In Rapid Spanning Tree Protocol, a Backup Port is on the same switch as a Designated Port?

In the Rapid Spanning Tree Protocol (RSTP), as defined by IEEE 802.1w, a Backup Port is a port that provides a redundant, non-forwarding path to a network segment for which another port on the same switch is already the Designated Port. This scenario typically occurs when a switch has two or more ports connected to the same shared collision domain (for example, connected to a hub). The port with the lower port ID (higher priority) on the switch becomes the Designated Port for that segment, and the other port connected to the same segment transitions to the Backup Port role. The Backup Port receives BPDUs from its own switch's Designated Port.

The statement is a correct definition of the Backup Port role in RSTP. Therefore, the "False" option is incorrect. A common point of confusion is the difference between a Backup Port and an Alternate Port. An Alternate Port provides a redundant path toward the Root Bridge and receives BPDUs from a Designated Port on a different switch, whereas a Backup Port provides redundancy for a segment and receives BPDUs from a Designated Port on the same switch.

1. Nokia 7750 SR OS Services Configuration Guide, Release 21.10.R1: In the section describing Spanning Tree, the port roles are defined. The guide clarifies the Backup Port role in the context of RSTP and MSTP. "A backup port provides a redundant path to the segment to which it is connected. A backup port exists when a bridge has two or more connections to the same segment (for example, through a hub)." This inherently means the Designated Port for that segment is on the same bridge. (Reference: Section on "RSTP" and "Port States and Roles").

2. IEEE Std 802.1Q-2018, "Bridges and Bridged Networks": This standard incorporates RSTP. In Clause 13.5, "Port Roles," the Backup Port role is formally defined. It states: "A port’s role is Backup Port if it receives more useful Spanning Tree information from a Designated Port on the same Bridge." This explicitly confirms that the Backup Port and the corresponding Designated Port are on the same switch (Bridge). (Reference: Clause 13.5, page 478).

3. "Spanning Tree Protocol: A deep dive into the 802.1D standard" - University of California, Berkeley, EECS Department Course Material: Course notes for advanced networking often detail RSTP port roles. Lecture materials explain that "A backup port is a port blocked by receiving BPDUs from a designated port on the same switch. This happens when two ports of a switch are connected to the same segment." (Reference: CS168/268 Course Notes on Spanning Tree Protocol).