See the UDN Sync Meeting notes: https://docs.google.com/document/d/1wjT8lSDfG6Mj-b45_p9SlbpCVG0af-pjDlmAUnM5mOI/edit#bookmark=id.zemsagq71ou2

In our current UDN API, subnets field is mandatory always for primary role and optional for secondary role. This is because users are allowed to have a pure L2 without subnets for secondary networks. However, in the future if we want to add egress support on secondary networks, we might need subnets...

CNV has many different use cases:

1. For UDPNs, we always need subnets for L2 and L3 why not make them optional and let users get default values? -> drawback is loosing visibility and this podsubnet now conflicting with other internal subnets and customer in their ignorange have the oopsy stage, we have seen this in plenty with joinsubnets already
2. For UDSNs, we may or maynot have the need for IPAM, today this subnets field is optional, but then when we do need subnets we cannot set default values here so its icky.

This card tracks the design changes to the API and the code changes needed to implement this. See https://github.com/openshift/enhancements/pull/1708 for details.