Inter cluster connections can be created through the Enterprise Manager. To do this, firstly connect to a realm in each cluster. Then, once both clusters are displayed in the Enterprise Manager, click on the "Inter-Cluster Connections" tab under one of the cluster panels.

Next, select "Add" and choose the remote cluster from the dropdown list in the popup dialog which will now appear:

The inter-cluster connections should now be established, and inter-cluster joins can now be formed through the Enterprise Manager or programmatically.

To delete an inter-cluster connection, simply select the connection from the list and click "Delete".