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400-007 · Question #88
400-007 Question #88: Real Exam Question with Answer & Explanation
The correct answer is A: The Reported Distance from a successor is lower than the local Feasible Distance.. EIGRP guarantees a loop-free alternate path only when the feasibility condition is satisfied (neighbor RD less than local FD) and a feasible successor is actually present in the topology table.
Question
Which two conditions must be met for EIGRP to maintain an alternate loop-free path to a remote network? (Choose two.)
Options
- AThe Reported Distance from a successor is lower than the local Feasible Distance.
- BThe Reported Distance from a successor is higher than the local Feasible Distance.
- CThe feasibility condition does not need to be met.
- DThe Feasible Distance from a successor is lower than the local Reported Distance.
- EA feasible successor must be present.
Explanation
EIGRP guarantees a loop-free alternate path only when the feasibility condition is satisfied (neighbor RD less than local FD) and a feasible successor is actually present in the topology table.
Common mistakes.
- B. A neighbor's RD being higher than the local FD fails the feasibility condition, meaning that neighbor could be a downstream router and is explicitly excluded as a feasible successor to prevent loops.
- C. The feasibility condition is mandatory and non-optional - it is the core mathematical guarantee within DUAL that ensures all feasible successors are loop-free without requiring full topology recalculation.
- D. This reverses the relationship: the feasibility check compares the candidate neighbor's RD against the local FD, not the successor's FD against a local RD, so this condition does not represent valid EIGRP logic.
Concept tested. EIGRP feasibility condition and feasible successor selection
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