To be a CCIE we need a good grasp of switching and STP. This post by Petr Lapukhov (again) is one of the best I’ve ever seen on STP. This post describes PVST+ in detail. Read it here.
Spanning tree – notes
Electing the root Only one switch can be the root bridge. From the start all switches announce themselves as the root, when a switch hears of a superior BPDU it stops announcing itself as the root and instead forwards the