400-007 Cisco Certified Design Expert (CCDE v3.1) Free Practice Exam Questions (2025 Updated)

In service provider Ethernet transport environments such as VPLS, Ethernet OAM (Operations, Administration, and Maintenance) is used to provide fault detection, monitoring, and troubleshooting capabilities. The two relevant components here are:

A (Unicast heartbeat messages between MEPs): Maintenance End Points (MEPs) are configured at the edges of the OAM domain (SP-SW1 and SP-SW2). Heartbeat messages can be used to proactively monitor and detect loss of continuity between the endpoints.

B (Enable Connectivity Fault Management): CFM (IEEE 802.1ag) provides end-to-end fault detection, continuity check messages (CCMs), loopback, and link trace mechanisms that operate between MEPs at Layer 2. CFM enables proactive detection of failures and service-level assurance across the provider’s Ethernet segment.

Other options explained:

C: Upward MEPs are not applicable here since these are typically used for customer-facing or hierarchical maintenance domains.

D: E-LMI (Ethernet Local Management Interface) operates between CE and PE for service activation—not applicable for SP-SW to SP-SW fault detection across VPLS.

E: LLDP (Link Layer Discovery Protocol) is for neighbor discovery on directly connected interfaces—not suitable for end-to-end fault detection across a VPLS domain.

This design solution aligns fully with CCDE v3.1 principles for service provider Layer 2 VPN design and Ethernet OAM integration.

B (MPLS over BGP over mGRE):This design allows enterprises to run MPLS VPNs across their own infrastructure (Overlay VPN) while using MP-BGP for control plane distribution of VPNv4 routes. The mGRE tunnel structure allows scalability as branches grow, while MPLS VPN labels ensure traffic separation.

Other options explained:

A: EIGRP OTT is not scalable for large VPN deployments.

C: DMVPN per VRF becomes complex with high scale growth.

D: Point-to-point GRE per VRF lacks scalability for 60+ sites.

B (MST — Multiple Spanning Tree): Bundles multiple VLANs into fewer STP instances, minimizing the scope of TCN propagation, which helps reduce MAC table flushing and unicast flooding.

Why other options are incorrect:

A: PVRSTP still processes TCNs per VLAN, increasing flooding.

C: Legacy STP behaves similarly but is not optimized for multiple VLANs.

D: PVSTP+ generates TCNs per VLAN like PVRSTP.

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B (OpenConfig):OpenConfig YANG models are vendor-neutral, community-driven standards designed to simplify multi-vendor network automation and interoperability — ideal for heterogeneous SDN fabrics.

Other options explained:

A: Proprietary models limit flexibility and interoperability.

C: Native models are vendor-specific.

D: IETF YANG models exist but are not as comprehensive for full operational SDN automation as OpenConfig.

B (Use only secure protocols): Management and administrative access to Internet edge routers must use secure protocols (SSH, SNMPv3, HTTPS) to prevent interception or unauthorized access.

E (Restrict administrative access): Limiting administrative access via interface ACLs and clear login banners ensures that only authorized personnel can access the system, satisfying compliance and security requirements.

Other options explained:

A: Filtering infrastructure IP space is good hygiene but not directly related to compliance.

C: Logging is valuable for operations and incident response but not a compliance control by itself.

D: EBGP advertisements relate to routing policy, not compliance regulation.

SNMPv3 is recommended as it supports authentication and encryption, protecting SNMP traffic even across service provider MPLS VPN backbones.

Healthcare environments require strong privacy and compliance (e.g., HIPAA), making SNMPv3 the correct protocol.

Why other options are incorrect:

B & C: Syslog is unrelated to SNMP traps.

D: SNMPv2 lacks security (unencrypted community strings).

E: SSH secures CLI access but not SNMP.

C. Fragment data packets: On slow WAN links, large data packets can delay small voice packets (serialization delay). Fragmentation ensures that voice packets are interleaved and not delayed behind large data frames (Link Fragmentation and Interleaving - LFI).

E. Prioritize voice packets: QoS mechanisms (LLQ, priority queuing) ensure that voice traffic is serviced first, reducing jitter and delay.

These are both critical QoS design principles for real-time application performance in constrained branch WAN scenarios, as outlined in CCDE v3.1.

Why other options are incorrect:

A: Increasing bandwidth may help but doesn’t address serialization or prioritization.

B: Memory upgrades do not directly improve voice quality.

D: Fiber upgrades do not address WAN-specific serialization or QoS.

D (GRE Key and Sequence Number extensions):The GRE Key field provides session identification for distinguishing between multiple GRE tunnels. The Sequence Number extension allows endpoints to track packet ordering and detect lost or out-of-order packets, enhancing reliability at the tunnel level if required.

Other options explained:

A: Protocol Type identifies payload type; Checksum detects errors but doesn't provide sequencing.

B: GRE Version and Reserved0 fields are not used for session or sequencing.

C: GRE does support optional extensions, contrary to this statement.

Let’s calculate the total cost for each solution based on the most likely maximum duration (20 + 10 = 30 months) to ensure conservative, flexible planning.

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DWDM over dark fiber:

CAPEX = $200,000

OPEX (annual): $100,000⇒for 30 months = (2.5 × $100,000) = $250,000

Installation fee = $30,000

Total = $200,000 + $250,000 + $30,000 = $480,000

CWDM over dark fiber:

CAPEX = $150,000

OPEX (annual): $100,000⇒for 30 months = (2.5 × $100,000) = $250,000

Installation fee = $25,000

Total = $150,000 + $250,000 + $25,000 = $425,000

MPLS wires only:

CAPEX = $50,000

OPEX (annual): $180,000⇒for 30 months = (2.5 × $180,000) = $450,000

Installation fee = $5,000

Total = $50,000 + $450,000 + $5,000 = $505,000

Metro Ethernet:

CAPEX = $65,000

OPEX (annual): $100,000⇒for 30 months = (2.5 × $100,000) = $250,000

Installation fee = $5,000

Total = $65,000 + $250,000 + $5,000 = $320,000

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Analysis:

Metro Ethernet has the lowest overall cost at $320,000 and provides sufficient flexibility for workload migration since "all connectivity options meet technical requirements."

Metro Ethernet is typically more flexible than DWDM/CWDM for temporary or dynamic migration projects because it does not require optical expertise or complex dark fiber management.

MPLS is more expensive here and less flexible for large-scale Layer 2 migrations.

CWDM/DWDM are suitable for permanent solutions where long-term investment is justified, but not optimal here due to cost.

Therefore, best ROI and flexibility: Metro Ethernet

Final correct answer: D

In OSPF multi-area designs with multiple ABRs, when there is temporary inconsistency between the ABRs’ type-3 summary LSAs, microloops can occur during convergence. These loops happen due to slight differences in LSA arrival and SPF calculations across routers while the network is converging.

Microloops are short-lived but can cause brief packet loss.

This becomes more likely as the number of ABRs grows and IGP flooding domains increase.

CCDE v3.1 emphasizes careful ABR design and possible use of loop avoidance mechanisms (e.g., LFA, microloop prevention techniques) in large-scale OSPF designs.

Why other options are incorrect:

A: LSA flooding in OSPF scales well; type-3 LSA replication is not the primary scalability issue.

B: ABRs process all LSAs regardless; load is not split.

D: Multiple ABRs all independently summarize and advertise into the backbone.

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SNMPv1 and SNMPv2c use plaintext community strings and lack built-in encryption or authentication, making them vulnerable to various attacks, including spoofing and message tampering. SNMPv3 addresses these weaknesses by introducing:

Authentication (to prevent impersonation or "masquerade")

Encryption (privacy)

Message integrity

“Masquerade threats” involve an attacker pretending to be a trusted source, which SNMPv3 can prevent via cryptographic authentication mechanisms.

Although SNMPv3 does provide improved security features like integrity and privacy, it is not specifically designed to mitigate volumetric attacks like DDoS or dictionary brute-force. SNMPv3 does not inherently stop man-in-the-middle attacks unless secure key exchanges and trusted paths are fully enforced, which may require additional protocols.

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The IoT ecosystem continues to evolve around industry-wide agreements on protocols, frameworks, security, interoperability, and standards:

D: Multiple IoT consortia (such as Industrial Internet Consortium, Open Connectivity Foundation, etc.) are still developing open frameworks and interoperability models.

E: IoT standards for security, data privacy, management, and protocol interoperability are still maturing as the market rapidly evolves.

Why other options are incorrect:

A: Wi-Fi protocols (such as 802.11ax) are already mature and standardized for IoT.

B: Regulatory domains (frequency allocations, power levels) are already well-established.

C: Low-energy Bluetooth sensors are already standardized and widely implemented.

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Zero Trust principles cover multiple domains:

A (Workload): Securing application workloads regardless of location.

C (Workplace): Securing user access to services across office, remote, or hybrid work models.

Zero Trust design ensures authentication, authorization, and policy enforcement at every access point for both users and applications.

Why other options are incorrect:

B, D, E: These terms are not recognized Zero Trust domains in CCDE or industry frameworks.

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D (Neighbor Discovery):Control plane actions manage routing and signaling, such as ND discovering routers in IPv6. The control plane manages state and network intelligence, while data plane performs forwarding.

Other options explained:

A/B/C: These describe data plane forwarding operations.

D (Enables innovation):SDN allows new services, business models, and automation capabilities.

E (OpEx/CapEx reduction):Automation reduces operational effort, and commodity hardware reduces CapEx.

Other options explained:

A: Redundancy depends on physical design.

B: SDN centralizes management.

C/F: SDN doesn't directly impact latency or capacity.

A modular, scalable network design aims to:

Localize faults

Reduce impact radius of failures

Enable automated fault detection and recovery

The primary operational driver is to reduce the need for manual intervention during failures, which translates to:

Faster recovery times

Consistency in troubleshooting

Improved service reliability

While minimizing app downtime (B) is a goal, it is a result of reducing human-required failure recovery. Option C is a business process goal, and D is an architectural challenge, not an operational driver.

This aligns with CCDE v3.1's “Network Architecture Principles” for building operationally resilient networks.

B (IPFIX telemetry data):IPFIX provides detailed flow-level visibility, enabling identification of traffic patterns, data flows, and destinations. This data is critical for understanding current traffic behavior to identify governance gaps and improve policy compliance.

Other options explained:

A: Secure tunnels protect traffic but do not identify governance gaps.

C: Firewalls provide limited flow visibility compared to telemetry.

D: Workload policies enforce security but do not aid initial visibility analysis.

B (OTV — Overlay Transport Virtualization): Allows Layer 2 extension across data centers while maintaining fault isolation by not extending STP across the WAN. Control plane handles MAC learning, which provides stability and loop avoidance between data centers.

Why other options are incorrect:

A: FabricPath is mainly for intra-data center Layer 2 fabric.

C: Advanced VPLS extends Layer 2 but carries STP across the WAN.

D: LISP operates at Layer 3, not for Layer 2 extension.

E: TRILL also focuses on intra-DC Layer 2 but not DCI fault isolation.

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D (L1/L2 for ABRs and L1 for internal routers):This hierarchical approach minimizes LSDB size inside areas (L1 routers only maintain intra-area routes) while L1/L2 routers handle inter-area route propagation, reducing neighbor adjacencies and improving scalability.

Other options explained:

A: Level 2 everywhere results in larger LSDBs across all routers.

B: Only L2 routers at ABRs would isolate L1 domains improperly.

C: Pure L1 design prevents inter-area reachability.

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