352-011 · Question #38
Which mechanism provides fast path failure detection?
The correct answer is E. Fast hello packets. Fast hello packets directly address failure detection speed by reducing the hello interval between routing protocol neighbors (e.g., from the default 10 seconds down to 1 second or less), so a dead neighbor is identified in milliseconds to seconds rather than tens of seconds…
Question
Which mechanism provides fast path failure detection?
Options
- ANon-Stop Forwarding
- BCarrier delay
- CGraceful restart
- DUDLD
- EFast hello packets
- FiSPF
How the community answered
(43 responses)- A5% (2)
- B9% (4)
- C2% (1)
- D2% (1)
- E81% (35)
Explanation
Fast hello packets directly address failure detection speed by reducing the hello interval between routing protocol neighbors (e.g., from the default 10 seconds down to 1 second or less), so a dead neighbor is identified in milliseconds to seconds rather than tens of seconds.
Why the distractors are wrong:
- A. Non-Stop Forwarding (NSF) - Keeps traffic flowing during a control-plane restart; it's about survivability after a failure is detected, not detecting one.
- B. Carrier delay - Actually slows detection by delaying interface state-change notifications to suppress flapping; the opposite of fast detection.
- C. Graceful restart - Lets a router preserve forwarding state while its routing process restarts; again, a continuity mechanism, not a detection mechanism.
- D. UDLD (Unidirectional Link Detection) - Detects a specific condition (one-way traffic on a link), not general path failures, and operates on a slower timescale.
- F. iSPF (Incremental SPF) - Speeds up convergence by only recomputing affected SPF tree branches after a failure is already known; it does nothing to detect the failure itself.
Memory tip: The word "fast" is in the answer itself - Fast hello packets = fast failure detection. If a choice literally contains the word from the question goal, that's your signal.
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