Server load balancing is a way to manage which servers receive traffic. Server load balancing provides failover redundancy to ensure users continue to receive service in case of failure. It also enables your deployment to handle more traffic than one server can process while offering a single host name for clients.

Server load balancing serves two primary purposes. It reduces the impact of server failures within an exchange organization. In addition, server load balancing ensures that the load on the CAS and transport services are optimally distributed.

As OWA is rendered on the same server that is hosting the user’s mailbox database; if a client hits a different CAS, there is no performance degradation because the session rendering for that user is already up and running.

Forms-based authentication is improved. The authentication cookie is provided to the user after logon and it is encrypted using the CAS’s SSL certificate. This allows a logged in user to resume their session on a different CAS without having to re-authenticate (if servers share the same SSL certificate).