The networking shown in the figure, SWA, SWB, SWC and SWD run RSTP, which of the following statements is correct? (Multiple choice)

Question

Options

• AAfter the edge port receives the BPDU, it will re-participate in the calculation of the spanning tree
• BAfter being configured as an edge port, the interface can quickly enter the forwarding state
• CThe edge port can be enabled on the GE0/0/2 port of the SWB, so that the interface connected to the terminal can quickly enter the forwarding state
• DThe edge port can be enabled on the GE0/0/2 port of the SWC, so that the interface connected to the terminal can quickly enter the forwarding state

• A
  83% (24)
• B
  3% (1)
• C
  10% (3)
• D
  3% (1)

Explanation

Option A is correct because RSTP edge ports are designed for end-device connections and bypass normal spanning tree state transitions - but this is contingent on never receiving a BPDU. The moment an edge port receives a BPDU, RSTP recognizes the port must be connected to another bridge, immediately revokes the edge port designation, and forces the port to re-participate in spanning tree calculation from scratch. This is a built-in security/stability mechanism that prevents topology loops.

B is incorrect because while edge ports do enter forwarding quickly under normal conditions, the statement is unconditionally phrased - it ignores that receipt of a BPDU (as in option A) will cause the port to lose edge status and must go through the full RSTP state machine instead of bypassing it.

C is incorrect because, per the figure, SWB's GE0/0/2 is an inter-switch uplink, not a terminal-facing port. Enabling edge port on a switch-to-switch link is both inappropriate and dangerous, as it could suppress loop detection.

D is incorrect because SWC's GE0/0/2 in the figure similarly connects to another switch, not an end device - same reasoning as C applies.

Memory tip: Think of edge ports as "fast-track lanes" - they skip the queue (STP state machine) only as long as no other switch shows up. The moment a BPDU arrives (another switch detected), the fast-track closes and the port joins the regular queue for spanning tree recalculation.

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