When I was teaching a clustering for Windows Server 2003 course in Richmond BC a few weeks ago, this question came up which I did not answer. The question was what takes priority, if I confogure an interface as private for internal cluster communications, or if it is first in the binding order in the list of networks.
The answer is actually both. Let me clarify. The default configuration for the internal node-node communication network if more than 1 interface is present in the cluster is private. This can also be mixed. The default setting for the client-node communication network is mixed. This is the public network side of the cluster.
Now, the configuration can be left in this order and the cluster will function fine. If you want the node-node communication to happen over the same link as the client-node communication, change nothing in the default configuration, but place the network configured as mixed first in the binding order. Reasons for doing this may be, transition period while changing hardware or infrastructure or better equipment with more bandwidth available on the public side. The main reason mixed was left as a selection for network type was to allow this flexibility.
If you want the node-node communication to happen over the link configured as private and another interface exists that is configured as mixed, make sure the private network is first in the binding order.
This can get confusing as far as concepts go... If you have dedicated network cards for each type of communication in the cluster, the simplest solution would be to leave the node-node communication as private but change the client-node communication from mixed to public. If this is done, only the network configured as private will show up in the binding list of the network configuration and the intent is clear.
It goes without saying that cluster configuration choices should always be documented in the event of a rebuild. Hopefully this clears up some confusion.