CCNA Switching and Network Access Practice Question
Which TWO statements correctly describe the behavior of PortFast and BPDU Guard on a Cisco switch?
⚠ Common exam trap
Cisco often tests the misconception that PortFast itself blocks or filters BPDUs, when in fact it only accelerates the transition to forwarding; BPDU Guard is a separate feature that must be explicitly enabled to disable the port upon BPDU reception.
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
✓
PortFast immediately transitions a port from blocking to forwarding state, bypassing listening and learning.
PortFast immediately transitions an access port from blocking to forwarding, bypassing listening and learning (Option A). BPDU Guard errdisables a PortFast-enabled port if any BPDU is received, protecting against accidental loops (Option B). Option C is incorrect because PortFast does not alter BPDU handling; the port still processes BPDUs and reverts to normal STP if one is received. Option D is false because BPDU Guard disables the port entirely rather than ignoring BPDUs. Option E is incorrect because BPDU Guard is typically configured on access ports connected to end devices, not on trunk ports.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
PortFast immediately transitions a port from blocking to forwarding state, bypassing listening and learning.
Why this is correct
PortFast is a feature applied to access ports connecting end hosts, allowing the port to skip the listening and learning states and transition directly from blocking to forwarding. This reduces the time a host takes to start sending traffic by avoiding the 30-second STP convergence delay. It does not disable STP; the switch still participates in STP but the port is forwarding immediately.
- ✓
BPDU Guard disables a PortFast-enabled port if it receives any BPDU.
Why this is correct
BPDU Guard complements PortFast by monitoring for BPDUs on a port that should never receive them. If a BPDU arrives, the switch immediately places the port in err-disable state, effectively shutting it down to prevent a potential bridging loop. This protects the network from misconfigured devices or accidental connections, and the port remains disabled until manually re-enabled or configured with errdisable recovery.
- ✗
PortFast allows BPDUs to pass through the port normally, but the port remains in forwarding state.
Why it's wrong here
PortFast does not affect BPDU processing at all; BPDUs are still received and forwarded to the STP process normally. The only change PortFast makes is to move the port immediately to forwarding state, bypassing listening and learning. If a BPDU is received after PortFast has brought the port up, the switch will still process it and may change port roles, which is why BPDU Guard should be used in conjunction with PortFast on access ports.
- ✗
BPDU Guard prevents the port from becoming a root port or designated port by ignoring superior BPDUs.
Why it's wrong here
This statement describes Root Guard, not BPDU Guard. BPDU Guard does not influence STP election processes; it does not ignore BPDUs or alter root port and designated port calculations. Instead, when a BPDU is received on a PortFast-enabled access port, BPDU Guard err-disables the port. Root Guard, in contrast, places a port in an inconsistent state if it receives a superior BPDU, but it does not disable the port based on mere BPDU reception.
- ✗
BPDU Guard is typically configured on trunk ports to prevent loops between switches.
Why it's wrong here
BPDU Guard is not intended for trunk ports between switches. Trunk links are expected to exchange BPDUs as part of STP, so enabling BPDU Guard on a trunk would immediately err-disable the port upon receiving a normal BPDU. BPDU Guard is designed for access ports running PortFast that connect to end hosts, where any BPDU indicates a possible loop or unauthorized switch.
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.
✓PortFast immediately transitions a port from blocking to forwarding state, bypassing listening and learning.Correct answer▾
Why this is correct
PortFast is a feature applied to access ports connecting end hosts, allowing the port to skip the listening and learning states and transition directly from blocking to forwarding. This reduces the time a host takes to start sending traffic by avoiding the 30-second STP convergence delay. It does not disable STP; the switch still participates in STP but the port is forwarding immediately.
✗PortFast allows BPDUs to pass through the port normally, but the port remains in forwarding state.Wrong answer — click to see why▾
Why this is wrong here
PortFast does not filter BPDUs; it still processes them normally. If a BPDU is received on a PortFast port, the port will still participate in STP and may transition to a blocking state, defeating the purpose of PortFast. The statement incorrectly claims BPDUs pass through while the port remains forwarding, which is not true.
Why candidates choose this
Students may confuse PortFast with BPDU filtering or think that PortFast ignores BPDUs entirely. The phrase 'allows BPDUs to pass through normally' might seem plausible because PortFast does not block BPDUs, but the key error is that the port does not remain in forwarding state if a BPDU is received.
✗BPDU Guard prevents the port from becoming a root port or designated port by ignoring superior BPDUs.Wrong answer — click to see why▾
Why this is wrong here
BPDU Guard does not affect STP election processes; it simply err-disables the port upon receiving any BPDU. It does not ignore superior BPDUs or prevent the port from becoming a root or designated port. That behavior is associated with Root Guard, not BPDU Guard.
Why candidates choose this
The description of 'ignoring superior BPDUs' sounds similar to the function of Root Guard, which prevents a port from becoming a root port. Students often mix up BPDU Guard and Root Guard because both involve BPDU handling and port protection.
✗BPDU Guard is typically configured on trunk ports to prevent loops between switches.Wrong answer — click to see why▾
Why this is wrong here
BPDU Guard is intended for access ports with PortFast, not for trunk ports. Trunk ports between switches are expected to exchange BPDUs for normal STP operation; applying BPDU Guard on a trunk would cause the port to err-disable upon receiving legitimate BPDUs, disrupting the network.
Why candidates choose this
Students might think that BPDU Guard prevents loops, and since trunk ports can be involved in loops, they might assume it is appropriate. However, the correct loop prevention on trunk ports is achieved through STP itself, not BPDU Guard.
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?”
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Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
PortFast
PortFast is a Cisco switch feature that immediately brings a port into the forwarding state, bypassing the normal Spanning Tree Protocol (STP) listening and learning phases, so that devices connected to that port can start communicating right away.
Key term
BPDU
A Bridge Protocol Data Unit is a layer 2 frame that switches use to exchange information about the Spanning Tree Protocol (STP) to prevent network loops.
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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.