set to `Managed`, set to `FullMesh` so every node runs a BGP router and peers with all other nodes.

`spec.defaultNetwork.ovnKubernetesConfig.noOverlayConfig.asNumber`::
Specifies the BGP autonomous system (AS) number for the default VRF. When routing is set to `Managed`, optional BGP AS number for the default VRF. When omitted, the default is `64512`.
