In which two port states does a switch learn MAC addresses and process BPDUs in a PVST network? (Choose two.)

Question

BlackTom AI · Accepted Answer

In PVST, only ports in the learning and forwarding states both populate the MAC (CAM) table and actively participate in STP by processing BPDUs.

1) Relevant concepts
- PVST (Per-VLAN Spanning Tree) runs an STP instance per VLAN; ports transition through STP states.
- STP port states: blocking, listening, learning, forwarding, disabled.
- BPDU (Bridge Protocol Data Unit) is the control frame STP uses; switches must process BPDUs to determine topology.
- MAC learning: the switch examines source MACs on received frames and adds them to the CAM table to forward future frames.

2) Step-by-step reasoning
- Forwarding state: switch forwards user frames, learns source MAC addresses from those frames (updates CAM), and sends/receives and processes BPDUs to maintain STP. Thus it both learns MACs and processes BPDUs.
- Learning state: switch does not forward user frames yet, but it does examine incoming frames to learn source MAC addresses and also processes BPDUs as part of the STP convergence process. Therefore it also meets both criteria.
- Listening state: switch processes BPDUs (determining topology) but does not yet populate the MAC table — it discards user frames and does not learn addresses.
- Blocking state: switch receives and processes BPDUs to detect loops but neither forwards frames nor learns MAC addresses.
- Disabled: the port is administratively down and does not participate in STP or learning; it does not process BPDUs.

3) Why the correct answers are correct
- Learning and forwarding are the only two states that populate the MAC table; both also process BPDUs. That matches the requirement of “learn MAC addresses and process BPDUs.”

4) Why the other options are incorrect
- Blocking: processes BPDUs but does not learn MAC addresses.
- Listening: processes BPDUs but does not learn MAC addresses.
- Disabled: neither processes BPDUs nor learns MAC addresses.

Conclusion: The correct port states are forwarding and learning, which matches the provided answer.

In which two port states does a switch learn MAC addresses and process BPDUs in a PVST network? (Choose two.)多项选择题

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