A method for balancing load among firewall security devices (FSDs) is provided. According to one embodiment, a switching device performs adaptive load balancing among cluster units of an HA cluster of firewall security devices. A load balancing (LB) function implemented by the switching device is configured based on information received from a network administrator. A LB table is maintained that forms associations between hash values output by the LB function and corresponding ports of the switching device to which the cluster units are coupled. Network traffic received by the switching device is directed to appropriate cluster units based on the LB function and the LB table. A traffic load on each of the cluster units is monitored. Responsive to a deviation from a predefined ideal traffic distribution, an attempt is made to improve performance of the HA cluster by dynamically adjusting the LB balancing table to address the deviation.