A simple load-balancing solution is to assign a multicast MAC address to the Service IP. In this case the clients target the Service IP, and a hub or switch before the firewall hosts forwards all requests to the multicast MAC address, resulting in all nodes of the cluster receiving all packets sent to the Service IP. The IP addresses of the clients are distributed between the nodes using some logic (for example, one nodes serves only clients with odd, the other one clients with even IP addresses), and the packet filter of each node is configured to accept only the packets of the clients they are responsible for.