2.3 Spanning Tree Alg. contd.
nThe root then proceeds to  construct the tree. If two paths are of equal length, then the one pointing to the bridge with the lower  MAC address is chosen (again here bridge priority maybe used instead).
nNot all bridge ports will be activated at all times, i.e., some LAN segments may not be used by some bridges as they do not form part of the spanning tree (note: that does not mean the LAN segment is isolated, it basically means that it is reachable via another route/bridge).