Network Load Balancing (NLB) Cluster models

A Network Load Balancing (NLB) cluster host can use any one of four Network Load Balancing (NLB) models shown below.

Windows Server 2003 Network Load Balancing (NLB) does not support a mixed unicast mode and multicast mode together in a Network Load Balancing (NLB) cluster. All hosts in the Network Load Balancing (NLB) cluster must be either multicast or unicast.

• Single network adapter in unicast NLB cluster mode

• Single network adapter in multicast NLB cluster mode

• Multiple network adapters in unicast NLB cluster mode

• Multiple network adapters in multicast NLB cluster mode

Single network adapter in unicast NLB cluster mode

In this model, only one Network Interface Card (NIC) is required and the cluster is operating in unicast mode of communication. This is cheap, since only one Network Interface Card (NIC) is required. The limitations of this model are 1) Reduced network performance 2) Ordinary communications between hosts are disabled and 3) NetBIOS support is disabled.

Single network adapter in multicast NLB cluster mode

Here also only one Network Interface Card (NIC) is required for the host, but the host is working on multicast instaed on unicast. The ordinary communications are possible between hosts in this mode. Still some limitations are there in this mode similiar to Single network ndapter unicast mode. 1) Reduced network performance 2) Multicast MAC addresses are not supported by some routers 3) NO NetBIOS support.

Multiple network adapters in unicast NLB cluster mode

Multiple network adapters in unicast mode is the preferred configuration for NLB clusters. You require two Network Interface Card (NIC) cards configured on the servers to operate in this mode, but it has many advantages. 1) Increased network performance 2) NetBIOS support is available.

Multiple network adapters in multicast NLB cluster mode

If you have some hosts in the cluster with a single Network Interface Card (NIC), and if you have enabled multicast mode on that servers, you need to configure Multiple network adapters in multicast mode on a server with multiple Network Interface Cards (NIC). You cannot run some hosts in unicast mode and some other hosts in multicast mode in a Network Load Balancing (NLB) cluster