H12-821_V1.0 · Question #866
If the MSTP VR ID IP has only one BPDU type, its value is 2, and there is no TCN BPDU.
The correct answer is A. TRUE. Option A is correct because MSTP (IEEE 802.1s) inherits its BPDU structure from RSTP, using a single BPDU type with the value 2 (0x02) - the MST BPDU. Unlike classic STP (802.1D), which had two distinct BPDU types (Configuration BPDU = 0x00 and TCN BPDU = 0x80), MSTP eliminates…
Question
Options
- ATRUE
- BFALSE
How the community answered
(36 responses)- A75% (27)
- B25% (9)
Explanation
Option A is correct because MSTP (IEEE 802.1s) inherits its BPDU structure from RSTP, using a single BPDU type with the value 2 (0x02) - the MST BPDU. Unlike classic STP (802.1D), which had two distinct BPDU types (Configuration BPDU = 0x00 and TCN BPDU = 0x80), MSTP eliminates the separate Topology Change Notification BPDU entirely; instead, topology change information is signaled using the TC flag bit within the single MST BPDU itself. Option B (FALSE) is wrong because it contradicts this well-defined behavior - MSTP genuinely has only one BPDU type and genuinely lacks a standalone TCN BPDU.
Memory tip: Think "MSTP = 1 BPDU, value 2, TC goes inside." The number 2 is easy to remember because MSTP is based on 802.1s → RSTP → type 2. And since RSTP/MSTP are rapid protocols, they're efficient: no wasted separate TCN message - the TC bit rides along in the same frame.
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