CCNA Switching and Network Access Practice Question
Which TWO of the following statements about Spanning Tree Protocol (STP) and Rapid PVST+ are true?
⚠ Common exam trap
Cisco often tests the misconception that PortFast and BPDU Guard are automatically linked, when in fact they are separate features that must be configured independently, and the trap is that candidates assume enabling PortFast also enables BPDU Guard.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The root bridge in STP is elected based on the lowest bridge ID.
The root bridge in STP is elected based on the numerically smallest bridge ID (priority + MAC address). Option D is correct because BPDU Guard, when enabled on a PortFast-enabled port, immediately error-disables the port if a BPDU is received, protecting against accidental loops. Option B is incorrect because the root bridge is chosen by the lowest bridge ID, not the highest. Option C is incorrect because PortFast and BPDU Guard are independent features; PortFast does not automatically enable BPDU Guard. Option E is incorrect because both traditional STP (802.1D) and Rapid PVST+ (RSTP-based) use the same root bridge election process—lowest bridge ID.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The root bridge in STP is elected based on the lowest bridge ID.
Why this is correct
Spanning Tree elects the root bridge through BPDU exchange, and the switch with the lowest bridge ID becomes root. The bridge ID is an 8-byte value combining the configurable priority field and the switch's MAC address; when priorities tie, the lowest MAC address breaks the tie. This deterministic election logic is identical across traditional STP and Rapid PVST+.
- ✗
The root bridge in STP is elected based on the highest bridge ID.
Why it's wrong here
Choosing the root bridge by the highest bridge ID would violate the core spanning-tree rule that the switch with the most preferred, numerically lowest BID wins. STP compares bridge IDs, and the lowest combination of priority and MAC address is considered the root. A higher bridge ID is actually at a disadvantage in the election, so this statement is false.
- ✗
PortFast automatically enables BPDU Guard on an interface.
Why it's wrong here
PortFast and BPDU Guard are independent STP features: PortFast simply moves a switch port directly to forwarding, skipping the listening and learning states to support an end host. Enabling PortFast does not implicitly turn on BPDU Guard; administrators must configure BPDU Guard separately, either per interface or globally as a default, on ports where unexpected BPDUs should trigger an error-disabled state.
- ✓
BPDU Guard places a PortFast-enabled port into an error-disabled state if a BPDU is received.
Why this is correct
BPDU Guard is an STP protection feature intended for PortFast-configured access ports, which should never receive BPDUs from an end host. If a BPDU arrives on such a port, BPDU Guard immediately places the port into the error-disabled state, effectively shutting it down to preserve the spanning-tree topology. Recovery normally requires manual re-enabling or the errdisable auto-recovery mechanism.
- ✗
Rapid PVST+ uses a different root bridge election process than traditional STP.
Why it's wrong here
Rapid PVST+ accelerates convergence with RSTP-based BPDU exchange and improved port roles, but it does not alter the root bridge election logic. Both classic IEEE 802.1D STP and Rapid PVST+ select the root switch by comparing bridge IDs, where the lowest bridge ID (priority plus MAC address) wins. Therefore, claiming Rapid PVST+ uses a different election process is incorrect.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓The root bridge in STP is elected based on the lowest bridge ID.Correct answer▾
Why this is correct
Spanning Tree elects the root bridge through BPDU exchange, and the switch with the lowest bridge ID becomes root. The bridge ID is an 8-byte value combining the configurable priority field and the switch's MAC address; when priorities tie, the lowest MAC address breaks the tie. This deterministic election logic is identical across traditional STP and Rapid PVST+.
✗The root bridge in STP is elected based on the highest bridge ID.Wrong answer — click to see why▾
Why this is wrong here
STP elects the root bridge using the lowest bridge ID, not the highest. The bridge ID consists of a configurable priority and the switch's MAC address; the switch with the numerically smallest bridge ID becomes the root.
Why candidates choose this
Students may confuse the root bridge election with other protocols that use highest values (e.g., OSPF DR election) or mistakenly think higher priority is better.
✗PortFast automatically enables BPDU Guard on an interface.Wrong answer — click to see why▾
Why this is wrong here
PortFast and BPDU Guard are independent features. PortFast speeds up convergence on access ports, while BPDU Guard must be explicitly enabled (e.g., via 'spanning-tree bpduguard enable') to protect against rogue BPDUs.
Why candidates choose this
Since PortFast is often used with BPDU Guard in best practices, some may assume PortFast automatically enables BPDU Guard, but they are separate configurations.
✗Rapid PVST+ uses a different root bridge election process than traditional STP.Wrong answer — click to see why▾
Why this is wrong here
Both traditional STP (802.1D) and Rapid PVST+ (802.1w) use the same root bridge election process: the switch with the lowest bridge ID becomes the root. Rapid PVST+ improves convergence but does not change the election mechanism.
Why candidates choose this
The name 'Rapid PVST+' might imply a different election process, but the root election remains identical; only the state machine and convergence mechanisms differ.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
Go deeper
Related to this question
Learn chapter
Root Guard, Loop Guard, and BPDU Guard in Rapid PVST+
Key term
STP
Shielded Twisted Pair (STP) is a copper cable that wraps each twisted pair in foil or braid to block electromagnetic interference.
Key term
RSTP
RSTP (Rapid Spanning Tree Protocol) is a network protocol that quickly detects and recovers from link failures in Ethernet networks to prevent loops and ensure fast convergence.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.