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352-001 · Question #792
352-001 Question #792: Real Exam Question with Answer & Explanation
The correct answer is B: Ti-LFA. Ti-LFA and MPLS-FRR both rely on pre-computed backup paths that activate in under 50ms upon link failure, without waiting for full routing reconvergence.
Question
Which two design solutions ensure sub 50 msec of the convergence time after a link failure in the network? (Choose two)
Options
- ABFD
- BTi-LFA
- Cminimal BGP scan time
- DMPLS-FRR
- EIGP fast hello
Explanation
Ti-LFA and MPLS-FRR both rely on pre-computed backup paths that activate in under 50ms upon link failure, without waiting for full routing reconvergence.
Common mistakes.
- A. BFD accelerates failure detection but is only a detection mechanism; the actual convergence speed still depends on the reaction of the routing protocol, which alone does not guarantee sub-50ms restoration.
- C. Reducing the BGP scan timer improves BGP convergence speed but does not provide pre-computed local repair, so restoration times typically remain well above 50ms.
- E. IGP fast hellos shorten failure detection time but do not install pre-computed backup paths, meaning the network must still wait for full SPF recalculation and RIB/FIB updates before traffic is restored.
Concept tested. Sub-50ms convergence using FRR pre-computed backup paths
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