the c-mode vm's must be on the same host.
From the guide:
Creating a cluster network
When running Data ONTAP in Cluster-Mode, you must create a network for the cluster traffic that is
separate from the network for data traffic. This effectively creates a virtual machine port group.
About this task
Note that both Simulate ONTAP instances in the cluster must be running on the same ESX server.
If you are running Data ONTAP in 7-Mode, skip this section.
Steps
1. Log in to the vSphere Client and select the ESX host from the inventory panel.
2. Select the Configuration tab and click Networking (under the Hardware list).
3. In the Virtual Switch view, click Add Networking.
The Add Network Wizard is launched.
4. In the Connection Type page, select Virtual Machine and click Next.
5. In the Virtual Machines - Network Access page, perform the following steps:
a) Select the vSwitch to use, or select Create a virtual switch to create a new vSwitch.
b) Do not select a check box to identify a virtual network adapter. Not selecting a virtual NIC
makes the network internal to the ESX host.
c) Click Next.
6. In the Virtual Machines - Connection Settings page, perform the following steps:
a) In the "Network Label" field, enter a name that identifies the network you are creating, for
example, "Cluster Network".
b) Click Next.
7. In the Ready to Complete page, verify the details about the Virtual Machine port group you are
adding and click Finish. Note that you can click Back if you need to make any corrections.
