Setup:
Sites and Servers: I have two-2 sites (A and B) with three-3 servers on each site which include 2 MBX and CAS and 1 just MBX.
DAG: There are two-2 DAGs each containing three-3 servers. Two-2 servers that are MBX and CAS on each site have the third partner from the other site that is just holding the MBX role.
Internet Facing: Site A is internet facing. All e-mail is sent and received from this site. There is no connectivity from Site B to the outside world. It relay or gets relayed everything to and fro through Site A.
Routing and Access: At Site A, there is a Load Balancer in place for CAS load balancing which only includes CAS servers of Site A. E-mail is sent from these CAS servers to the outside world. For Web Access (OWA, etc.), TMG is being used for external users. Internal users directly access Load Balancer to get service.
Question: I want to test site failure that is from Site B to Site A. As there is little dependency on internet routing and access, I believe there is only DAG part to worry about. Kindly, confirm if I have the correct understanding. I want to mimic the failure at Site B and serve all the clients from Site A. How can I achieve this goal.