The answer is UplinkFast and BackboneFast, two Cisco-proprietary STP features designed specifically to improve convergence time after a topology change. UplinkFast accelerates recovery when a switch’s root port fails by immediately transitioning an alternate root port to forwarding, bypassing the usual 30-second listening and learning delay through artificially lowering the switch’s bridge priority to trigger a topology change notification. BackboneFast reduces convergence time by detecting indirect link failures in the backbone, allowing a switch to expire its Max Age timer immediately rather than waiting the full 20 seconds, thus speeding the transition to a new root port. On the ENCOR 350-401 exam, these features often appear in questions about STP optimization, with a common trap being confusion over which feature handles direct versus indirect failures. A helpful memory tip: UplinkFast fixes your own broken link (direct failure), while BackboneFast fixes a broken link somewhere else in the backbone (indirect failure).
CCNP Network Assurance Practice Question
This 350-401 practice question tests your understanding of network assurance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which TWO STP features are used to improve convergence time after a topology change?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
UplinkFast
UplinkFast is correct because it enables a switch to immediately use an alternate root port when its current root port fails, bypassing the usual 30-second listening and learning delay. This is achieved by artificially lowering the bridge priority of the switch to trigger a topology change notification, allowing the backup port to transition directly to forwarding. BackboneFast is correct because it reduces convergence time by detecting indirect link failures in the backbone and allowing a switch to expire its Max Age timer (default 20 seconds) immediately, rather than waiting for the full timer to expire, thus speeding up the transition to a new root port.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
UplinkFast
Why this is correct
UplinkFast accelerates convergence after a direct link failure.
Related concept
Read the scenario before looking for a memorised answer.
✓
BackboneFast
Why this is correct
BackboneFast reduces convergence time after an indirect link failure.
Related concept
Read the scenario before looking for a memorised answer.
✗
Root Guard
Why it's wrong here
Root Guard prevents a switch from becoming root, but does not improve convergence.
✗
BPDU Guard
Why it's wrong here
BPDU Guard is a security feature to prevent rogue switches.
✗
PortFast
Why it's wrong here
PortFast is for immediate transition to forwarding on access ports, not for convergence after topology change.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between features that improve convergence (UplinkFast, BackboneFast) versus features that provide security or edge-port behavior (Root Guard, BPDU Guard, PortFast), leading candidates to mistakenly select PortFast because it also speeds up initial port transition, but it does not react to topology changes.
Detailed technical explanation
How to think about this question
UplinkFast works by simulating a topology change and sending multicast frames with a dummy MAC address to flush the CAM tables of downstream switches, while BackboneFast relies on the receipt of an inferior BPDU on a blocked port to trigger a Root Link Query (RLQ) protocol exchange, which confirms the root bridge is still reachable and allows immediate expiration of the Max Age timer. In real-world scenarios, combining UplinkFast and BackboneFast can reduce STP convergence from 30-50 seconds to under 5 seconds, which is critical for high-availability networks like data centers or VoIP environments.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Assurance — This question tests Network Assurance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: UplinkFast — UplinkFast is correct because it enables a switch to immediately use an alternate root port when its current root port fails, bypassing the usual 30-second listening and learning delay. This is achieved by artificially lowering the bridge priority of the switch to trigger a topology change notification, allowing the backup port to transition directly to forwarding. BackboneFast is correct because it reduces convergence time by detecting indirect link failures in the backbone and allowing a switch to expire its Max Age timer (default 20 seconds) immediately, rather than waiting for the full timer to expire, thus speeding up the transition to a new root port.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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