Which improvement is not part of RSTP compared to STP?

The rationale for D being the correct answer lies in the fundamental operation of RSTP (Rapid Spanning Tree Protocol) compared to STP (Spanning Tree Protocol).

In RSTP, the protocol operates with an improved convergence mechanism, allowing rapid recovery from topology changes. The specifics regarding how BPDUs (Bridge Protocol Data Units) are used in RSTP do not dictate that the lack of received BPDUs over a specific number of Hello intervals means that negotiation is successful. In fact, RSTP uses a more proactive and efficient approach to communication by having all switches consistently send BPDUs rather than relying on the absence of them to make determinations about port statuses.

The significance of RSTP's design is in its ability to detect and react to changes in the network more quickly than STP, which relies heavily on a more passive approach where devices only react when they do not hear from each other for a certain time. This built-in discrepancy means that the statement about the successful negotiation based on the absence of BPDUs is inaccurate for RSTP.

In contrast to this, other improvements mentioned, such as the reduction of port states and incorporation of new port roles, as well as the regular sending of configuration B