To effectively use the Network Load Balancing (NLB) capability that is built into Windows, it's important that the servers sharing the common virtual IP address be plugged into a hub, not a switch. The reason for this is that these servers share a common virtual MAC address. A switch would get confused when it tries to "learn" the appropriate port for the virtual MAC address. This is why a whitepaper that I recently read recommends:
- plugging the servers in the cluster into a hub - uplinking that hub into a switch
This ensures that each server in the cluster is able to see each packet destined for the virtual MAC address. This is all pretty standard stuff, but here's the thing: I don't want to have to mount a separate hub in my rack for each cluster. Can I accomplish the same thing with a "managed switch"? I've never used a managed switch before, so I'm not sure.
Let's say I have a managed switch with 24 ports. I fill up ports 1-16 with Ethernet cables from various machines on my LAN... but I then plug in the two servers in my cluster into ports 23-24. I want ports 23-24 to act like a hub that is unlinked to the rest of the switch. Eventually, the switch would learn that the shared MAC address of the cluster lives behind ports 23-24 and all traffic destined for that MAC address would be*broadcast* to those two ports. Does that make sense?
I'm not sure what the appropriate jargon/terminology is for this type of setup, but I've done some research and I think it's called a VLAN. The crucial point to note here, though, is that ports 23-24 would act as a hub (all traffic is broadcast) instead of a switch.
All comments are appreciated.