In the update to a new OS for the 3.0 and 3.5 DataNow appliances, the clustering configuration has changed. In the old 2.0 Appliance you would configure the clustering in the server console and set the port you would like to utilize for communications. The communication was VLAN specific and was done via Broadcast.
With 3.0 and 3.5 appliances, you no longer specify ports. The communications are now Multicast and utilizes ports TCP 5701 and UDP 54327. For communications to work the switching environment will need to be configured to allow Multicast traffic. Clustering is still VLAN dependent.
DataNow clustering in version 4 and above use broadcast based clustering - multicast support is no longer required. For further details on clustering, please refer to the product documentation and our support knowledgebase