Which ports will be STP designated ports if all the links are operating at the same bandwidth?

Refer to the topology shown in the exhibit.

Which ports will be STP designated ports if all the links are operating at the same bandwidth?
(Choose three.)

A.
Switch A – Fa0/0

B.
Switch A – Fa0/1

C.
Switch B – Fa0/0

D.
Switch B – Fa0/1

E.
Switch C – Fa0/0

F.
Switch C – Fa0/1

Explanation:
This question is to check the spanning tree election problem.
1. First, select the root bridge, which can be accomplished by comparing the bridge ID, the
smallest will be selected. Bridge-id= bridge priority + MAC address. The three switches in the

figure all have the default priority, so we should compare the MAC address, it is easy to find that
SwitchB is the root bridge.
2. Select the root port on the non-root bridge, which can be completed through comparing root
path cost. The smallest will be selected as the root port.
3. Next, select the Designated Port. First, compare the path cost, if the costs happen to be the
same, then compare the BID, still the smallest will be selected. Each link has a DP. Based on the
exhibit above, we can find DP on each link. The DP on the link between SwitchA and SwitchC is
SwitchA’Fa0/1, because it has the smallest MAC address.