A network engineer is evaluating the Rapid PVST+ topology operational mechanics across a enterprise LAN segment. A switch has multiple active connections to adjacent switches and redundant interswitch links. Which two statements correctly describe Rapid PVST+ port role operations and behaviors in this environment? (Select two.)
- An Alternate port receives BPDUs from a neighbor switch, provides an alternate path to the root bridge, and remains in the Discarding state.Answer
- A Backup port receives BPDUs originated by its own local switch over a shared collision domain or redundant link to the same segment and remains in the Discarding state.Answer
- CAn Alternate port immediately replaces a failed Designated Port on the local switch to maintain forwarding on the local segment.
- DA Backup port transitions directly to the Forwarding state whenever PortFast is globally enabled on trunk interfaces.
Answer
The correct statements are that an Alternate port receives BPDUs from a neighbor switch to provide an alternate path toward the root bridge in the Discarding state, and a Backup port receives BPDUs sent by its own switch to provide redundancy for a Designated Port on the same collision domain.
In Rapid PVST+ (IEEE 802.1w implementation in Cisco switches), an Alternate port receives BPDUs from other switches and stands by to replace the Root Port if the active path to the root bridge fails. A Backup port receives BPDUs transmitted by its own switch over a shared media connection and stands by to replace the Designated Port for that specific segment. Both roles maintain a Discarding state to prevent Layer 2 loops.
Step-by-Step Solution
Key Concept
Rapid PVST+ Port Roles (Root, Designated, Alternate, Backup) and Operational States