In the switching network shown in the figure, all switches run the STP protocol. When the topology is stable, modifying the sending cycle of the configuration BPDU on which of the following switches…

Question

Options

• ASTC
• BSWA
• CSWD
• DSWB

• A
  16% (5)
• B
  3% (1)
• C
  75% (24)
• D
  6% (2)

Explanation

In STP, only the Root Bridge originates and sends configuration BPDUs; all other switches simply relay (forward) the BPDUs they receive from the root out their designated ports. Since SWD is the Root Bridge in this topology, it is the only switch whose Hello Time setting actually controls the BPDU sending cycle for the entire network - changing it on SWD propagates the new interval everywhere.

Why the distractors are wrong: STC (A), SWA (B), and SWB (D) are non-root bridges. Even if you change the Hello Time parameter on these switches locally, they do not generate BPDUs themselves - they only forward BPDUs originated by the Root Bridge at the interval the root dictates. Local Hello Time changes on non-root switches are effectively ignored in a stable STP topology.

Memory tip: Think "only the Root rules the rhythm." Whichever switch is the Root Bridge owns the clock for the entire STP domain - all timing in the network flows from it.

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