Question 1mediummulti select
Full question →mediummulti selectObjective-mapped
An engineer wants rapid transition to forwarding on end-user switchports while still protecting the topology from accidental switch connections. Which two STP-related features fit that design?
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
PortFast on user-facing access ports
PortFast skips the usual listening/learning delay for edge endpoints.
B
Best answer
BPDU Guard on those same access ports
BPDU Guard disables the port if a switch sends BPDUs into the edge port.
C
Distractor review
Root Guard on every user-facing port instead of PortFast
Root Guard serves a different purpose and does not provide rapid edge forwarding.
D
Distractor review
Loop Guard on hosts to accelerate DHCP
Loop Guard is not used to speed host startup.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is selecting Root Guard or Loop Guard as solutions for rapid port forwarding on end-user ports. Root Guard is designed to protect the root bridge election by blocking ports that attempt to become root ports, but it does not speed up the STP port state transition. Loop Guard prevents loops caused by unidirectional link failures but does not affect the forwarding delay on edge ports. Candidates may confuse these features with PortFast and BPDU Guard because all relate to STP, but only PortFast and BPDU Guard together provide rapid forwarding and topology protection on user-facing ports.
Technical deep dive
How to think about this question
Spanning Tree Protocol (STP) is designed to prevent Layer 2 switching loops by selectively blocking redundant paths in a switched network. However, STP introduces a delay when ports transition from blocking to forwarding states, typically taking 30 to 50 seconds. This delay can negatively impact end-user devices that expect immediate connectivity upon link activation. Cisco's PortFast feature addresses this by allowing edge ports connected to end devices to bypass the usual STP listening and learning states, transitioning immediately to forwarding. This rapid transition improves user experience by reducing network access time. While PortFast accelerates port activation, it introduces a risk if a switch is accidentally connected to a PortFast-enabled port, potentially causing loops. To mitigate this, BPDU Guard is used alongside PortFast. BPDU Guard monitors for Bridge Protocol Data Units (BPDUs) on edge ports; if any BPDU is received, indicating a switch connection rather than an end device, BPDU Guard disables the port to protect the network topology. This combination ensures rapid forwarding on legitimate end-user ports while preventing accidental topology changes caused by misconnected switches. A common exam trap is confusing Root Guard and Loop Guard with PortFast and BPDU Guard. Root Guard prevents a port from becoming a root port, protecting the root bridge placement, but does not speed up port transitions. Loop Guard prevents loops caused by unidirectional link failures but does not affect port forwarding delay. Understanding the specific roles of these STP features is critical. In practice, enabling PortFast and BPDU Guard on access ports is a best practice for edge devices, ensuring fast connectivity and topology protection without risking STP instability.
KKey Concepts to Remember
- PortFast enables immediate transition of edge switch ports to the forwarding state, bypassing STP's listening and learning delays to speed up host connectivity.
- BPDU Guard disables a PortFast-enabled port if it receives BPDUs, preventing accidental switch connections from causing network loops or topology changes.
- Root Guard protects the root bridge placement by blocking ports that attempt to become root ports but does not accelerate port forwarding on edge ports.
- Loop Guard prevents STP loops caused by unidirectional link failures but does not influence the speed of port state transitions for end devices.
- STP ports without PortFast undergo a 30-50 second delay during listening and learning states before forwarding, impacting user experience on access ports.
- Combining PortFast and BPDU Guard on user-facing access ports ensures rapid forwarding while maintaining network topology integrity against misconnected switches.
- BPDU Guard reacts to unexpected BPDUs on edge ports by shutting down the port, effectively protecting the network from accidental switch uplinks.
- PortFast should only be enabled on ports connected to end devices, never on ports connecting to other switches, to avoid STP topology issues.
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 enables immediate transition of edge switch ports to the forwarding state, bypassing STP's listening and learning delays to speed up host connectivity.
What is the correct answer to this question?
The correct answer is: PortFast on user-facing access ports — PortFast improves the user experience on edge ports, and BPDU Guard keeps those ports from becoming unintended switch uplinks.
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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