Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
Why is BPDU Guard commonly enabled on PortFast-enabled access ports?
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
Distractor review
To make STP root election happen faster
BPDU Guard is a protection feature, not a speed optimization for root election.
B
Distractor review
To disable STP permanently on access ports
STP is not permanently disabled.
C
Best answer
To err-disable a port if it receives unexpected BPDUs
That is the core purpose of BPDU Guard.
D
Distractor review
To allow only one MAC address on the access port
That would be port security.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is selecting the answer that BPDU Guard speeds up STP root election or disables STP permanently on access ports. Some candidates mistakenly believe BPDU Guard optimizes STP convergence or turns off STP to allow faster port activation. However, BPDU Guard’s sole purpose is to protect the network by err-disabling a PortFast port if it receives unexpected BPDUs, which usually indicate a switch connected where only an end device should be. Misunderstanding this can lead to incorrect answers and confusion about STP behavior on access ports.
Technical deep dive
How to think about this question
Spanning Tree Protocol (STP) is designed to prevent Layer 2 loops in a switched network by selectively blocking redundant paths. PortFast is a Cisco feature that immediately transitions a switch port into the forwarding state, bypassing the usual STP listening and learning states. This is intended for access ports connected to end devices, such as workstations or servers, where no switching loops are expected. However, if a PortFast-enabled port receives Bridge Protocol Data Units (BPDUs), it indicates that another switch or bridging device is connected, which could cause loops. BPDU Guard is a security feature that protects the network by err-disabling a PortFast-enabled port if it receives unexpected BPDUs. This behavior prevents potential Layer 2 loops caused by unauthorized switches connecting to access ports. When BPDU Guard is enabled, the port shuts down immediately upon receiving a BPDU, effectively isolating the potential loop source and maintaining network stability. A common exam trap is misunderstanding BPDU Guard as a feature that speeds up STP convergence or disables STP permanently on access ports. In reality, BPDU Guard only acts as a protective mechanism to err-disable ports receiving BPDUs unexpectedly. Practically, enabling BPDU Guard on PortFast ports ensures that only end devices connect to these ports, preventing accidental or malicious introduction of switches that could disrupt the STP topology.
KKey Concepts to Remember
- PortFast immediately transitions an access port to the forwarding state, bypassing STP's listening and learning states to speed up device connectivity.
- BPDU Guard err-disables a PortFast-enabled port if it receives any BPDUs, preventing potential Layer 2 loops caused by unauthorized switches.
- Receiving BPDUs on a PortFast port usually indicates a misconfiguration or unauthorized device, triggering BPDU Guard to protect the network.
- BPDU Guard does not disable STP permanently; it only shuts down the port temporarily until manual intervention or re-enabling.
- PortFast should only be enabled on ports connected to end devices, never on ports connecting to other switches or bridging devices.
- BPDU Guard helps maintain STP topology integrity by preventing unexpected switches from participating in STP on access ports.
- The err-disable state caused by BPDU Guard requires network administrator action to re-enable the port after verifying the cause.
- BPDU Guard is a critical security feature in Cisco networks to prevent accidental or malicious Layer 2 loops on access ports.
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.
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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 immediately transitions an access port to the forwarding state, bypassing STP's listening and learning states to speed up device connectivity.
What is the correct answer to this question?
The correct answer is: To err-disable a port if it receives unexpected BPDUs — PortFast ports are meant for end devices, not for switches. BPDU Guard protects the LAN by shutting down a PortFast port that unexpectedly starts receiving BPDUs, which usually means an unauthorized switch was connected.
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.
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