Network Load Balancing
Network Load Balancing (NLB) is a Microsoft implementation of server clustering and load balancing that is intended to provide high availability and high reliability, as well as high scalability.
Microsoft NLB may be enabled in one of two modes: unicast or multicast. These modes determine the network characteristics of the cluster nodes. Enterasys Matrix and SecureStack switches currently support multicast NLB, and limited unicast NLB in hardware.