Spanning Tree Protocol Root bridge election

The switch with least bridge priority is elected as Root bridge.

If all switches in a single spanning tree have the same bridge priority, the switch with the lowest MAC address will become the root bridge.

32768 is the default value out of a range 0 to 61440 in increments of 4096. Valid bridge priority values are 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768, 36864, 40960, 45056, 49152, 53248, 57344, and 61440. All other values are rejected.

You can set the bridge priority to a low value to make it a root bridge manually. The default priority is (8) x 4096 = 32768 for most of the vendors.