A client has approached you about deploying very fast IS-IS hello timers across an intercontinental high speed SONET link. What should you recommend?

Question

Options

• AFast hello timers are a good choice for this link because on long haul SONET links the reporting
• BFast hello timers are not a good choice for this link because the link is physically long and the
• CFast hello timers are a good choice for this link because the length of the link indicates there will
• DFast hello timers are not a good choice for this link because SONET links provide link-down

• A
  3% (1)
• B
  3% (1)
• C
  12% (4)
• D
  82% (27)

Explanation

Fast IS-IS hello timers are unnecessary on SONET links because SONET provides built-in physical-layer link failure detection through its OAM (Operations, Administration, and Maintenance) mechanisms. When a SONET link fails, the hardware immediately signals a link-down event to the router without waiting for hello timer expiration. Fast hello timers exist to accelerate failure detection on media that lacks this native signaling (e.g., Ethernet). Deploying them on SONET only wastes bandwidth and CPU cycles. The intercontinental distance is irrelevant to this decision - SONET's native failure detection is the key factor.

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