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

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.

In an IS-IS design, placing the Level-1/Level-2 (L1/L2) boundary at the core limits the extent of the flooding domain, improving scalability and stability.

By limiting Level-2 flooding to the core, instability or frequent changes in the access/distribution layers (typically Level-1) do not impact the core.

The core remains stable, while routing changes are isolated within the Level-1 domains.

Other options explained:

A: Overlapping domains are not a design objective.

B: This has no direct impact on Layer 1 complexity.

C: IS-IS design must match topology hierarchy; this is not universally applicable.

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In 802.1d STP, convergence is influenced by hello timer, max_age, and forward_delay.

While hello_timer typically remains at 2 seconds, lowering max_age (default 20s) and forward_delay (default 15s) can speed up convergence.

Forward_delay controls the time spent in listening and learning states; max_age determines how long a BPDU is considered valid before recalculating topology.

Why other options are incorrect:

A, B, D: These timers (transit_delay, bpdu_delay, maximum_transmission_halt_delay) are not directly adjustable parameters in 802.1d implementations.

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B (IP Source Guard):IP Source Guard prevents IP address spoofing at Layer 2 by binding IP-to-MAC addresses and filtering unauthorized source IPs. It operates independently of encryption, so it has no impact on encryption performance.

Other options explained:

A: MACsec adds encryption and has performance implications.

C: DHCP snooping with DAI focuses on ARP spoofing, not IP address antispoofing specifically.

D: IPsec handles encryption, which directly impacts performance.

A (Working design over documentation):Agile prioritizes functional working solutions over exhaustive documentation, allowing continuous delivery and adaptability during the project lifecycle.

Other options explained:

B: Agile favors customer collaboration over contract negotiation.

C: Agile favors responding to change over rigid planning.

D: Agile favors individuals and interactions over processes and tools.

B (Route dampening): Route dampening suppresses the advertisement of flapping routes in BGP to protect the stability of the routing domain. Once the penalty threshold is reached, the unstable route is suppressed temporarily, preventing frequent updates from impacting the rest of the BGP network.

Other options explained:

A: Aggregation may help, but if the summary includes unstable subnets, flapping may still affect the summary.

C/D: Filtering removes the route entirely, which may be undesirable if occasional reachability is still needed.

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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 (Micro loops):OSPF Loop-Free Alternates (LFA) pre-calculate backup next-hops to reduce transient micro loops during the convergence process when primary routes fail.

Other options explained:

A: DTP relates to trunk negotiation, not loop prevention.

C: STP handles Layer 2 loops.

D: REP is a Cisco Layer 2 redundancy protocol, unrelated to OSPF loop prevention.

A (Financial and governance models): In the Define Strategy step, it's crucial to establish financial frameworks and governance structures that will guide the use of cloud services. This includes determining budgeting approaches (CapEx vs. OpEx), compliance, policy enforcement, risk management, and ownership of IT resources.

Governance models also define roles, responsibilities, and accountability for managing cloud services across the organization.

Other options explained:

B: Business alignment is important but comes after strategic governance and financial planning.

C: Due diligence is typically performed during vendor selection or migration readiness.

D: Contingency planning is part of exit or risk management phases, not the initial strategy step.

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Transparent Interconnection of Lots of Links (TRILL) is an IETF standard specifically designed to improve scalability, convergence, and loop prevention in data center environments while supporting virtualization at scale. TRILL replaces traditional Spanning Tree Protocol (STP) with a shortest path forwarding protocol, combining the benefits of routing with the simplicity of bridging.

TRILL uses IS-IS as its control plane protocol to calculate optimal paths dynamically, enabling better bandwidth utilization and faster failover—critical for server virtualization that demands highly available, resilient, and scalable Layer 2 networks.

Why other options are incorrect:

A. Data Center Bridging (DCB) is a set of enhancements for Ethernet but doesn’t directly address virtualization scaling.

B. Unified Fabric combines storage and data traffic but is not IETF standardized and focuses on cabling consolidation.

D. FabricPath is Cisco proprietary, not IETF standard.

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