The answer is increasing the BGP hold timer, route summarization, and BGP dampening. Increasing the hold timer gives a router more time to receive keepalive messages from a flapping peer, preventing premature neighbor resets and the associated routing table churn. Route summarization reduces the number of advertised prefixes, so a flapping specific subprefix is hidden behind a stable aggregate, limiting control-plane propagation. BGP dampening applies a penalty to a flapping prefix, suppressing its advertisement until it stabilizes. On the Cisco SPCOR 350-501 exam, this question tests your understanding of BGP prefix flapping mitigation techniques in a service provider context; a common trap is confusing dampening with route filtering, but dampening is reactive, not proactive. A useful memory tip is “DHS” — Dampening, Hold timer, Summarization — to recall the three core mitigation actions.
350-501 Networking Practice Question
This 350-501 practice question tests your understanding of networking. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 THREE actions can help mitigate the impact of BGP prefix flapping in a service provider network?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use route summarization.
Route summarization (A) reduces the number of BGP prefixes advertised, which inherently limits the impact of flapping because a single summary prefix represents many more-specific prefixes. If a specific subprefix flaps, the aggregate remains stable, preventing the flapping from propagating to BGP peers. This is a proactive approach to minimize the control-plane churn caused by unstable routes.
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.
✓
Use route summarization.
Why this is correct
Summarization aggregates multiple prefixes, reducing the impact of individual flaps.
Related concept
Read the scenario before looking for a memorised answer.
✓
Implement route dampening.
Why this is correct
Route dampening suppresses flapping prefixes by assigning penalties.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use BGP peer groups.
Why it's wrong here
Peer groups reduce configuration and CPU overhead but do not mitigate flapping.
✓
Increase the BGP hold timer.
Why this is correct
A longer hold timer gives more time for a flapping peer to stabilize before being declared down.
Related concept
Read the scenario before looking for a memorised answer.
✗
Apply BGP graceful restart.
Why it's wrong here
Graceful restart preserves forwarding during control plane restart, not for flapping.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between mechanisms that reduce control-plane churn (summarization, dampening) versus those that maintain forwarding during failures (graceful restart), leading candidates to incorrectly select graceful restart as a flapping mitigation tool.
Detailed technical explanation
How to think about this question
Route dampening (B) uses configurable penalty values (default 1000 per flap) and reuse/suppress thresholds (e.g., suppress at 2000, reuse at 750) to temporarily suppress flapping prefixes, reducing BGP update churn. Increasing the BGP hold timer (D) from the default 180 seconds to a higher value (e.g., 240 seconds) gives the router more time to detect a session failure, which can prevent premature session resets during transient flapping, but it does not filter prefix-level instability. In real-world scenarios, combining summarization with dampening is common to protect the control plane from unstable customer prefixes.
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 practitioner preparing for the 350-501 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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.
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use route summarization. — Route summarization (A) reduces the number of BGP prefixes advertised, which inherently limits the impact of flapping because a single summary prefix represents many more-specific prefixes. If a specific subprefix flaps, the aggregate remains stable, preventing the flapping from propagating to BGP peers. This is a proactive approach to minimize the control-plane churn caused by unstable routes.
What should I do if I get this 350-501 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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