A network engineer is analyzing the rapid convergence mechanism of Rapid PVST+ (IEEE 802.1w) on a point-to-point link between two Cisco Catalyst switches. Place the steps of the Rapid PVST+ Proposal-Agreement handshake sequence in the correct chronological order from first event to final event.
- 1The upstream switch transmits a BPDU with the Proposal bit set out of its Designated Port in the Discarding state.
- 2The downstream switch elects the receiving port as its new Root Port and places all non-edge Designated Ports into the Discarding state to synchronize.
- 3The downstream switch transmits an Agreement BPDU back to the upstream switch from its newly selected Root Port.
- 4The upstream switch receives the Agreement BPDU and immediately transitions its Designated Port to the Forwarding state.
Answer
The correct order of events in the Rapid PVST+ Proposal-Agreement handshake sequence is: 1) The upstream switch transmits a BPDU with the Proposal bit set. 2) The downstream switch selects the port as its new Root Port and blocks non-edge Designated Ports (synchronization). 3) The downstream switch sends an Agreement BPDU back to the upstream switch. 4) The upstream switch immediately transitions its Designated Port to the Forwarding state.
Rapid PVST+ (IEEE 802.1w) achieves rapid convergence on point-to-point links through an active handshake sequence between switch ports. First, the upstream switch transmits a proposal BPDU on its Designated Port. Second, the downstream switch recognizes the superior BPDU, adopts the receiving interface as its Root Port, and blocks all non-edge Designated Ports to synchronize the switch topology. Third, once synchronized, the downstream switch responds with an Agreement BPDU on its new Root Port. Finally, the upstream switch receives this agreement and immediately transitions its Designated Port to the Forwarding state without waiting for legacy forward delay timers.
Step-by-Step Solution
Key Concept
Rapid PVST+ Proposal-Agreement Handshake Convergence