An ASA 5505 configured with dual ISP backup supports cluster-based VPN load balancing over the two Ethernet ports available in the Internet zone. The load-balancing scheme involves a "virtual director" IP address that is the destination of incoming client connections. The server that share a virtual director IP address form a cluster, where one cluster member acts as the cluster master. The master receives a request sent to the virtual director and redirects the client, using a proprietary IKE notify message, to the optimal server in the cluster. The current ISAKMP session terminates, and a new session is attempted to the optimal server.
