I am assuming [Windows NT] sees the filer as a multihomed server and sees all

four IP's

But does it load balance between the 4 ports on the quad card?

A commonly asked question. I think I used to have a pointer to a Microsoft document that described this, but apparently that has gone walk-about, so I'm afraid you're stuck with my from-memory verbage below for now...

The Windows NT client usually starts out with the filer's name. It uses this name to queery WINS and gets returned a list of IP addresses (assuming the filer is multihomed). It then goes through the list of returned addresses and compares them with the address on its own, usually single interface. First it looks for an address to use that is on the same IP subnet as it finds itself on. If it finds multiple of those, it picks one at random, which will tend to balance the load to a single filer that has multiple interfaces connected to that same subnet as the client. If it doesn't find a match, it will look for an interface in the same IP network as it finds itself on. Again, if it finds multiple of those it will pick one at random, tending to balance the load to the target's interfaces. Finally, if it finds none of the above, it will just pick an address to use at random and go for it.

Per our 5.1 releases of Data ONTAP and higher, you also have the ability to control which interfaces the filer will register with WINS. This gives you the ability to stop certain Windows clients from choosing interfaces on the filer which they might not be able to access for various topological and/or routing issues.

Keith