You are designing a new multisite data center network within the same city. You are using the newest routers that run OSPF and DWDM point-to-point interfaces for site-to-site connectivity. Your…

Question

Options

• AUDLD
• BInterface event dampening
• CLoS/AIS event faults
• DFast-hello timers

• A
  11% (5)
• B
  4% (2)
• C
  64% (29)
• D
  20% (9)

Explanation

LoS (Loss of Signal) and AIS (Alarm Indication Signal) are hardware-level optical events built into DWDM interfaces that trigger the instant a fiber link fails - no timer expiration or protocol exchange required. Because DWDM operates at the optical (physical) layer, the transceiver detects signal loss in microseconds, making it the absolute fastest failure detection mechanism available.

Why the distractors are wrong:

• A. UDLD detects unidirectional Ethernet link failures using periodic Layer 2 hello messages - it's protocol-based, slower, and designed for Ethernet, not optical DWDM.
• B. Interface event dampening actually slows response to failures by suppressing flapping interfaces to prevent route instability - the opposite of fast detection.
• D. Fast-hello timers reduce OSPF dead-interval detection from 40 seconds down to ~1–3 seconds, but they still depend on timer expiration. Hardware-layer LoS/AIS is orders of magnitude faster.

Memory tip: Map the layer to the speed - optical hardware signals (LoS/AIS) never wait for a timer, while protocols (OSPF hellos, UDLD) always do. On a DWDM question asking for the fastest detection, always pick the mechanism closest to Layer 1 physics.

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