OpenVPN Access Server has the option to block traffic between VPN clients on a global scale. With global we mean to say; for all VPN clients. The VPN clients can still access resources they've been given access to, but they won't be able to contact other VPN clients. There is an override available for Administrators and for specific users. The override is explained further on in this document. This tutorial comes with screenshots for every step - just click on the blue line to see the accompanying screenshot for that step.
As mentioned above, once traffic between VPN clients is blocked, an exception can be made for Administrators or for specific users. To make an exception for all users with the 'Administrator' attribute you can do so under 'Advanced VPN' as described in the tutorial above. To make an exception for specific users follow the guide below;