Network Load Balancing (NLB) 2008 Dual NIC

Today i was attempting to configure a new 2008 R2 Network Load Balanced IIS servers for a highly available Moodle environment. I hit an issue that meant for some reason my NLB IP address wouldn't respond to pings, even after implementing my Cisco fix here. My PC was in a different subnet so i tried to ping from the same subnet, and this worked. 

Network Load Balanced (NLB) Multicast Array on VMware ESX 5 using Cisco Switches/Routers

When using VMware Virtual Machines (VM) and Microsoft Network Load Balancing (NLB) in Multicast mode, there is some extra configuration that needs to be completed on the switching/routing side of things.

Basically in multicast mode, each node's NLB NIC has two MAC addresses assigned to it. One is the original one and the other is a virtual one assigned by NLB. This causes some problems because almost all routers by default will drop Address resolution protocol (ARP) replies sent by nodes in the cluster. This is because the router receives packets addressed with a unicast IP address and a multicast MAC address. (it basically thinks that is WRONG :) and drops it). As a result the ARP table and MAC table's don't get updated.

Of course this means our packets don't go where they are meant to so it doesn't work. :(

VMware provides a KB article with some instructions, http://kb.vmware.com/kb/1006525, however i found that they left a few details out. So i thought i would rewrite it and throw in some extra information you may find useful.