352-001 · Question #77
Which two mechanisms can provide fast Layer 2 down detection in Frame Relay networks? (Choose two.)
The correct answer is A. asynchronous LMI C. A-bit signaling. Frame Relay fast Layer 2 down detection relies on asynchronous LMI status messages and A-bit signaling to detect PVC failures without waiting for polling intervals.
Question
Which two mechanisms can provide fast Layer 2 down detection in Frame Relay networks? (Choose two.)
Options
- Aasynchronous LMI
- Bmillisecond LMI timers
- CA-bit signaling
- DFrame BFD Lite
- Esection 9 LMI convergence
How the community answered
(37 responses)- A81% (30)
- B3% (1)
- D5% (2)
- E11% (4)
Why each option
Frame Relay fast Layer 2 down detection relies on asynchronous LMI status messages and A-bit signaling to detect PVC failures without waiting for polling intervals.
Asynchronous LMI allows a router to immediately send an unsolicited status enquiry rather than waiting for the normal polling timer, enabling near-instant detection of link state changes.
Standard LMI timers operate on a 10-second polling interval by default, and 'millisecond LMI timers' is not a defined Frame Relay mechanism for fast detection.
A-bit (Activity bit) signaling in Frame Relay LMI explicitly marks each DLCI as active or inactive in status messages; when the A-bit is cleared to 0 for a PVC, the router immediately knows that circuit is down without any timer expiration.
BFD (Bidirectional Forwarding Detection) is a separate protocol and 'Frame BFD Lite' is not a standard or recognized Frame Relay fast-detection mechanism.
'Section 9 LMI convergence' is not a real Frame Relay specification or standard mechanism for down detection.
Concept tested: Frame Relay LMI fast PVC down detection
Source: https://www.cisco.com/c/en/us/support/docs/wan/frame-relay/16571-lmi.html
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