STP question in CCIE

During my preparation for CCIE R&S (v5) written exam, I came along the question about Spanning Tree Protocol in which certain exhibit was shown.

STP4

There are couple of questions which rely on the same exhibit, so I took some time to determine which ports will be in which state after the network converges.

The questions are:

  • Which ports are forwarding traffic after STP converges?
  • Which ports are in blocking state after STP converges?
  • After STP converges the traffic from switch SWG to SWD takes less optimal path. What can be done to optimize the STP tree in this switched network?

With the picture above it’s easy to answer them.