If the switch is in a fail-open state it'll copy any packet from any port to all it's ports..

As for the solution.. It depends on how you've setup NLB (unicast/multicast) and what type of switch you use (layer2 or 3)..


If you connect Network Load Balancing hosts with a switch, the switch must be layer 2 instead of layer 3 or higher, because all the hosts share the same IP address (the cluster IP address), and layer 3 switches direct network packets (incoming client requests) according to the IP address of the destination computer.
http://support.microsoft.com/default...b;en-us;193602