352-001 · Question #122
What are the two preferred mechanisms for detecting Layer 2 link failures quickly? (Choose two.)
The correct answer is A. BFD D. loss of signal. BFD and loss of signal are the two preferred fast Layer 2 link failure detection mechanisms because they operate at or near the physical layer with minimal detection latency.
Question
What are the two preferred mechanisms for detecting Layer 2 link failures quickly? (Choose two.)
Options
- ABFD
- Bfast RSVP hellos
- CLDP keepalives
- Dloss of signal
How the community answered
(36 responses)- A92% (33)
- B6% (2)
- C3% (1)
Why each option
BFD and loss of signal are the two preferred fast Layer 2 link failure detection mechanisms because they operate at or near the physical layer with minimal detection latency.
BFD (Bidirectional Forwarding Detection) is a dedicated, lightweight protocol designed to detect forwarding path failures in milliseconds, making it the standard mechanism for rapid link failure detection independent of any specific routing protocol.
Fast RSVP hellos are used for MPLS traffic engineering path failure detection, not for detecting Layer 2 link failures at the interface level.
LDP keepalives are used to maintain MPLS Label Distribution Protocol sessions and detect LDP peer failures, not Layer 2 physical link failures.
Loss of signal is an immediate physical-layer indicator of a link failure, providing sub-millisecond detection as hardware directly senses the absence of an electrical or optical signal on the interface.
Concept tested: Layer 2 link failure fast detection mechanisms
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/bfd/configuration/xe-16/bfd-xe-16-book/bfd-main.html
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