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

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E: PPTP is outdated and insecure.

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The primary goal of resilient modular network design is to minimize the operational impact of failures by automating recovery and isolating fault domains.

C: Reducing failures that require manual intervention improves availability, reduces downtime, and ensures stability even under fault conditions.

Why other options are incorrect:

A: This is a limitation to avoid, not a design driver.

B: Minimizing app downtime is an outcome, not the operational driver itself.

D: Development time is not related to operational network resiliency.

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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.

The scenario prioritizes:

In-house management (not managed services)

Scalability (exponential branch growth)

OPEX reduction (low operational cost)

SD-WAN over L3VPN offers a balance of:

Mid-level ISP cost (leveraging L3VPN as transport)

Centralized management and automation (ZTP, templates)

Support for segmentation, application-aware routing, and path control

Lower OPEX due to simplified configuration and monitoring

Managed SD-WAN has higher ISP and OPEX cost, and DMVPN is more manual and complex to scale. SD-WAN over L2VPN might reduce ISP cost but is less common and not optimal for rapid scalability.

Traffic shaping buffers excess traffic and smooths traffic bursts, which is essential for DaaS traffic sensitive to periodic link congestion across WAN circuits.

It helps ensure consistent, predictable performance under fluctuating WAN conditions.

Why other options are incorrect:

A: Tail drop leads to congestion and packet loss.

C: WRED is used for congestion avoidance, but not ideal for real-time DaaS traffic shaping.

D: Policing drops excess traffic instead of buffering, worsening DaaS disconnections.

A (Distinguishing between config and operational data):NETCONF was designed to provide structured data models (such as YANG), clearly separating configuration from operational state data. SNMP lacks this built-in distinction and generally treats all data as MIB objects.

Other options explained:

B/C/D: Both protocols can perform actions and retrieve or modify data, but only NETCONF natively differentiates config vs. operational state.

B (Strategic planning): Long-term business-aligned decisions that shape future infrastructure needs.

D (Tactical planning): Short-to-mid-term activities that adjust design based on evolving operational realities, constraints, and priorities.

Why other options are incorrect:

A & E: While cost and business optimization are goals, they are not defined planning approaches.

C: Modular is a design methodology, not a planning approach.

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Loop Guardis designed to protect againstSTP loop conditionsthat may occur whenBPDUs are unexpectedly missingon a point-to-point link. This is especially relevant in cases where UDLD (Unidirectional Link Detection) might not detect the problem quickly enough. When BPDUs are absent, a switch might erroneously assume that the link is safe to forward, potentially leading to atemporary Layer 2 loop.

UsingLoop Guardensures that a port moves into aloop-inconsistentstate instead of forwarding traffic if BPDUs are missing, effectively stopping a loop before it forms. This makes it acomplementary mechanism to UDLD, which focuses on detecting unidirectional links at the physical layer, not STP control plane failures.

This recommendation aligns with CCDE v3.1 best practices forresilient Layer 2 designs, which emphasize using multiple mechanisms in tandem to proactively prevent failure conditions before traffic is impacted.

Why other options are incorrect:

A. Root Guard: Prevents an unauthorized switch from becoming the root bridge but doesn't protect against missing BPDUs.

B. BPDU Guard: Used mainly on access ports to prevent BPDU reception; not intended for core loop prevention.

D. BPDU Filtering: Suppresses BPDU exchange entirely, which increases loop risk and is not suited for loop mitigation.

OSPF throttling timers control the pacing and frequency of SPF calculations and LSA generation. They help strike a balance between fast convergence and control-plane stability. The key timers include:

LSA generation throttling (min/max interval between LSA originations)

SPF calculation throttling (delays between consecutive SPF runs)

By tuning these timers, network designers can:

Prevent CPU overload caused by rapid or repeated LSA updates due to flapping links

Smooth out instability while still enabling responsive convergence

This approach aligns with CCDE v3.1 under “Protocol Design Implications” for optimizing IGP behavior in large, dynamic topologies.

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When both networks use overlapping private IP addresses, a single Cisco IOS NAT router can handle bidirectional NAT with dynamic NAT (overload). However, it requires careful configuration using:

Two distinct NAT pools: One for traffic sourced from side A, and one for traffic sourced from side B.

ip nat inside source and ip nat outside source commands with the overload keyword.

Interfaces must be properly defined with ip nat inside and ip nat outside to reflect traffic directionality.

Option D is correct because it explicitly reflects the requirement to use two different NAT pools for overload in both directions, which ensures proper address translation and session tracking.

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A (MLAG/MC-LAG): Multi-chassis Link Aggregation (MLAG or MC-LAG) provides fast convergence by eliminating STP dependency and creating active-active Layer 2 uplinks.

E (UDLD): UniDirectional Link Detection helps quickly detect and disable one-way fiber failures, preventing loops before STP reacts.

Why other options are incorrect:

B: DHCP snooping provides security against rogue DHCP but not redundancy or fast convergence.

C: Root guard protects root bridge integrity but doesn’t enhance failover speed.

D: BPDU guard protects edge ports but does not contribute to core redundancy or convergence.

Comprehensive and Detailed Explanation:

To reduce oscillation and improve resiliency:

D: Increasing unequal-cost multipath (UCMP) paths allows the routing protocol to load-share over more than one path, preventing traffic congestion from oscillating between nodes.

E: Dual links to each site improve bandwidth and failover options, reducing reliance on overloaded peers.

Other options:

A: Increasing redundant paths may worsen convergence complexity and doesn't solve oscillation.

B: Removing inter-spoke links reduces redundancy.

C: Increasing convergence timers delays recovery and stability.

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A (Design expecting outages and attacks):In WAN design, resiliency requires assuming that failures and attacks will occur. This drives the use of redundancy, diverse paths, and proactive failure mitigation techniques.

Other options explained:

B/C/D: While important, these focus on operational efficiency rather than core resiliency principles.

EIGRP’s convergence time is heavily impacted by the size of the query domain — the group of routers involved when a route goes into active state. The larger the query domain, the longer the convergence. Summarization naturally bounds query propagation because routers receiving a summary have no knowledge of individual prefixes beyond that summary, preventing them from being queried about specifics they don’t track.

This design technique is emphasized in CCDE v3.1 because:

Summarization reduces the query scope.

Faster convergence happens as fewer routers process queries.

Hierarchical design is enabled for stability and scalability.

Why other options are incorrect:

A: Distribute lists filter prefixes but don't reduce query propagation.

B & C: Triangulated or squared physical topology doesn’t control protocol-level query scope.

E: Default routes may help limited routing domains but don’t optimize EIGRP convergence specifically.

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D (SAML2.0):SAML2.0 is widely used for federated identity management in enterprise environments, supporting Single Sign-On (SSO) across multiple applications and domains.

Other options explained:

A: OAuth2 is primarily for authorization, not identity federation.

B: OpenID Connect extends OAuth2 for authentication but is more common for consumer web apps than enterprise SSO.

C: OpenID is older and largely replaced by OpenID Connect.

C (Significant effort and time): In a Waterfall model, changes introduced after the design phase require rework of multiple design documents, validations, and downstream impacts on implementation and testing. This leads to significant delays and resource consumption compared to more flexible models like Agile.

Other options explained:

A: Creativity is not the primary impact.

B: Rework is true but doesn’t fully capture the scope of additional effort.

D: Waterfall does not provide inherent flexibility to absorb late changes.

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Control plane hardening is a critical aspect of securing infrastructure devices. Recommended measures include:

A. Routing protocol authentication: Prevents unauthorized devices from injecting false routes by requiring secure key-based authentication (e.g., MD5 or SHA for OSPF/BGP).

B. SNMPv3: Provides secure management through authentication and encryption, preventing interception or modification of SNMP traffic.

C. Control Plane Policing (CoPP): Enforces rate limits and filtering for traffic directed to the device's CPU, protecting against DoS and control plane overloads.

Why other options are incorrect:

D. Redundant AAA servers support authentication resilience but are more about access control than direct control plane protection.

E. Warning banners are a legal and administrative best practice, not a technical control plane defense.

F. Enabling unused services is the opposite of best practices and increases the attack surface.

These control-plane protections are emphasized in CCDE v3.1 design guidance for resilient and secure infrastructure designs.

B (RPVST+ — Rapid Per VLAN Spanning Tree Plus): Provides fast convergence while blocking redundant paths to prevent loops — fail closed behavior under failure scenarios.

C (MST — Multiple Spanning Tree): Provides loop prevention and isolates failures to specific instances (VLANs), maintaining fail closed protection.

Why other options are incorrect:

A: EIGRP is a routing protocol; does not operate at Layer 2 to provide fail-closed loop protection.

D: L2MP (Layer 2 Multipathing) allows multiple active links but requires additional loop prevention mechanisms.

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A (Enhance TCP performance):Path MTU Discovery allows TCP to dynamically learn the maximum transmission unit (MTU) along the path and avoid fragmentation. This reduces retransmissions, maximizes throughput, and improves efficiency for TCP-based applications such as BGP.

Other options explained:

B/C: PMTUD does not affect convergence times.

D: Loop prevention is unrelated to MTU discovery.