350-501 Question #53: Real Exam Question with Answer & Explanation

Question

On Cisco IOS XR devices, which action improves failure reaction for Link OAM when Path Isolation with Ethernet Failure Detection is used?

Options

• ABring down the line protocol interface state when a problem is detected
• BClose the gap when UDLD detects that Ethernet ports are miswired
• CChange the interface status to error-disable operating at Layer 1
• DTriggers port suspend when heartbeat is lost

Explanation

To improve failure reaction for Link OAM with Path Isolation on Cisco IOS XR, the line protocol interface state is brought down when a problem is detected, ensuring rapid network convergence.

Common mistakes.

• B. UDLD is designed to detect unidirectional links due to miswiring or port errors, which is a different specific fault domain than general Link OAM path isolation failure detection, and 'close the gap' is not a standard action for improving failure reaction in this context.
• C. While error-disable is a type of interface state, Link OAM primarily operates at Layer 2. Bringing down the line protocol state, which implies L2/L3 communication cessation, is a more direct and impactful way for Link OAM to signal a failure to the overall network.
• D. 'Port suspend' might be a specific action, but bringing down the line protocol interface state is a more comprehensive and universally understood mechanism for a link failure to immediately impact network routing and improve overall failure reaction.

Concept tested. Cisco IOS XR Link OAM failure reaction

Reference. https://www.cisco.com/c/en/us/td/docs/iosxr/ncs500/routing/b-routing-ncs5k-iosxr-53x-book/b-routing-ncs5k-iosxr-53x-book_chapter_0100.html#concept_3C523B06297C474D90CE15EF8214300D

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