RFE: Support Multi-NIC and Multi-Subnet Networking for Windows Containers in OpenShift

1. Summary of Request:

Windows Containers running on OpenShift currently do not support multiple NICs or subnets within the host networking model. While Calico CNI supports multi-subnet and multi-interface networking for Windows containers in Kubernetes ([Microsoft documentation][1]), OpenShift today only supports OVN-Kubernetes CNI for Windows node networking via the Windows Machine Config Operator (WMCO).

This RFE requests a feasibility study and potential support for:

• Multi-NIC / multi-subnet networking on Windows container hosts in OpenShift

• Evaluating support for alternative CNIs such as Calico or hybrid plugin architectures

2. Current Limitations:

• Windows node support in OpenShift is currently restricted to OVN-Kubernetes as the only supported CNI.

• WMCO and OVN-Kubernetes integration does not expose or manage multiple interfaces on the Windows host.

• Kubernetes community efforts for multi-NIC/multi-subnet support (e.g., [multi-network plugins via Multus]) are primarily Linux-focused and not fully functional or tested on Windows nodes.

• Calico's native support for multi-subnet networking on Windows nodes cannot be used in OpenShift due to lack of official CNI support.

3. Business Justification / Use Cases:

Several customer scenarios require multi-interface or multi-subnet support, including:

• Telco and Edge deployments that use separate networks for data plane and control plane.

• Secure workloads where ingress and egress are isolated over different network paths.

• High-throughput applications that use interface bonding or distinct NICs per protocol stack.

• Customers migrating from upstream Kubernetes with Calico CNI already in use for Windows nodes.

Lack of support for multi-NIC configurations blocks adoption of OpenShift for these scenarios.

4. Requested Enhancement:

Evaluate and implement support for multi-NIC / multi-subnet networking for Windows containers in OpenShift through one of the following:

a) Native OVN-Kubernetes enhancement:

• Investigate feasibility of extending OVN-Kubernetes and WMCO to support assigning and managing multiple interfaces on Windows nodes.

• Enable support for container workloads to utilize multiple networks in a supported and stable manner.

b) Support for alternative CNIs (e.g., Calico):

• Explore introducing Calico CNI as a supported CNI for Windows nodes in OpenShift clusters.

• Enable dual CNI use cases where Linux nodes use OVN-Kubernetes and Windows nodes use Calico (if feasible).

• Consider community-supported hybrid CNI models if compliant with OpenShift networking standards.

c) Integration with Multus and SR-IOV for Windows:

• Assess feasibility of Multus plugin support on Windows, either upstream or via Red Hat engineering.

• Enable extensibility for customers needing deterministic network attachment definitions (NADs) on Windows nodes.

5. Affected Components:

• Windows Machine Config Operator (WMCO)

• OVN-Kubernetes CNI

• OpenShift Networking stack (Multus, SR-IOV)

• CNI plugin support matrix for Windows