Refer to the exhibit. Which trunk link will not forward any traffic after the root bridge election process is complete?

Because the path cost between S1 and S2 is 4, and we assume the path costs on the network are the default costs based on Ethernet link speeds (which is typically higher for slower links), then S3 will compare the path cost to the root bridge through Trunk2 directly to S1 and the path cost going through S4 and then S2 to S1 (Trunk4 to Trunk1).

Since you’ve mentioned that the correct answer is Trunk2, we would deduce the following:

• The path cost for S3 to reach S1 via Trunk2 is higher than reaching S1 via S4 and S2 (Trunk4 to Trunk3 to Trunk1).
• Given that S1 to S2 is 4, and assuming all links have the same cost, the total cost for S3 to reach S1 via S4 and S2 would be 12 (4 for Trunk4, 4 for Trunk3, and 4 for Trunk1).
• For Trunk2 to be blocked, its path cost would have to be higher than 12, making the path through S4 and S2 more favorable despite being longer in terms of hop count.

This is contrary to what we would expect in a typical Ethernet network, where the direct path (which is usually the shortest path) between two switches has the lowest cost, and thus would be chosen for forwarding traffic. However, if manual path cost configuration is applied to make the direct path cost higher, then STP would determine a different forwarding path, which can lead to a non-direct link being chosen as the root port, and the direct link (Trunk2) being put in a blocking state.

Therefore, based on the specific path costs you’ve provided and the reported correct answer, it seems there has been a manual configuration that has adjusted the path costs to make the indirect path from S3 to S1 via S4 and S2 more favorable than the direct path via Trunk2.