300-320 · Question #223
Which four Cisco proprietary Spanning Tree Protocol enhancements are supported with rapid per- VLAN Spanning-Tree plus? (Choose four.)
The correct answer is A. PortFast C. loop guard D. root guard E. BPDU guard. Answers A (PortFast), C (Loop Guard), D (Root Guard), and E (BPDU Guard) are correct. Rapid PVST+ (IEEE 802.1w applied per-VLAN) retains compatibility with these four Cisco STP enhancements: PortFast transitions edge ports immediately to forwarding, BPDU Guard disables a…
Question
Which four Cisco proprietary Spanning Tree Protocol enhancements are supported with rapid per- VLAN Spanning-Tree plus? (Choose four.)
Options
- APortFast
- BUplinkFast
- Cloop guard
- Droot guard
- EBPDU guard
- FBackboneFast
How the community answered
(62 responses)- A92% (57)
- B5% (3)
- F3% (2)
Explanation
Answers A (PortFast), C (Loop Guard), D (Root Guard), and E (BPDU Guard) are correct. Rapid PVST+ (IEEE 802.1w applied per-VLAN) retains compatibility with these four Cisco STP enhancements: PortFast transitions edge ports immediately to forwarding, BPDU Guard disables a PortFast port if a BPDU is received, Root Guard prevents an unauthorized switch from becoming the root, and Loop Guard prevents a port from transitioning to forwarding in the absence of BPDUs (protecting against unidirectional link failures). UplinkFast (B) is NOT supported with Rapid PVST+ because Rapid PVST+ already provides fast uplink convergence natively through its proposal/agreement mechanism, making UplinkFast redundant. BackboneFast (F) is also NOT needed because Rapid PVST+ natively handles indirect link failures - the functionality of BackboneFast is built into the 802.1w standard.
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