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

C (Synchronous replication across data centers):Synchronous replication ensures zero or near-zero data loss (very low RPO), as data is written simultaneously to both sites. For an RPO of under 10 seconds, synchronous replication is mandatory.

Other options explained:

A: Asynchronous replication may result in higher RPO.

B/D: Single site designs introduce single points of failure for business continuity.

During massive BGP update events (such as after a topology change), a route reflector may struggle processing both BGP updates and the resulting TCP acknowledgments required for reliable BGP session communication.

Increasing the hold queue size allows the router to buffer more packets waiting for processing (including TCP acknowledgments), helping the router handle bursts of BGP updates without dropping TCP segments or tearing down sessions.

This queue tuning is a well-known scalability optimization in CCDE v3.1 when designing route reflector clusters handling large-scale control plane updates.

Why other options are incorrect:

B & C: Adjusting buffer sizes does not directly address TCP acknowledgment backlog.

D: Keepalive timers control session liveliness, not update processing.

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D (Aggregation layer termination):The aggregation layer is the ideal demarcation for Layer 2 interconnects because it maintains clear boundaries between Layer 2 and Layer 3 domains, simplifies STP and routing design, and preserves hierarchical scalability.

Other options explained:

A: Core should remain strictly Layer 3 for scalability and stability.

B: Access-layer interconnection introduces STP complexity.

C: Security concerns are handled via policy, not termination layer

D (Deploy SD-WAN edge routers in data center, then controllers, then branches):This allows the SD-WAN fabric to be built and stabilized centrally first, then controllers are brought online for policy orchestration, and finally, branch migrations happen gradually without impacting existing traffic paths.

Other options explained:

A/B/C: These approaches risk service disruption or poor controller orchestration readiness during branch migrations.

Public cloud offers scalability, flexibility, and consumption-based pricing, which directly reduces capital expenditures (CAPEX) and minimizes operational burden (less IT staff needed for infrastructure maintenance).

Public cloud eliminates upfront hardware investments and shifts cost to predictable operational expenses.

Public cloud providers handle hardware maintenance, upgrades, and scalability, making it highly cost-effective for government agencies with fluctuating workloads.

Why other options are incorrect:

A: On-premises increases CAPEX and requires significant IT staff.

B: Private cloud reduces some OpEx but still requires infrastructure management and higher CAPEX.

D: Hybrid cloud increases complexity and operational costs.

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B (Encapsulation at source and destination):Overlay networks encapsulate payloads inside another protocol (e.g. VXLAN, GRE, MPLS), adding headers that enable separation from the underlay network while introducing minor overhead due to encapsulation.

Other options explained:

A: Describes underlay behavior.

C: Overlay encapsulation occurs independently of L3/L4 reliability.

D: NAT or VRF are isolation mechanisms but not how overlays function.

Inbound traffic engineering is best controlled by manipulating how external ASes view your routes.

AS path prepending on the 91.7.0.0/16 prefix towards AS 200 makes AS 500 prefer the less-prepended path through AS 100.

This allows granular inbound control for that specific prefix while leaving the rest of the traffic unchanged.

Why other options are incorrect:

B: Extended community is not used for direct inbound path manipulation.

C: Local preference affects outbound traffic, not inbound path selection by remote ASes.

D: MED is only compared between the same AS; it won't affect AS 500's choice.

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A (DAI - Dynamic ARP Inspection): Prevents ARP spoofing attacks on the data plane.

B (IP Source Guard): Prevents IP address spoofing by verifying IP/MAC bindings against DHCP snooping tables.

Both are directly applied to securing the data plane (traffic forwarding layer).

Why other options are incorrect:

C (BEEP): A transport protocol, not a data plane security feature.

D (CPPr): Protects the control plane, not data plane.

E (MPP): Protects management plane, not data plane.

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