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352-001 · Question #480
352-001 Question #480: Real Exam Question with Answer & Explanation
The correct answer is D: Deploy LFA.. Loop-Free Alternates (LFA) reduce IGP microloops by providing pre-computed backup next-hops that are mathematically guaranteed to be loop-free during convergence.
Question
Which design option reduces the occurrence of IGP microloops?
Options
- ADeploy LSA throttle.
- BTune the SPF hold time to be lower than the SPF runtime on all nodes.
- CTune the SPF runtime to be lower than the SPF hold time on all nodes.
- DDeploy LFA.
Explanation
Loop-Free Alternates (LFA) reduce IGP microloops by providing pre-computed backup next-hops that are mathematically guaranteed to be loop-free during convergence.
Common mistakes.
- A. LSA throttle controls the rate at which LSAs are originated and flooded to reduce CPU load, but it does not prevent microloops that arise from asynchronous SPF completion and route installation across different nodes.
- B. Setting SPF hold time lower than SPF runtime is operationally contradictory and does not resolve microloops - microloops are caused by different nodes installing updated routes at different times, which is independent of the inter-SPF hold interval.
- C. SPF runtime is governed by topology size and algorithm complexity and is not directly configurable; even if all nodes ran SPF faster, asynchronous route installation across nodes would still produce transient microloops during convergence.
Concept tested. IGP microloop reduction using LFA fast-reroute
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