Red Hat build of MicroShift

OVN-Kubernetes IPv6 and dual-stack limitations

The OVN-Kubernetes network plugin has specific IPv6 and dual-stack networking configuration limitations. These limitations affect gateway configuration, routing layouts, and infrastructure environment stability.

For clusters configured for dual-stack networking, both IPv4 and IPv6 traffic must use the same network interface as the default gateway.

If this requirement is not met, pods on the host in the ovnkube-node daemon set enter the CrashLoopBackOff state.

If you display a pod with a command such as oc get pod -n openshift-ovn-kubernetes -l app=ovnkube-node -o yaml, the status field has more than one message about the default gateway, as shown in the following output:
```
I1006 16:09:50.985852   60651 helper_linux.go:73] Found default gateway interface br-ex 192.168.127.1
I1006 16:09:50.985923   60651 helper_linux.go:73] Found default gateway interface ens4 fe80::5054:ff:febe:bcd4
F1006 16:09:50.985939   60651 ovnkube.go:130] multiple gateway interfaces detected: br-ex ens4
```
The only resolution is to reconfigure the host networking so that both IP families use the same network interface for the default gateway.
For clusters configured for dual-stack networking, both the IPv4 and IPv6 routing tables must contain the default gateway.

If this requirement is not met, pods on the host in the ovnkube-node daemon set enter the CrashLoopBackOff state.

If you display a pod with a command such as oc get pod -n openshift-ovn-kubernetes -l app=ovnkube-node -o yaml, the status field has more than one message about the default gateway, as shown in the following output:
```
I0512 19:07:17.589083  108432 helper_linux.go:74] Found default gateway interface br-ex 192.168.123.1
F0512 19:07:17.589141  108432 ovnkube.go:133] failed to get default gateway interface
```
The only resolution is to reconfigure the host networking so that both IP families contain the default gateway.
If you set the ipv6.disable parameter to 1 in the kernelArgument section of the MachineConfig custom resource (CR) for your cluster, OVN-Kubernetes pods enter a CrashLoopBackOff state. Additionally, updating your cluster to a later version of {product-title} fails because the Network Operator remains on a Degraded state. Red Hat does not support disabling IPv6 addresses for your cluster so do not set the ipv6.disable parameter to 1.