Which RSTP port role functions as a backup to the root port?

In Rapid Spanning Tree Protocol (RSTP), the port role that functions as a backup to the root port is known as the Alternate port. The Alternate port allows for quick recovery in case the root port fails, enabling the network to maintain connectivity and stability.

The primary role of a root port is to connect the switch to the root bridge, which is the central point of the spanning tree topology. If this connection were to fail, the Alternate port can take over to ensure that there is still a path to the root bridge without causing a disruption in the network. This capability is crucial for reducing downtime and improving the efficiency of the network.

In addition to the Alternate port role, there are other roles in RSTP such as Designated and Root ports, serving different purposes within the network. However, it is the Alternate port that specifically acts as that backup to the root port, thus facilitating a rapid failover in the network topology.