Multicast NLB with ISA 2006

Multicast support for integrated NLB
Previous versions of ISA Server supported integrated Network Load Balancing (NLB) in unicast mode only. This compromised the use of bidirectional affinity (BDA). In unicast mode, computers in an NLB cluster are all designated a single virtual IP address by ISA Server. The NLB driver assigns a new unicast MAC to all computers to be used by the virtual IP. When traffic arrives, the switch that controls which computer to send packets cannot differentiate between ports; therefore because all computers in the cluster share the same virtual address, traffic is sent to all ports in the switch. This behavior causes switch flooding. In multicast mode, NLB designates a multicast MAC address to all computers in the cluster. Multicast combined with Internet Group Management Protocol (IGMP) prevents all ports being flooded.
SP1 adds support for unicast, multicast, and multicast with IGMP modes.
For configuration steps and more details, see Microsoft article 938550: An update enables multicast operations for ISA Server integrated NLB. http://support.microsoft.com/kb/938550/

Creating NLB with ISA:

In the ISA Server Management console, enable integrated NLB. To do this, follow these steps:

a. In the console tree, expand Arrays, expand the node that corresponds to the array, expand Configuration, right-click Network, and then click Enable Network Load Balancing Integration.
b. fill out a VIP on the interface on which you choose to enable NLB

b. Wait until all array members have synchronized the configuration.