What are two possible drawbacks of ending Loop-Free Alternate to support fast convergence for

Question

Options

• AThe IGP topology might need to be adjust
• BLoop-free alternate's convergence in less than 100 milliseconds is not possible
• CLoop-free alternate's are supported only for prefixes that are considered external tot the IGP
• DLoop-free alternates are not supported in global VPN VRF OSPF instances
• EAdditional path computations are needed

Explanation

Loop-Free Alternate (LFA) Drawbacks

The two correct answers are A and E.

Why A and E are correct: LFA (IP Fast Reroute) requires the router to pre-compute backup next-hops using additional SPF calculations beyond the primary path computation - this extra processing load is a tangible drawback (E). Furthermore, LFA coverage is topology-dependent; not every destination will have a qualifying loop-free alternate, which may force network engineers to redesign or tune the IGP topology to improve coverage (A).

Why the distractors are wrong:

• B is incorrect because achieving sub-50ms (well under 100ms) convergence is precisely the goal and capability of LFA - this is a strength, not a limitation.
• C is backwards; LFA is primarily applied to internal IGP prefixes, not external ones. External prefix support is actually more limited.
• D is a very specific platform/implementation constraint (VRF OSPF support), not a general architectural drawback of LFA as a technology.

Memory tip: Think of LFA's two costs as "Compute + Configure" - you pay extra in computation (more SPF runs) and may need extra configuration effort (topology adjustments) to ensure backup paths actually exist for all destinations.

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