With IEEE 802.1S Multiple Spanning Tree Protocol, an Ethernet operator can define different network regions. A Common Spanning Tree (CST) is defined in such a way that a link failure inside a region does not affect the CST outside the region and additional Spanning Trees inside each region can be configured to achieve better load balance. We propose a procedure to determine the MSTP parameters configuration with multiple regions that optimize load balance and show its efficiency through computational results. We compare multiple region solutions with single region solutions, using a previous work on the single region case, and show that the multiple regions approach is better when traffic is mainly between switches belonging to the same region.