400-007 Exam Dumps - Cisco Certified Design Expert (CCDE v3.1)

STP Bridge Assuranceis a mechanism used to protect againstunidirectional link failureson point-to-point STP connections in environments likeRapid PVST+ and MST. When Bridge Assurance is enabled, BPDUs are expected on all BPDUs-capable interfaces. If a switch stops receiving BPDUs on a point-to-point link where Bridge Assurance is enabled, it assumes the link has failed and transitions the port to blocking to prevent a loop.

This is especially useful in high-availability enterprise designs that require protection from unexpected switch behavior or partial link failures.

Why other options are incorrect:

A. BPDU Guard: Protects access ports by placing them in an err-disabled state if BPDUs are received—useful at the edge, not for core loop protection.

C. MSTP: Refers to the protocol itself but does not solve the unidirectional link issue on its own.

D. TRILL: A different architecture (layer 2 routing) and not applicable to Rapid PVST+ or MST-specific protection.

Fate-sharing describes a situation where two or more services or components are tied together such that failure in one leads to failure in others. In resilient design, the goal is often to eliminate fate-sharing by decoupling dependencies.

A: A single point of failure (like a shared power supply or converged service path) that brings down multiple components exemplifies fate-sharing.

B is incorrect because fate-sharing is a risk, not a protective measure.

C and D refer to device behavior (stateful inspection, transport layer behavior) rather than architectural dependency.

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B (R1 adjusts to R2’s Required Min RX):In BFD, each side advertises itsDesired Min TX IntervalandRequired Min RX Interval. Each device adjusts its transmission interval to match the remote side’s ability to receive packets (Required Min RX). So R1 reduces its transmission rate to 100 ms to match R2 ' s platform limitations.

Other options explained:

A: R2 does not adjust to R1’s Desired Min TX; it’s the sender who adapts.

C: BFD quickly converges after initial negotiation.

D: P-bit and F-bit are not involved in this specific interval negotiation.

Application performance depends on the end-to-end delay experienced by the traffic, which includes:

Queuing delay at each device.

Serialization delay based on link speed and packet size.

Propagation delay.

For the application to meet its performance SLA, the total of all delays (queuing + serialization + propagation) must remain within the application ' s maximum tolerable delay budget. This is critical for delay-sensitive applications such as voice or real-time video.

This directly aligns with CCDE v3.1 business-driven design, where application requirements dictate network performance guarantees.

Why other options are incorrect:

A: Focusing on individual devices ignores cumulative delay.

B: Uniform queuing delay isn’t practical or necessary.

C: Default queue sizes are not always suitable for real-time applications.

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