Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A port connected to an end host is configured with PortFast and BPDU Guard. What is the most likely result if a small unmanaged switch is connected and starts sending BPDUs?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
The port is error-disabled by BPDU Guard.
This is correct because BPDU Guard disables an edge port when it receives a BPDU.
B
Distractor review
The port automatically becomes the root port.
This is wrong because BPDU Guard does not promote the port into STP forwarding roles.
C
Distractor review
The port is converted into a trunk.
This is wrong because BPDU receipt does not trigger automatic trunk conversion here.
D
Distractor review
The port ignores the BPDU because PortFast disables STP entirely.
This is wrong because PortFast does not remove BPDU Guard protection.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is assuming that PortFast disables STP entirely and thus the port ignores BPDUs. This misconception leads to selecting answers that suggest the port continues forwarding or changes roles upon receiving BPDUs. In reality, PortFast only speeds up port activation but does not remove BPDU processing. BPDU Guard is designed to detect unexpected BPDUs on PortFast ports and immediately error-disable the port to prevent loops. Misunderstanding this interaction can cause candidates to overlook the critical protective role of BPDU Guard and select incorrect options such as the port becoming a root port or converting to a trunk.
Technical deep dive
How to think about this question
PortFast is a Cisco feature applied to switch ports connected directly to end devices, such as workstations or servers, to speed up the transition to the forwarding state by bypassing the usual Spanning Tree Protocol (STP) listening and learning states. This reduces the delay in port activation, allowing devices to connect and communicate faster. However, PortFast does not disable STP entirely; it only changes the port's behavior to assume it is an edge port, which should not receive Bridge Protocol Data Units (BPDUs). BPDU Guard is a complementary STP security feature designed to protect the network topology by shutting down a PortFast-enabled port if it receives any BPDUs. This is because receiving a BPDU on a PortFast port indicates that the port is connected to another switch or device that could cause loops or topology changes. When BPDU Guard detects BPDUs on such a port, it places the port into an error-disabled state to prevent potential STP topology issues. A common exam trap is misunderstanding the interaction between PortFast and BPDU Guard. Some may incorrectly believe that PortFast disables STP and thus ignores BPDUs, or that the port automatically becomes a root port or trunk upon receiving BPDUs. In reality, BPDU Guard enforces strict protection by disabling the port immediately, preventing loops and preserving network stability. This behavior is critical in enterprise access-layer designs to maintain fast connectivity while safeguarding the STP topology.
KKey Concepts to Remember
- PortFast enables a switch port to transition immediately to forwarding state, bypassing STP listening and learning states for faster host connectivity.
- BPDU Guard monitors PortFast-enabled ports and disables the port if any BPDUs are received, protecting the network from potential loops.
- Receiving a BPDU on a PortFast port signals that the port is connected to another switch or device, which is unexpected and triggers BPDU Guard.
- When BPDU Guard activates, it places the port into an error-disabled state, effectively shutting down the port to prevent topology changes.
- PortFast does not disable STP entirely; it only changes port behavior to assume it is connected to an end device, not another switch.
- A port receiving BPDUs does not automatically become a root port or convert to a trunk port; STP roles and port modes are not changed by BPDU Guard.
- BPDU Guard is commonly used in enterprise access layers to combine fast host connectivity with protection against misconfigurations or unauthorized switches.
- The error-disabled state caused by BPDU Guard requires manual intervention or errdisable recovery to restore port functionality.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
CCNA DHCP practice questions
Practise DHCP scopes, relay, leases and troubleshooting.
CCNA show ip route practice questions
Practise routing-table output, longest-prefix match, AD and route selection.
CCNA show interfaces trunk practice questions
Practise trunk verification and VLAN forwarding across switches.
CCNA wireless security practice questions
Practise WLAN security, authentication and wireless architecture concepts.
CCNA IPv6 practice questions
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
PortFast enables a switch port to transition immediately to forwarding state, bypassing STP listening and learning states for faster host connectivity.
What is the correct answer to this question?
The correct answer is: The port is error-disabled by BPDU Guard. — The most likely result is that the port is placed into an err-disabled state by BPDU Guard. In practical terms, PortFast tells the switch to treat the interface like an edge port for a normal endpoint, which is why it starts forwarding quickly. BPDU Guard protects that assumption. If the port suddenly receives a spanning-tree BPDU, the switch treats that as a sign that the port is no longer connected to a simple end device. This combination is common in enterprise access-layer design because it improves user startup time while still protecting the topology. The correct answer is the one that describes the port being shut down automatically when BPDUs appear unexpectedly.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
Discussion
Loading comments…
Sign in to join the discussion.