400-007 Cisco Exam Lab Questions

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.

The issue described is classic route flapping, where a single unstable prefix (10.1.5.0/24) causes repeated route withdrawals and advertisements, triggering churn in the BGP control plane across the entire network. This behavior can be mitigated using the following scalable and non-disruptive design approach:

D. Route Aggregation: Aggregating routes at the edge router (in this case, the LA router) means that multiple more specific prefixes (such as 10.1.4.0/24 through 10.1.7.0/24) are advertised as a single summarized prefix (e.g., 10.1.4.0/22). As a result, the instability of 10.1.5.0/24 will not affect upstream routers (Chicago and New York), as they will only see the aggregated route.

Key benefits aligned with CCDE v3.1 design guidance:

Isolates flapping to the edge while maintaining reachability

Reduces control plane churn in BGP

Preserves scalability and simplifies the routing table in upstream routers

Why other options are incorrect:

A (Route dampening): While effective, route dampening is less favored today due to convergence delay and side effects; it’s also a reactive measure versus a design-based solution.

B and C (Filtering): Filtering the route prevents reachability to that subnet, which violates availability requirements and causes data black-holing.

Thus, aggregation is the most scalable, nondisruptive, and design-aligned choice in this context.

OSPF uses pacing timers to control how quickly it sends LSAs to neighbors to prevent network flooding and CPU spikes:

C. Retransmission-pacing timer: Controls spacing between retransmitted LSAs queued after a lost or unacknowledged transmission.

E. Flood-pacing timer: Controls spacing between consecutive LSAs when flooding new information to peers.

These timers are critical in scaling OSPF in dense or unstable topologies and are key to tuning control plane convergence performance without destabilizing routers.

A (Risk-based and adaptive access policies): After verifying user identity within a Zero Trust architecture, the next logical step is to apply continuous, adaptive risk-based policies that evaluate contextual factors (device posture, behavior, location, etc.) before granting access. This approach dynamically responds to threats such as phishing attacks by adjusting access permissions based on real-time risk.

Other options explained:

B/C/D: These are supporting mechanisms, but risk-based policies directly address dynamic attack mitigation.