For my setup I need to build kubernetes cluster on nodes with 4 network interfaces each. First interface will be used for cluster networking, while other 3 interfaces connect the nodes to (private) networks, not visible among each other. External services reside in those networks.

Pods in the cluster should be able to talk to those services which are external to the cluster.

I tried to find documentation where similar use case is described from perspective of kube-proxy, but it is not available. So I am a bit lost here.

The question here is what (if anything) I have to do so that kube-proxy can make iptables rules for forwarding of traffic to right NICs?

Many thanks for the hints!