Cisco Certified Network Professional 2025 – 400 Free Practice Questions to Pass the Exam

The backup port in Rapid Spanning Tree Protocol (RSTP) is indeed less preferable than the designated port because of its role within the network topology. A backup port is used when there is already a designated port in the same segment. Its primary function is to provide redundancy for the designated port; however, it cannot forward traffic unless the designated port fails.

In RSTP, the designated port is the port on a network switch that has the best path to the Root Bridge and is responsible for forwarding traffic towards the root. Since the designated port is actively forwarding traffic, the backup port remains in a blocking state until it is needed.

This design ensures network resilience while maintaining efficiency; the backup port acts as a safety net but is not engaged in regular traffic forwarding, which defines its subordinate position compared to the designated port. The other port types—such as the root port, which is the best path from a switch to the Root Bridge, or the edge port, which connects to end devices and can directly transition to the forwarding state—have functions that allow them to actively manage traffic, making them more preferable in terms of participation in the network.