Pass the Cisco CCDE v3.0 400-007 Questions and answers with CertsForce

Low-Latency Queuing (LLQ) offers strict priority queuing to real-time traffic (voice/video), ensuring minimal delay, jitter, and packet loss.

This satisfies real-time application requirements which are extremely sensitive to delay variation.

Why other options are incorrect:

A: WFQ offers fairness but no strict prioritization.

B: WRED avoids congestion but is not suited for real-time traffic.

D: FIFO provides no QoS differentiation.

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Let’s calculate total 1-year cost for each option using the provided table:

DWDM over dark fiber:

CAPEX = $250,000

OPEX (1 year) = $100,000

Installation fee = $30,000

Total = $250,000 + $100,000 + $30,000 = $380,000

CWDM over dark fiber:

CAPEX = $150,000

OPEX (1 year) = $100,000

Installation fee = $25,000

Total = $150,000 + $100,000 + $25,000 = $275,000

MPLS wires only:

CAPEX = $50,000

OPEX (1 year) = $80,000

Installation fee = $5,000

Total = $50,000 + $80,000 + $5,000 = $135,000

BUT: MPLS does not allow customer-controlled QoS policies as stated in the requirement (cannot run its own varying QoS profiles without SP interaction). Therefore disqualified.

Metro Ethernet:

CAPEX = $45,000

OPEX (1 year) = $100,000

Installation fee = $5,000

Total = $45,000 + $100,000 + $5,000 = $150,000

BUT: Metro Ethernet is also typically a service provider-managed solution where customer-controlled QoS is usually limited depending on SP capabilities. May not fully meet the requirement.

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The key technical requirement:

“Be able to run its own varying QoS profiles without service provider interaction.”

This clearly favors dark fiber solutions (CWDM and DWDM), as these give full Layer 1 control to the customer, allowing complete freedom in managing QoS, traffic engineering, and prioritization internally.

Among the two dark fiber options, CWDM over dark fiber is the most cost-effective choice for one year at $275,000.

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Therefore, final correct answer:

B (IPsec): Provides encryption over the public Internet for secure data transfer.

C (DMVPN): Creates a dynamic, scalable private WAN overlay across the Internet allowing direct site-to-site connectivity.

Why other options are incorrect:

A: S-VTI requires more static configuration and lacks DMVPN’s scalability.

D: GET VPN is best for MPLS/private WAN, not Internet underlays.

E: PPTP is outdated and insecure.

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PBR overrides the normal routing table behavior, potentially leading to microloops during reconvergence because forwarding decisions are based on policies rather than updated routing tables.

During fast topology changes, PBR decisions may not adapt as quickly as dynamic routing protocols, causing brief routing inconsistencies.

Why other options are incorrect:

A: PBR can add complexity but does not inherently limit scalability.

C/D: PBR does not directly affect convergence speed but can introduce inconsistency.

Increasing jitter buffer size smoothens jitter but at the cost of introducing additional delay.

Excessive jitter buffering can lead to perceptible audio or video lag, impacting user experience.

C: Therefore, the undesired effect is increased transport delay, potentially leading to quality issues if the buffer size is too large.

Why other options are incorrect:

A and D: Jitter buffering does not improve jitter itself; it masks it at the expense of delay.

B: Jitter compensation doesn ' t increase jitter, but delay.

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A (BPDU Guard on access ports): Prevents accidental connection of switches or bridging devices on access ports, which could cause unexpected topology changes or loops.

C (Root Guard on aggregation switch downlinks): Ensures access switches cannot send superior BPDUs to challenge aggregation switch root status, maintaining predictable STP root placement.

Why other options are incorrect:

B: Aggregation downlinks are not normally configured with BPDU Guard (since they expect BPDUs from access switches).

D: Root guard on access ports is unnecessary as those ports should not participate in STP.

E: Edge port (Rapid STP concept) is good for faster convergence but doesn ' t address stability.

F: STP root and backup root election is important but not a specific STP feature — this is a design decision, not a stability feature.

B (EAP - Extensible Authentication Protocol):EAP is commonly used for 802.1X port-based authentication, allowing identity-based control for users on the network. This enables policy enforcement, identity-based segmentation (micro/macro segmentation), and leverages existing domain credentials via backend integration.

Other options explained:

A: LDAP is backend directory, not an authentication protocol for access ports.

C: TACACS+ is used primarily for administrative access.

D: RADIUS transports the EAP exchange but is not the authentication protocol itself.

D (Lifecycle model):The lifecycle model aligns directly with traditional project management (such as Waterfall). It follows a sequential, phase-driven process: requirement gathering, design, implementation, testing, and maintenance. Each phase must be completed before moving to the next, with defined milestones and documentation.

Other options explained:

A: " Static model " is not a standard recognized development model.

B: Agile is iterative and adaptive, opposite of traditional models.

C: Evolutionary delivery is more incremental, not fully aligned with traditional models.

C (Scalable):For rapidly growing or contracting businesses, scalability is the highest priority to ensure that the network can adapt to changes in size, services, and demand without major redesigns.

Other options explained:

A: Hierarchical design improves structure but does not guarantee scalability.

B: Modularity aids scalability but is a design approach, not the ultimate priority.

D: A dedicated core is part of hierarchical designs but not always essential for startups.