The text below from RHOSO "Configuring Persistent Storage" guide section 2.4 gives the impression that the RHOSO cluster needs to be L2 connected to the external Ceph storage cluster, by asking the OSP_Storage network to have the same configuration as the Ceph public network:

"Check the storage interface defined in your NodeNetworkConfigurationPolicy (nncp) custom resource to confirm that it has the same network configuration as the public_network of the Red Hat Ceph Storage cluster. This is required to enable access to the Red Hat Ceph Storage cluster through the Storage network. The Storage network should have the same network configuration as the public_network of the Red Hat Ceph Storage cluster."

It should be clarified that the OSP_Storage network can be different from the external Ceph public network and routed (L3) connectivity is possible as long as appropriate routes are added on the OSP_Storage network to reach the external Ceph public network